Stratigraphic Evolution and Architectural Analysis Of

Home , Modelo Formation, Pico Formation, Turbidite

STRATIGRAPHIC EVOLUTION AND ARCHITECTURAL ANALYSIS

OF STRUCTURALLY CONFINED SUBMARINE FANS:

A TRIPARTITE OUTCROP-BASED STUDY

Gregory S. Gordon

A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Geology).

Golden, Colorado

Date ______

Signed: ______

Gregory S. Gordon

Signed: ______Dr. David R. Pyles

Thesis Advisor Golden, Colorado

Date ______

Signed: ______

Dr. Paul Santi Professor and Head

Department of Geology and Geological Engineering

ABSTRACT

Structurally confined and ponded turbidite systems can serve as prolific hydrocarbon reservoirs, as well as important records of relative sea-level fluctuations, sediment transfer from shallow-marine environments to the deep sea, and tectonic episodes. Outcrop studies of these depositional systems yield sub-seismic levels of sedimentologic and stratigraphic detail. This dissertation comprises outcrop-based studies from two different structurally confined, distributive submarine fans: the Eocene Guaso I turbidite system, Ainsa basin, Spain, and the

Miocene upper Modelo Formation, eastern Ventura basin, California.

In Chapter 2, geologic mapping, paleocurrent measurements, architectural analysis, and correlation of stratigraphic columns document that the ponded Guaso I turbidite system was fed by westward- and northwestward-oriented channels currently exposed in the Southeast (Updip)

Field Area. The oldest channels in this area longitudinally transfer to lobes on the interpreted basin floor, in the Northwest (Downdip) Field Area. The lobes are overlain by a mixed association of channels, lobes, and MTDs that contain a wider variance in paleocurrent values, indicating that the system became more distributive through time. Further, these observations reveal an increase in architectural diversity and compensational stacking of elements through time. These patterns are attributed to an increase in depositional area, and a decrease in accommodation relative to sediment supply (A:S), as the bowl-shaped basin filled. Isopach mapping reveals a prominent thick, which nearly coincides with the depositional axis of the

Guaso I. Proximally, this thick comprises a mass-transport complex, as well as channels and mudstone sheets. On the basin floor, the thick is largely due to a significant succession of high- reservoir-quality sandstone. A geometric model presented herein relates reservoir connectivity and compensational stacking to effective area of deposition.

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The subject of Chapter 3 is the submarine channel-lobe transition zone (CLTZ), the region on a submarine fan that marks the interface between updip channels and downdip lobes.

At the scale of an individual architectural element, the CLTZ governs sandstone connectivity between a channel and a lobe, and it serves as the link between locally confined and unconfined conditions for sediment gravity flows that build the submarine fan. Outcrops of the Guaso I turbidite system of Ainsa basin, Spain, include a continuous, ~4-km-long, paleocurrent-parallel transect through a channel-lobe element. Key longitudinal changes across the CLTZ in this depositional system are: thickening of the element in a downcurrent direction, due to oldest bedsets of the proximal lobe that thin and pinch out completely onto the erosive lower contact in an upcurrent direction; a basinward decrease in the amount of erosion at the base of the element; basinward decreases in intra-element erosion and amalgamation surfaces; sandstone continuity from the updip channel to the downdip lobe; a base-of-slope depositional angle of ~2°, based upon stratigraphic thickness measurements. Point counting and grain-size analyses document that sandstones of the CLTZ and the lobe are generally finer-grained and better sorted than channel sandstones. This is interpreted to be due to different combinations of depositional processes operating in the locally confined (channel) domain and the unconfined (CLTZ and lobe) domain. A four-stage sequential model that describes the stratigraphic architecture and evolution of a channel-lobe element is presented herein. Results of this study have important implications for reservoir and fluid-flow modeling in distributive channel-lobe systems.

Chapter 4 is a study of the stratigraphy, paleogeography, and depositional controls of the upper Modelo Formation. Outcrops of this depositional system represent a longitudinal transect through a fault-controlled deepwater depositional system, from proximal structural terraces, through a submarine canyon, to the basin floor and basin margin. This study area is divided into

iv three regions based on geographic location, stratigraphic character, and interpreted paleogeographic environment: Region 1 (Feeder System), Region 2 (Proximal Basin Floor), and

Region 3 (Medial-Distal Basin Floor). Region 1 contains syndepositionally active normal faults

(e.g., Devil Canyon fault) near the proximal basin margin; these faults are associated with abrupt changes in depositional environments, lithofacies associations, paleobathymetry, and stratigraphic thickness. The submarine canyon was an area of bypass, and it has a low net- sandstone content. Isopach maps reveal that gross thickness is greatest near the interpreted canyon mouth. In Region 2, a proximal-basin-floor fairway located immediately basinward of the canyon contains the highest sandstone content in the basin. In Region 3, gradual changes in proportions of lithofacies associations result from subtle variations in the gradient of the basin floor near the distal basin margin, as interpreted from the isopach map. In this area, channel complexes comprising structureless, amalgamated sandstone overlie thin-to-medium bedded,

“dirty” sandstones deposited at the lobe fringe. This upward architectural pattern is interpreted to result from an outwardly expanding depocenter through time.

TABLE OF CONTENTS

ABSTRACT ...... iii LIST OF FIGURES ...... x LIST OF TABLES...... xii ACKNOWLEDGMENTS...... xiii

CHAPTER 1. INTRODUCTION TO DISSERTATION...... 1 1.1. Introduction ...... 1 1.2. Organization and Content...... 2 1.2.1. Chapter 2 ...... 2 1.2.2. Chapter 3 ...... 3 1.2.3. Chapter 4 ...... 4 1.3. References ...... 5

CHAPTER 2. STRATIGRAPHIC EVOLUTION, ARCHITECTURAL ANALYSIS, AND GEOMETRIC MODEL OF A PONDED SUBMARINE FAN: THE GUASO I TURBIDITE SYSTEM, AINSA BASIN, SPAIN ...... 7

2.1. Abstract ...... 7

2.2. Introduction ...... 8

2.3. Geologic Background ...... 12

2.3.1. Previous Work on the Guaso System...... 15

2.4. Data and Methods ...... 16

2.4.1. Lithofacies ...... 18

2.5. Architectural Elements ...... 18

2.5.1. Mudstone Sheets ...... 19

2.5.2. Lobes ...... 19

2.5.3. MTDs ...... 20

2.5.4. Channels...... 21

2.6. Geology of the Guaso I System ...... 23

2.6.1. Southeast (Updip) Field Area ...... 24

2.6.2. Northwest (Downdip) Field Area ...... 26

2.6.3. Isopach Maps ...... 27

2.7. Paleogeographic Interpretation ...... 28

2.8. Discussion ...... 32

2.8.1. Stratigraphic Evolution of the Guaso I Turbidite System ...... 32

2.8.2. Geometric Model...... 34

2.8.3. Applications to Hydrocarbon Exploration ...... 37

2.9. Conclusions ...... 39

2.10. Acknowledgments ...... 40

2.11. References ...... 40

CHAPTER 3. FLOW PROCESSES, SEDIMENTATION, AND STRATIGRAPHIC EVOLUTION OF THE SUBMARINE CHANNEL-LOBE TRANSITION ZONE: AN OUTCROP-BASED STUDY ...... 69

3.1. Abstract ...... 69

3.2. Introduction ...... 70

3.3. Geologic Setting ...... 73

3.4. Data and Methods ...... 75

3.5. Stratigraphy of the Field Area...... 77

3.5.1. Observations ...... 77

3.5.2. Interpretation: Channel-Lobe Element ...... 80

3.6. Grain Size and Sorting Along the Channel-Lobe Element ...... 84

3.7. Discussion ...... 85

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3.7.1. Flow Processes, Sedimentation, and Sequential Evolution of the Channel- Lobe Element...... 85

3.7.2. Sandstone Continuity, Hydraulic Jumps, and the CLTZ ...... 90

3.7.3. Implications for Hydrocarbon Reservoirs ...... 91

3.8. Conclusions ...... 93

3.9. Acknowledgments ...... 94

3.10. References ...... 95

CHAPTER 4. FROM SUBMARINE CANYON TO BASIN MARGIN: FAULT AND BATHYMETRIC CONTROLS ON SUBMARINE FAN STRATIGRAPHY AND DISTRIBUTION OF LITHOFACIES ASSOCIATIONS, UPPER MODELO FORMATION, EASTERN VENTURA BASIN, CALIFORNIA .... 114

4.1. Abstract ...... 114

4.2. Introduction ...... 115

4.3. Geologic Background ...... 117

4.4. Data and Methods ...... 121

4.4.1. Lithofacies and Lithofacies Associations ...... 122

4.4.2. Architectural Elements...... 123

4.5. Geology of the Upper Modelo Formation in the EVB ...... 123

4.5.1. Region 1: Feeder System ...... 124

4.5.2. Region 2: Proximal Basin Floor ...... 128

4.5.3. Region 3: Medial-Distal Basin Floor ...... 131

4.6. Paleogeographic Interpretation ...... 135

4.7. Discussion ...... 136

4.7.1. Fault and Bathymetric Controls on the Distribution of Lithofacies Associations ...... 136

4.7.2. Hydrocarbon Reservoirs in Fault-Bounded Deepwater Basins ...... 139

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4.8. Conclusions ...... 141

4.9. Acknowledgments ...... 144

4.10. References ...... 144

CHAPTER 5. CONCLUSIONS TO DISSERTATION ...... 171

5.1. Summary Conclusions and Contributions ...... 171

5.2. Chapter 2 Conclusions and Contributions...... 171

5.3. Chapter 3 Conclusions and Contributions...... 172

5.4. Chapter 4 Conclusions and Contributions...... 173

5.5. References ...... 174

APPENDIX A : Measured Sections – SUPPLEMENTAL ELECTRONIC MATERIAL ...... 177

APPENDIX B : Uninterpreted Photos – SUPPLEMENTAL ELECTRONIC MATERIAL ...... 178

APPENDIX C : Data and Spreadsheets – SUPPLEMENTAL ELECTRONIC MATERIAL.... 179

APPENDIX D : Permissions Letters – SUPPLEMENTAL ELECTRONIC MATERIAL ...... 180

LIST OF FIGURES

Figure 1.1. Paleogeographic maps of two confined deepwater depositional systems ...... 6

Figure 2.1. Diagram of a ponded, distributive submarine fan ...... 53 Figure 2.2. Stratigraphy and regional geology of Ainsa basin ...... 54

Figure 2.3. Geologic map of the Guaso I depositional system ...... 55 Figure 2.4. Stratigraphic relationships in the Guaso I depositional system ...... 56

Figure 2.5. Lithofacies of the Guaso I depositional system ...... 57 Figure 2.6. Architectural elements in the Guaso I depositional system ...... 58

Figure 2.7. Stratigraphic cross section of the Southeast (Updip) Field Area ...... 59 Figure 2.8. Photographs of the Roadside Channel Complex ...... 60

Figure 2.9. Stratigraphic cross section of the Northwest (Downdip) Field Area ...... 61 Figure 2.10. Photographs of the Rio Ena locality ...... 62

Figure 2.11. Isopach map of the third-order Guaso system ...... 63 Figure 2.12. Isopach maps of the Guaso I depositional system ...... 64 Figure 2.13. Paleogeography of the Guaso I depositional system ...... 65

Figure 2.14. Geometric model for ponded deepwater basins ...... 66 Figure 3.1. Examples of submarine channel-lobe transition zones ...... 103

Figure 3.2. Stratigraphy and regional geology of Ainsa basin ...... 104

Figure 3.3. Geologic map of the Guaso I depositional system ...... 105

Figure 3.4. Paleogeographic interpretation and map of channel-lobe element ...... 106 Figure 3.5. Photographs of the mapped sandstone unit ...... 107

Figure 3.6. Cross section and lithofacies of the channel-lobe transect...... 108 Figure 3.7. Diagram of the channel-lobe transition zone ...... 109

Figure 3.8. Plot of mean grain size vs. sorting ...... 110 Figure 3.9. Longitudinal grain-size and sorting trends ...... 111

Figure 3.10. Evolution of a channel-lobe element ...... 112

Figure 4.1. Map of Ventura and Los Angeles basins ...... 153 Figure 4.2. Geologic map of the northeastern Ventura basin...... 154

Figure 4.3. Stratigraphy of the Ventura basin ...... 155 Figure 4.4. Cross section of late Miocene strata in EVB ...... 156 Figure 4.5. Isopach map of Mohnian strata in EVB ...... 157

Figure 4.6. Lithofacies of the upper Modelo Formation ...... 158 Figure 4.7. Lithofacies associations of the upper Modelo Formation ...... 159

Figure 4.8. Photographs of Region 1 strata ...... 160 Figure 4.9. Paleogeography of Region 1 ...... 161

Figure 4.10. Photographs of the Narrows area in Region 2 ...... 162 Figure 4.11. Photographs of Region 2 strata ...... 163

Figure 4.12. Photographs of Region 3 strata ...... 164 Figure 4.13. Paleogeography of the upper Modelo Formation ...... 165

Figure 4.14. Distribution of lithofacies associations in the upper Modelo Formation ...... 166

Figure 4.15. Summary diagram of EVB ...... 167

Figure 5.1. Isopach patterns for distributive submarine fans ...... 176

LIST OF TABLES

Table 2.1. Lithofacies of the Guaso I depositional system ...... 67

Table 3.1. Grain-size and sorting data for the Guaso I channel-lobe element ...... 113 Table 4.1. Lithofacies of the upper Modelo Formation ...... 168

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ACKNOWLEDGMENTS

The past 4+ years in Colorado have been arduous, eventful, challenging, and very rewarding. There are so many people to thank, and organizations to acknowledge, for their roles in the facilitation and success of this project. I want to start by thanking my beloved wife, partner, and best friend: Jessamyn. As I write this, she is right by my side, as she has been literally and figuratively throughout this time. Jessamyn has been the manager of our homefront, as well as the loving mother of our three wonderful, rambunctious children, Joshua, Nathan, and

Annemarie (our “Colorado addition”). Needless to say, I could not have succeeded in this endeavor without her support, devotion, patience, prodding, and sacrifice.

I want to thank my advisor, David Pyles, for the personal stake he has taken in me as a student and geologist. From David I have learned how to formulate meaningful hypotheses, efficiently collect field data, quantify stratigraphic concepts, and effectively communicate my results; in short, I have learned much about being a scientist and stratigrapher from him during my Ph.D. years. I appreciate all of the conversations on stratigraphy, science, political philosophy, California geology, academia, child rearing, Europe’s “Butter Line”, and radical new conglomerate classification schemes we’ve shared. I am relieved that our friendship appears to have survived this dissertation review process!

I thank my committee members Steve Sonnenberg, Bruce Trudgill, Azra Tutuncu, Julian

Clark, and Morgan Sullivan. I appreciate their time, patience, and flexibility. Manika Prasad,

Debbie Cockburn, and Summer Jackson at the Colorado School of Mines have also been quite helpful.

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In terms of facilitating the “day-to-day” operations at the Chevron Center of Research

Excellence (CoRE), Charlie Rourke and Cathy Van Tassel have been enthusiastic, instrumental, and very professional. Both of these individuals have gone “above and beyond” to help with travel, logistics, funding, academic questions, and numerous other items. Charlie’s hospitality at the Rourke Family cabin in Estes Park was much appreciated. Linda Martin has provided technical support, and Mark Kirschbaum has provided good cheer and technical reviews.

For forbearing an occasional rant, and for their good humor (well, mostly), I want to thank past/current CoRE students and colleagues: Matt Hoffman, Jeremiah Moody, Alexandra

Fleming, Jane Stammer, Kasi Sendziak, Grace Ford, Jesse Pisel, Tim O’ Toole, and Brad Nuse.

I hope our paths continue to cross in the future.

This dissertation would not have been possible without the data collected from my field areas in Spain and California. I want to thank field assistants Jeremiah Moody, Jane Stammer,

Grace Ford, Matt Hoffman, Gary Listiono, Erich Heydweiller, Brad Nuse, Martin Jimenez,

Stuart Gordon, Denise Gordon, and Tim “Blue Steel” O’ Toole. Also, I want to thank all of the landowners, local geologists, rangers, and water district employees that helped with land access.

Special thanks are in order for my parents, who offered moral support and encouragement when things got tough. I know they’re always in my corner. I also want to thank my extended family and friends for the positivity (and prayers!).

I am pleased to thank Chevron (via the Chevron Center of Research Excellence at the

Colorado School of Mines) for primary funding of this project. Chevron ETC also provided mentoring, support, and field experiences with Morgan Sullivan, Julian Clark, and other top- flight geoscientists. Additional funding was graciously provided by a GCS SEPM Ed Picou

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Fellowship, a ConocoPhillips SPIRIT Scholarship, the Bartshe Family Fellowship, and a Devon

Energy Scholarship.

CHAPTER 1.

INTRODUCTION TO DISSERTATION

1.1. Introduction

All varieties of Earth’s siliciclastic continental margins, whether convergent, divergent, or transform, host sediment deposited as submarine fans in structurally confined deepwater basins (Bouma, 2004). Structural confinement of these basins can result from salt diapirs, allochthonous salt bodies, mud diapirs, thrust-cored anticlines, normal-fault scarps, or other structures (Bouma, 2004; Lomas and Joseph, 2004; Weimer and Pettingill, 2007). Distributive submarine fans in confined basins are often fully ponded (sensu Van Andel and Komar, 1969), meaning that all of their sediment is trapped within the basin by basin-bounding features, and they can serve as prolific hydrocarbon reservoirs in petroliferous regions (Pettingill and Weimer,

2001; Weimer and Pettingill, 2007). This dissertation focuses on outcrops of two distributive submarine fans originally deposited in structurally complex, confined basins: the Guaso I turbidite system (Figures 1.1A, B) in Ainsa basin, Spain, and the upper Modelo Formation

(Figure 1.1C) in eastern Ventura basin, California. The stratigraphic evolution, sandstone distribution, paleogeography, architecture, and sedimentologic features of both of these submarine fans are documented in detail in the subsequent chapters. Results from this dissertation add sub-seismic-resolution detail on how these fans evolve and distribute their sediment. The architectural information presented herein is relevant to petroleum geoscientists exploring for and developing turbidite reservoirs in structurally confined deepwater basins around the world. Results from this dissertation are also important to sedimentologists and

1 geomorphologists because they add to the growing body of knowledge of processes and products that shape continental margins and their constituent basins.

1.2. Organization and Content

This dissertation contains three main chapters (Chapters 2, 3, and 4) that have been submitted for publication in peer-reviewed journals. Each is described below.

1.2.1. Chapter 2

Chapter 2 is titled “Stratigraphic evolution, architectural analysis, and geometric model of a ponded submarine fan: the Guaso I turbidite system, Ainsa basin, Spain.” Geologic mapping, architectural analysis, and stratigraphic correlations indicate that the Guaso I turbidite system is a ponded, distributive submarine fan (Figure 1.1A). Isopach mapping documents a thick region of sediment that coincides with the axis of the depositional system. In the proximal part of the system, the thick largely comprises a mass-transport complex, whereas on the downdip basin floor, the thick largely comprises a succession of high-reservoir-quality sandstone. This chapter provides a highly detailed element-scale documentation of the evolution of a reservoir-scale system. Initially, channel elements fed lobe elements that stacked aggradationally on the basin floor. Through time, the system became more distributive; paleocurrents diverged and compensational stacking of elements increased as the depositional area increased. A geometric model for basin infilling presented herein relates compensational stacking to effective depositional area and association of architectural elements. Results of this chapter are widely applicable to turbidite systems in structurally confined basins around the

2 world. The co-authors of the publication that results from this chapter are David Pyles, Julian

Clark, and Matt Hoffman.

1.2.2. Chapter 3

Chapter 3 is titled “Flow processes, sedimentation, and stratigraphic evolution of the submarine channel-lobe transition zone: an outcrop-based study.” This chapter documents an exceptionally well exposed longitudinal transect through a channel element and its basinward lobe element (Figure 1.1B) in the Guaso I turbidite system. In the vicinity of the channel-lobe transition zone (CLTZ), which is the interface between the channel and the lobe, there is a thickening of the element in a downcurrent direction and a downdip decrease in erosion at the base of the element, as well as a general decrease in internal scouring and amalgamation surfaces. In this outcrop example, there is sandstone continuity between the channel and lobe; this observation contrasts with some previous channel-lobe models (e.g., Mutti and Normark,

1987). Analyses of grain size and sorting, which are key textural properties of sediments that control resulting porosity and permeability (Beard and Weyl, 1973), indicate that sandstones of the channel are generally coarser-grained and more poorly sorted than sandstones of the CLTZ and proximal lobe. Critically, longitudinal changes in mean grain size and sorting are gradual, rather than abrupt. This chapter builds upon the build-cut-fill-spill model (Gardner and Borer,

2000; Gardner et al., 2003), and proposes a four-phase sequential evolution for channel-lobe systems at the element-scale, based on outcrop ground-truthing. This outcrop example is, perhaps, one of the best exposed channel-lobe transects documented to date, and this chapter adds key element-scale details to the growing body of stratigraphic and sedimentologic

3 knowledge of the CLTZ. The co-author of the publication that results from this chapter is David

Pyles.

1.2.3. Chapter 4

Chapter 4 is titled “From submarine canyon to basin margin: fault and bathymetric controls on submarine fan stratigraphy and distribution of lithofacies associations, upper Modelo

Formation, eastern Ventura basin, California.” This chapter documents a longitudinal transect through a structurally confined, fault-controlled deepwater depositional system, from proximal structural terraces, through a submarine canyon, to the basin floor and basin margin (Figure

1.1C). Key contributions of this chapter include documentation of syndepositionally active normal faults near the proximal margin of the basin (e.g., Devil Canyon fault) that are associated with abrupt changes in depositional environments, lithofacies associations, paleobathymetry, and stratigraphic thickness. Gradual changes in observed proportions of lithofacies associations are interpreted to result from subtle variations in depositional gradient on the basin floor near the distal basin margin; in this area, channel complexes comprising thick-bedded, structureless, amalgamated sandstone overlie thin-to-medium bedded, argillaceous lobe-fringe strata. This chapter also documents spectacular exposures (e.g., the Narrows outcrop) of a prominent proximal-basin-floor fairway located immediately basinward of the mouth of a submarine canyon. The observations and interpretations in this chapter contribute to the understanding of structurally complex, fault-controlled turbidite systems; results presented herein are particularly relevant to hydrocarbon reservoirs in petroliferous provinces such as the North Sea and

California. The co-author of the publication that results from this chapter is David Pyles.

1.3. References

Beard, D.C., and P.K. Weyl, 1973, Influence of texture on porosity and permeability of unconsolidated sand: AAPG Bulletin, v. 57, p. 349-369.

Bouma, A.H., 2004, Key controls on the characteristics of turbidite systems, in S.A. Lomas and P. Joseph, eds., Confined Turbidite Systems: Geological Society (London) Special Publication 222, p. 9-22.

Gardner, M.H., and J.M. Borer, 2000, Submarine channel architecture along a slope to basin profile, Brushy Canyon Formation, West Texas, in A.H. Bouma and C.G. Stone, eds., Fine-Grained Turbidite Systems: AAPG Memoir 72/SEPM Special Publication 68, p. 195-214.

Gardner, M.H., J.M. Borer, J.J. Melick, N. Mavilla, M. Dechesne, and R.N. Wagerle, 2003, Stratigraphic process-response model for submarine channels and related features from studies of Permian Brushy Canyon outcrops, West Texas: Marine and Petroleum Geology, v. 20, p. 757-787.

Lomas, S.A., and P. Joseph, 2004, Confined turbidite systems, in S.A. Lomas and P. Joseph, eds., Confined Turbidite Systems: Geological Society (London) Special Publication 222, p. 1-7.

Mutti, E., and W.R. Normark, 1987, Comparing examples of modern and ancient turbidite systems: problems and concepts, in J.K. Leggett and G.G. Zuffa, eds., Marine Clastic Sedimentology: Concepts and Case Studies: London, Graham and Trotman, p. 1-38.

Pettingill, H.S., and P. Weimer, 2001, World-wide deep water exploration and production: Past, present, and future, in R.H. Fillon, N.C. Rossen, P. Weimer, A. Lowrie, H. Pettingill, R.L. Phair, H.H. Roberts, and B. van Hoorn, eds., Petroleum Systems of Deep-Water Basins: Global and Gulf of Mexico Experience: Gulf Coast Section SEPM 21st Annual Perkins Research Conference, p. 1-22.

Van Andel, T.H., and P.D. Komar, 1969, Ponded sediments of the Mid-Atlantic Ridge between 22° and 23° North latitude: Geological Society of America Bulletin, v. 80, p. 1163-1190.

Weimer, P., and H.S. Pettingill, 2007, Global overview of deep-water exploration and production, in T.H. Nilsen, R.D. Shew, G.S. Steffens, and J.R.J. Studlick, eds., Atlas of Deep-Water Outcrops: Tulsa, Oklahoma, AAPG Studies in Geology 56, p. 7-11.

Figure 1.1. Paleogeographic maps of the deepwater depositional systems studied in this dissertation: A) the Guaso I turbidite system in Ainsa basin, Spain (Chapter 2); B) an individual channel-lobe element in the Guaso I turbidite system (Chapter 3); C) the upper Modelo Formation in eastern Ventura basin, California (Chapter 4).

CHAPTER 2.

STRATIGRAPHIC EVOLUTION, ARCHITECTURAL ANALYSIS,

AND GEOMETRIC MODEL OF A PONDED SUBMARINE FAN:

THE GUASO I TURBIDITE SYSTEM,

AINSA BASIN, SPAIN

A paper that has been submitted to the Journal of Sedimentary Research

Gregory S. Gordon, David R. Pyles, Julian Clark, and Matthew Hoffman

2.1. Abstract

Guaso I turbidite system (Lutetian) crops out in the Ainsa basin, northeastern Spain, and its exposures reveal a ponded, distributive submarine fan confined at the distal end of the basin by a syndepositionally active anticline.

Geologic mapping, paleocurrent measurements, architectural analysis, and correlation of stratigraphic columns document that the Guaso I turbidite system was fed by westward- and northwestward-oriented channels currently exposed in the Southeast (Updip) Field Area. The oldest channels in this area longitudinally transfer to lobes on the interpreted basin floor, in the

Northwest (Downdip) Field Area. The lobes are overlain by a mixed association of channels,

7 lobes, and mass-transport deposits that contain a wider variance in paleocurrent values, indicating that the system became more distributive through time. Further, these observations reveal increases in architectural diversity and compensational stacking of elements through time.

These patterns are attributed to an increase in depositional area, and a decrease in accommodation relative to sediment supply (A:S), as the bowl-shaped basin filled. Isopach mapping reveals a prominent thick, which nearly coincides with the depositional axis of the

2.2. Introduction

Confined turbidite systems are deepwater clastic depositional systems whose development and resulting architectures have been affected by topographic features of the basin floor and/or basin margin (definition modified from Lomas and Joseph, 2004, p. 1). Basin- margin topographic features can include anticlinal seafloor highs, salt diapirs, and fault scarps

(Figure 2.1). The depositional patterns and stratigraphic architectures that are produced from the interaction of turbidity currents with these features can differ from those where basin-margin topographic features are not present, such as in unconfined basin-floor settings (Mutti and

Normark, 1987; Mutti and Normark, 1991; Lomas and Joseph, 2004; Amy et al., 2007; Covault and Romans, 2009; Mutti et al., 2009; Callec et al., 2010; Mayall et al., 2010). The nature of this interaction between turbidity currents and basin margins includes flow deflection and/or

8 reflection (Pickering et al., 1992; Haughton, 1994; Kneller and McCaffrey, 1999; Felletti, 2002), full “containment” and ponding (Van Andel and Komar, 1969; Pickering and Hiscott, 1985;

Sinclair, 1992; Prather et al., 1998; Muzzi Magalhaes and Tinterri, 2010), a spatial change in flow/depositional processes due to a subtle variation in seafloor gradient (e.g., change in suspended sediment fallout rate; Kneller and McCaffrey, 1999; Kneller and Buckee, 2000;

Smith, 2004; Amy et al., 2004), and upslope flow and bypass (Muck and Underwood, 1990).

Hence, the size and shape of the basin (e.g., Figure 2.1), as well as the spatial variation in subsidence, are critical controls on resultant stratigraphic architecture (Lomas and Joseph, 2004;

Pyles, 2008; Bernhardt et al., 2011). Fully confined (ponded) turbidite systems often scale to the size of the minibasins they fill, which generally vary from 5-40 km in diameter (Beaubouef and

Friedmann, 2000; Amy et al., 2007; Pyles, 2008). Therefore, the shape of the basin can control the shape of the submarine fan (Clark et al., 1992; Covault and Romans, 2009). This study documents the evolving architecture and depositional patterns of the Guaso I turbidite system, which is a ponded submarine fan that was deposited in a relatively small, structurally confined basin.

Structurally confined and ponded turbidite systems are common features on most of

Earth’s continental margins and also in some intra-continental basins. They are located in forearc and trench-slope basins (Underwood and Norville, 1986; Thornburg and Kulm, 1987;

Pickering et al., 1992; Bailleul et al., 2007), ovular- to rhomboid-shaped transtensional basins

(Pyles, 2008), salt-withdrawal minibasins (Pratson and Ryan, 1994; Prather et al., 1998;

Beaubouef and Friedmann, 2000; Booth et al., 2000; Madof et al., 2009), piggyback basins

(sensu Ori and Friend, 1984) and foredeep-margin depocenters (Sinclair, 1992; Fernandez et al.,

2004; Covault et al., 2009; Sutcliffe and Pickering, 2009; Moody et al., 2012), deepwater fold-

9 and-thrust-belt settings (Morley and Leong, 2008; Morley, 2009), and depocenters formed due to mobile mudstone substrates and mud diapirism (Pirmez et al., 2000; Adeogba et al., 2005;

Armitage et al., 2012). Due to their locations and abundances, particularly on continental slopes, confined turbidite systems are scientifically important records of relative sea-level fluctuations, sediment transfer from continents to deep ocean basins, and tectonic episodes (e.g., subduction- related earthquakes, basin inversion, etc.). Confined turbidite systems are also economically important, as sandstones in these systems are often prolific hydrocarbon reservoirs in provinces such as the Gulf of Mexico, offshore West Africa, the North Sea, and onshore California (Hsu,

1977; Webb, 1981; Hodgson et al., 1992; Damuth, 1994; Prather et al., 1998; Booth et al., 2000;

Clark et al., 2000; Booth et al., 2003; Mallarino et al., 2006). Geoscientists and petroleum explorationists seek to bridge the gap between scientific knowledge about these deepwater depositional systems and enhanced recovery of hydrocarbons in confined turbidite reservoirs

(Sullivan et al., 2004; Weimer and Pettingill, 2007).

Most scientific knowledge of confined turbidite systems comes from seismic data and near-seafloor studies (e.g., Satterfield and Behrens, 1990; Winker, 1996; Prather et al., 1998;

Beaubouef and Friedmann, 2000; Twichell et al., 2000; Deptuck et al., 2008; Covault and

Romans, 2009; Prather et al., 2012). These and similar studies yield valuable contributions to understanding the medium- to large-scale stratigraphic infill patterns and seismic facies variations of deepwater depositional systems in confined depocenters and minibasins.

Subsurface data such as conventional cores and well logs provide highly detailed information on vertical stacking patterns and facies juxtapositions, but these data are often expensive, one- dimensional, and relatively rare, particularly in deepwater drilling environments. Several recent experimental laboratory-based studies have been instrumental in advancing knowledge of

10 turbidity-current flow dynamics and deposition in confined depocenters (e.g., Brunt et al., 2004;

Lamb et al., 2004; Violet et al., 2005; Lamb et al., 2006; Toniolo et al., 2006); however, in these studies, the receiving basins were very small relative to the heights and widths of incoming turbidity currents, and in several cases, only a small number of beds (turbidity current deposits) were created and analyzed.

Outcrop-based studies, which can serve as analogs for subsurface reservoirs, yield sub- seismic levels of sedimentologic and stratigraphic detail (Moraes et al., 2004; Pyles, 2008; Pyles et al., 2010), but they are inherently limited by the quality and extent of exposures. Seminal stratigraphic models of ponded deepwater basins (e.g., “fill and spill”) have been proposed and assessed based on outcrop work in a few well-known localities such as the Alpine foreland basin in southeast France (Sinclair, 2000; Sinclair and Tomasso, 2002; Amy et al., 2007) and the North

Alpine foreland basin in eastern Switzerland (Sinclair, 1992). These models were among the first to describe long-term, third-order depositional packages (representing ~1-2 m.y.; sensu

Mitchum and Van Wagoner, 1991) and facies trends in ponded deepwater basins. Pyles (2008) is an outcrop study that quantitatively documents the landscape evolution, as well as stratigraphic architectures and upward changes in depositional patterns, of a ponded, distributive submarine fan (the Ross Sandstone) from one fourth-order cycle (representing ~0.1-0.2 m.y.; sensu

Mitchum and Van Wagoner, 1991) to the next.

To date, no outcrop study has been focused on a high-resolution, element-scale stratigraphic analysis (cf. Pyles, 2007) of the architecture, evolution, and sandstone distribution within one fourth-order (reservoir-scale) ponded submarine fan. The Eocene Guaso I turbidite system, a fourth-order cycle in the Ainsa basin of Spain, contains near-continuous exposures of slope-to-basin deposits in a fully confined deepwater fold-and-thrust-belt setting (Hoffman,

2009; Sutcliffe and Pickering, 2009); hence, it provides an excellent opportunity to test previous models and gain detailed stratigraphic knowledge about ponded deepwater depositional systems.

The goals of this study are to: (1) quantitatively document element-scale stratigraphic architecture, spatial changes in sandstone content, and paleogeographic evolution of the Guaso I turbidite system; (2) relate the location of isopach thicks to the locations of maximum sandstone content and non-reservoir strata; and (3) propose a generalized geometric model for the stratigraphic evolution of ponded-phase deepwater fill. These results can be used by geoscientists to help predict locations and stratigraphic architectures of sandy turbidite reservoirs in ponded basins.

2.3. Geologic Background

The Guaso system crops out in the Ainsa basin, which is located in the south-central

Spanish Pyrenees Mountains, in northeastern Spain (Figure 2.2A). The Pyrenees orogen comprises a doubly-vergent fold-thrust belt (Figure 2.2B) that originated in the Mesozoic due to the north-south convergence of the Afro-Iberian and European plates (Muñoz, 1992; Coney et al., 1996; Morris et al., 1998; Poblet et al., 1998; Fernandez et al., 2004; Sutcliffe and Pickering,

2009). Throughout the Eocene, thin-skinned thrusting in the South Pyrenean foreland basin system took place on a detachment layer of lower Triassic evaporites (Garrido-Megias, 1973;

Muñoz, 1992; Muñoz et al., 1994; Holl and Anastasio, 1995; Poblet et al., 1998). The Ainsa basin, a subsidiary of the larger Tremp-Graus-Ainsa-Jaca basin in the South Pyrenean foreland basin system, formed in the early Eocene (Ypresian) as a local foredeep west of the Montsec thrust (Figure 2.2A; Farrell et al., 1987; Fernandez et al., 2004; Falivene et al., 2010). In the middle Eocene (Lutetian), the basin evolved into a piggyback basin as thrusting undercut the

12 basin and propagated southwestward toward the foreland (Figure 2.2B; Fernandez et al., 2004;

Falivene et al., 2010). The main structural features in the Ainsa basin have a north-south orientation. These features (Figures 2.2A, 2.2C, 2.3), which were syndepositionally active during the Eocene (Mutti, 1977; Farrell et al., 1987; Poblet et al., 1998; Fernandez et al., 2004;

Pickering and Corregidor, 2005; Hoffman, 2009), are: (1) the Añisclo anticline on the northern margin, (2) the Boltaña anticline on the western margin, (3) the Buil syncline (roughly coinciding with the axis of the basin), and (4) the Mediano anticline on the eastern margin. The anticlines are oriented almost perpendicular to the broader west-east orientation of the Pyrenees

(Holl and Anastasio, 1995), and they served as confining topography that affected turbidite deposition in the basin during the Lutetian (Sutcliffe and Pickering, 2009; Moody et al., 2012).

The Eocene Ainsa basin-fill succession comprises the Hecho and Campodarbe Groups

(Figures 2.2C, 2.2D; Mutti et al., 1972; Mutti, 1977; Mutti et al., 1985; Moss-Russell, 2009;

Moody et al., 2012). The turbidite systems of the Hecho Group were deposited in the Ypresian and Lutetian; various workers have described them (Figures 2.2C, 2.2D; Pickering and Bayliss,

2009). These sand-rich turbidite systems are the Fosado, Los Molinos, Charo/Arro (Millington and Clark, 1995), Gerbe, Banaston, Ainsa (Clark and Pickering, 1996; Pickering and Corregidor,

2000), Morillo (Labourdette et al., 2008; Setiawan, 2009; Moody et al., 2012), and Guaso

(Stocchi, 1992; Stocchi et al., 1992; Sutcliffe and Pickering, 2009). The boundaries between the turbidite systems (sensu Mutti and Normark, 1987) are interpreted as condensed sections, each of which is encased in a 100-150-m-thick mudstone package (Hoffman, 2009; Moody et al., 2012).

The Hecho Group is ~4 km thick (Pickering and Bayliss, 2009), and was deposited contemporaneously with platform carbonate deposits (the Guara Formation) located along the southwestern margin of the basin (Figure 2.2A; Dreyer et al., 1999; Mochales et al., 2012). The

13 top of the Hecho Group and of the Guara Formation (La Patra Member), dated at 41.6 Ma, is a stratigraphic surface that corresponds to a regional anoxic level (Mochales et al., 2012). In the

Ainsa basin, the turbidites of the Hecho Group overlie mixed carbonate and siliciclastic strata

(Mesozoic to earliest Eocene in age) and underlie fluviodeltaic sediments of the latest Lutetian-

Priabonian Campodarbe Group (Figures 2.2C, 2.2D; Garrido-Megias, 1973; Fernandez et al.,

2004; Moss-Russell, 2009; Silalahi, 2009).

Each of the turbidite systems of the Hecho Group is a third-order unit (Pickering and

Bayliss, 2009). Within these turbidite systems, there are ~25 constituent sandbodies, or turbidite sub-systems; each is a fourth-order submarine fan in its own right (Pickering and Bayliss, 2009).

The depocenters of successive third-order turbidite systems in the Ainsa basin shift south- southwestward through time (Hoffman, 2009), and constituent submarine fans within each system are located in progressively more westward locations (Pickering and Bayliss, 2009). The

Guaso system, the youngest third-order turbidite system in the Hecho Group (Figure 2.2D), is underlain by the Morillo system, a weakly confined submarine channel system (Setiawan, 2009;

Moody et al., 2012). The Guaso system is conformably overlain by the Campodarbe Group

(Moss-Russell, 2009). The Sobrarbe Formation, the lowest unit of the Campodarbe Group

(Figure 2.2D), records the progradation of a linked shelf-to-basin depositional system into the basin (Dreyer et al., 1999; Moss-Russell, 2009; Silalahi, 2009; Clark et al., 2010). This progradational unit represents the transition from fully marine to non-marine deposition in the

Ainsa basin, and it reflects a probable increase in sediment supply relative to structurally-induced accommodation (Clark et al., 2010).

2.3.1. Previous Work on the Guaso System

The Guaso system is divided into two fourth-order sub-systems: Guaso I and Guaso II

(Pickering and Bayliss, 2009; Sutcliffe and Pickering, 2009; Figure 2.2D). This study focuses on the Guaso I sub-system, referred to herein as the Guaso I turbidite system in order to maintain conformance with the definition of turbidite systems provided by Mutti and Normark (1987, p.4).

The Guaso I is also referred to as the “O Grao turbidite system” in other studies (e.g., Fernandez et al., 2004). Outcrop and foraminiferal studies on the Lutetian-aged Guaso system indicate that

Guaso strata were deposited in shallowest upper-bathyal water depths (Pickering and Corregidor,

2005; Heard and Pickering, 2008; Sutcliffe and Pickering, 2009). Heard and Pickering (2008) document that the Guaso system contains a fundamentally different trace-fossil assemblage than the other turbidite systems in the basin. This distinct assemblage includes ichnotaxa such as

Asterosoma, Agrichnium, and Arenituba, which are relatively rare in deep-marine deposits

(Heard and Pickering, 2008). As such, Heard and Pickering (2008) interpret the Guaso system to be the final and shallowest turbidite system in the basin, preceding the progradational Sobrarbe deltaic system.

Das Gupta and Pickering (2008) and Mansurbeg et al. (2009) document the petrology and diagenetic evolution of the Hecho Group turbidite systems, respectively. The moderately sorted, very fine- to medium-grained sandstones of the Guaso system are classified as feldspathic litharenites on a QFL plot; on the basis of carbonate components, they are carbonate extrarenites, or calcilithites (Das Gupta and Pickering, 2008). Sandstones in the Guaso and Morillo systems are higher in extrabasinal carbonate grains than older systems in the basin, suggesting a common source area for the two systems as well as syndepositional uplift and erosion of pre-basinal carbonate strata exposed in the Mediano anticline (Das Gupta and Pickering, 2008; Moody et al.,

2012). The Guaso system is interpreted as being ponded within the Ainsa basin, as no correlative counterparts are documented west of the Boltaña anticline, in the distal Jaca basin

(Das Gupta and Pickering, 2008; Heard and Pickering, 2008).

The general architecture of the Guaso system has been documented by Stocchi (1992),

Stocchi et al. (1992), and Sutcliffe and Pickering (2009). Stocchi (1992) and Stocchi et al.

(1992) interpreted the system to contain several discrete sandbodies infilling up to 450 m of erosional accommodation. Sutcliffe and Pickering (2009) interpreted the Guaso system to be a structurally confined, low-relief clastic ramp that contained shallow, ephemeral channels fed from the south or southeast. Some of the previous interpretations described above differ considerably with results and interpretations presented herein.

2.4. Data and Methods

Data collected and compiled in order to address the goals of this study are: (1) locations of contacts between turbidite systems, as well as locations of large-scale sandstone, mudstone, and chaotic/contorted bodies in the Guaso I; (2) strike-and-dip measurements of bedding; (3)

~500 paleocurrent measurements from flutes, grooves, parting lineations, and ripples; (4) ~2050 m of cm-scale stratigraphic columns that document bedding contacts and thickness values, amalgamation surfaces, grain sizes, and sedimentologic features such as cross-stratification, dewatering, and presence of trace fossils; and (5) photographs and photopanels that are used to document stratigraphic architecture, lithofacies relationships, and erosional features.

The geologic contacts, strike-and-dip data, and locations of stratigraphic units were compiled with aerial images to produce a geologic map of the Guaso I (Figure 2.3).

Stratigraphic columns were correlated to create cross sections, which document spatial distributions of architectural elements and thickness trends. Also, thickness data from cross sections and field mapping were compiled to produce isopach maps. The isopach maps were used in conjunction with cross sections and paleocurrent data to produce paleogeographic maps.

Hoffman (2009) mapped the boundaries between the uppermost third-order turbidite systems of the Hecho Group (i.e., Ainsa, Morillo, and Guaso) in the Ainsa basin as laterally persistent, dark-gray mudstone layers (Figures 2.3, 2.4). These dark-gray mudstone layers are time-significant surfaces interpreted as condensed sections (Hoffman, 2009). This approach to mapping turbidite depositional systems is similar to Galloway’s “genetic stratigraphic sequences” approach (1989), in which flooding surfaces and three-dimensional facies analyses are elevated in stratigraphic significance over diachronous sequence-bounding unconformities

(cf. Vail et al., 1984; Van Wagoner et al., 1987). Sequence-bounding unconformities (sequence boundaries), which are typically interpreted as being present at the bases of large-scale turbidite sandstone bodies, and their correlative conformities are often equivocal or poorly exposed in the field. Utilizing the condensed section mapping approach in a stratigraphic study has two main advantages: (1) the condensed sections are easily recognizable, topographically recessive intervals that are 2-4 m in thickness; and (2) the condensed sections are chronostratigraphically significant datums for correlation panels (Hoffman, 2009). In this study, the basal condensed section of the Guaso system, coinciding with the base of the Guaso I turbidite system, is locally remapped from Hoffman (2009). The top of the Guaso I is mapped as a laterally persistent dark gray mudstone unit (Figures 2.3, 2.4) that overlies sandstones of the Guaso I and underlies sandstones of the Guaso II.

2.4.1. Lithofacies

Fourteen lithofacies are identified in the clastic portion of the Guaso I depositional system (Figure 2.5; Table 2.1). These lithofacies are differentiated according to their physical, observable characteristics, which are grain size, sorting, bedding thickness values, and primary and secondary physical sedimentary structures. In this study, lithofacies are used to characterize the infill of architectural elements. Table 2.1 is a summary of these lithofacies and their properties. Lithofacies are listed in order of increasing modal grain size.

2.5. Architectural Elements

Architectural-element analysis was first introduced as a field method and classification scheme for fluvial deposits (Miall, 1985). This method subdivides strata of depositional systems into three-dimensional sedimentary bodies, and, as such, it is an improvement over former methods that employed one-dimensional facies models (Miall, 1985). The architectural element approach has subsequently been applied to deepwater clastic deposits, in both modern and ancient turbidite systems (e.g., Mutti and Normark, 1987; Mutti and Normark, 1991; Clark and

Pickering, 1996; Pyles, 2007; Moody et al., 2012; Straub and Pyles, 2012). Four principal architectural elements are identified within the Guaso I depositional system: mudstone sheets, lobes, mass-transport deposits (MTDs), and submarine channels (Figure 2.6). This study employs a hierarchical scheme (e.g., elements, complexes) similar to the one used to classify deposits of the Morillo system, as summarized by Moody et al. (2012).

2.5.1. Mudstone Sheets

Mudstone-sheet elements are laterally extensive (up to tens of kilometers), and are up to tens of meters thick. They maintain a relatively constant thickness across the basin except where they onlap and drape basin-bounding structures. Their bases and tops are planar surfaces (Figure

2.6A) that are conformable with strata above and below, except where locally eroded.

Mudstone-sheet elements comprise laminated to structureless beds of clay- and silt-sized particles. Lithofacies 1 is the preponderant stratigraphic fill of these elements, with subordinate

Lithofacies 4 (Figure 2.5).

Mudstone-sheet elements are interpreted to result from hemi-pelagic deposition, occurring during times when turbidity currents were rare. Hypo-pycnal plumes from a deltaic system to the east or southeast are interpreted to be the source of the fine-grained sediment of the hemi-pelagic deposits. An alternate interpretation for some of the mudstone sheets, however, is that they were deposited as relatively fine-grained levees adjacent to slope channels.

2.5.2. Lobes

Lobe elements are discrete, convex-upward units of sandstone and siltstone that are laterally and longitudinally extensive over a distance of at least 1 kilometer (Pyles, 2007;

Deptuck et al., 2008; Straub and Pyles, 2012). They are thicker in their axes than in their margins. Lobe elements have relatively planar bases (Figure 2.6B), with minor erosional relief located near their depositional axes and in proximal locations. They are mostly conformable with underlying strata. Lobe elements comprise two or more bedsets. Lithofacies 8 is prevalent in lobe elements, but Lithofacies 5, 6, 9, and 10 are also present in lesser proportions (Figure

2.5). Lobe elements are located immediately basinward of their genetically related channels (cf.

Mutti, 1977; Mutti and Normark, 1987).

Lobe elements are interpreted as the deposits of multiple, genetically related turbidity currents that were fed from the same channel. Upon exiting the channel, the turbidity currents expanded radially on the relatively flat basin floor, resulting in laterally extensive beds that are wider than their upstream channel counterparts.

2.5.3. MTDs

Three types of MTDs are identified in the Guaso I depositional system (Figure 2.6C).

Type 1 MTDs extend for tens or hundreds of meters laterally, and they are generally <10 m in thickness. They can have irregular and/or erosional bases, and mudstones within them are commonly deformed. Type 1 MTDs are dominated by Lithofacies 2. Type 2 MTDs extend for tens to hundreds of meters laterally, and they are <10 m in thickness. They have planar or irregular bases which might be locally erosional. Type 2 MTDs comprise varying amounts of

Lithofacies 2 and 12, and clasts within them are angular carbonate granules and pebbles, as well as bioclastic material. Type 3 MTDs can extend for several kilometers in the depositional-dip orientation. They are generally 1-20 m in thickness. Their bases are commonly relatively planar detachment surfaces, and their tops are irregular, planar, or convex-upward. Type 3 MTDs are composed of Lithofacies 3, with lesser amounts of Lithofacies 2 or 12. Sandstone and siltstone beds within Type 3 MTDs are folded and/or contorted. Boulder-sized sandstone and siltstone clasts in a muddy matrix are also present (Figure 2.6C).

MTDs are interpreted to comprise gravity-induced deposits in which the principal transport mechanism involved shear failure along a basal deformed zone accompanied by

20 translation, rotation, and/or folding of the sediment, or distributed shear and laminar flow throughout the body of sediment (Moscardelli and Wood, 2008; Armitage et al., 2009; Amerman et al., 2011). MTDs, therefore, include submarine slumps, slides, and even debris-flow deposits

(debrites), but not turbidites (Moscardelli and Wood, 2008; Armitage et al., 2009). However, individual debrites are not necessarily MTDs, as they can also occur within channels. Type 1

MTDs are interpreted as a comprehensive unit containing mud-rich slumps, slides, and debrites.

Type 2 MTDs are interpreted as carbonate-rich debrites and slides derived from mass failures of carbonate strata located south of the study area. Type 3 MTDs are interpreted as intraformational slumps and slides, comprising previously deposited sediment.

2.5.4. Channels

Channel elements (channels) are stratal units that are thicker in their depositional axes relative to their lateral margins. They are tens or hundreds of meters wide, and they are several kilometers in length. Each channel has an erosional base that is concave-upward and is often mantled by flutes. The amount of erosional relief in channels is similar to the total thickness of the element. The tops of channel elements are often planar and conformable with strata above, except when eroded by younger units. Four different types of channel element are identified in this study (Figure 2.6D).

1. Type 1 channels contain non-amalgamated fills (i.e., discrete bedding contacts within,

and little to no evidence for interbed erosion), and they generally have moderate-to-low

aspect ratios (width:thickness) of ~15-30. Lithofacies 5 and 6 are abundant, with lesser

amounts of Lithofacies 4.

2. Type 2 channels contain non-amalgamated or semi-amalgamated (i.e., sand-on-sand

contacts with internal amalgamation in basal and axial positions, and discrete, non-

erosive bed boundaries at higher and marginal positions) fills and have relatively high

aspect ratios (> 80). These channels comprise Lithofacies 5, 6, and 8. Erosional relief of

these channels is minor, and they are usually < 2 m thick.

3. Type 3 channels contain semi-amalgamated or amalgamated (i.e., high sand content with

extensive internal amalgamation) fills and have low aspect ratios (< 20). These channel

elements can have symmetric or highly asymmetric forms (Figure 2.6D), and they have

highly erosional, fluted bases. Type 3 channels contain Lithofacies 11, 13, or 14 near

their bases and thalwegs, and upper channel fill often comprises Lithofacies 5, 6, 7, and

8. Lithofacies 7 is commonly observed at channel margins.

4. Type 4 channels contain muddy fills and have low aspect ratios (< 20). Their muddy fills

are often debritic. They contain dominantly Lithofacies 2, with minor Lithofacies 1.

A channel generally evolves in two main phases: an initial downcutting phase recorded by a composite erosional surface at the base of the element, and a filling phase which is capped by an abandonment surface or avulsion (Clark and Pickering, 1996; Sprague et al., 2002; Pyles,

2007; Pyles et al., 2010). However, channel elements can sometimes evolve with multiple episodes of erosion and infilling (Clark and Pickering, 1996). Channel elements are conduits in which multiple turbidity currents, and in some cases debris flows, transport sediment downcurrent (Damuth et al., 1983; Mutti and Normark, 1991; Mayall and Stewart, 2000; Moody et al., 2012). Channel elements with finer-grained and/or thin-bedded fills, whether turbiditic

(e.g., Type 1 and 2) or debritic (e.g., Type 4), are interpreted as bypass conduits with varying extents of erosional relief. These channels are interpreted to record predominantly bypass due to

22 the paucity of coarser-grained sediments, which are interpreted as having been transported and deposited farther downcurrent. Also, mudstone drapes, which are interpreted as the tails of bypassing turbidity currents, are often present in Type 1 channels. In contrast, Type 3 channels are usually infilled with coarser-grained sandstone or even conglomerate, and they do not contain evidence for predominant bypass, other than clast-rich lithofacies present above their erosive bases.

It is possible that the different channel types observed in this study represent different phases in the evolution of channels in this depositional system. Under this interpretation, some or all of the channel types would be “genetically related” to one another. For example, broad, shallow Type 2 channels might represent a very early stage in slope channel development; erosional deepening of the channels through time might result in an evolution into Type 1 or

Type 3 channels (Figure 2.6D). Some of the Type 3 channels in proximal areas contain abundant conglomeratic infill (Lithofacies 14; Figure 2.5); these channels might reflect delivery of coarse- grained material (i.e., rounded pebble- to cobble-sized clasts) directly from a deltaic feeder system, or even failure of the updip shelf edge. Type 4 channels, which contain structureless, muddy fills with floating carbonate clasts, might represent distinct downcutting and infilling processes (e.g., early erosion and then mass failure into the channel conduit), however.

2.6. Geology of the Guaso I System

The Guaso I turbidite system crops out along the perimeter of the Buil syncline in the

Ainsa basin (Figure 2.3). Sandstone-rich areas of the outcrop belt of the Guaso I are primarily located along the eastern and northern margins of the basin, whereas areas that contain

23 predominantly mudstone and carbonate strata are located along the western margin of the basin

(Figure 2.3). The outcrop belt is relatively unfaulted, with the exception of a relatively small reverse fault located on the western side of the basin (Figure 2.3). Guaso I paleocurrent data are used to divide the outcrop belt into two principal field areas: the Southeast Field Area and the

Northwest Field Area (Figure 2.3). Paleocurrent measurements in the Southeast Field Area are dominantly westward-directed, whereas paleocurrent measurements in the Northwest Field Area are dominantly northwestward-directed. As such, the Southeast Field Area contains strata deposited in the updip part of the depositional system, and the Northwest Field Area contains strata deposited in the downdip part of the depositional system. Observations from each field area are included below.

2.6.1. Southeast (Updip) Field Area

The Southeast (Updip) Field Area is a 6-km-wide part of the outcrop belt, and it extends from ~2 km southeast of the village of Camporrotuno to ~1 km southwest of the village of

Morillo de Tou (Figures 2.3, 2.7). Most of this field area is located immediately east of the main road to Ainsa, A-138. South of the Southeast (Updip) Field Area, the Guaso I outcrop belt comprises a muddy section that is covered by recent sediment at Embalse de Mediano (Figure

2.3), as well as carbonate-rich debrites and platform carbonates near the southeastern margin of the basin.

Cross section A-A’ (Figure 2.7) documents stratigraphic relationships and architectural elements in the Southeast (Updip) Field Area. The datum for the cross section is surface T5, which is a laterally persistent mudstone layer at the top of the Guaso I interval. The lower bounding surface is T0, which represents the condensed section that is the boundary between the

Guaso and underlying Morillo system (Hoffman, 2009). Correlation surfaces T1-T4 are approximate timelines within the Guaso I.

The Southeast (Updip) Field Area contains mudstone sheets (84.4% of cross-sectional area), MTDs (14.9%), and channel elements (0.7%). There are no lobe elements present in the

Southeast (Updip) Field Area (Figure 2.7). Of the cross-sectional area comprising MTDs, 93.0% is Type 3 MTDs, 6.6% is Type 2, and 0.4% is Type 1. MTDs are most abundant near the middle part of the Southeast (Updip) Field Area, and they decrease in abundance laterally to the southeast and northwest (Figure 2.7). The location of the highest abundance of MTDs, which is south of the village of Coscojuela de Sobrarbe, is near the area where the Guaso I is thickest (215 m), and is therefore termed the “axis” of the Southeast (Updip) Field Area. Several similar Type

3 MTDs are present in a vertical succession at the axis, forming a mass-transport complex

(MTC). This MTC comprises >40% of the total stratigraphic thickness in the axial area (Figure

2.7). Type 3 MTDs are thickest (5 to 20 m) in the lower and middle parts of the Guaso I interval, and are mostly <5 m thick in the upper part of the interval. Type 2 (carbonate-rich) MTDs are located exclusively at the southeast end of the Southeast (Updip) Field Area (Figure 2.7), near the coevally deposited carbonate platform. Type 1 MTDs (muddy debrites and slumps) are rare, and exclusively underlie channel elements.

Of the cross-sectional area comprising channel elements in the Southeast (Updip) Field

Area, 63.9% is Type 2, 15.3% is Type 1, 15.2% is Type 3, and 5.6% is Type 4. Type 2 channel elements are generally <2 m thick, and are located throughout the Southeast (Updip) Field Area at various stratigraphic positions. The largest channel elements are Type 3 and 4 channels comprising the “Roadside Complex” in the northwest part of the Southeast (Updip) Field Area

(Figures 2.7, 2.8). Type 1 channels are only located in the upper part of the Guaso I interval.

The mean paleocurrent direction of turbidites in channel elements throughout the Southeast

(Updip) Field Area is 277°. All channel elements of the Southeast (Updip) Field Area are directed into the cross section (Figure 2.7), toward the axis of the Buil syncline.

2.6.2. Northwest (Downdip) Field Area

The Northwest (Downdip) Field Area extends for ~10 km, comprising the outcrop belt running from ~1.5 km west of Morillo de Tou to ~2.5 km west-southwest of the village of Guaso

(Figures 2.3, 2.9). Much of the extent of this field area includes a prominent ridge formed by

Guaso I sandstone (Figure 2.4B). The northern terminus of this ridge is at the Rio Ena locality, which features the best and most complete exposures of Guaso I sandstone in the Ainsa basin

(Figures 2.3, 2.10). Northwest of the village of Guaso, Guaso I strata are locally covered by modern alluvium from Rio Ara (Figure 2.3). Sandstone in the Guaso I terminates to the west and southwest.

Cross section B-B’ (Figure 2.9) documents stratigraphic relationships and architectural elements in the Northwest (Downdip) Field Area. This cross section utilizes the same datum and timeline surfaces as those in cross section A-A’ (Figure 2.7). Total stratigraphic thickness in outcrops of the Northwest (Downdip) Field Area is greatest (194 m) at the Rio Ena locality

(Figures 2.9, 2.10), and it decreases gradually to the southeast and abruptly to the northwest of this locality (Figure 2.9).

The Northwest (Downdip) Field Area contains mudstone sheets (78.7% of cross-sectional area), MTDs (9.8%), lobe elements (7.2%), and channel elements (4.3%). The proportion of mudstone sheets increases, and total stratigraphic thickness decreases, to the west with increasing proximity to the Boltaña anticline (Figure 2.9). MTDs are thickest and most abundant in the

26 southeast part of the Northwest (Downdip) Field Area, where they comprise ~40% of the Guaso

I strata. All MTDs in the Northwest (Downdip) Field Area are Type 3. MTDs gradually decrease in abundance to the northwest, as the proportion of lobe elements increases (Figure

2.9). The Rio Ena locality features sand-rich lobes (Figure 2.10A) overlain by a mixed association of channels (Figures 2.10B, 2.10C), lobes, and MTDs, which are then overlain by thin-bedded turbidites and mudstone sheets (Figure 2.9). Paleocurrent measurements in lower

Guaso I strata at the Rio Ena locality are consistently northwestward, whereas those higher in the

Guaso I have greater variance, indicating more dispersive sediment transport directions.

Southeast of the bend in cross section B-B’, the proportion of channel elements remains relatively constant, whereas southwest of the bend in section, the abundance of channel elements abruptly decreases (Figure 2.9). Of the channel elements in the Northwest (Downdip) Field

Area, 69.5% are Type 3, 28.2% are Type 1, 1.4% are Type 4, and 0.9% are Type 2. The prominent ridge of Guaso I sandstone (Figure 2.4B) comprises exposures of Type 3 channel elements cropping out nearly continuously, and parallel to sediment transport direction (~345°), for ~3.5 km (Figure 2.9); the ridge is dominated by outcrops of one channel element, with the margins of additional channel elements present. These channel elements are at the same stratigraphic level as the channels of the Roadside Complex (Figure 2.8), and they are in stratigraphic continuity with the lobes in the lower part of the Rio Ena locality (Figures 2.9,

2.10A).

2.6.3. Isopach Maps

Hoffman (2009) used the dip-vector projection method and constructed stratigraphic surfaces (e.g., base Guaso, top Guaso) in a three-dimensional model of the subsurface of the

Ainsa basin based on mapped unit boundaries, strike and dip of bedding, a Digital Elevation

Model (DEM), and two interpreted seismic lines that run perpendicular and parallel to the axis of the basin. The surfaces were used to construct isopach maps for the Ainsa, Morillo, and Guaso depositional systems. The isopach map for the entire Guaso system (Figure 2.11; Hoffman,

2009) is used to guide the contour patterns of the Guaso I gross-interval and net-sand isopach maps (Figure 2.12).

Map patterns documented in Figures 2.11 and 2.12 demonstrate that outcrops of the

Guaso system and Guaso I sub-system, respectively, are thickest in the axis of the Southeast

(Updip) Field Area and at the Rio Ena locality. The thickest succession of Guaso I strata overall is interpreted to be located in the subsurface southwest of the Rio Ena locality, near the axis of the Buil syncline (Figure 2.12A). This isopach “thick” corresponds to the sandiest interval of the

Guaso I (Figure 2.12). However, the outcrop “thick” in the axis of the Southeast (Updip) Field

Area corresponds to an area of low sandstone content. The Guaso I thins drastically to the west, toward the Boltaña anticline; where the Guaso I interval is thin, it has a low sandstone content

(Figure 2.12).

2.7. Paleogeographic Interpretation

A comprehensive paleogeographic interpretation of the Guaso I depositional system is discussed herein. This interpretation is based on the compilation of sandstone- and chaotic- contorted-body mapping (Figure 2.3), paleocurrent indicators (Figures 2.3, 2.7, 2.9), architectural element analysis (Figures 2.7, 2.9), and stratigraphic thickness data (Figures 2.7, 2.9, 2.12). A key assumption of this interpretation is that each channel element entering the outcrop belt in the

Southeast (Updip) Field Area (Figures 2.3, 2.7) is linked to a volume of sediment (i.e., a lobe element) that was deposited on the basin floor, currently located in the subsurface of the Buil syncline or in the outcrop belt of the Northwest (Downdip) Field Area (Figures 2.3, 2.9). This assumption is predicated on a key outcrop example, the ridge-forming Type 3 channels that correlate to lobes at the Rio Ena locality (Figures 2.9, 2.10A). The paleogeographic interpretation is divided into five time intervals (T0-T1; T1-T2; T2-T3; T3-T4; and T4-T5), based on correlated surfaces documented in the stratigraphic cross sections (Figures 2.7, 2.9).

Time T0 reflects the inherited boundary condition that is interpreted as being the result of an increased rate of tectonically induced subsidence relative to sediment supply (cf. trends documented in the Auger basin by Booth et al., 2000). At T0, no sandstone was deposited anywhere in the Ainsa basin, and deposition of the condensed section at the base of the Guaso system took place (Figure 2.13). Sediment supply to the Ainsa basin might have been reduced at

T0 due to changes in relative sea level and associated factors (e.g., locations of sediment sequestration), or climatic changes (Pickering and Bayliss, 2009). From T0-T1, turbidite channels served as conduits for turbidity currents traveling westward and northwestward to deposit volumes of sediment (i.e., lobes) in the nascent, areally confined depocenter (Figure

2.13), which is currently only present in the subsurface of the Buil syncline. Some of these channels exposed in the Southeast (Updip) Field Area contain conglomeratic fills defined by an abundance of rounded clasts; these Type 3 channels might represent incision of the shelf with delivery of deltaic material to the upper slope. A small number of MTDs were also deposited during this time interval (T0-T1), mostly in the Southeast (Updip) Field Area (Figure 2.13).

These channels and MTDs comprise the early deposits of the Guaso I feeder system, which generally coincides with the Southeast (Updip) Field Area (Figures 2.3, 2.7, 2.13). From T0-T1,

29 the ratio of accommodation generation relative to sediment supply (A:S) was higher than all subsequent depositional intervals of the Guaso I.

From T1-T2, westward-oriented channels in the Southeast (Updip) Field Area continued to feed lobes on the areally confined basin floor (Figure 2.13). All of these lobes are interpreted to be present in the modern subsurface, as no sand-rich lobe elements crop out in the Northwest

(Downdip) Field Area between T0 and T2 (Figures 2.9, 2.13). Several large MTDs were also deposited and stacked to form an MTC in the axis of the feeder system (Figures 2.7, 2.13). It is possible that these MTDs travelled through existing channels, or even partially excavated broader conduits as they traveled downdip. During this interval, A:S decreased slightly relative to T0-T1, and effective area of deposition is interpreted to have increased slightly (Figure 2.13).

From T2-T3, we interpret that the effective area of deposition broadened more rapidly than in previous intervals. The evidence for this interpretation is the observation that lobe elements first appear in the outcrop belt of the Northwest (Downdip) Field Area in the T2-T3 stratigraphic interval (Figures 2.9, 2.13), whereas channel elements are present in the outcrop belt of the Southeast (Updip) Field Area as early as the T0-T1 interval (Figures 2.7, 2.13). This observation implies that the older channels were feeding older volumes of sediment that currently must be present in the areally confined subsurface, as no sand-rich strata crop out along the western flank of the Buil syncline at this lower stratigraphic interval (Figures 2.3, 2.13).

Paleocurrent data indicate that much of the outcrop belt of the Northwest (Downdip) Field Area is in an off-axis position relative to the entire Guaso I depositional system; the main depositional axis lies in the subsurface west of most of the sandstone of the Northwest (Downdip) Field Area

(Figures 2.3, 2.13). The ridge-forming Type 3 channels are eastern outliers, relative to other

30 channels of the depositional system (Figure 2.13). From T2-T3, A:S continued to decrease as lobe elements were deposited in a larger area on the basin floor.

From T3-T4, channels of the feeder system continued to feed lobes on the interpreted basin floor (Figure 2.10A), at Rio Ena and other localities in the northern part of the Northwest

(Downdip) Field Area (Figures 2.9, 2.13). There are also channels (Figures 2.10B, 2.10C) and

MTDs present at these basin-floor localities, suggesting a new trend observed in the vertical and spatial associations of Guaso I architectural elements. Paleocurrent measurements at these localities indicate a wide range (almost 180°) in sediment transport directions (Figure 2.9). From these paleocurrent and architectural trends, we interpret an increase or broadening of the effective area of deposition through time as the Guaso I submarine fan built outward to the west, north, and east, and the basin continued to fill (Figure 2.13). There was a marked decrease in

A:S during this interval.

In the stratigraphic interval from T4-T5, the abundance of sand-rich elements and MTDs decreased considerably (Figures 2.7 and 2.9), which is interpreted to record the waning of the

Guaso I depositional system. Lobe elements in this interval are relatively thin, areally extensive, and dominantly comprise Lithofacies 5 and 6. MTDs in this interval are also thinner compared to older MTDs. As a result of the observations above, this interval is interpreted to have the broadest effective area of deposition (Figure 2.13), but the least accommodation; A:S was relatively low. At T5, the areally extensive top Guaso I mudstone was deposited, effectively blanketing the basin at the end of Guaso I deposition.

2.8. Discussion

The following section integrates the observations and interpretations of this study into discussions of the stratigraphic evolution of this depositional system, as well as a geometric model for ponded deepwater basins and applications of this study to hydrocarbon exploration.

2.8.1. Stratigraphic Evolution of the Guaso I Turbidite System

The Guaso I turbidite system is interpreted here as a ponded, distributive submarine fan, meaning that all coarse sediment that entered the Ainsa basin from the east or southeast was trapped within the accommodation defined by the relief between the basin floor and the basin’s distal sill, the crest of the syndepositionally active Boltaña anticline (cf. “ponded basin fill” in

Beaubouef and Friedmann, 2000). This interpretation is supported by isopach trends (e.g., thinning toward the Boltaña anticline; Figures 2.11, 2.12), paleocurrent data (Figures 2.3, 2.7,

2.9), and the lack of any age-equivalent strata in the nearby Jaca basin (Das Gupta and Pickering,

2008; Heard and Pickering, 2008).

This study’s interpretation of the Guaso I turbidite system as a ponded, distributive submarine fan is somewhat at odds with the previous interpretation that the system was a low- relief clastic ramp containing shallow, ephemeral channels sourced from a delta prograding into the basin from the south (cf. Sutcliffe and Pickering, 2009). Thickness patterns in isopach maps, as well as paleocurrent data, suggest that the Guaso I system was mostly fed from the east

(Figures 2.3, 2.7, 2.11, 2.12). If the Guaso I had been fed by northward-directed channels, which would have necessarily incised the carbonate platform on the southern margin of the basin

(Figure 2.13), then there would have to be relatively coarse carbonate fragments within the

Guaso I sandstone; such evidence is not present, except at the most southeastern outcrops in the field area. Observations of unequivocal, discrete, westward- and northwestward-directed channels in the Southeast (Updip) Field Area, as well as lobes overlain by a mixed association of architectural elements in the Northwest (Downdip) Field Area, support a ponded, distributive fan interpretation (Figure 2.13). Furthermore, the sandstone content at downdip localities such as

Rio Ena is much higher than updip localities (Figure 2.12B), implying that there was some degree of bypass on the slope with preferential deposition of sand on or near the basin floor.

Various workers have documented that large-scale (i.e., third-order) stratigraphic infill patterns in initially ponded deepwater accommodation usually include an early phase that contains predominantly sheet-sand deposits in the downdip part of a basin, followed by a later channelized phase recording a temporal increase in flow stripping and then bypass (Beaubouef and Friedmann, 2000; Booth et al., 2000; Sinclair and Tomasso, 2002). These patterns reflect gradually decreasing accommodation during deposition, and they are partly analogous to the trend documented within the fourth-order cycle of the Guaso I turbidite system, which is: initial aggradation of lobes on the areally confined basin floor, followed by an upward increase in channel elements accompanied by a more distributive arrangement of channels, lobes, and MTDs in an expanding depocenter. Paleocurrent data confirm that the Guaso I turbidite system became more distributive through time (Figure 2.13). However, leveed channel complexes are not present in the basin-floor deposits of the Guaso I, unlike the various depositional systems documented in the Brazos-Trinity slope basins, and there is no evidence for a flow-stripping-to- bypass phase. The final stage of the Guaso I cycle (T4-T5) exhibits evidence for decreasing depositional energy of the system (e.g., thin-bedded, areally extensive strata), followed by deposition of a capping mudstone.

The apparent increase in compensational stacking, which is the tendency for sediment transport systems to preferentially fill topographic lows before switching to a new locus of deposition (Straub et al., 2009), of Guaso I elements is interpreted as an autocyclic response to decreasing A:S and increasing depositional area through time. This process results in greater diversity in architectural element stacking patterns at later stages within ponded, fourth-order submarine fan growth. This study is the first to document this pattern in ponded, fourth-order submarine fans, although the trends described above are similar to those reported for third-order units in the Ross Sandstone (Pyles 2008). Subsequent, younger fourth-order cycles might also exhibit a high level of architectural diversity. However, these later cycles have different depositional patterns because they are influenced increasingly by factors such as flow stripping and bypass which are not as influential during initial stages of ponding (Sinclair and Tomasso,

2002).

2.8.2. Geometric Model

This article documents upward, lateral, and longitudinal changes in the stratigraphic architecture of the Guaso I turbidite system. Here we derive a geometric model that is based on observations and interpretations from the Guaso I. This model can be applied to other ponded, distributive submarine fans where depositional area increases upward within fourth-order depositional cycles. The model describes how compensational stacking of lobe and channel elements increases upward in the succession, and how this process is imprinted on the stratigraphic succession.

Figure 2.14A presents diagrammatic maps of two phases in the sequential evolution of a ponded, distributive submarine fan. The map on the left represents the early or lower part of the

34 succession, which is based on the stratigraphic architecture of the lower part of the Guaso 1 system (i.e., T0-T2; Figures 2.9, 2.13). In this map, the distributive submarine fan inherits a ponded, bowl-shaped basin where the effective area of deposition is similar to the area of individual lobe elements. As such, successive lobe elements stack aggradationally, and the axes of stratigraphically adjacent lobes are nearly superimposed and have similar orientations.

Therefore, the amount of compensational stacking () is suppressed and can be described as

lim κ = 0 (1), 퐴푙→퐴푒푓푓

where Al is the area of a lobe element and Aeff is the effective area of deposition. Straub et al.

(2009) developed a metric for quantifying compensational stacking (), where =1 represents strongly compensational systems and =0 represents non-compensational systems. Figure 2.14B is a graph that describes how  relates to Aeff/Al (for a ponded, distributive submarine fan). The limit expressed in Equation 1 represents point 1 (1,0) on the plot. As the bowl-shaped basin fills, the effective area of deposition increases, resulting in a condition where Aeff greatly exceeds Al.

This is the condition shown in the map on the right of Figure 2.14A . In this scenario, the  is high and can be described as

lim κ = 1 (2). 퐴 푙 →0 퐴푒푓푓

This is similar to the architectural style documented in the upper part of the Guaso I system (T2-

T4) at Rio Ena (Figures 2.9, 2.13). The limit expressed in Equation 2 represents point 2 (∞, 1) on the graph in Figure 2.14B.

An alternate approach to modeling this process is to use longitudinal proportions of channel and lobe elements in the ponded, distributive submarine fan. The graphs to the left of the schematic diagrams in Figure 2.14A document cumulative proportions of channel elements and lobe elements along longitudinal profiles through the basins. In the lower part of the basin fill, where Al ≈ Aeff, channel elements are not located in the depocenter of the distributive fan.

This is a geometric necessity that is evident in the lower Guaso I system. This concept can be described as

퐴 퐴 lim 푐 = 0; lim 푙 = 1 (3), 퐴푙→퐴푒푓푓 퐴푒푓푓 퐴푙→퐴푒푓푓 퐴푒푓푓

where Ac is the area of channel elements. The stratigraphic manifestation of this process is shown in the lower part of Figure 2.14C. In contrast, in the upper part of the basin fill, where

Al<

퐴 lim 푐,푙 = 1 (4), 퐴 퐴 푙 →0 푒푓푓 퐴푐,푙

where Ac,l is the area of the fan with a mixed association of channel and lobe elements. The stratigraphic manifestation of this process is shown in upper part of Figure 2.14C.

Collectively, equations 1 through 4 describe the patterns defined in the Guaso I turbidite system using geometrically reasonable limits that relate compensation and architectural associations to Al/Aeff such that Ac,l/Aeff . One important characteristic documented in this article is that the Guaso I system transfers from a low to high architectural diversity when Aeff/Al

≈ 5 (Figure 2.13). This value represents point 3 on the graph in Figure 2.14B. Therefore, 

36 begins to asymptotically approach 1 when Aeff/Al ≈ 5 (Figure 2.14B). The observations indicate that Aeff/Al is related to , which is semi-empirically modeled as

퐴푒푓푓 −0.5( −1) 퐴푒푓푓  = 1 − 푒 퐴푙 , where ≥ 1 (5). 퐴푙

This model honors the natural limits expressed in equations 1-4, intersects points 1, 2, and 3 in

Figure 2.14B, and provides a plausible model that can be applied to subsurface studies where effective area of deposition (Aeff) and area of lobe (Al) can be delineated. However, in instances where Al cannot be defined, we encourage use of outcrop and subsurface analogs. For example, lobe dimensions reported from the Navy fan (Normark et al., 1979), the Ross Sandstone (Pyles,

2007), Karoo basin (Prelat et al., 2009), and the Corsica fan (Deptuck et al., 2008) are remarkably similar.

2.8.3. Applications to Hydrocarbon Exploration

Turbidite sandstone reservoirs with good static reservoir connectivity and high porosity and permeability values are common in ponded and structurally confined slope basins in the Gulf of Mexico and around the world (Weimer and Pettingill, 2007). Isopach thicks due to MTCs often occur near the entry points to these basins (Badalini et al., 2000; Beaubouef and

Friedmann, 2000; Winker and Booth, 2000). These MTCs exhibit low-amplitude, chaotic seismic facies character, and they are generally very poor reservoirs (Beaubouef and Friedmann,

2000; Booth et al., 2003). They can also influence subsequent deposition of turbidite sandstone in the basin (Badalini et al., 2000; Winker and Booth, 2000). The downdip basin floor is often where the thickest successions of high-reservoir-quality turbidite sandstone are deposited,

37 particularly in the earliest phases of a basin’s ponded phase (Beaubouef and Friedmann, 2000;

Winker and Booth, 2000; Booth et al., 2000).

The above observations from ponded basin-fill successions align closely with observations from the Guaso I depositional system. This study, however, provides an enhanced level of detail documenting internal architectural trends within isopach/isochron thicks in a ponded basin-fill phase (Figures 2.12, 2.13). It is this detailed understanding of isopach/isochron map trends that augments seismic interpretations of ponded turbidite reservoirs, particularly for those in areas of sparse well data. There are two prominent thicks in the outcrop belt of the

Guaso I (Figure 2.12A): one in the Southeast (Updip) Field Area (feeder system), and the other in the Northwest (Downdip) Field Area (basin floor). In the feeder system, the isopach thick comprises mudstone sheets and a prominent MTC (composed of several discrete MTDs), with some channels (Figure 2.7). In the basin-floor area, the isopach thick includes the sandiest exposed section in the depositional system, comprising lobes and channels, as well as mudstone sheets and muddy MTDs (Figure 2.9). These outcrop thicks actually comprise just one continuous thick coinciding with the axis of the depositional system (Figure 2.12A).

This study also documents an increasing diversity in stacking patterns of sand-rich elements in a fourth-order, reservoir-scale package through time (Figures 2.9, 2.13); aggradation of elements decreases and compensational stacking increases. As the effective area of deposition expands, the likelihood of encountering a non-reservoir element (e.g., MTD) between stratigraphically adjacent sand-rich channels and lobes increases. The geometric model proposed herein (Equations 1-5 and Figure 2.14) has important implications for trends in static reservoir connectivity within a fourth-order submarine fan; static reservoir connectivity decreases upward within the initial ponded depositional cycle of a confined deepwater basin.

2.9. Conclusions

The Guaso I turbidite system is a fourth-order, reservoir-scale package that was deposited in the Ainsa basin during the Lutetian (middle Eocene). This structurally confined, ponded distributive submarine fan was fed by westward- and northwestward-oriented channels (Figure

2.13) currently exposed in the Southeast (Updip) Field Area and parts of the Northwest

(Downdip) Field Area (Figures 2.3, 2.7, 2.9). The syndepositionally active Boltaña anticline

(Figures 2.3, 2.12, 2.13) served as the confining topography at the distal northwestern end of the basin during deposition of the Guaso I turbidite system; strata become thinner toward this structure (Figures 2.11, 2.12).

This study documents an isopach thick that coincides with the axis of the Guaso I depositional system. In the proximal feeder system, the isopach thick is due to a mass-transport complex; on the basin floor, the isopach thick is largely due to a thick succession of reservoir- quality sandstone. The depocenter of this structurally confined deepwater basin is the location of greatest sandstone content (Figures 2.12, 2.13).

We employ the architectural-element approach in order to document the stratigraphic evolution of the Guaso I turbidite system. We find that in early stages of this depositional system, lobe elements aggraded on the relatively confined basin floor. As the basin filled, depositional area increased; this resulted in an upward increase in compensational stacking of architectural elements. Paleocurrent data confirm that the system became more distributive through time. Therefore, architectural diversity increased upward. These upward patterns can be explained by a simple geometric model that relates compensational stacking (κ) to the ratio of effective depositional area to area of lobe elements (Aeff/Al). Documenting and predicting these patterns has important implications for static reservoir connectivity and hydrocarbon production.

This study is unique in that it provides a detailed (i.e., element-scale) documentation of architectural diversity and stratigraphic evolution within a fourth-order, ponded turbidite system.

2.10. Acknowledgments

This paper has benefitted from enlightening discussions with Renaud Bouroullec, Chris

Guzofski, Morgan Sullivan, Thomas Heard, Jeremiah Moody, Jane Stammer, Rob Amerman, and Jesse Pisel. GSG would like to thank his field assistants in the Ainsa basin: Erich

Heydweiller, Jane Stammer, Jeremiah Moody, and Grace Ford. Primary funding for GSG’s

Ph.D. research was provided by the Chevron Center of Research Excellence at the Colorado

School of Mines; additional funding has come from a GCS SEPM Ed Picou Fellowship, a

ConocoPhillips SPIRIT Scholarship, the Bartshe Family Fellowship, and a Devon Energy

Scholarship. We thank Charlie Rourke, Cathy VanTassel, and Linda Martin at the Chevron

Center of Research Excellence for indispensable logistical and technical support.

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Figure 2.1. Diagram of an intraslope basin and its constituent ponded, distributive submarine fan, where channel elements of the feeder system longitudinally transfer to lobe elements on the basin floor. Thrust-cored anticlines are the confining topographic features in this illustration; however, in different basins, salt-related structures or normal faults may form the confining topography.

Figure 2.2. A) Paleogeographic map of the Southern Pyrenees region during deposition of turbidite systems in the Ainsa basin (Ypresian-Lutetian). Inset map shows location of Ainsa basin in modern-day Spain. (Maps modified from Muñoz et al., 1998; Fernandez et al., 2004; Moody et al., 2012.) B) Tectonic cross section of the doubly-vergent Pyrenees fold-thrust belt in the Lutetian (modified from Puigdefabregas et al., 1992). C) Cross-sectional stratigraphic diagram for Ainsa and Jaca basins in the Eocene (modified from Das Gupta and Pickering, 2008; Pickering and Bayliss, 2009; Moody et al., 2012). Ainsa basin strata are located in between the Mediano and Boltaña anticlines (locations shown at the bottom of the diagram). D) Chronostratigraphic chart for Ainsa basin in the Eocene (modified from Moody et al., 2012). Third-order depositional systems are included in this chart as formations.

Figure 2.3. Geologic map of the Guaso I depositional system, Ainsa basin. The outcrop belt of the Guaso I lies between the base Guaso condensed section (bold blue line) and the top Guaso I mudstone (bold green line). Inset map shows the position of the Guaso system in the basin, relative to other depositional systems and to the key syndepositionally active bounding structures, which are the Boltaña and Mediano anticlines (modified from Hoffman, 2009; Moody et al., 2012). (Parts of the base Guaso condensed section, locations of folds and faults, and some strike-dip measurements are from Hoffman, 2009, and Setiawan, 2009.)

Figure 2.4. Annotated photopanels documenting stratigraphic relationships in the Guaso I depositional system. A) Base of Guaso I sandstone at the Rio Ena and El Grado localities, with base Guaso I condensed section (blue line) below and top Guaso I mudstone (green line) above. The Guaso system is named after the village of Guaso (see Figure 2.3 for location), located near the top of this photograph. Guaso village is built upon outcrops of Guaso II. View looking northwest. B) View of Guaso I outcrops located along the eastern flank of the Buil syncline. This view is looking northwest toward the Boltaña anticline. See Figure 2.3 for location of Buil syncline and Embalse de Mediano.

Figure 2.5. Representative photographs and brief descriptions of the lithofacies of the Guaso I depositional system. The lithofacies are ordered according to their grain sizes, with Lithofacies 1 being the finest-grained and Lithofacies 14 being the coarsest-grained. See Table 2.1 for a full description and interpretation of these lithofacies.

Figure 2.6. Representative photographs of the different types of architectural elements in the Guaso I depositional system: A) mudstone sheets; B) lobe, with internal bedset boundaries (yellow lines); C) Type 1-3 MTDs; and D) Type 1-4 channel elements. A detailed description of each is included in the text.

Figure 2.7. Stratigraphic cross section (A-A’), cumulative proportion curves, and pie charts documenting the stratigraphy and architectural elements of the Southeast (Updip) Field Area (see Figure 2.3 for location). Architectural elements shown in the covered regions are interpreted based on adjacent elements and nearby topographic features. Sediment transport directions are generally into the page and to the right (~westward), as expressed in the rose diagram.

Figure 2.8. Photographs of the Roadside Channel Complex, located immediately east of the main road to Ainsa (A-138). Location of this channel complex is shown on Figures 2.3 and 2.7. Sediment transport direction is out of the page and to the right. A) Interpreted photopanel and stratigraphic columns documenting the architecture of the Roadside Channel Complex. This channel complex comprises parts of three channel elements. Boundaries between elements are indicated by bold red lines. The margin of channel element 1 is exposed, and it is composed of Lithofacies 7. Channel element 2 is in erosional contact with channel element 1, and it is composed entirely of Lithofacies 2. Channel element 3 is in erosional contact with channel element 2, and it contains semi-amalgamated fill. The best reservoir-quality sandstone in the complex is composed of Lithofacies 8 and 11 (Figure 2.5, Table 2.1), and it is present in channel element 3. Static reservoir connectivity (sensu Funk et al., 2012) between each of these channel elements is low. B) Photograph of the fluted, erosional base of channel element 3. This erosional base separates Lithofacies 11 (above) from Lithofacies 2 (below). C) Red dashed line is a representative amalgamation surface between stratigraphically adjacent beds of Lithofacies 11 in channel element 3.

Figure 2.9. Stratigraphic cross section (B-B’), cumulative proportion curves, and pie charts documenting the stratigraphy and architectural elements of the Northwest (Downdip) Field Area (see Figure 2.3 for location). Architectural elements shown in the covered regions are interpreted based on adjacent elements and nearby topographic features. Sediment transport directions are generally to the northwest, as expressed in the rose diagrams. However, in the vicinity of the Rio Ena and El Grado localities, channel and lobe elements contain a wide range of paleocurrent values. Paleocurrent data and field mapping of the outcrop belt indicate that several channel and lobe elements enter and exit the plane of this cross section, particularly at higher stratigraphic levels. All MTDs in the Northwest (Downdip) Field Area are Type 3 MTDs.

Figure 2.10. Photographs of Guaso I strata at/near the Rio Ena locality (see Figures 2.3, 2.12, 2.13 for location). A) Photopanels of a lobe exposed on a cliff above Rio Ena. Yellow lines are conformable boundaries between constituent bedsets, whereas red lines are erosive and scoured surfaces. Intra-element erosion and scouring are present at this locality. B) Channel element exposed in the upper part of the Rio Ena section. The axis of this element contains Lithofacies 11 and 13, whereas the margin contains Lithofacies 7 (see Figure 2.5). Red line at the base of the channel denotes the erosional boundary of the element. C) Two offset-stacked channel elements in the upper part of the Rio Ena section. Red lines indicate the erosional lower boundaries of the channel elements. Stratigraphic-up is toward the top of the page. D) Relatively thick succession (~60 m of visible strata) of high-net-sandstone-content Guaso I strata at “Waterfall Canyon” section (Rio Ena locality). This succession comprises lobes at the base that are overlain by a mixed association of lobes with channels and MTDs, which are in turn overlain by thin-bedded turbidites and mudstone sheets.

Figure 2.11. Gross-interval isopach map for the entire third-order Guaso system (modified from Hoffman, 2009). The map is based on structural modeling of field data, seismic profiles, and stratigraphic surfaces, and it is used to help guide subsurface contour interpretations for the Guaso I isopach maps (Figure 2.12). Compaction effects have not been removed; compaction might be enhanced preferentially in sand-poor areas.

Figure 2.12. Gross-interval (A) and net-sand (B) isopach maps of the Guaso I depositional system. Red dots denote outcrop-based data points that constrain the interpretation. Dashed lines indicate areas that are extrapolated beyond the outcrop belt, whereas dashed-and-dotted lines indicate areas in the subsurface that are interpreted. A) Gross-interval isopach map of the Guaso I. The gross-interval isopach thick for the Guaso I is located in the subsurface southwest of the Rio Ena locality. Compaction effects have not been removed; compaction might be enhanced preferentially in sand-poor areas. B) Net-sand isopach map of the Guaso I. The net- sand isopach thick is located in the subsurface southwest of the Rio Ena locality, and it coincides with the gross-interval isopach thick.

Figure 2.13. Paleogeographic interpretation of the Guaso I turbidite system, from time T0 (deposition of the basal condensed section) through T5 (deposition of the top Guaso I mudstone), showing cumulative changes in the depositional system. Each of the time surfaces (T0-T5) between the intervals is labeled on Figures 2.7 and 2.9. The current outcrop belt of the Guaso I is defined as the area between the blue and green lines (base Guaso condensed section and top Guaso I mudstone, respectively). Light blue, brown, and beige elements are MTDs. Sandstone-rich elements (e.g., channels and lobes) are colored various shades of yellow.

Figure 2.14. Geometric model for the stratigraphic infill of ponded deepwater basins. A) Mapview and diagrammatic cross sections of two phases in the sequential evolution of a ponded, distributive submarine fan. The effective area of deposition comprises varying proportions of architectural elements (e.g., lobes vs. channels) at different stratigraphic stages. B) Graph relating the amount of compensational stacking (κ), to the ratio of effective depositional area to depositional area of lobes (Aeff/Al). See text for discussion of points 1-3 (red dots on graph). C) Pseudo-gamma-ray log profile for the lower and upper parts of a ponded deepwater cycle. This profile, which is based on observations at the Rio Ena locality, applies for a well located near the middle of the basin; a well located along the margin of the basin would have a different profile. The lower and upper parts of the profile have distinctive vertical trends and associations of architectural elements. These differences are interpreted to reflect increased compensational stacking upward due to increased depositional area.

Table 2.1. Characteristics of lithofacies in the Guaso I depositional system.

Lithofacies Modal Net- Interpreted Interpreted Comparison to other grain sand depositional process flow type studies size(s) content (%) hypo-pycnal 1) Gray, nodular-to-fissile Te (Bouma, 1962); F9a [Te] clay 0 suspension plume; fine-grained mudstone (Mutti, 1992) turbidity current 2) Structureless, gray mudstone clay [clasts: frictional freezing, F1 (Mutti, 1992); Facies 1 (Cronin matrix, w/ rounded dark gray granules- 0 muddy debris flow cohesive freezing et al., 1998) carbonate clasts pebbles] Facies 2 (Cronin et al., 1998); 0 (no 3) Contorted/folded sandstone and clay [sand "Type Ia MTCs" (Pickering and effective siltstone beds; boulders and fraction: frictional freezing slumps, slides Corregidor, 2005); "slump", reservoir cobbles in muddy matrix fine sand] "slide" (Martinsen and Bakken, sandstone) 1990) clay [sand 4) Thin-bedded, interbedded sandstone: Ta, Tb, or Tc (Bouma, fraction: suspension and tractive sandstone and mudstone; < 10% < 10 turbidity current 1962); mudstone: Td or Te very fine sedimentation net-sand content (Bouma, 1962); F9a (Mutti, 1992) sand] clay [sand sandstone: Ta, Tb, or Tc (Bouma, 5) Thin-bedded, interbedded fraction: suspension and tractive 1962); mudstone: Td or Te sandstone and mudstone; 10 - 10 - 50 turbidity current very fine sedimentation (Bouma, 1962); F9a (Mutti, 1992); 50% net-sand content sand] Facies 3 (Pyles et al., 2010) fine sand sandstone: Ta, Tb, or Tc (Bouma, 6) Thin-bedded, interbedded [mud suspension and tractive 1962); mudstone: Td or Te sandstone and mudstone; > 50% > 50 turbidity current fraction: sedimentation (Bouma, 1962); Facies 4 (Pyles et net-sand content clay] al., 2010) Tc (Bouma, 1962); F9a [Tc] tractive sedimentation 7) Thin-bedded, ripple-laminated to (Mutti, 1992); Facies 11 or 13 very fine (lower flow regime); climbing-ripple-laminated ~60-80 turbidity current (Gardner et al., 2003); CRCL (Jobe sand mixed tractive and sandstone et al., 2012); “channel-margin suspension sedimentation facies” (Mutti, 1977)

Ta [structureless], Tb [planar- 8) Thin- to thick-bedded, suspension [structureless]; laminated] (Bouma, 1962); Facies structureless to planar-laminated, fine sand 100 tractive [planar- turbidity current 7 [structureless] and 8 [planar- well-sorted sandstone laminated] laminated] (Gardner et al., 2003) initial suspension or 9) Thin- to thick-bedded sandstone tractive sedimentation, with dewatering and/or load fine sand > 90 turbidity current Ta or Tb (Bouma, 1962) followed by dewatering, structures or loading from above Facies 4, Facies 6 (Gardner et al., 10) Medium- to thick-bedded 2003); base of Tt division (Lowe, sandstone w/ cross-stratification fine sand > 95 tractive sedimentation turbidity current 1982); F6 (Mutti, 1992); Facies 7 (and/or “dune” bedforms) (Pyles et al., 2010) 11) Medium- to thick-bedded, medium S3 (Lowe 1982); Facies 5 (Gardner commonly amalgamated > 95 suspension turbidity current sand et al., 2003); F5 (Mutti, 1992) sandstone w/ rare shale clasts 12) Structureless, poorly-sorted 0 (no sandstone matrix w/ granule- and medium sandy debris flow, F1 (Mutti, 1992); possibly "slurry- reservoir- pebble-sized clasts (rounded sand [clasts: cohesive freezing or possibly a flow deposits" (Lowe and Guy, quality carbonates and sub-angular pebbles] “hybrid flow” 2000) sandstone) sandstone)

13) Medium- to thick-bedded, medium possibly F3 (Mutti, 1992), Facies 2 primarily matrix-supported suspension and tractive high-density sand [clasts: ~70-90 (Gardner et al., 2003), or Facies 8 shale-clast conglomerate; matrix sedimentation turbidity current pebbles] (Pyles et al., 2010) is medium-grained sand 20-40 14) Medium- to thick-bedded, clast- (dependent supported pebble-cobble fine sand upon high-density conglomerate in sandy matrix; [clasts: tractive/bedload F3 (Mutti, 1992); R3 (Lowe, 1982) shape and turbidity current clasts are rounded carbonate and pebbles] diameters sandstone of clasts) ______

CHAPTER 3.

FLOW PROCESSES, SEDIMENTATION, AND STRATIGRAPHIC EVOLUTION OF

THE SUBMARINE CHANNEL-LOBE TRANSITION ZONE:

AN OUTCROP-BASED STUDY

A paper that has been submitted to Sedimentology

Gregory S. Gordon and David R.Pyles

3.1. Abstract

The submarine channel-lobe transition zone (CLTZ) is the region on a submarine fan that marks the interface between updip channels and downdip lobes. At the scale of an individual architectural element, the CLTZ governs sandstone connectivity between a channel and a lobe, and it serves as the link between locally confined and unconfined conditions for sediment gravity flows that build the submarine fan. Outcrops of the Guaso I turbidite system of Ainsa basin,

Spain, include a continuous, ~4-km-long, paleocurrent-parallel transect through a channel-lobe element. Key longitudinal changes across the CLTZ in this depositional system are: thickening of the element in a downcurrent direction, due to oldest bedsets of the proximal lobe that thin and pinch out completely onto the erosive lower contact in an upcurrent direction; a basinward decrease in the amount of erosion at the base of the element; basinward decreases in intra- element erosion and amalgamation surfaces; sandstone continuity from the updip channel to the downdip lobe; a base-of-slope depositional angle of ~2°, based upon stratigraphic thickness measurements. Point counting and grain-size analyses document that sandstones of the CLTZ

and the lobe are generally finer-grained and better sorted than channel sandstones. This is interpreted to be due to different combinations of depositional processes operating in the locally confined (channel) domain and the unconfined (CLTZ and lobe) domain. A four-stage sequential model that describes the stratigraphic architecture and evolution of a channel-lobe element is presented herein. Results of this study have important implications for reservoir and fluid-flow modeling in distributive channel-lobe systems.

3.2. Introduction

Distributive submarine fans contain channels and their basinward lobes that compensationally stack to build a radially dispersive map pattern (Figure 3.1). The interface between channels and lobes is broadly referred to as the channel-lobe transition zone (Mutti and

Normark, 1987; Wynn et al., 2002; Pyles, 2004). The term channel-lobe transition zone (CLTZ) applies to a range of different scales. At the scale of an entire submarine fan, the term applies to the region between the updip channelized area and the downdip area that contains predominantly lobes (Figure 3.1A). At the smallest scale, the term applies to the interface between an individual channel element and its basinward lobe element (Figure 3.1B).

The CLTZ is perhaps the least documented morphologic region on submarine fans

(Wynn et al., 2002). At various scales of observation, however, the CLTZ has been shown to contain a diverse assemblage of both erosional and depositional features (Normark et al., 1979;

Mutti and Normark, 1991; Vicente Bravo and Robles, 1995; Wynn et al., 2002). Identification of the CLTZ in outcrops of ancient systems can be equivocal (Wynn et al., 2002; Mutti and

Normark, 1991), due to a paucity of continuous exposures of updip channels to basinward lobes.

Previous outcrop studies have documented sandbodies of the larger-scale canyon-to-basin transition (e.g., Millington and Clark, 1995), or facies associations and sedimentologic features

(e.g., scours, megaflutes) interpreted to be indicative of the CLTZ (e.g., Kemp, 1987; Smith,

1987; Vicente Bravo and Robles, 1995; Cornamusini, 2004). Studies of submarine fans and their constituent CLTZs on the modern seafloor, which employ side-scan sonar and multibeam bathymetric mapping technology, provide lateral resolutions up to 1.5 m and vertical resolutions up to 0.3 m (e.g., Normark et al., 2009), but these studies essentially document a static image of relatively local fan relief and morphology in a dynamic depositional environment (Fildani et al.,

2013). Deposits of the CLTZ, at any scale, are thought to have a relatively low preservation potential due to their position in an erosive environment that is adjacent to their genetically related channels (Wynn et al., 2002). Further, studies of modern and ancient turbidite systems provide inherently differing levels of detail, due to differences in seismic, side-scan sonar, and outcrop-based datasets (Mutti and Normark, 1991; Morris and Normark, 2000). Gaining a greater knowledge of the stratigraphy and sedimentology of the CLTZ, however, remains very important, as this region governs longitudinal continuity of sandstone between channels and their genetically related lobes (Wynn et al., 2002), and it serves as the link between locally confined and unconfined conditions for sediment gravity flows that build the submarine fan.

It has been reported that the CLTZ is a region where rapid flow transformations can take place, as channel relief diminishes and turbidity currents encounter a locally less confined setting

(Mutti, 1977; Mutti and Normark, 1987, 1991; Mulder and Alexander, 2001; Gardner et al.,

2003; Pyles, 2004; Kane and Ponten, 2012). The CLTZ is reported to be present near a break in slope (Kenyon et al., 1995; Millington and Clark, 1995; Wynn et al., 2002; Habgood et al.,

2003). As flows exit a channel and traverse across an area of reduced gradient, they slow down

and spread laterally, and, often, their heights increase (Komar, 1971; Mutti and Normark, 1987;

Beaubouef et al., 2003; Deptuck et al., 2008). At this zone, the flows become depletive and are thought to undergo a hydraulic jump, a change from supercritical to subcritical flow (Komar,

1971; Mutti and Normark, 1987; Garcia and Parker, 1989; Garcia, 1993; Wynn et al., 2002;

Toniolo et al., 2006). The hydraulic jump is interpreted to lead to locally enhanced turbulence, increased scouring resulting in the formation of megaflutes and other erosional features, a decrease in competence and capacity of the flows, and, in some cases, mudstone drapes (Mutti and Normark, 1987, 1991; Kenyon et al., 1995; Millington and Clark, 1995; Morris and

Normark, 2000; Mulder and Alexander, 2001; Wynn et al., 2002; Gardner et al., 2003; Pyles,

2004; Macdonald et al., 2011). Deposition of relatively coarse bedload sediment can take place in the terminal part of the channel or near the CLTZ, whereas the finer suspended load is deposited farther downstream (Garcia and Parker, 1989; Gardner et al., 2003). The above processes have been interpreted to result in an isolated lobe of sandstone that is detached from its feeder channel (Mutti and Normark, 1987, 1991), particularly for larger turbidite systems with high-volume flows (Wynn et al., 2002).

It is not known, however, how abruptly or systematically erosion, grain size, and sorting change from the channel through the CLTZ to the basinward lobe deposit. This has significant implications for turbidite reservoir quality in hydrocarbon production and exploration. Also poorly understood are factors that control differences in the architecture and connectivity of the resultant channel-lobe deposit (e.g., attached vs. detached lobes). Previous studies have proposed different models, based on observations of the modern seafloor or outcrop- and facies- based interpretations of varying flow efficiency and other parameters (cf. Mutti, 1977; Mutti and

Normark, 1987; Bouma, 2000; Gardner and Borer, 2000; Wynn et al., 2002; Gardner et al., 2003;

Pyles, 2004).

To date, no study has provided a detailed documentation of a channel-to-lobe transect – including its constituent CLTZ – based on a continuous, paleocurrent-parallel outcrop. The outcrop belt of the Guaso I turbidite system (Ainsa basin, Spain) contains a well exposed, continuous ~4-km transect from an updip channel element to its attached downdip lobe element.

This study of the Guaso I system has three primary goals: (1) to document, for the first time, the stratigraphic architecture and sandstone connectivity of a longitudinal transect from a channel element to its genetically related lobe element, with emphasis on the CLTZ; (2) to test the hypotheses that grain size and sorting metrics of sandstones (key proxies for reservoir quality;

Beard and Weyl, 1973) change abruptly at or immediately downstream of the CLTZ; and (3) to critically examine and discuss the sequential evolution of a channel-lobe element. The broader aim of this study is to enhance current knowledge of the CLTZ, a pivotal region for understanding depositional processes and resulting stratigraphy of submarine fans. Results of this study can be used to improve reservoir models, and will aid in hydrocarbon production and exploration.

3.3. Geologic Setting

The Eocene Guaso I turbidite system crops out in the Ainsa basin, in northeast Spain

(Figure 3.2A). This basin originated during the early Eocene (Ypresian) as a local foredeep in the South Pyrenean foreland basin system (Figure 3.2A; Farrell et al., 1987; Fernandez et al.,

2004; Falivene et al., 2010). Thrusting propagated toward the foreland in the middle Eocene

(Lutetian), and the Ainsa basin evolved into a piggyback basin (Figure 3.2B; Fernandez et al.,

2004; Hoffman, 2009; Falivene et al., 2010). Syndepositionally active fault-related folds formed the margins of the Ainsa basin during the Lutetian (Figures 3.2A, 3.2C, 3.2D, 3.2E; Pickering and Corregidor, 2005; Pickering and Bayliss, 2009; Sutcliffe and Pickering, 2009). These anticlines are the Mediano on the east, the Boltaña on the west, and the Añisclo to the north

(Figure 3.3).

The Ypresian-Lutetian turbidite sedimentary fill of the Ainsa basin and nearby Jaca basin comprises the Hecho Group (Figures 3.2C, 3.2D; Mutti et al., 1972; Mutti, 1977; Mutti et al.,

1985). Each of the sandy turbidite systems of the Hecho Group is bounded above and below by laterally extensive mudstone units, interpreted as including condensed sections (Hoffman, 2009;

Moody et al., 2012). In the Ainsa basin, the Guaso system, the youngest third-order depositional system in the Hecho Group, overlies a weakly confined turbidite channel system (the Morillo system; Setiawan, 2009; Moody et al., 2012) and underlies a progradational shelf-to-basin system (the Sobrarbe Formation, at the base of the Campodarbe Group; Figures 3.2C, 3.2D;

Dreyer et al., 1999; Moss-Russell, 2009; Silalahi, 2009).

The third-order Guaso system (comprising the fourth-order Guaso I and Guaso II turbidite systems) was deposited over the course of ~800 ka during the Lutetian (Pickering and

Bayliss, 2009; Sutcliffe and Pickering, 2009). The syndepositionally active anticlines of the

Ainsa basin served to confine and pond the Guaso system, and the Boltaña anticline prevented this turbidite system from passing through the Ainsa basin and depositing in the more distal Jaca basin to the west-northwest (Figures 3.2A, 3.2C, 3.2E, 3.3; Mutti, 1977; Farrell et al., 1987;

Poblet et al., 1998; Fernandez et al., 2004; Pickering and Corregidor, 2005; Das Gupta and

Pickering, 2008; Hoffman, 2009; Sutcliffe and Pickering, 2009; Gordon et al., in review).

Hence, the Guaso system is restricted to the Ainsa basin.

The depositional setting and stratigraphic architecture of the structurally confined, ponded Guaso system (Figure 3.2E) have been documented by Stocchi (1992), Stocchi et al.

(1992), Sutcliffe and Pickering (2009), and Gordon et al. (in review). The Guaso I turbidite system was fed by submarine channels that entered the basin from the east and southeast (Figure

3.2E; Sutcliffe and Pickering, 2009; Gordon et al., in review). Paleocurrent data indicate that the channels turned north-northwestward and transferred to lobes on the basin floor (Figure 3.2E;

Gordon et al., in review). Foraminiferal analysis indicates deposition in shallowest upper bathyal water depths (Pickering and Corregidor, 2005; Heard and Pickering, 2008; Sutcliffe and

Pickering, 2009). Gordon et al. (in review) used measured sections to build isopach maps of the

Guaso I depositional system; this unit is interpreted to be thickest in the axis of the basin, and it thins toward the basin-bounding structures.

3.4. Data and Methods

The study area encompasses one of the channel-lobe elements documented in Gordon et al. (in review; Figure 3.2E). This element forms a longitudinally continuous outcrop of a sandstone unit that overlies mudstones in the lower part of the Guaso I outcrop belt, located along the eastern flank of the Buil syncline (Figures 3.3, 3.4). Key data that were collected, prepared, and analyzed for this study are: hundreds of paleocurrent measurements (from flutes, grooves, lineations, and ripples); a detailed geologic map; fifteen hand samples collected from five different localities; and centimeter-scale stratigraphic logs that document bed thicknesses

and contacts, grain sizes, physical sedimentary structures, and depositional facies. The data listed above, as well as observations of erosional surfaces, architectural elements, bedding pinchouts and truncations, and general stratigraphic trends (see photos in Figure 3.5), were integrated to construct a stratigraphic cross section through the area. This cross section is oriented approximately parallel to the sediment transport direction.

This study employs a similar architectural nomenclature and hierarchical scheme to those in Moody et al. (2012) and Gordon et al. (in review). Several genetically-related bedsets stack to build an element (e.g., channel element), which is the fundamental architectural unit (Sprague et al., 2002; Pyles, 2007; Moody et al., 2012). The amount of offset between depositional axes of successive bedsets is less than the amount of offset between stratigraphically adjacent elements

(cf. Straub and Pyles, 2012). The boundary between adjacent architectural elements records an avulsion, and/or the abandonment of the older element (Sprague et al., 2002; Moody et al.,

2012). Two or more genetically related elements with similar architectural trends deposited adjacent to one another comprise a complex (Sprague et al., 2002; Pyles et al., 2010; Moody et al., 2012). This study documents the CLTZ for an individual channel-lobe element (Figure 3.4).

At each of the sampled localities (Figure 3.4), one sample was collected from the lower part of the sandstone unit (between 0 and 10 cm above the base of the package). Additional samples were collected at stratigraphically higher positions in the unit. One standard-size thin section was prepared for each hand sample, and detrital framework grains were point-counted for grain size. Several basic statistical values related to grain size were calculated for each sample

(Table 3.1). Sorting was quantified using the inclusive graphic standard deviation method, which was first utilized by Folk and Ward (1957), and was later summarized by Pettijohn et al.

(1987). The inclusive graphic standard deviation (σ1) is defined as:

훷84 − 훷16 훷95− 훷5 σ1 = + (1), 4 6.6 where Φ is the base-two logarithmic transform of grain size in mm (Krumbein, 1938). The variable Φ was recorded from a cumulative frequency distribution graph of grain sizes at the 5th,

th th th 16 , 84 , and 95 percent-finer-than values. The advantage in using σ1 to estimate sorting for sandstones is that σ1 better incorporates trends from the tails of the grain-size histogram compared to other metrics such as standard deviation, which might weight the central tendency more heavily (Pettijohn et al., 1987). Lower σ1 values indicate a narrower spread in grain-size values, and hence, better sorting. Higher σ1 values indicate poor sorting.

3.5. Stratigraphy of the Field Area

This study is focused on a ~4-km-long transect through a longitudinally persistent sandstone unit. Paleocurrent measurements indicate that the transect is generally oriented parallel to depositional dip. The field area is located between Bruello Road to the south and El

Grado Road to the north (Figure 3.4), and it is divided into geologically distinctive regions. The regions are: outcrops along Sierra de Bruello (updip region), the vicinity of Osqueta da Calura, and the vicinity of Rio Ena and El Grado Road (the downdip region; see Figure 3.4). These regions are described below.

3.5.1. Observations

Sierra de Bruello (the updip region) is a prominent ridge that extends north- northwestward from Bruello Road to near the Osqueta da Calura locality (Figure 3.4). This ridge reaches a maximum elevation of 859 m above sea level, and is capped by a package of Guaso I

sandstone. Along Sierra de Bruello, strata dip 17-28° to the southwest (Figure 3.3). The stratigraphic thickness of the sandstone exposure ranges from 4-10 m (Figure 3.6A); in some locations, the lower or upper parts of the unit are poorly exposed. Paleocurrent measurements along Sierra de Bruello, which were mostly collected from the bases of beds in overhanging ledges, are generally north-northwestward, parallel or sub-parallel to the ridge itself (Figure 3.4).

In some locations where paleocurrents are obliquely oriented relative to the ridge, there are marked changes in the nature of the basal contact, facies associations, and thickness of the sandstone unit (e.g., planar, less erosive basal contact, finer-grained facies, and thinning of the unit). These observed changes are interpreted to reflect lateral (i.e., perpendicular to sediment transport direction), axis-to-margin variations in depositional processes within the sandstone unit.

Field mapping and measured sections along Sierra de Bruello indicate that the sandstone unit overlies a 1-3-m-thick zone of structureless mudstone with sandstone clasts and contorted sandstone and siltstone beds (Figures 3.5A, 3.6A). Like the sandstone unit, this chaotic zone is present for the entire length of the ~4-km transect (Figure 3.6A). The boundary between the sandstone unit and the chaotic zone along Sierra de Bruello is commonly irregular, and erosive in nature (Figure 3.5A). The lower ~50 cm of the sandstone unit commonly contains medium- grained structureless sandstone with abundant pebble- and cobble-sized mudstone clasts (Figures

3.5B, 3.6B). The sandstone unit generally fines upward; however, amalgamation surfaces, local scours, and bedding contacts with coarser grains juxtaposed above finer grains are present in the middle and upper parts of the unit (Figure 3.6B). Planar- and ripple-laminated sandstones, along with beds of structureless sandstone, are abundant in the middle and upper parts of the unit along

Sierra de Bruello (Figure 3.6B).

Osqueta da Calura (ODC) is near the northwest end of Sierra de Bruello (Figure 3.4).

The elevation of the ridge decreases to the northwest toward the Rio Ena locality, where the sandstone unit is incised by the river; however, outcrops of the Guaso I sandstone unit continue to El Grado Road and beyond (Figures 3.3, 3.4). In this region, strata dip 15-25° to the southwest (Figure 3.3). In the vicinity of ODC, the ~11-m-thick sandstone unit begins to thicken abruptly in the downcurrent direction, to the northwest (Figures 3.4, 3.6A). Thickening is primarily due to the updip onlap of bedsets onto the lower erosional contact (Figure 3.6A).

These lowest bedsets pinch out via onlap completely to the southeast. Stratigraphic thickness measurements taken in a paleocurrent-parallel orientation indicate that the angle formed between the tops of the bedsets and the lower erosional contact averages 1.9°. At ODC, as well as along

Sierra de Bruello, there are abrupt thickness changes in an orientation perpendicular to paleocurrent (Figure 3.5C). Paleocurrent measurements in the vicinity of ODC indicate sediment-transport directions that are generally between 310° and 330° (Figure 3.4).

At ODC, the sandstone unit overlies the 1-3-m-thick chaotic zone (Figure 3.6A). The lower boundary of the sandstone unit contains minor erosional relief (Figure 3.5C). The lower part of the sandstone unit has a fluted base, and sandstone is mostly fine-grained (Table 3.1).

Some structureless sandstone beds contain pebbles near their bases, and there are also planar- and ripple-laminated sandstones present (Figure 3.6B). The lower part of the sandstone unit contains large-scale cross stratification, up to 40 cm in height (Figure 3.5D). Large-scale cross stratification is only present in the area between ODC and the Rio Ena locality (Figure 3.6B).

The lower and middle parts of the sandstone unit contain internal scours and amalgamation surfaces (Figure 3.5E), which are almost as abundant at ODC as they are at localities farther to the south-southeast along Sierra de Bruello (Figure 3.6B). These amalgamation surfaces often

juxtapose medium- to coarse-grained, granule-rich sandstone with fine-grained sands. Some scours and erosive surfaces near ODC (such as in the cliffs above the Rio Ena locality) have several meters of relief. The middle and upper parts of the sandstone unit at ODC also contain cross-stratified, structureless, and planar- or ripple-laminated sandstones (Figure 3.6B). Near

ODC, beds often de-amalgamate in a west-northwestward, or downcurrent, direction.

The Rio Ena and El Grado Road localities, which comprise the downdip region, are located northwest of ODC (Figure 3.4). In this region, the sandstone unit is up to ~16 m in thickness (Figure 3.6A). Paleocurrent measurements indicate sediment-transport directions that are between 310° and 330°, similar to ODC.

The nature of the boundary between the sandstone unit and the underlying chaotic zone changes from erosional at ODC to relatively planar and conformable at the downdip Rio Ena and

El Grado Road localities (Figure 3.6A). Within the sandstone unit, scouring, amalgamation, and erosional features decrease markedly between ODC and the downdip localities. At Rio Ena and

El Grado Road (Figure 3.4), contacts between stratigraphically adjacent beds are mostly planar and conformable in nature, however, in the middle part of the sandstone unit exposed in the cliff above Rio Ena, there are scours and apparent megaflutes that are >1 m in relief. Bedsets at Rio

Ena and El Grado Road tend to be laterally persistent, and are often offset-stacked. Thickness changes in bedsets are gradual over tens or hundreds of meters. Strata are mostly very fine- or fine-grained structureless sandstones (Figure 3.6B).

3.5.2. Interpretation: Channel-Lobe Element

The stratigraphic observations of the regions listed above are integrated here in order to build a comprehensive interpretation of the architecture of the sandstone unit, as well as the

underlying chaotic zone. Due to the presence of contorted beds and sandstone clasts in a muddy matrix, as well as the lack of coherent bedding, the 1-3-m-thick chaotic zone is interpreted as deposits of slumps, slides, and also, possibly, debris flows. Collectively, this chaotic zone is referred to as a mass-transport deposit (MTD).

Along Sierra de Bruello (the updip region), the sandstone unit directly above the MTD commonly contains an erosional lower boundary that is overlain by sandstone beds that contain pebble- to cobble-sized mudstone clasts (Figures 3.5A, 3.5B, 3.6). The nature of the lower boundary and lithofacies of the lower part of the sandstone unit change markedly where paleocurrent data are oblique to the outcrop. These marked changes suggest lateral (i.e., axis-to- margin) heterogeneity within the sandstone unit; this lateral heterogeneity is often observed in submarine channels (e.g., Jobe et al., 2010). Bedsets at ODC and along Sierra de Bruello also exhibit rapid thickness changes perpendicular to paleocurrent (Figure 3.5C). Along Sierra de

Bruello, there is generally a fining-upward trend within the unit, except where amalgamation surfaces and scours are present. Collectively, these observations are interpreted to reflect that the sandstone unit exposed between Bruello Road and ODC is a channel element (Figure 3.4).

Relatively coarse-grained sandstones containing clasts are most abundant near the interpreted depositional axis, or thickest part, of the channel, where shear stress was likely greatest. The exposure of the channel along Sierra de Bruello is parallel or sub-parallel to paleocurrent orientations; however, at localities south and southeast of Bruello Road (e.g., Roadside Complex; see Figure 3.4 for location), there are unequivocal channelform geometries that are well exposed perpendicular to sediment transport direction. These channels are constituents of a channel complex that has been correlated to the stratigraphic level of the mapped sandstone unit

(channel) exposed along Sierra de Bruello (Gordon et al., in review). Margins of additional

channel elements are poorly exposed at the southern end of Sierra de Bruello, but these additional channel elements are not exposed at all farther to the north. The dimensions of the channels exposed at Roadside Complex and other localities south of Bruello Road are used to calibrate the width of the channel depicted in Figure 3.4; the channels are < 200 m wide, and they are asymmetrical in cross-sectional view. Paleocurrent data indicate that the channel along

Sierra de Bruello has a low sinuosity (<1.05) along this transect (Figure 3.4); the plan-view shape and orientation of the channel in Figure 3.4 honor the trends and features mapped along

Sierra de Bruello.

In the downdip localities of Rio Ena and El Grado Road (Figure 3.4), the sandstone unit that overlies the MTD has a relatively planar, conformable base (Figure 3.6A). Exposures in this area are perpendicular and oblique to the sediment transport directions (Figure 3.4); these exposures show that the unit comprises laterally extensive bedsets that are offset-stacked and exhibit gradual thickness changes. Rapid facies changes similar to those observed between

Bruello Road and ODC are generally not present. These observations are collectively interpreted to reflect that the sandstone unit is a lobe at the Rio Ena and El Grado Road localities (Figures

3.4, 3.6A). This lobe is locally up to ~16 m thick (Figure 3.6A), and it is overlain by additional lobes, channels, and MTDs (Gordon et al., in review) that are not the focus of this study. The shape of the lobe in Figure 3.4 is interpretive, due to the fact that much of the lobe has been eroded away, or is currently located in the subsurface. The dimensions of the lobe were largely constrained by extrapolation of thickness trends along the outcrop belt.

The depositional location of ODC between the channel to the south-southeast (Sierra de

Bruello) and the lobe to the northwest (Rio Ena and El Grado localities) defines this locality as an element-scale CLTZ (such as those depicted in Figure 3.1B). Therefore, critical observed

characteristics of the CLTZ of this system are: (1) sandstone continuity from the channel to its attached basinward lobe; (2) stratigraphic thickening in a downcurrent direction due to updip pinchouts and onlapping of lower bedsets onto the erosive base of the element; (3) a base-of- slope depositional angle of ~2°; and (4) decreasing basal erosion, amalgamation between beds, and amount of internal scouring in a downcurrent direction. (See Figure 3.7 for a diagrammatic summary of these characteristics.)

An alternate interpretation is that the Guaso I sandstone unit exposed between Bruello

Road and El Grado Road is part of a laterally extensive, low-gradient channelized sheet, with thickness variations controlled only by basin margins (cf. Sutcliffe and Pickering, 2009).

Channelized sheets are broad features, characterized by high aspect ratios, the lack of unique depositional axes, and numerous ephemeral channels that coalesce into one sandbody. This interpretation is not favored here, however, for three reasons. First, there are fundamental architectural variations observed along the longitudinal transect; there are unequivocal, relatively narrow channels exposed to the south (e.g., Roadside Complex), whereas there are laterally extensive sandstone-rich strata exposed at Rio Ena and El Grado Road (Figure 3.4). Second, the natures of the lower boundary of the sandstone unit (Figures 3.5A, 3.6A, 3.7) as well as the overlying constituent lithofacies (Figures 3.5B, 3.6B) are fundamentally different between Sierra de Bruello and the Rio Ena and El Grado Road localities; this longitudinal variation suggests a clear distinction between the channel domain and the lobe domain. Third, lateral thickness variations of the sandstone unit and pinchouts of bedsets perpendicular to paleocurrent direction along Sierra de Bruello and at ODC occur over distances of only meters (e.g., Figure 3.5C) or tens of meters; these are local features that are interpreted to be the result of erosion and deposition within a master channel, and they are not interpreted as basin-margin interaction.

However, isopach maps indicate that the large-scale (i.e., km-scale) thickness of the entire Guaso

I depositional system is indeed controlled by basin-bounding structures such as the Boltaña anticline (Gordon et al., in review).

3.6. Grain Size and Sorting Along the Channel-Lobe Element

Results from point counting and grain-size analysis of the channel-lobe element are presented in this section. Samples from the channel at the Bruello Ridge and Above Ranito localities (Figure 3.4) are medium-grained or fine-upper sandstones, whereas samples from the

CLTZ at ODC and samples from the lobe at the Rio Ena and El Grado Road localities are dominantly fine-grained sandstones (Figure 3.8; Table 3.1). A salient outlier at Rio Ena is sample RE-04 (Figure 3.8), which is a medium-lower sandstone. This sample was collected ~3 m above the base of the lobe, directly above an amalgamation surface. A t-test (at a 0.95 confidence level) demonstrates that the populations representing the channel, CLTZ, and lobe are distinct (Figure 3.8).

The distinctions between the channel, CLTZ, and lobe are further illustrated in Figure

3.9. Along the channel-to-lobe transect, the mean grain sizes of the lower and upper parts of the element decrease gradually in the downcurrent direction, whereas sorting increases. Therefore,

CLTZ and lobe strata are generally better sorted and finer-grained than channel strata (Figures

3.8, 3.9; Table 3.1). Furthermore, mean grain size and sorting are inversely related. This pattern mostly holds even when standard deviation is normalized against mean grain size (Table 3.1).

These trends and changes are interpreted to result from the specific flow processes within these distinctive depositional areas, which are described in detail below.

3.7. Discussion

The following section integrates the observations and interpretations of this study into discussions of flow processes, sedimentation, and sequential evolution of the channel-lobe element, as well as stratigraphic continuity through the CLTZ. The section also discusses this study’s applications to hydrocarbon reservoirs.

3.7.1. Flow Processes, Sedimentation, and Sequential Evolution of the

Channel-Lobe Element

Observations of lithofacies, mean grain sizes, sorting, erosional surfaces, and stratigraphic relationships are integrated here in order to interpret the sequential evolution of this submarine channel-lobe element. This section also discusses flow and depositional processes that build the element; the next section discusses how these processes govern sandstone continuity in a channel-lobe system. The analysis presented herein builds upon several previous studies that have documented the temporal evolution of channels, as well as the development of lobes in distributive submarine-fan depositional systems. Earlier work relates submarine channel erosion and filling to trends of increasing then decreasing energy (e.g., Pickering et al., 1995;

Clark and Pickering, 1996; Pyles et al., 2010; McHargue et al., 2011; Pyles et al., 2012; Alpak et al., 2013). The phases of channel development can be summarized as: (1) initial excavation of the channel, with formation of a composite lower erosional surface and extensive sediment bypass; (2) infilling of the channel, mostly by backfilling processes; (3) abandonment of the channel. Various other studies have documented the backstepping of channel-mouth or proximal-lobe deposits through time (e.g., Pyles, 2004; Amy et al., 2007), or the initiation and development of lobes (e.g., Hodgson et al., 2006; Prélat et al., 2009; Prélat et al., 2010).

However, it was the “build-cut-fill-spill” model (BCFS) of Gardner and Borer (2000) and

Gardner et al. (2003) that linked the stratigraphic architecture, facies patterns, and evolution of channelized strata and their lobe counterparts. BCFS can be applied at a variety of temporal and spatial scales (Gardner and Borer, 2000). The complete BCFS succession, which is documented to occur only at the base of slope position, comprises non-channelized build-phase deposits, incision by channelized cut-and-fill-phase deposits, and then deposition of non-channelized spill- phase deposits (Gardner et al., 2003). The juxtaposition of channels overlying lobes or lobes overlying channels implies a basinward advance or landward retreat, respectively, of the CLTZ, which corresponds to the waxing-waning life cycle of a channel-lobe system (Gardner et al.,

2003; Pyles, 2004). The sequential evolution presented and discussed in this study is divided into four discrete phases (Figure 3.10), and it modifies BCFS and applies it at the element scale.

Phase 1 corresponds to the initial formation and excavation of the channel, and deposition of oldest bedsets of the downdip lobe (Figure 3.10). This phase contains a composite lower erosional surface at the base of the channel (Figures 3.5A, 3.6A, 3.7, 3.10), which is interpreted as evidence for sediment bypass. The material that was excavated and then transported, along with sediment from farther upcurrent, through the channel was deposited beyond the channel as the oldest bedsets of the lobe (Figure 3.10). These sand-rich, laterally extensive bedsets thin and pinch out completely in an upcurrent direction, onlapping the erosive lower contact in the CLTZ

(Figures 3.6A, 3.7). Hence, during the early development of the channel-lobe element, the

CLTZ is interpreted as the boundary between erosion and deposition along a longitudinal profile.

The oldest lobe deposits (Phase 1) at Rio Ena and El Grado Road are generally fine-grained

(Table 3.1) and structureless, and are often normally graded; it is interpreted here that they result

from suspension sedimentation out of waning, depletive flows in an area of reduced depositional gradient.

Phase 2 corresponds to continued bypass within the channel, as well as a basinward advance of the CLTZ (Figure 3.10). Relatively coarse-grained strata that contain pebble- and cobble-sized clasts are commonly present immediately above the erosive base of the channel near its axis, where shear stress would have been greatest. The clasts tend to be in contact with one another, and they are imbricated. These clasts are interpreted as lag deposits of Phase 2

(Figure 3.10). It is interpreted here that the turbidity currents that passed through the channel and left behind the lag deposits contained finer grains which were either stripped from the tops of the flows, or remained in turbulent suspension until the flows decelerated at or near a decrease in gradient (i.e., at a break in slope near the CLTZ). Indeed, sandstones at ODC, and farther downdip at Rio Ena and El Grado Road, are generally finer grained than their associated channel sandstones at Bruello Ridge and Above Ranito (Figure 3.9; Table 3.1), although there appear to be rare, local pebbly lag deposits at ODC. At the CLTZ, the magnitude in the break of slope is interpreted to be ~2°, based on onlap and measurements of stratal thinning at ODC (Figure

3.6A). It has been reported that deceleration at a reduction in gradient causes a decrease in competence of turbulent flows (Garcia and Parker, 1989; Gardner et al., 2003; cf. Hiscott, 1994), and hence, the finer grains left in the flows can be deposited out of suspension beyond the channel mouth in the unconfined domain. Here we interpret that the reason deposits at ODC,

Rio Ena, and El Grado Road are generally finer-grained and better sorted than channel sandstones (Figure 3.8; Table 3.1) of Phases 1 and 2 is a decrease in competence occurring at the

CLTZ’s reduced gradient. Sand-rich strata at ODC contain large-scale cross-stratification

(Figures 3.5D, 3.6B, 3.7), interpreted as the result of tractive reworking at the mouth of the

channel in the CLTZ. During Phase 2, the CLTZ advanced basinward as bedsets built out over, and locally eroded into, the previously deposited bedsets of Phase 1 (Figure 3.10); evidence of the waxing energy of the system is observed in the cliffs above Rio Ena where some scours and erosive surfaces have several meters of relief.

Phase 3 corresponds to the interpreted large-scale waning of the depositional energy of the channel-lobe system, resulting in backstepping (landward retreat) of the CLTZ and backfilling of the channel (Figure 3.10). In the channel above the relatively coarse-grained deposits of Phase 2, structureless fine- to medium-grained sandstone is common, but planar- laminated and rippled sandstones are also present in bedsets of Phase 3 (Figure 3.6B). There is a general paucity of clast-rich, relatively coarse-grained strata in Phase 3. Normal grading is common in the structureless sandstones. These structureless sandstones are interpreted to record suspension sedimentation, whereas the planar-laminated and rippled sandstones are interpreted to record tractive deposition in a waning, depletive flow regime. Critically, Phase 3 contains bedsets that are longitudinally continuous from the channel into the basinward lobe.

Phase 4 corresponds to additional backfilling and local “spilling” of the channel, especially near the CLTZ where channel confinement decreases (Figure 3.10). Observations at

ODC document that older bedsets thin more abruptly in an orientation perpendicular to paleocurrent than more laterally extensive, younger bedsets of Phase 4 do (Figure 3.5C); this is interpreted to reflect the backstepping and “spilling” of Phase 4 deposits. As in Phase 3, bedsets of Phase 4 tend to be longitudinally continuous from the channel to the lobe; they contain structureless and planar-laminated sandstone beds that are occasionally capped by thin-bedded, fine-grained, rippled strata (Figure 3.6B). This fourth phase reflects waning energy of the

system, and it might be followed by complete abandonment or an avulsion of the system due to reduced accommodation within the backfilled channel (cf. Armitage et al., 2012).

The observation that locally confined (channel) and unconfined (lobe and CLTZ) samples are statistically distinctive in terms of mean grain size and sorting (Figure 3.8) is interpreted to result from the different depositional mechanisms that are prevalent in each domain. It has been widely interpreted in previous studies (e.g., Clark and Pickering, 1996; Carr and Gardner, 2000;

Gardner et al., 2003; Pyles et al., 2010; Jobe et al., 2011; Pyles et al., 2012), as well as this study, that within a submarine channel, both tractive and suspension sedimentation processes operate.

Deposition due to tractive and suspension sedimentation processes during erosive and filling phases of channel development accounts for the wide range of sedimentary structures and grain sizes (fine-grained sandstone to cobble-sized clasts), as well as the relatively poor sorting observed within the channel element at the Bruello Ridge and Above Ranito localities (Table

3.1). The observation that sorting of the deposits of the unconfined domain tends to be better than sorting within the locally confined (channel) domain (Figure 3.8) is interpreted to result from the winnowing of the grain-size population by depositional processes operating along the longitudinal transect; most of the coarsest grains have already been deposited in the channel before turbulent flows exit the channel mouth at the CLTZ. Anomalously coarser-grained and poorly sorted samples (e.g., RE-04) are rare (Figure 3.6B), but are present in the lobe

(unconfined domain). These samples represent deposits of energetic, erosive flows that carried relatively coarse grains well beyond the CLTZ and scoured into older bedsets on the proximal lobe. The increase in sorting from channel to proximal lobe due to the loss of coarsest grains from the flows stands in contrast with decreased sorting observed at the distal fringes of lobes due to relative enrichment in clay- and silt-sized particles (cf. Pyles and Jennette, 2009).

3.7.2. Sandstone Continuity, Hydraulic Jumps, and the CLTZ

The continuity of the mapped sandstone unit through the CLTZ (at ODC) -- and the observation that the lobe is attached to the channel (Figures 3.6A, 3.7) -- has important implications for interpreting the roles of various flow and depositional processes operating in the vicinity of the CLTZ. In contrast with previous, generalized CLTZ models (e.g., Mutti and

Normark, 1987), hydraulic jumps (i.e., changes from supercritical to subcritical flow) need not be invoked to explain the majority of strata observed near the CLTZ of the Guaso I channel-lobe transect. Scour features and erosive surfaces, which are often cited as lines of evidence suggesting a hydraulic jump, are observed in the CLTZ and even in the proximal lobe deposits.

For the most part, however, these features have minor relief, often less than those in the updip channel. Mud-draped scours are rare near ODC, and the observation that sand-rich bedsets of

Phases 3 and 4 are continuous from the channel into the lobe suggests that bypass was not prevalent during the later, backfilling stages of the element’s life cycle. It is only during Phases

1 and 2 when extensive bypass within the channel is interpreted to have occurred; early, highly erosive turbidity currents that created and cut the channel might have experienced hydraulic jumps at the base of slope, depositing their sediment loads farther downcurrent. The stratigraphic continuity created during Phases 3 and 4 (backfilling and spilling) indicates that it is less likely that later turbidity currents underwent hydraulic jumps near the CLTZ. Mutti and

Normark (1987) suggest that turbidity currents of different volumes might undergo hydraulic jumps at more proximal or distal positions relative to the CLTZ; however, in the Guaso I channel-lobe transect, evidence for hydraulic jumps taking place in locations other than the

CLTZ (e.g., within the channel, or in the downdip lobe) is rare. In this channel-lobe transect, it is interpreted that the reduction in depositional gradient (~2°) and loss of confinement near the

CLTZ triggered a decrease in competence (cf. Hiscott, 1994) as well as any flow transformations that occurred there.

3.7.3. Implications for Hydrocarbon Reservoirs

Observations of mean grain size, sorting, and architecture of the channel-lobe transect, as well as ensuing interpretations, are integrated here in order to discuss the implications for predicting hydrocarbon-reservoir quality and connectivity. Permeability and porosity are key metrics of reservoir quality; permeability is the most important control on fluid flow in hydrocarbon reservoirs (Dreyer et al., 1990). Depositional variations in porosity and permeability are often amplified during diagenesis (Houseknecht, 1984; Morad et al., 2010), and, hence, they can have a profound effect on ensuing reservoir quality. Of all of the textural properties of natural clastic sediments, grain size and sorting are the most important with respect to porosity and permeability (Beard and Weyl, 1973). Generally, well sorted sandstones have higher porosity and permeability values than poorly sorted sandstones (Beard and Weyl, 1973).

Coarser-grained sandstones have higher permeabilities than finer-grained sandstones (Beard and

Weyl, 1973; Reynolds, 2000), if other factors (e.g., sorting) are held equal. Also, coarser- grained sandstones often have higher porosity values than finer-grained sandstones, although the relationship between grain size of sandstones and porosity remains somewhat equivocal (cf.

Beard and Weyl, 1973; Houseknecht, 1984; Reynolds, 2000). In turbidite sandstones, it is reported that structureless suspension deposits (Ta division of Bouma, 1962) tend to be better reservoirs (i.e., higher values of porosity and permeability) than tractive/bedload deposits, which are the Tb and Tc divisions of Bouma, 1962 (Slatt et al., 1993; Jobe et al., 2011).

Results presented in sections above demonstrate that sorting and grain size of the channel-lobe system vary spatially (i.e., longitudinally) in systematic, predictable ways (Figure

3.9). The channel sandstones, which are coarser-grained and more poorly sorted (Figure 3.8), are interpreted as relatively proximal deposits of both suspension and tractive processes. The structureless lobe sandstones, which are finer-grained and better sorted (Figure 3.8), are mostly interpreted as suspension deposits in a more distal, unconfined setting (Figures 3.4, 3.6A).

Longitudinal trends in grain size and sorting (Figure 3.9) are gradual rather than abrupt, probably due to overlapping depositional processes in the channel and proximal lobe, particularly during later phases of the element’s development (Figure 3.10). Even though the locally confined

(channel) and unconfined (CLTZ and lobe) domains are statistically significant and discrete sample populations (Figure 3.8), the channel, CLTZ, and lobe sandstones are mostly composed of lithofacies that are interpreted here to be moderate- to high-quality reservoirs (LF 2 and LF 3;

Figure 3.6B). No sandy debrites or co-genetic-flow deposits (sensu Talling et al., 2004) were documented in this study’s channel-lobe transect, and thin-bedded, rippled lithofacies of lower reservoir quality (Jobe et al., 2011) were a relatively minor constituent. However, based upon results of this study, as well as the results of Slatt et al. (1993), it is interpreted here that proximal lobe deposits at Rio Ena and El Grado Road (mostly structureless sandstones) are of higher reservoir quality than clast-rich, poorly sorted strata in the lower part of the channel. It is beyond the scope of this study to determine the relative importance of sorting vs. mean grain size in controlling resultant reservoir quality.

In this study’s field area (Figures 3.4, 3.6A), there is sandstone continuity between a submarine channel and its genetically related lobe. The documentation of bedsets that demonstrate channel-lobe connectivity through the CLTZ has important implications for

reservoir geometries and fluid flow, which can be accounted for in the construction of object- based reservoir models of distributive channel-lobe systems. This is also important because contrary to alternate channel-lobe models (e.g., Mutti and Normark, 1987, 1991), slope-channel reservoirs need not be considered distinct and disconnected from sandy, basin-floor-lobe reservoirs.

3.8. Conclusions

In the outcrop belt of the Guaso I turbidite system, a well exposed ~4-km-long transect through a sandstone unit comprises a stratigraphically continuous, paleocurrent-parallel channel- lobe profile. The following points are key conclusions of this chapter:

 In the vicinity of the CLTZ, this study documents: (A) thickening of the element in a

downcurrent direction; (B) a basinward decrease in the amount of erosion at the base of

the element; (C) internal scouring and amalgamation surfaces that generally decrease in

abundance in a downcurrent direction; (D) oldest bedsets of the proximal lobe that thin

and pinch out completely onto the erosive lower contact in an upcurrent direction; (E)

sandstone continuity through the CLTZ, from the channel to the downdip lobe; (F) a

base-of-slope depositional angle of ~2°, based upon stratigraphic thickness measurements

near ODC.

 Sandstones of the CLTZ and lobe are generally finer-grained and better sorted than

channel sandstones. Differences in grain size and sorting between the locally confined

and unconfined domains are attributed to the different combinations of flow/depositional

processes that operate in each of the domains.

 The longitudinal changes in mean grain size and sorting, which are proxies for reservoir

quality, observed in this element-scale channel-lobe system tend to be gradual, rather

than abrupt. The channel-lobe transect in this study demonstrates reservoir connectivity

from the slope to the basin floor. The above observations have important implications for

reservoir-quality modeling and reservoir architecture in deepwater channel-lobe

hydrocarbon reservoirs.

 The channel-lobe element documented in this study evolved in a four-phase process that

is similar to that proposed in Gardner and Borer’s build-cut-fill-spill model (2000). The

model presented herein relies upon the continuous exposures of the Guaso I turbidite

system to facilitate an interpretation of the stratigraphic evolution of a channel-lobe

system at the highest levels of detail (element-scale).

3.9. Acknowledgments

This study has benefitted greatly from logistical assistance and technical support from

Charlie Rourke, Cathy Van Tassel, and Linda Martin at the Chevron Center of Research

Excellence (CoRE), Colorado School of Mines. Julian Clark, Morgan Sullivan, and Wendy

Harrison participated in enlightening discussions that aided this project. Elsevier and Chevron graciously granted us permission to use the seismic image in Figure 3.1A; we thank Jake

Covault, Morgan Sullivan, and Amandine Prélat for their assistance. GSG thanks field assistants

Erich Heydweiller and Bradley Nuse. Bradley Nuse also was very helpful with statistical analysis in a software package. We thank Mark Kirschbaum for reviewing an early version of this manuscript. Primary funding for this project and GSG’s Ph.D. research was provided by

Chevron. Additional funding for GSG’s Ph.D. research was provided by a GCS SEPM Ed Picou

Fellowship, a ConocoPhillips SPIRIT Scholarship, the Bartshe Family Fellowship, and a Devon

Energy Scholarship.

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Figure 3.1. Mapview examples of the submarine channel-lobe transition zone (CLTZ), shown at the same scale. (A) Amplitude extraction (10 ms window) of a fan-scale channel-lobe transition zone, denoted by the red oval. (Image modified from Prélat et al., 2010; the image, used with permission from Elsevier and Chevron, is from offshore Nigeria.) (B) Line drawing of the Navy fan, offshore southern California, showing multiple element-scale channel-lobe transition zones. (Figure redrawn and modified from Normark et al., 1979.)

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Figure 3.3. Geologic map of the Guaso I turbidite system in the Ainsa basin. Key stratigraphic contacts in this map are the lower and upper contacts of the Guaso system, and the upper boundary of the Guaso I sub-system. The study area is denoted by the red rectangle. Inset map depicts locations of the other depositional systems of the Ainsa basin, as well as the key bounding structures of the basin: the Mediano, Añisclo, and Boltaña anticlines. Maps modified from Hoffman, 2009; Moody et al., 2012; and Gordon et al., in review.

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Figure 3.4. Map of the study area showing sample localities, modern towns and villages, outcrop belt of the studied channel-lobe element, paleocurrent measurements, and paleogeographic interpretation of the element.

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Figure 3.5. Photographs of stratigraphic relationships, lithofacies, and sedimentary features of the sandstone unit mapped in this study. Locations of photos are shown in Figure 3.4. (A) Sandstone unit overlying the chaotic zone, which comprises clasts and contorted sandstone and siltstone beds in a muddy matrix. The contact (red line) between the sandstone and the chaotic zone is erosional. These strata are located near the Above Ranito locality. (B) Cobble-sized mudstone clast within medium-grained sandstone near Above Ranito. Recessed areas were formed by pebble-sized mudstone clasts. (C) Lower part of the sandstone unit exposed at the Osqueta da Calura (ODC) locality. The contact (red line) between the sandstone unit and underlying muddy chaotic zone is erosional. Sediment transport direction is directly out of the plane of the page. Stratigraphic thinning of basal sandstone bed is perpendicular to sediment transport direction. (D) Large-scale cross stratification at the ODC locality. Sediment transport direction is to the right. (E) Amalgamation surface (red dashed line) in the sandstone unit.

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Figure 3.6. (A) Depositional-dip-oriented cross section of the channel-lobe transect exposed from Sierra de Bruello to beyond El Grado Road (see Figures 3.3, 3.4 for location). The channel-lobe element abruptly thickens near the CLTZ at the interpreted basin floor, and it overlies a 1-3-m-thick MTD. Sediment transport direction is to the right (generally north- northwestward). The cross section is datumed in such a way as to preserve original depositional gradient, as interpreted from stratigraphic relationships near ODC. (B) Cumulative proportions of lithofacies (LF 1-4) along the channel-lobe transect. The lithofacies information comes from measured sections at the localities. Horizontal scale is the same as in Figure 3.6A.

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Figure 3.7. Schematic, dip-oriented cross-sectional diagram of the CLTZ and the proximal basin floor, based on observations at the ODC locality (see Figure 3.4). Intra-element erosion, basal erosion, and internal amalgamation surfaces generally decrease in abundance in a basinward direction, whereas gross thickness of the element increases. The lower bedsets onlap the erosive base of the element in an upcurrent direction. Thin black lines represent bedset boundaries, whereas the thick black line represents the non-erosional base of the element.

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Figure 3.8. Plot of mean grain size values vs. inclusive graphic standard deviation (σ1) values for Guaso I sandstone samples. The channel, CLTZ, and lobe samples comprise statistically distinct populations. The salient outlier is sample RE-04, which is located in the proximal lobe. Sample localities are shown in Figure 3.4.

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Figure 3.9. Plots showing the relationships between mean grain size, inclusive graphic standard deviation (σ1), and distance along the depositional (longitudinal) profile that is illustrated in Figure 3.6. These plots (A and B) are arranged in stratigraphic order. Sample localities are shown in Figure 3.4. (A) Plots of mean grain size vs. distance (along the Sierra de Bruello transect), and inclusive graphic standard deviation (σ1) vs. distance (along the Sierra de Bruello transect), for samples collected near the base of the channel-lobe element. Mean grain size and inclusive graphic standard deviation generally decrease along the longitudinal transect, from channel to lobe. The black lines are the second-order polynomial trendlines. (B) Plots of mean grain size vs. distance (along the Sierra de Bruello transect), and inclusive graphic standard deviation (σ1) vs. distance (along the Sierra de Bruello transect), for samples collected in the middle and upper parts of the channel-lobe element. The trends exhibit significant scatter, but generally both mean grain size and inclusive graphic standard deviation decrease along the transect, from channel to lobe. The black lines are the second-order polynomial trendlines.

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Figure 3.10. Diagrammatic model of the evolution of a channel-lobe element in four phases (1- 4). Slices A-D are cross-sectional views of the element at different positions in the longitudinal profile. This model builds upon and modifies the “build-cut-fill-spill” model (Gardner and Borer, 2000; Gardner et al., 2003), which relates facies and architecture of vertical stratigraphic successions of submarine fans to different positions along a slope-to-basin profile.

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Table 3.1. Grain size and sorting data for samples collected in the Guaso I sandstone unit. Also refer to Figs 3.8, 3.9. Sandstone Inclusive classification Standard graphic Mean (based on Median deviation of Std. standard grain size mean grain grain size Mode, grain mean grain dev./mean deviation, σ1 Sample Locality Depositional environment (mm) size) (mm) size (mm) size (mm) grain size (phi units) BR-04 Bruello Ridge base of channel 0.26 ml 0.22 0.20 0.18 0.70 0.78 BR-06 Bruello Ridge channel 0.29 ml 0.26 0.25 0.15 0.51 0.73 AR-06 Above Ranito base of channel 0.19 fu 0.15 0.08 0.11 0.59 0.73 AR-08 Above Ranito channel 0.37 mu 0.35 0.25 0.20 0.55 0.75 AR-10 Above Ranito channel (upper part) 0.23 fu 0.21 0.18 0.11 0.46 0.59 ODC-01 Osqueta da Calura base of CLTZ 0.17 fl 0.15 0.12 0.09 0.51 0.57 ODC-04 Osqueta da Calura CLTZ 0.19 fu 0.16 0.10 0.10 0.51 0.68 ODC-07 Osqueta da Calura CLTZ 0.18 fu 0.16 0.15 0.08 0.44 0.62 ODC-22 Osqueta da Calura base of CLTZ/proximal lobe 0.18 fu 0.16 0.15 0.09 0.48 0.54 RE-01 Rio Ena base of lobe 0.14 fl 0.12 0.10 0.09 0.62 0.64 RE-03 Rio Ena lobe 0.17 fl 0.15 0.15 0.07 0.39 0.47 RE-04 Rio Ena lobe 0.30 ml 0.28 0.35 0.15 0.50 0.81 EG-01 El Grado Road base of lobe 0.13 fl 0.12 0.08 0.07 0.55 0.54 EG-02 El Grado Road lobe 0.10 vfu 0.09 0.07 0.06 0.54 0.53 EG-04 El Grado Road lobe 0.21 fu 0.19 0.21 0.09 0.45 0.64 vfu = very-fine upper; fl = fine lower; fu = fine upper; ml = medium lower; mu = medium upper

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CHAPTER 4.

FROM SUBMARINE CANYON TO BASIN MARGIN: FAULT AND BATHYMETRIC

CONTROLS ON SUBMARINE FAN STRATIGRAPHY AND DISTRIBUTION OF

LITHOFACIES ASSOCIATIONS, UPPER MODELO FORMATION,

EASTERN VENTURA BASIN, CALIFORNIA

A paper that has been submitted to AAPG Bulletin

Gregory S. Gordon and David R. Pyles

4.1. Abstract

Sand-rich turbidite systems in structurally complex, fault-bounded deepwater basins often form prolific hydrocarbon reservoirs. Outcrop studies of ancient examples of these turbidite systems provide information on their architectures, depositional controls, and sandstone distributions. Outcrops of the Miocene upper Modelo Formation in the eastern Ventura basin,

California, represent a longitudinal transect through a fault-controlled deepwater depositional system, from proximal structural terraces, through a submarine canyon, to the basin floor and basin margin. This study area is divided into three regions based on geographic location, stratigraphic character, and interpreted paleogeographic environment: Region 1 (Feeder System),

Region 2 (Proximal Basin Floor), and Region 3 (Medial-Distal Basin Floor). Region 1 contains syndepositionally active normal faults (e.g., Devil Canyon fault) near the proximal basin margin; these faults are associated with abrupt changes in depositional environments, lithofacies associations, paleobathymetry, and stratigraphic thickness. The submarine canyon was an area of bypass, and it has a low net-sandstone content. Isopach maps reveal that gross thickness is

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greatest near the interpreted canyon mouth. In Region 2, a proximal-basin-floor fairway located immediately basinward of the canyon contains the highest sandstone content in the basin. In

Region 3, gradual changes in proportions of lithofacies associations result from subtle variations in the gradient of the basin floor near the distal basin margin, as interpreted from the isopach map. In this area, channel complexes comprising structureless, amalgamated sandstone overlie thin-to-medium bedded, “dirty” sandstones deposited at the lobe fringe. This upward architectural pattern is interpreted to result from an outwardly expanding depocenter through time.

4.2. Introduction

Submarine fans deposited in relatively small (<40 km [~25 mi] in diameter), structurally complex or fault-bounded basins have received increasing interest from geoscientists in the petroleum industry in the past few decades (e.g., Booth et al., 2003). These basins are common features on all varieties of siliciclastic-dominated continental margins around the world, whether convergent, passive, or transform; their constituent clastic deepwater depositional systems often serve as prolific hydrocarbon reservoirs (Redin, 1991; Yeats et al., 1994; Davis et al., 1996;

Booth et al., 2003; Weimer and Pettingill, 2007; Eriksen et al., 2003). The fine-scale morphologies, external geometries, and depositional features of fault-controlled, structurally confined turbidite systems on the modern seafloor have been well documented, particularly in areas such as the California Borderland province (e.g., Normark, 1970; Haner, 1971; Normark et al., 1979; Covault and Romans, 2009; Normark et al., 2009). Subsurface studies of confined turbidite systems in fault-bounded basins in petroliferous regions employ 3-D seismic images, well logs, and conventional core (e.g., Lonergan and Cartwright, 1999; Hooper et al., 2002;

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Booth et al., 2003; Jackson et al., 2011); however, seismic images often cannot resolve individual architectural elements that comprise the submarine fans, and well data can be sparse and are inherently one-dimensional. Although relatively few in number, outcrop-based studies of ancient confined turbidite systems in fault-bounded depocenters have revealed broad depositional trends and structural controls on sedimentation and resultant deposits (e.g.,

Haughton, 1994; Haughton, 2000; Shultz and Hubbard, 2005; Pyles, 2008). Depending upon the quality and extent of exposures, additional outcrop-based studies can provide documentation of internal architectural and sedimentologic trends along continuous transects, thereby enhancing knowledge gained from modern-seafloor and subsurface datasets. This enables geoscientists and petroleum explorationists to design and implement better-informed geologic models that incorporate complexities and details that have been observed in natural systems.

Outcrops of the Miocene upper Modelo Formation in the eastern Ventura basin,

California, comprise a longitudinal transect through a structurally confined, fault-controlled distributive submarine fan. These outcrops include deposits of the structurally terraced feeder system, submarine canyon, basin floor, and basin margin. This study utilizes observations and interpretations of these exposures to advance knowledge of fault-controlled distributive submarine fans. Specifically, this study addresses the following goals: (1) to interpret the paleogeography and evolution of the upper Modelo depositional system in the eastern Ventura basin; (2) to document fault and bathymetric controls on the distribution of lithofacies associations; (3) to evaluate how thickness trends relate to locations of maximum sandstone content and distributions of architectural elements; and (4) to document basin-margin controls on reservoir architecture and stacking patterns.

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4.3. Geologic Background

The eastern Ventura basin (EVB) is located in southern California, ~60 km (~37 mi) northwest of downtown Los Angeles (Figure 4.1). The EVB is bordered by the city of Santa

Clarita and the San Gabriel fault on the east, the Santa Susana Mountains on the south, the town of Fillmore on the west, and Ridge basin and the Piru-Topatopa Mountains (part of California’s

Transverse Ranges) on the north (Figure 4.1). This sub-basin is the easternmost constituent of the greater Ventura basin, a highly petroliferous basin that continues offshore as the Santa

Barbara channel (Yeats et al., 1994; Davis et al., 1996).

In the early middle Miocene, a series of major, regional tectonic events consisting of uplift, erosion, and volcanic eruptions preceded the formation of the EVB (Clark, 1988; Dibblee,

1989; Crowell, 2003a), and these events seem to have at least partly coincided with the rotation of the Western Transverse Ranges and formation of the Los Angeles basin (Luyendyk, 1991;

Redin, 1991; Crouch and Suppe, 1993; Ingersoll and Rumelhart, 1999). These tectonic events, referred to collectively as the Lompocian orogeny (Dibblee, 1989), reconfigured the landscape of southern California, and created the conditions for the formation of the EVB. The EVB formed as a graben in the middle Miocene due to rifting that took place adjacent to the transform boundary between the Pacific and North American plates (Blake et al., 1978; Yeats et al., 1994;

Davis et al., 1996). This nascent transtensional basin was bounded on the south-southwest by the

Oak Ridge-Simi Hills structural shelf, and on the northeast by a granitic ridge parallel to the San

Gabriel fault (Yeats et al., 1994; Yeats and Stitt, 2003). A north-dipping normal fault, the ancestral Oak Ridge fault system, appears to have separated the structural shelf from the basin floor (Namson, 1987; Namson and Davis, 1988; Davis et al., 1996), and syndepositionally active

(during middle-late Miocene time) down-to-the-southwest normal faults such as the Devil

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Canyon and Canton faults (Figure 4.2) separated granitic and other basement rocks from the basin floor (Yeats et al., 1994; Crowell, 2003b; Yeats and Stitt, 2003). Subsidence of the EVB was relatively rapid during the middle and late Miocene, but waned during the latest Miocene and Pliocene (Davis et al., 1996). Isopach maps and structural contour maps of basement (Nagle and Parker, 1971; Yeats et al., 1994; Davis et al., 1996) indicate that the deepest part of the basin in the late Miocene was located in an area 10-20 km (~6-12 mi) east of the modern town of

Fillmore (Figures 4.1 and 4.2).

The San Gabriel fault initiated right-lateral slip ~12 m.y. ago, and was the active transform boundary through the latest Miocene or early Pliocene (Yeats et al., 1994; Rumelhart and Ingersoll, 1997; Ingersoll and Rumelhart, 1999). After right-lateral slip on the San Gabriel fault ceased in most locations, tectonic inversion of the basin and ~north-south contraction commenced in the mid-late Pliocene; the basin entered a transpressional phase (Yeats et al.,

1994; Davis et al., 1996; Nicholson et al., 2007) and right-lateral slip was transferred to the San

Andreas fault. The uplift of the Santa Susana Mountains on the southern margin of the EVB

(Figure 4.1), inversion of the Oak Ridge fault, and the initiation of reverse movement on the San

Cayetano fault near the northern margin (Figures 4.1 and 4.2), began in the Pleistocene (Çemen,

1989; Yeats et al., 1994; Nicholson et al., 2007) during a pulse of shortening referred to as the

Pasadenan orogeny (Reed and Hollister, 1936; Stille, 1936; Nagle and Parker, 1971). Strata of the EVB, including the Modelo Formation, are exposed in surface anticlines and synclines

(Figure 4.2) associated with the Pasadenan orogeny and Recent uplift (Yeats et al., 1994).

Basement of the EVB comprises metamorphic, igneous, and lower Tertiary sedimentary rocks (Dibblee, 1989; Yeats et al., 1994; Crowell, 2003a; Figures 4.2 and 4.3A). Gneissic basement, correlative to the Mendenhall Gneiss of the western San Gabriel Mountains, is dated

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at ~1.7 Ga (Silver, 1966; Yeats et al., 1994; Crowell, 2003a), and it is segmented by various faults such as the San Gabriel and Canton faults (Yeats et al., 1994; Figure 4.2). Igneous basement rocks such as granite, granodiorite, and quartz monzonite crop out in the Whitaker

Peak area, near the Devil Canyon, Canton, and San Gabriel faults (Yeats et al., 1994; Crowell,

2003a; Figure 4.2). The pre-EVB stratigraphic succession comprises Eocene marine units that nonconformably overlie the crystalline basement rocks; the Eocene units are overlain by sedimentary rocks of the Sespe, Vaqueros, and Rincon Formations (Yeats et al., 1994; Dibblee,

1995; Crowell, 2003a; Figure 4.3A). Earliest infill of the EVB was the middle-late Miocene

Modelo Formation, which comprises marine siltstones, sandstones, and conglomerates, as well as rare pelagic and hemi-pelagic deposits (Stitt, 1986; Dibblee, 1989). Locally, the lower

Modelo Formation unconformably overlies the Rincon Formation (Clark, 1988). The Modelo

Formation correlates to the Monterey Formation (calcareous and siliceous mudstones with thin turbidite sandstone intervals) and the Sisquoc Formation (clay-rich and diatomaceous mudstone with thin turbidite sandstone intervals), both located farther west in the Ventura basin (Dibblee,

1989; Yeats et al., 1994; Figure 4.3A). The Modelo Formation is overlain by the coarse-clastic

Towsley Formation, which is composed of deepwater conglomerates, sandstones, and mudstones

(Winterer and Durham, 1962; Yeats et al., 1994). The Towsley Formation was deposited during the latest Miocene-early Pliocene (Yeats et al., 1994; Figure 4.3B). In the study area (Figure

4.2), the Modelo-Towsley contact is overlain locally by the Hasley conglomerate, the lowest member of the Towsley Formation (Yeats et al., 1994). The Pico Formation, a unit that records shoaling of the EVB (Davis et al., 1996), overlies the Towsley Formation (Winterer and Durham,

1962; Dibblee, 1995; Figure 4.3). The Pico Formation comprises shallow marine strata in the eastern part of the basin (Yeats et al., 1994), which longitudinally transfer to turbidite strata in

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the western part of the basin (Hsu, 1977). The youngest lithified unit in the EVB is the Saugus

Formation, which is composed of shallow-marine to non-marine strata (Yeats et al., 1994). This unit overlies and interfingers with the Pico Formation (Yeats et al., 1994; Figure 4.3A).

The Modelo Formation was first named by Eldridge and Arnold (1907), and its lithofacies, mineralogic composition, provenance, hydrocarbon reservoir potential, and outcrop geology have subsequently been described by various workers (e.g., Kew, 1924; Hudson and

Craig, 1929; Winterer and Durham, 1962; Stitt, 1986; Trembly, 1987; Clark, 1988; Dibblee,

1989; Yeats et al., 1994; Dibblee, 1995; Rumelhart and Ingersoll, 1997; Crowell, 2003a). The type locality of the Modelo Formation is Modelo Canyon (Eldridge and Arnold, 1907; Yeats et al., 1994), which is located in the hanging wall of the south-vergent San Cayetano thrust fault

(Çemen, 1977, 1989; Figure 4.2). Along the northern margin of the EVB, particularly west of

Piru Creek, the Modelo Formation is divided into five members, based on lithology and benthic foraminiferal assemblages (Çemen, 1977, 1989; Dibblee, 1989; Yeats et al., 1994; Figure 4.3B):

(1) Tm1, the Relizian-Luisian lower mudstone; (2) Tm2, the Relizian-Luisian sandstone overlying and interfingering with Tm1; (3) Tm3, the Mohnian middle mudstone; (4) Tm4, the

Mohnian upper sandstone; (5) Tm5, the Mohnian upper mudstone, roughly correlative to the

Sisquoc Formation. The Mohnian section of the Modelo Formation (Tm3, Tm4, and Tm5) reaches a maximum stratigraphic thickness of >2500 m (>8200 ft) in the subsurface of the EVB

(Yeats et al., 1994). The focus of this study is the Mohnian section, particularly Tm4, the upper

Modelo sandstone.

In the middle and late Miocene, the Modelo Formation and its equivalents were deposited as several different submarine fans in the EVB and northern Los Angeles basin (e.g., “Tarzana fan” of Sullwold, 1960; Rumelhart and Ingersoll, 1997). The Modelo Formation of the EVB

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includes the “Piru fans” (Dibblee, 1989), which are the lower and upper Modelo sandstones

(Tm2 and Tm4). The provenance for these submarine fans has been interpreted as the western edge of the San Gabriel Mountains, located on the east side of the San Gabriel fault (Crowell,

1952; Trembly, 1987; Clark, 1988; Dibblee, 1989; Rumelhart and Ingersoll, 1997; Ehlert, 2003).

During and after deposition of the Piru submarine fans, the San Gabriel Mountains were gradually transported at least 45 km (~28 mi) to the southeast via right-lateral slip on the San

Gabriel fault (Crowell, 1952; Dibblee, 1989; Rumelhart and Ingersoll, 1997; Crowell, 2003a); coarse-grained clastic detritus was shed from the mountains, across a shallow submarine shelf, and down into the deep trough of the EVB to the southwest (Trembly, 1987; Clark, 1988;

Rumelhart and Ingersoll, 1997). The Modelo Formation is generally coarser-grained and more conglomeratic near the San Gabriel fault, and relatively finer-grained away from the fault to the southwest (Crowell, 1952; Dibblee, 1989; Crowell, 2003a). The conglomerate of the Modelo

Formation is referred to as the Devil Canyon conglomerate, and it contains distinctive boulder- and cobble-sized clasts of anorthosite, syenite, gabbro, quartz monzonite, and ilmenite (Trembly,

1987; Clark, 1988; Dibblee, 1989; Crowell, 2003a; Ehlert, 2003).

4.4. Data and Methods

Field-based data that were collected and compiled in order to address the goals of this study are: (1) locations of geologic contacts, sandstone bodies, and faults; (2) strike-and-dip measurements of bedding; (3) ~1,400 m (~4,600 ft) of detailed stratigraphic columns documenting bedding surfaces and thickness values, lithofacies and lithofacies associations, amalgamation surfaces, grain sizes, and sedimentologic features; (4) paleocurrent measurements from flutes, grooves, clast imbrications, and cross-beds; (5) photographs and photopanels

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documenting lithofacies and lithofacies associations, as well as stratigraphic architecture and relationships; and (6) hand samples for microfaunal (foraminiferal) analyses of the upper Modelo

Formation. A geologic map (Figure 4.2) was compiled based on the field data collected for this study, as well as modifications to previous maps of the area (Cordova, 1956; Çemen, 1977;

Dibblee, 1990; Dibblee, 1991; Dibblee, 1993; Dibblee, 1996; Dibblee, 1997; Crowell, 2003a). A principal northeast-southwest-oriented cross section (Figure 4.4) was constructed based on correlation of the stratigraphic columns, mapped locations of key sandstone bodies and architectural elements, and photopanel interpretations. Additionally, two stratigraphic columns from Trembly (1987) detailing the Devil Canyon and Canton Canyon areas were utilized for construction of the cross section, and for tabulation of lithofacies associations. Outcrop-based stratigraphic thickness measurements were used to modify the upper Modelo (Mohnian) isopach map of Yeats et al. (1994; Figure 4.5). Paleogeographic interpretations presented herein are based on paleocurrent measurements, locations of sandstone bodies, and foraminiferal analyses, which yield broad ranges for paleobathymetry at various localities.

4.4.1. Lithofacies and Lithofacies Associations

Fifteen lithofacies (LF 1-15) are documented in the study area (Figure 4.6; Table 4.1).

These lithofacies are organized according to modal grain size, and they range from siliceous mudstones through cobble-boulder conglomerates and breccias (Figure 4.6). Ten distinct lithofacies associations (LFA 1-10) are documented (Figure 4.7); each is composed of depositionally related lithofacies. The lithofacies associations are organized according to modal grain size, with LFA 1 as the finest-grained and LFA 9 and LFA 10 as the coarsest-grained

(Figure 4.7). Lithofacies associations occur in varying proportions at different positions along

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the depositional profile of the upper Modelo. These proportions are tabulated and reported for key localities, and are discussed below.

4.4.2. Architectural Elements

Upper Modelo strata are grouped into architectural elements (cf. Miall, 1985; Pyles,

2007). Each architectural element comprises a number of genetically related bedsets that share similar depositional axes; the boundary between stratigraphically adjacent elements records a mappable avulsion or shift in the location of the depositional axes (Pyles, 2007). Principal architectural elements present in this depositional system are lobes, channels, and mudstone sheets. Mass-transport deposits (MTDs; i.e., slumps and slides) and levees are also present, but in lower proportions relative to the other architectural elements. Architectural elements are composed of varying proportions of lithofacies associations. A complex comprises two or more genetically related architectural elements that exhibit similar stacking patterns and depositional trends (Sprague et al., 2002; Pyles et al., 2010; Moody et al., 2012).

4.5. Geology of the Upper Modelo Formation in the EVB

The study area is divided into three regions (Figures 4.2 and 4.4), based on geographic location, stratigraphic character and architectures, and interpreted paleogeographic environment.

These three regions are: (1) Region 1, the Feeder System; (2) Region 2, Proximal Basin Floor; and (3) Region 3, Medial-Distal Basin Floor. Observations and interpretations presented below collectively build to a comprehensive interpretation that the outcrops of the upper Modelo

Formation comprise a longitudinal transect through a deepwater depositional system.

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4.5.1. Region 1: Feeder System

Region 1 is bounded by the San Gabriel fault on the northeast, the Santa Felicia fault on the southeast, the Agua Blanca fault zone and southwestern extent of Canton Canyon to the west, and a major angular unconformity in the vicinity of Canton Canyon to the northwest (Figure

4.2). At the angular unconformity, gently southward- and eastward-dipping upper Modelo strata onlap vertical beds of Eocene- through lower-middle-Miocene-aged formations (Figures 4.2 and

4.8A; Trembly, 1987; Crowell, 2003a; Link and Crowell, 2003). This angular unconformity is the main local evidence for the pre-EVB Lompocian orogeny (sensu Dibblee, 1989). Younger

(Pleistocene-aged) eastward- and southeastward-plunging folds are common in this area (Figure

4.2). The Santa Felicia fault is currently a northwestward-vergent thrust (Yeats et al., 1994), and the Agua Blanca fault zone comprises southwest-vergent thrusts (Clark, 1988; Crowell, 2003a;

Figure 4.2). Region 1 (the Feeder System), which contains steep, canyon-dissected topography, is subdivided and partitioned by the Devil Canyon fault (Figure 4.2).

The area east of the Devil Canyon fault contains abundant lenses of coarse-grained (LFA

9) and interbedded chaotic-contorted and folded (LFA 10) upper Modelo strata (Figures 4.2, 4.4,

4.8B, and 4.8C), along with mudstone and siltstone beds (LFA 2). Strata are most breccia-rich adjacent to strands of the Canton fault, near the Devil Canyon Truck Trail (DCTT; Figure 4.2).

Some conglomerates of LFA 9 in this area are fossiliferous and contain brackish or fresh-water ostracods and plant material; other conglomerates lack fossils and are orange in color (Trembly,

1987). Sandstones of LFA 9 are mostly medium-coarse-grained and poorly sorted; they commonly contain tractive sedimentary structures such as planar laminations and cross-bedding.

Structureless sandstones are also present, but are less abundant than sandstones with tractive features, in LFA 9. Sandstones and siltstones of LFA 10 are locally contorted and folded (Figure

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4.8C). Folded layers are mostly 0.5-1.5 m (~1.6-4.9 ft) thick and are intercalated between planar, undeformed sandstone and siltstone beds of LFA 10. The net-sandstone content of this area is relatively high. A composite stratigraphic column from near a strand of the Canton fault reveals that LFA 9 comprises 84.2% of the stratigraphic thickness in that locality, LFA 2 comprises 11.9%, and LFA 10 comprises 3.9%. However, this was only a partial column that did not document the entire upper Modelo interval, from the base of the Mohnian Modelo to the base of the Towsley Formation (Hasley conglomerate). Exposures east of the Devil Canyon fault generally do not contain complete vertical transects through the Mohnian section, due to uplift and erosion. Foraminiferal analysis indicates that upper Modelo strata in this area were deposited during the upper part of the Mohnian, between ~9 and 6.5 Ma (Crowell, 2003a).

Composite stratigraphic columns (Trembly, 1987) and correlations (Figure 4.4) are used to estimate that in various outcrop localities east of the Devil Canyon fault, the upper Modelo

(Mohnian) is between 500 and 1,000 m (1,640-3,281 ft) in thickness (Figure 4.5). However, wells located southeast of the field area and east of the Devil Canyon fault indicate that Mohnian strata are only 300-400 m (~1,000-1,300 ft) in total thickness in the subsurface (Figure 4.5; Yeats et al., 1994). Paleocurrent measurements (e.g., clast imbrications) are highly variable, but they generally document southwestward- and southeastward-oriented sediment transport directions

(Trembly, 1987). Kinematic indicators within slumped and folded beds of LFA 10 reveal southwestward transport (Link and Crowell, 2003).

The area west of the Devil Canyon fault (Figure 4.2) contains exposures that are very steep and inaccessible (Figure 4.8D), and they prevent complete measured sections through the

Mohnian upper Modelo interval. This area contains predominantly LFA 2, comprising thick packages of mudstone with intercalated siltstone beds (Figure 4.8D). There are rare, lenticular,

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10-15-m-thick (~33-49 ft) units of sandstone encased in the thick mudstone packages. These sandstone units are hundreds of meters wide, and they contain cross-bedded and structureless sandstones interbedded with mudstones (LFA 6), as well as highly amalgamated, medium- to very-coarse-grained sandstones (LFA 7). Chaotic-contorted strata of LFA 10 are also present in minor proportions. Conglomerates and breccias of LFA 9 (Devil Canyon conglomerate) are much less abundant in outcrops west of the Devil Canyon fault than they are in outcrops east of the fault (Figure 4.4). The net-sandstone content of most of this area is relatively low (estimated at <10%). Wells drilled west of the Devil Canyon fault near the southern part of this region contain a locally thick (>2,500 m; >8,202 ft) Mohnian section (Yeats et al., 1994; Figure 4.5), the thickest in the EVB. Critically, Mohnian strata in the footwall of the Devil Canyon fault are markedly thinner than Mohnian strata in the downthrown hanging wall to the southwest (Figure

4.5; Yeats et al., 1994; Yeats and Stitt, 2003).

The above observations of stratal relationships and lithofacies associations suggest that there are two distinct depositional environments in the Feeder System (Region 1) that are separated by the Devil Canyon fault (Figures 4.2, 4.4, and 4.5). The relatively coarse-grained strata (e.g., conglomerates and breccias) located east of the Devil Canyon fault are interpreted as grain-flow deposits, debris-flow deposits, and channelized high-density turbidites that were deposited as part of a fan-delta system that prograded into the area from the north or northeast

(Trembly, 1987; Crowell, 2003a). The orange color of some of the conglomerates indicates oxidation; these conglomerates, which lack marine fossils, are interpreted as deposits of the subaerial part of the fan delta (Trembly, 1987). Trembly (1987) documents that other conglomeratic units east of the Devil Canyon fault contain marine fossils, and structureless and planar-laminated sandstones are interpreted as deposits of subaqueous sediment gravity flows

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(turbidites) on the distal part of the fan delta. The contorted and folded strata of LFA 10 are interpreted as MTDs, which were generated due to higher gradients at the subaqueous fan-delta- front, adjacent to syndepositionally active normal faults (e.g., Canton fault). These down-to-the- southwest faults generated locally steep gradients, and paleobathymetry is interpreted to have increased abruptly southwest of the Devil Canyon fault.

Stratigraphic relationships (e.g., several disconformable and nonconformable surfaces) demonstrate that the angular unconformity along the northwest boundary of the Feeder System region (Figures 4.2 and 4.8A) is a composite erosional surface that formed during deposition of the Modelo Formation. This surface is interpreted as the northwestern wall of a mid-late

Miocene submarine canyon (Figure 4.9). The canyon wall extends west to the Agua Blanca fault zone where its erosional relief diminishes completely; the angular unconformity transitions to a conformable, or possibly disconformable, surface between Modelo strata and underlying Rincon strata (Figures 4.2, 4.3). In Region 1 west of the Devil Canyon fault, isopach mapping demonstrates that Mohnian strata thin to the southeast toward a linear, northeast-southwest- trending feature that coincides with the location of the modern Santa Felicia fault (Figures 4.2 and 4.5). This feature is interpreted as a normal-fault ancestor of the Santa Felicia fault, and it comprises the southeastern boundary of the interpreted ~4-km- (~2.5 mi-) wide submarine canyon (Figure 4.9). The thickest succession of Mohnian strata in the basin is located near the mouth of the submarine canyon (Figure 4.5). West of the Devil Canyon fault, sandstone units that are encased in mudstone are interpreted as turbidite channels, which served as conduits that transported relatively coarse-grained sediment through the submarine canyon to the basin floor

(Figure 4.9). The relatively low net-sandstone content west of the Devil Canyon fault is

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interpreted to reflect abundant fine-grained levees or the mud-rich tails of sediment gravity flows that predominantly bypassed this area (the submarine canyon).

4.5.2. Region 2: Proximal Basin Floor

Region 2 is located in the vicinity of Lake Piru, and it is bounded by the Agua Blanca fault zone and Canton Canyon to the north, Region 1 and the Santa Felicia fault to the east, the

Temescal anticline and related folds to the south, and the Arundell fault and hills surrounding

Lake Piru to the west (Figure 4.2). In this region, the upper Modelo is partially exposed in several eastward-plunging folds that commonly form steep topography and cliffs, particularly at the northern and southern ends of Lake Piru (Figures 4.2 and 4.10). The outcrops at the northern end of Lake Piru on the east side of Piru Creek are referred to as “the Narrows” (Figures 4.2, 4.4, and 4.10). At the Narrows, almost 400 m (~1,312 ft) of upper Modelo strata are exposed (Figure

4.10A). Southwest of the Narrows, there is a complete transect through the upper Modelo in

Reasoner Canyon, which is a steep and brush-covered locality in the northwestern part of the

Proximal Basin Floor region.

At the northern extent of the Narrows (Fustero Point; see Figure 4.2 for location), the lowest exposure of upper Modelo contains several lenticular sandstone packages with erosional bases (Figure 4.11A). The infill of these packages is thin-bedded sandstones and siltstones (LFA

3) and structureless, amalgamated sandstone (LFA 7). There are additional LFA 3 strata above and below the packages. Above the lowest exposure, and to the south at the Narrows, there is a stratigraphic interval that is ~300 m (~984 ft) thick (Figures 4.4 and 4.10A); this interval contains several relatively thick sandstone packages, each separated by mudstones and siltstones

(LFA 2). The sandstone packages have erosional bases, and their exposures are continuous for

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up to 1,800 m (~5,900 ft) in a north-south orientation. At the southern end of the Narrows, these packages, which range from 15 to 40 m (~49-131 ft) in thickness, trend into the subsurface on the southern limb of an anticline (Figures 4.2 and 4.10A). They contain highly amalgamated medium- to very-coarse-grained, pebbly, structureless sandstone of LFA 7 (Figure 4.11B) and cross-bedded sandstones of LFA 6. There are also rare contorted beds of LFA 10, and poorly sorted, thin- to medium-bedded sandstones of LFA 4. Paleocurrent data from the vicinity of

Fustero Point are highly variable, with a mean value of 220°. Paleocurrent indicators are scarce in upper strata at the Narrows; however, correlations indicate that several of the packages present at the Narrows are not present on the west side of Piru Creek, ~200 m (~656 ft) away. This is indicative of abrupt westward pinchouts or lateral confinement, as no fault is mapped here.

Benthic foraminifera from an upper Modelo sample collected across Piru Creek (just west of

Fustero Point) document paleobathymetry values in the upper middle bathyal range range (from

500-1500 m [1,640-4,921 ft]; Kristin McDougall, personal communication, 2012).

At the southern end of Lake Piru, on the northern flank of the Temescal anticline, there is a continuous exposed section through the upper part of the upper Modelo (Figures 4.2 and 4.4).

This section is 611 m (~2,005 ft) in thickness, and it is characterized by several sandstone packages up to 40 m (~131 ft) in thickness (Figure 4.4). These packages contain abundant LFA

7, with lesser amounts of LFA 3 and LFA 6. Within LFA 7, there are common cobble-sized mudstone rip-up clasts (Figure 4.11C). The sandstone packages are separated by thick successions of LFA 1 (siliceous mudstone with interbedded shale and siltstone) and LFA 2

(Figure 4.4). At this locality, which is a partial stratigraphic column through the Mohnian upper

Modelo (Figure 4.4), LFA 2 comprises 54.5% of the stratigraphic thickness, LFA 7 comprises

21%, LFA 3 comprises 14%, LFA 1 comprises 8.2%, LFA 6 comprises 1.6%, and LFA 4

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comprises 0.7%. The net-sandstone content at this locality is ~37%, and is estimated to be slightly lower than at the Narrows. Paleocurrent indicators at this locality are scarce; where present, they indicate sediment transport directions to the west-southwest.

At Reasoner Canyon, there is a composite transect through the upper Modelo (Figures 4.2 and 4.4). Total stratigraphic thickness of the Mohnian section at this locality is ~1,300 m

(~4,265 ft); the thickness is estimated, due to the equivocal nature of the base of the Mohnian here. Geologic mapping and measured sections in this area reveal that this locality contains several composite sandstone packages (Figure 4.4). There are erosive surfaces at the base and within some of these packages, and they contain LFA 7, with lesser amounts of shale clast conglomerate with thick-bedded sandstone (LFA 8), LFA 3, and LFA 6. These sandstone packages are separated by thick mudstone and siltstone successions (LFA 2). Of the 1,045 m of measured stratigraphic columns and mapped strata at this locality, LFA 2 comprises 85.7% of the stratigraphic thickness, LFA 7 comprises 10.4%, LFA 3 comprises 2.5%, LFA 6 comprises

0.7%, and LFA 8 comprises 0.7%. Net-sandstone content is ~14%, much lower than the exposures at the Narrows and at southern Lake Piru. Paleocurrent data at Reasoner Canyon average 203°.

Exposures in Region 2 (Figures 4.2 and 4.4) are interpreted to represent axial and off-axis positions in a sandstone-rich fairway located in upper middle bathyal water depths immediately basinward of the mouth of the submarine canyon. At the Narrows and southern Lake Piru, the prevalent 15-40-m (~49-131 ft) -thick sandstone packages with erosional bases and coarse- grained, amalgamated fills are interpreted as southward- and southwestward-oriented channel complexes (Figures 4.4 and 4.10). At the southern end of Lake Piru, the thick successions of

LFA 1 between channel complexes are interpreted as siliceous mudstone sheets that represent

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local quiescence in between turbidity-current depositional events. These mudstone sheets do not necessarily comprise more areally extensive correlation surfaces. Thin-bedded sandstones and siltstones above and below the channels with non-amalgamated and semi-amalgamated infills at

Fustero Point are interpreted as levees. There are some lobes present at various localities in

Region 2, but most of the thick-bedded and amalgamated strata are interpreted as channels, which are constituents of channel complexes (Figures 4.4 and 4.10). Isopach map trends document that the upper Modelo is thickest in the eastern part of Region 2, and is thinner west of

Lake Piru at localities such as Reasoner Canyon (Figure 4.5). The relatively high net-sandstone successions at the Narrows and southern Lake Piru represent axial (or nearly axial) positions in the fairway, whereas the lower net-sandstone succession at Reasoner Canyon represents an off- axis position.

4.5.3. Region 3: Medial-Distal Basin Floor

Region 3 is bounded by east-west striking faults and highlands of lower Modelo sandstone to the north, Piru Creek to the east, the San Cayetano fault trace to the south, and the town of Fillmore and the San Cayetano fault trace to the west (Figure 4.2). In this region, the upper Modelo is exposed in the flanks of a series of east-west-trending anticlines and synclines

(Figure 4.2). Exposures of upper Modelo sandstone form cliffs and steep slopes; the most accessible outcrops are located at the base of modern canyons such as Modelo Canyon and

Hopper Canyon (Figure 4.2). The Angels Pass locality is located on a mountainside high above

Fillmore and the valley below, and it contains vertical to overturned beds of upper Modelo sandstone in the north limb of a syncline (Figures 4.2 and 4.12D). The San Cayetano fault is an active thrust that juxtaposes Miocene strata on top of Pleistocene strata (Çemen, 1989; Nicholson

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et al., 2007); in the hanging wall, Modelo mudstone successions (within Tm3) that are several tens of meters thick are commonly contorted and deformed due to flexural slip within folds.

Sandstone-rich packages (within Tm4) remain mostly undeformed by flexural slip within these folds.

Modelo Canyon contains a nearly complete transect through the Mohnian section (Figure

4.2 and 4.4), although the mudstone-rich uppermost part of the Modelo is not well exposed here.

Total stratigraphic thickness is estimated at 1,207 m (~3,960 ft), based on geologic mapping and compilation of measured stratigraphic sections (Figure 4.4). The base of the upper Modelo sandstone (Tm4) rests above the petroliferous middle mudstone (Tm3), which contains active oil seeps. The oldest upper Modelo sandstone strata at this locality comprise a steeply-dipping composite unit that is 83 m (~272 ft) in thickness. There are thin- to medium-bedded sandstones and siltstones (LFA 3), as well as lesser amounts of LFA 1, 2, 4, and 5 within this unit (Figure

4.12A). The lower boundaries of sandstone beds are mostly planar and non-erosive (Figure

4.12A). Some of the beds within LFA 4 are poorly sorted and contain floating lithic clasts within a sandy matrix (Figure 4.12B). This basal unit is overlain by a mudstone interval and several steeply-dipping packages of thick-bedded, amalgamated sandstone of LFA 7 (Figure

4.4). Each of these packages is 10-40 m (~33-131 ft) in thickness, and they contain erosional surfaces within them. The packages are separated from one another by tens to hundreds of meters of mudstones and siltstones (LFA 2). At this locality, LFA 2 comprises 87.6% of the stratigraphic thickness, LFA 3 comprises 5.0%, LFA 7 comprises 4.9%, LFA 1 comprises 2.2%,

LFA 4 comprises 0.3%, and LFA 5 comprises a small proportion (well under 0.1%). Net- sandstone content is ~10%. Rare paleocurrent data indicate west-southwestward- and southward-oriented sediment transport directions. Foraminiferal analysis from a sample

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collected near the lower part of the upper Modelo sandstone indicates paleobathymetry values in the upper middle bathyal range range (from 500-1500 m [1,640-4,921 ft]).

The Hopper Canyon locality contains partial exposures of the Mohnian section of the

Modelo in a series of anticlines and synclines (Figures 4.2 and 4.12C). The base of the upper

Modelo sandstone overlies the petroliferous middle mudstone, Tm3 (composed of LFA 1), which contains active oil seeps. The oldest upper Modelo sandstone strata at this locality comprise a unit of thin- to-medium-bedded LFA 3, 4, 5, and 10, with lesser amounts of LFA 7 (Figure

4.12C). The bases of these beds are generally planar and non-erosive. Loaded and dewatered beds are common within LFA 5, and poorly sorted sandstones that contain floating lithic and charcoal clasts are common in LFA 4. Some intercalated mudstone and siltstone beds in this unit contain folded and contorted strata of LFA 10; these strata are 1-2 m (~3.3-6.6 ft) in thickness.

The basal upper Modelo strata summarized above are overlain by several packages of thick- bedded, highly amalgamated sandstone that are 10-20 m (~33-66 ft) in thickness (Figure 4.4).

The uppermost packages are exposed in inaccessible cliffs high above the canyon floor; the stratigraphic thickness values reported here are estimates. Paleocurrent measurements from the lowest part of the upper Modelo sandstone at Hopper Canyon indicate southwestward-oriented sediment transport.

The Angels Pass locality (Figure 4.12D) contains a nearly complete transect through the

Mohnian section, although the top of the upper mudstone (Tm5) is absent due to erosion. The total stratigraphic thickness is estimated at 700 m (~2,297 ft), based on local stratigraphic measurements and correlations (Figure 4.4). Near the contact between the lower sandstone

(Tm2) and the middle mudstone (Tm3), there is an interpreted local reverse fault zone, the

Angels Pass fault zone (Figure 4.12D). Beds in this zone are deformed and folded. The upper

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Modelo sandstone (Tm4) is 158 m (~518 ft) in thickness (Figure 4.12D). This relatively high- sandstone-content interval comprises several packages of thick-bedded, highly amalgamated, medium-coarse-grained sandstone (LFA 7), with lesser amounts of LFA 3 and 8. The bases of these sandstone packages are erosional, and mudstone rip-up clasts are common within amalgamated beds. The middle mudstone (Tm3) below, and upper mudstone (Tm5) above, comprise LFA 2. At this locality, LFA 2 comprises 79.2% of the total stratigraphic thickness,

LFA 7 comprises 17.7%, LFA 3 comprises 2.9%, and LFA 8 comprises 0.2%. Net-sandstone content is ~21%. No paleocurrent indicators were observed here. Benthic foraminifera from an upper Modelo sample collected at this locality document paleobathymetry values in the upper middle bathyal range (from 500-1500 m [1,640-4,921 ft]; Kristin McDougall, personal communication, 2012).

In the Medial-Distal Basin Floor region, the thin- to medium-bedded sandstones with non-erosive bases are interpreted as lobe-fringe strata. Figure 4.4 documents that the margin of the submarine fan, as defined by the lobe fringes, steps outward (radially) and southwestward through time. Above the basal lobe strata at localities such as Modelo Canyon and Hopper

Canyon, the thick-bedded, highly amalgamated sandstone packages represent channel complexes that correlate to lobe strata farther to the southwest and to the south (Figure 4.4). The highly amalgamated sandstone strata at Angels Pass also represent channel complexes (Figure 4.4) that correlate to lobe strata farther to the southwest and to the south. Isopach map trends document that in Region 3, strata gradually become thinner to the west (Figure 4.5). Stratigraphic thickness data, paleocurrent indicators, and documentation of architectural elements and complexes present in Region 3 reveal the lateral-distal (west-southwest) margin of the fan (and the EVB). The western boundary of the EVB (the “Fillmore high”) was a local high that

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separated the EVB from the greater Ventura basin; this high represents a distal sill and an interpreted increase in seafloor gradient (Figure 4.4). Lobe-fringe strata in Region 3 onlap the margin of the basin in increasingly southwestward locations (Figure 4.4), and the channel complexes above them document an outwardly expanding submarine fan responding to increased depositional area through time. A similar trend has been documented by Pyles (2008), Pyles and

Jennette (2009), and in a geometric model for structurally confined basins proposed by Gordon et al. (in review).

4.6. Paleogeographic Interpretation

Collectively, the observations and interpretations presented above lead to the interpretation that outcrops of the upper Modelo Formation in the study area represent a longitudinal transect through a structurally confined submarine fan, from shallow-marine structural terraces, through a submarine canyon, to the basin floor and basin margin (Figure

4.13). Geologic mapping, stratigraphic correlations, and paleocurrent data document that coarse- grained strata sourced from a fan delta were deposited on relatively shallow-marine structural terraces located east of the Devil Canyon fault (Figures 4.9 and 4.13). Conglomerates and breccias containing crystalline clasts are only located on the structural terraces, as the relatively finer-grained sediments of the fan-delta front were shed southwestward into the submarine canyon located between the Devil Canyon fault on the east and the Agua Blanca fault zone on the west (Figure 4.13). The submarine canyon has a mudstone-rich fill and is interpreted as an area of predominant sand bypass; sandstone-filled channels are present, but relatively rare

(Figures 4.9 and 4.13). Near the mouth of the submarine canyon, there is a sandstone-rich fairway on the proximal basin floor that contains southward- and southwestward-oriented

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channel complexes (Figures 4.10 and 4.13). These channel complexes longitudinally transfer to lobe strata located in more distal positions in the basin (Figures 4.4 and 4.13).

The four distinct paleogeographic maps in Figure 4.13 represent four phases of the submarine fan’s development. Each phase is constrained by the correlation surfaces labeled in

Figure 4.4. In early phases (e.g., Time 1), the submarine fan was relatively confined in and near the deepest part of the basin, where the fan deposits are thickest. Lobe-fringe strata that represent the distal reaches of the submarine fan at that time were deposited in the Modelo

Canyon locality. During Time 2 and Time 3, the submarine fan built out farther to the south and southwest, resulting in the juxtaposition of channel complexes above lobes at Modelo Canyon

(Time 2) and at Hopper Canyon (Time 3). Channel complexes were prevalent at Angels Pass at

Time 3. At Time 4, channels are interpreted to have fed lobes near the southern margin of the

EVB.

4.7. Discussion

The following section integrates the observations and interpretations of this study into discussions of depositional controls on distributions of lithofacies associations, as well as hydrocarbon reservoirs in fault-bounded deepwater basins.

4.7.1. Fault and Bathymetric Controls on the Distribution of Lithofacies

Associations

Here we discuss paleogeographic features and their influence on the resultant stratigraphy. Isopach mapping (Figure 4.5) demonstrates that stratigraphic thickness values change abruptly across some faults (e.g., Devil Canyon fault, Santa Felicia fault). The changes

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in stratigraphic thickness are interpreted to indicate abrupt changes in paleobathymetry and depositional environment (Figure 4.13). There are also abrupt changes in the proportions of lithofacies associations and net-sandstone content across some faults (Figures 4.4, 4.14, and

4.15). As such, these faults are interpreted to have been syndepositionally active. In the EVB, the Canton and San Gabriel faults comprise the proximal boundary of the basin, and the Agua

Blanca fault zone might have controlled the position of the canyon-to-basin-floor transition

(Figures 4.4, 4.13, and 4.15). All of the faults mentioned above are associated with middle- to late-Miocene rifting and the transtensional tectonic regime (Yeats et al., 1994).

The various localities in the three distinct regions of this study area contain systematic variations in the proportions of lithofacies associations (Figure 4.14). Generally, higher proportions of coarser-grained strata (e.g., LFA 7 or 9) are located in proximal localities, whereas higher proportions of finer-grained strata (e.g., LFA 2) are located in more distal localities (Figures 4.14 and 4.15). In the Feeder System region east of the Devil Canyon fault, coarse-grained debrites, high-density turbidites, and grain-flow deposits of LFA 9 are abundant

(Figure 4.14), possibly due to proximity to the source area and locally steep gradients generated by syndepositionally active faults (e.g., Canton fault). Due to the relative paucity of conglomerates west of the Devil Canyon fault, it is interpreted that only rare high-energy flows and depositional events were capable of transporting boulder- and cobble-sized clasts to more basinward localities. The Devil Canyon fault formed the western boundary of a relatively shallow-marine structural terrace that provided accommodation for the coarse-grained proximal deposits.

The interface between the submarine canyon and the basin floor (Proximal Basin Floor region) contains an abrupt transition from predominantly mud-rich strata in the canyon to sand-

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rich strata on the basin floor. Basinward of the mouth of the submarine canyon, there is a relatively high proportion of LFA 7 (Figures 4.10, 4.14, and 4.15). This proximal-basin-floor fairway is separated from the structural terraces of the Feeder System by the submarine canyon, an area dominated by turbidity-current bypass (Figure 4.15) and deposition of LFA 2. Due to the stark difference in sandstone content between the submarine canyon and the proximal-basin- floor fairway (Figure 4.15), it is interpreted that turbidity currents that traveled through the submarine canyon decelerated and underwent a reduction in flow capacity (cf. Hiscott, 1994;

Millington and Clark, 1995) upon reaching the reduced gradient of the canyon-to-basin-floor transition; the turbidity currents then deposited medium- and coarse-grained sand as well as pebbles (LFA 7) on the proximal basin floor.

A large volume of finer-grained sand and mud-sized particles was transported by turbidity currents to more distal and off-axis localities in the Medial-Distal Basin Floor region, where erosion, amalgamation, and bypass are comparatively rare (Figure 4.15). Thin- to medium-bedded, non-amalgamated, poorly sorted clast-rich sandstones and argillaceous sandstones (LFA 4) occur along with LFA 3 in lobe-fringe strata at the base of the Modelo

Canyon and Hopper Canyon sections (Figures 4.4, 4.12A, 4.12B, 4.12C, and 4.15). These poorly sorted and argillaceous beds of LFA 4 are interpreted as deposits of hybrid sediment gravity flows (cf. Haughton et al., 2009; Hodgson, 2009). Hybrid flows record transitions from fully turbulent conditions to increasingly cohesive and laminar-flow conditions (Davis et al.,

2009), and their deposits are reported to be common near the margins of structurally confined submarine fans (Haughton et al., 2003; “transition zone” of Pyles and Jennette, 2009) and in the fringes of basinward-stepping lobes (Hodgson, 2009). The hybrid-flow deposits of the upper

Modelo Formation are interpreted as being the result of initially erosive, turbulent sand-rich

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flows that traversed the muddy basin floor en route to the basin margin; as the flows encountered subtle bathymetric relief near the margin, they decelerated, deposited their coarsest grains, and hence, continued to the margin relatively enriched in mud. The increased proportion of mud

(i.e., clays) in the flows could have served to increase cohesion and suppress turbulence. Thick- bedded, amalgamated sandstones (LFA 7) generally decrease in abundance in basin-margin strata (Figures 4.14 and 4.15); they are only prevalent in medial-distal environments at higher stratigraphic positions (e.g., Angels Pass locality). This reflects the outward expansion of the basin’s depocenter through time.

Results and interpretations discussed above document that syndepositionally active faults are associated with abrupt changes in thickness, net-sandstone content, proportions of lithofacies associations, and depositional environments, whereas relatively subtle gradient transitions near a non-fault-controlled basin margin or distal sill result in gradual changes in the above characteristics (Figures 4.14 and 4.15). The canyon-to-basin-floor transition is a physiographic area capable of producing marked changes in proportions of lithofacies associations and net- sandstone content (Figures 4.14 and 4.15).

4.7.2. Hydrocarbon Reservoirs in Fault-Bounded Deepwater Basins

Structurally complex, fault-bounded deepwater basins are common features of Earth’s seafloor and continental margins. These basins and their constituent turbidite depositional systems have been documented in the North Sea (Lonergan and Cartwright, 1999; Lowe and

Guy, 2000; Haughton et al., 2003; Kane et al., 2003; Jackson et al., 2011), onshore and offshore

California (Gorsline and Emery, 1959; Haner, 1971; Redin, 1991; Rumelhart and Ingersoll,

1997; Covault and Romans, 2009; Romans et al., 2009; Normark et al., 2009), the Gulf of

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Mexico (Booth et al., 2003), onshore Spain (Haughton, 2000), and even along ancient mid-ocean ridges (Portner et al., 2011). Several of the above regions are highly petroliferous (e.g., North

Sea, California, Gulf of Mexico), and sandy turbidite systems within them often form prolific hydrocarbon reservoirs. The upper Modelo Formation of the EVB is a rare, well-exposed outcrop example of a fault-controlled turbidite system; as such, it provides an excellent opportunity to document potential stratigraphic traps and reservoir architectures in an ancient fault-bounded deepwater basin. Further, this deepwater depositional system provides the opportunity to relate isopach thicks to locations of greatest sandstone content, and to document reservoir quality trends in the context of paleogeographic environment and basin morphology.

Certain characteristics of modern inner Borderland basins of California are analogous to the EVB in the late Miocene. Documentation of these modern basins and their turbidite systems augments understanding of aspects of the EVB and similar ancient fault-bounded basins in petroliferous provinces. Margins of inner Borderland basins are often steep (~5-10°) and fault- controlled (Haner, 1971), and depositional systems transport relatively coarse-grained (i.e., sand- sized) sediment across a narrow shelf to the structurally confined basin floor below (Covault and

Romans, 2009; Romans et al., 2009), often in upper middle bathyal water depths (500-1,500 m;

~1,640-4,921 ft; Normark et al., 2009). Studies demonstrate that submarine canyons of

Borderland basins are the principal conduits that feed the sand-sized sediment from updip to the basin floor (e.g., Normark et al., 2009). For example, in the San Pedro basin, sand-rich turbidite channels extend basinward from the mouth of the Redondo submarine canyon (Haner, 1971;

Normark et al., 2009). This is very similar to the upper Modelo Formation in the EVB, where the area of highest sandstone content is in channel complexes on the proximal basin floor, in the vicinity of the canyon mouth (Figures 4.13 and 4.15). Critically, this area is manifested as an

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isopach thick (Figure 4.5), which represents the greatest stratigraphic thickness of the entire depositional system. The submarine canyon is an area of sand bypass and low-sandstone content

(Figure 4.15); hence, this sets up the potential for stratigraphic traps in updip pinchouts of proximal basin-floor sandstones.

In medial-distal localities of the EVB, the upper Modelo Formation contains thick- bedded, amalgamated channel-complex sandstones (good reservoir quality) overlying thin-to- medium-bedded, poorly sorted and argillaceous lobe-fringe sandstones (LFA 4, with LFA 3).

The poor sorting and “dirty” character of these lobe-fringe sandstones results in poor reservoir quality. This is similar to basin-margin trends documented in Pyles and Jennette (2009), where axially dispersive flows resulted in low net-to-gross, poor reservoir quality deposits that formed a wedge separating clean, good-reservoir-quality proximal sandstones from their distal lapout.

The above observations have important implications for reservoir stacking patterns and identification of vertical successions of lithofacies associations in structurally confined basins in the North Sea, Gulf of Mexico, and other petroleum provinces around the world.

4.8. Conclusions

This study is the first detailed documentation of the paleogeography, stratigraphy, and sedimentology of the entire upper Modelo depositional system in the northern part of the eastern

Ventura basin (EVB), California. Outcrops of the upper Modelo Formation, a structurally confined, fault-controlled submarine fan, comprise a longitudinal transect through a deepwater depositional system, from shallow-marine structural terraces near the San Gabriel fault, through a submarine canyon, to the basin floor and basin margin (Figures 4.13 and 4.15). Key conclusions of this study are:

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 Isopach mapping documents that the gross thickness of the upper Modelo Formation

(Mohnian) is greatest near the interpreted mouth of the submarine canyon, where it has

the highest sandstone content (Figures 4.5 and 4.15). Immediately northeast (updip) of

this area, in the submarine canyon, sandstone content is relatively low, even though gross

thickness is still relatively high (Figures 4.5 and 4.15). West and southwest of the mouth

of the submarine canyon, gross thickness values decrease gradually toward the

interpreted margins of the submarine fan depocenter (Figures 4.5 and 4.13).

 Relatively abrupt changes in depositional environments, stratigraphic thickness,

distributions of lithofacies associations, and net-sandstone content are related to

syndepositionally active faults. Gradual changes in stratigraphic thickness, proportions

of lithofacies associations, and net-sandstone content are related to interpreted subtle

variations in depositional gradients between the proximal basin floor and the medial-

distal basin floor (e.g., changes observed between southern Lake Piru and Modelo

Canyon; Figures 4.14 and 4.15).

 Certain depositional environments of structurally confined submarine fans are likely to

host specific lithofacies associations. For example, thin-medium-bedded, poorly sorted

sandstones and argillaceous sandstones (hybrid-gravity-flow deposits of LFA 4) are often

located in the fringes of lobes at the base of the submarine fan, near basin-margin

environments (Figure 4.4). However, the mere presence of specific lithofacies

associations is generally not diagnostic of one depositional environment over another.

Relating to the example above, the southern Lake Piru locality in the Proximal Basin

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Floor region also contains LFA 4. Similarly, LFA 7 is common in the Proximal Basin

Floor region, as well as at higher stratigraphic positions in more distal localities such as

Angels Pass (Figure 4.14).

 Sandstone-rich fairways containing stacked channel complexes (e.g., the Narrows; Figure

4.10) can occur near and immediately basinward of submarine canyon mouths (Figure

4.13), where gross thickness is greatest (Figure 4.5). The submarine canyon immediately

updip can be a region with low sandstone content, due to extensive bypass (Figure 4.15).

Stratigraphic traps comprising updip pinchouts of sand-rich proximal basin-floor strata

into the mud-rich submarine canyon might represent optimal well locations in canyon-fed

turbidite reservoirs.

 In structurally confined basins, upward increases in depositional area through time

produce specific architectures, with implications for stacking patterns of hydrocarbon

reservoirs. Near basin margins, an outwardly expanding depocenter is manifested as an

association of channel complexes overlying lobe strata. This trend is observed at the

Modelo Canyon and Hopper Canyon localities.

 Concepts developed herein have direct applications to petroleum reservoirs in fault-

bounded basins worldwide. These basins are located in regions such as the North Sea,

the Gulf of Mexico, and California.

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4.9. Acknowledgments

Primary funding for this research came from the Chevron Center of Research Excellence

(CoRE) at the Colorado School of Mines. Additional funding for GG’s Ph.D. research came from a GCS SEPM Ed Picou Fellowship, a ConocoPhillips SPIRIT Scholarship, the Bartshe

Family Fellowship, and a Devon Energy Scholarship. This study would not have been possible without the hospitality and cooperation of landowners in the eastern Ventura basin: John

Williams and the Williams family, the Snow family, Wally King, and Tim Cohen of Rancho

Temescal. Tony Ward, Clayton Strahan, the United Water Conservation District, and Sarah

Stillwell were very helpful in granting access to land surrounding Lake Piru. Greg Cavette and

DCOR, LLC, were very helpful in providing access to Hopper Canyon, and Dan Tappe of the

U.S. Fish & Wildlife Service was quite helpful in securing passage through Hopper Mountain

National Wildlife Refuge. We thank our plucky field assistants Gary Listiono, Martin Jimenez,

Denise Gordon, Stuart Gordon, and Tim “Blue Steel” O’Toole. Dan McKeel and Kristin

McDougall (U.S.G.S.) provided foraminiferal analysis of hand samples. We thank Greg Cavette,

Tom Hopps, and Jim Mansdorfer for their time, generosity, and assistance. Insightful geologic discussions with Morgan Sullivan, Julian Clark, Stuart Gordon, and Greg Cavette greatly aided this study. Charlie Rourke, Cathy Van Tassel, and Linda Martin graciously provided logistical and technical support.

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150

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Figure 4.1. Map of Ventura and Los Angeles basins, depicting nearby cities, mountain ranges, and major faults. Note that the Oak Ridge fault, currently a thrust fault, has been inverted. Red polygon indicates the location of the study area at the northern margin of the eastern Ventura basin. Inset map shows the location of the study area in California. (Map redrawn and modified from Dibblee, 1989; additional geologic data from Yeats et al., 1994, and Rumelhart and Ingersoll, 1997.)

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Figure 4.2. Geologic map of the northeastern Ventura basin, in the vicinity of Lake Piru. The upper Modelo sandstone (Tm4), the focus of this study, crops out in a northeast-southwest-oriented belt from the Devil Canyon area in the northeast to near the town of Fillmore in the southwest. West of Piru Creek, the outcrops of the upper Modelo Formation are located in the hanging wall of the San Cayetano thrust fault. Regions 1-3 are denoted by black dashed lines. (Geologic data and contacts compiled and modified from Cordova, 1956; Çemen, 1977; Dibblee, 1990, 1991, 1993, 1996, 1997; Crowell, 2003a.)

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Figure 4.3. (A) Cross-sectional schematic stratigraphic diagram for the Ventura basin (modified and redrawn from Dibblee, 1995; additional stratigraphic data from Nagle and Parker, 1971, and Yeats et al., 1994). The study area is mostly located in the Piru and NW Castaic areas. No vertical or horizontal scale implied. (B) Stratigraphic chart documenting California benthonic foraminiferal units and Neogene-Quaternary strata in the eastern Ventura basin (modified from Yeats et al., 1994). The focus of this study is the Mohnian upper Modelo sandstone, Tm4, and associated interfingering mudstones in Tm3 and Tm5.

155

Figure 4.4. Northeast-southwest-oriented cross section documenting the Mohnian upper Modelo Formation in the northern part of the eastern Ventura basin. The datum for the cross section is the contact between the Modelo and Towsley Formations. It is denoted by the bold green line. Thickness values are constrained by composite measured sections, and well data from Yeats et al. (1994). Sediment transport directions are approximately southwestward and parallel to this line of section, but some channel and lobe strata obliquely enter and exit the plane of this cross section (reflecting local westward or southward sediment transport). Canton fault and Devil Canyon fault (DCF) were syndepositionally active; faults are shown in their approximate late Miocene configurations. Late Pliocene-Recent tectonic shortening is not removed. Stratigraphic columns from northeast of the Devil Canyon fault are from Trembly (1987), as well as this study. The location of this cross section is labeled in Figure 4.2.

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Figure 4.5. Gross-interval isopach map for the Mohnian strata (Tm3, Tm4, and Tm5; Figure 4.3B) of the Modelo Formation in the eastern Ventura basin. Fault abbreviations on this map are the same as those in Figure 4.2. The thickness values in the southeastern part of the map reflect contributions from strata deposited as parts of additional, co-eval turbidite depositional systems (Yeats and Stitt, 2003) that are not the focus of this study. Late Pliocene-Recent tectonic shortening is not removed. (Map modified from Yeats et al., 1994.)

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Figure 4.6. Photographs and abbreviated descriptions of lithofacies (LF) documented in the study area.

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Figure 4.7. Stratigraphic columns or photographs of the ten lithofacies associations documented in this study. Each lithofacies association (LFA) comprises a distinct group of depositionally related lithofacies (LF).

159

Figure 4.8. Photographs documenting strata and stratigraphic relationships in Region 1, the Feeder System. See Figures 4.2, 4.4, and 4.5 for location of Region 1. (A) Angular unconformity (red line) in Canton Canyon between the gently-dipping Modelo Formation and near-vertical beds of older strata (Sespe Formation). View looking to the northeast. (B) Coarse- grained strata of LFA 9, located east of the Devil Canyon fault. (C) Folded and contorted beds of LFA 10, with planar, non-deformed beds above and below, located east of the Devil Canyon fault. (D) Thick succession of mudstones with rare, interbedded siltstone turbidites. This succession is located west of the Devil Canyon fault, near the angular unconformity. These mudstone exposures commonly form steep topography.

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Figure 4.9. Paleogeographic diagram of Region 1, the Feeder System, during deposition of the upper Modelo Formation. Faults depicted in the diagram are interpreted as being syndepositionally active. View looking to the east.

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Figure 4.10. Photopanels of the Narrows area in Region 2, the Proximal Basin Floor. See Figures 4.2, 4.4, and 4.5 for location of the Narrows in Region 2. (A) The Narrows outcrop locality is a north-south-oriented exposure of upper Modelo strata on the east side of Piru Creek at the northern end of Lake Piru. The Narrows outcrop is almost 2 km (~1.2 mi) wide, and almost 400 m (~1300 ft) tall. (B) Photographs of channel complexes exposed in the middle part of the Narrows outcrop. The complexes are composed of channel elements with amalgamated fills. Red lines represent the erosional bases of channel elements. Black lines represent the tops of channel complexes, which are shaded yellow. Sediment transport direction is to the right (~southward), parallel to the plane of the page. (C) Channelized strata present at the northern end of the Narrows. Red lines represent the erosional bases of channel elements. Black lines represent the tops of channel complexes, which are shaded yellow. Channel elements appear wider than they actually are because sediment transport direction (obliquely out of the page and to the right) is nearly parallel to the orientation of the outcrop.

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Figure 4.11. Photographs of upper Modelo strata exposed in Region 2, the Proximal Basin Floor. See Figures 4.2, 4.4, and 4.5 for location of Region 2. (A) Stacked channel elements comprising a channel complex at Fustero Point, the northern part of the Narrows outcrop locality. See Figures 4.2 and 4.10A for location of Fustero Point. Sediment transport is generally into the page and to the right. The non-amalgamated channel-fill exposures represent the northwestern margins of channels. (B) Coarse-grained, pebbly structureless sandstone (of LFA 7) exposed at the base of a channel axis in Region 2. (C) Mudstone rip-up clasts and amalgamation surface (dashed red line) within sandstone of LFA 7, at the southern Lake Piru locality.

163

Figure 4.12. Photographs of upper Modelo strata exposed in Region 3, the Medial-Distal Basin Floor. See Figures 4.2, 4.4, and 4.5 for location of Region 3. (A) Steeply-dipping thin- and medium-bedded strata exposed at the base of the upper Modelo sandstone section in Modelo Canyon. Stratigraphic-up is to the right. (B) Poorly sorted, lithic-rich sandstone bed exposed near the base of the upper Modelo sandstone in Modelo Canyon. (C) Thin- to medium-bedded strata at the base of the upper Modelo sandstone section in Hopper Canyon. These beds are composed of poorly sorted sandstones, argillaceous sandstones, sandstones with dewatering features, and thin-bedded, rippled and structureless sandstones (LFA 3, 4, and 5). Stratigraphic- up is to the left. (D) Photographs of vertical and overturned Modelo Formation beds at the Angels Pass locality, with superimposed measured section. The entire upper Modelo sandstone package (Tm4) is 158 m (~518 ft) in thickness here. Stratigraphic-up is to the left. View is looking to the west.

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Figure 4.13. Paleogeographic interpretation of the upper Modelo Formation in the northern part of the eastern Ventura basin during the late Miocene (Mohnian). The four time steps represent generalized phases in the sequential evolution of this submarine fan; these time steps correlate to the timelines labeled in the cross section in Figure 4.4. Black arrows indicate mean paleocurrent directions. Red dots indicate outcrop localities and principal measured sections utilized for this interpretation: DCTTP (Devil Canyon truck trail “proximal” section), DCTTC (Devil Canyon truck trail “channels” section), FP (Fustero Point, northern end of the Narrows), RC (Reasoner Canyon), SLP (southern Lake Piru), MC (Modelo Canyon), HC (Hopper Canyon), and AP (Angels Pass). Faults present are SGF (San Gabriel fault), CF (Canton fault), DCF (Devil Canyon fault), SFF (Santa Felicia fault), and ABF (Agua Blanca fault). Late Pliocene-Recent tectonic shortening is not removed. Co-evally deposited turbidite systems located to the southeast are not shown, as they are not the focus of this study and they do not crop out.

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Figure 4.14. Fan-scale distribution of lithofacies associations (LFA). Sandstone content generally decreases toward the distal submarine-fan localities (to the southwest); at Angels Pass, however, the percentage of sandstone-rich lithofacies associations (e.g., LFA 7) is relatively high due to channel complexes that had built out to that part of the submarine fan after Time 2 (see Figures 4.4 and 4.13). Abbreviations for faults and outcrop localities are the same as those in Figure 4.13. The three regions are denoted by red dashed polygons. Co-evally deposited turbidite systems located to the southeast are not shown.

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Figure 4.15. Schematic, cross-sectional summary diagram of the northern part of the eastern Ventura basin in the late Miocene, showing generalized basin-scale trends in sandstone content (net-sand thickness), degree of amalgamation, relative abundance of hybrid gravity-flow deposits, and degree of bypass. Abbreviations are the same as those in Figure 4.13

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Table 4.1. Descriptions and interpretations of lithofacies documented in the upper Modelo Formation of the eastern Ventura basin.

Modal Interpreted Interpreted Interpreted flow Lithoacies Description grain sediment support depositional Comparison to other studies type size(s) mechanism process

1 Siliceous mudstone, w/ clay hindered settling suspension pelagic rain Monterey Formation (Graham and porcelaneous or glassy Williams, 1985; Schwalbach et texture al., 2009)

2 Fissile, finely laminated, or clay hindered settling; suspension hypo-pycnal Te (Bouma, 1962); F9a [Te] structureless shale possibly fluid plume; fine- (Mutti, 1992) turbulence grained turbidity current

3 Laminated siltstone silt fluid turbulence tractive turbidity current Td (Bouma, 1962); F9a (Mutti, 1992)

4 Contorted or folded BI- matrix strength frictional slumps or slides "slump", "slide" (Martinsen and sandstones or mudstones MODAL: freezing, Bakken, 1990) clay; fine cohesive sand freezing

5 Shale/sandstone clast BI- dispersive pressure tractive/bedload high-density F3 (Mutti, 1992); possibly R3 conglomerate in a MODAL: (grain-grain and turbidity current (Lowe, 1982) disorganized sandy or clay; fine clast-clast muddy matrix sand collisions); matrix buoyant lift

168

6 Thin-bedded, intercalated BI- fluid turbulence suspension and turbidity current sand: Ta, Tb, or Tc (Bouma, very fine- to fine-grained MODAL: tractive 1962); mud: Td or Te (Bouma, sandstones with mudstones clay; fine sedimentation 1962); F9a (Mutti, 1992) (sand beds may be sand lenticular)

7 Argillaceous, poorly sorted very fine matrix strength frictional debris flow, or F1 (Mutti, 1992); possibly sandstone sand freezing, hybrid gravity "slurry-flow depostis" (Lowe and cohesive flow Guy, 2000) freezing

8 Thin-bedded, poorly sorted fine sand matrix strength frictional debris flow, or F1 (Mutti, 1992); possibly sandstone w/ angular freezing, hybrid gravity "slurry-flow deposits" (Lowe and carbonaceous or lithic cohesive flow Guy, 2000) fragments freezing

9 Very fine- to medium- fine sand fluid turbulence initial turbidity current Ta, Tb, or Tc (Bouma, 1962) grained sandstone with suspension or extensive loading and soft- tractive sediment-deformation sedimentation, features followed by loading from above

10 Thin- to medium-bedded, fine sand fluid turbulence suspension and turbidity current Ta, Tb, or Tc (Bouma, 1962) non-amalgamated sandstone tractive (may be structureless, sedimentation rippled, or planar- laminated)

11 Laminated to cross-stratified medium fluid turbulence tractive turbidity current Facies 4, Facies 6 (Gardner et al., sandstone (may be in close sand sedimentation 2003); base of Tt division (Lowe, association with 1982); F6 (Mutti, 1992) amalgamated sandstone or conglomerate)

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12 Medium- to thick-bedded, medium fluid turbulence suspension turbidity current S3 (Lowe, 1982); Facies 5 structureless sandstone sand (Gardner et al., 2003); F8, (often amalgamated; fine- possibly F5 (Mutti, 1992); Ta grained to pebbly; might be (Bouma, 1962) poorly sorted; may contain mudstone or sandstone rip- up clasts)

13 Poorly sorted sandstone, medium escaping pore mostly tractive high-density F7 (Mutti, 1992); possibly S2 often associated with sand fluid; fluid sedimentation turbidity current (Lowe, 1982) conglomerate; may be turbulence planar laminated, cross- stratified, or structureless

14 Clast-supported BI- dispersive pressure tractive/bedload turbidity current F3 (Mutti, 1992); R3 (Lowe, conglomerate (clasts are MODAL: ("high- 1982) moderately- to well- fine sand; concentration") or rounded, and up to boulder- cobble grain flow size) clasts

15 Breccia (contains angular BI- dispersive pressure tractive grain flow Violin Breccia (Link, 2003) pebble- to boulder-sized MODAL: sedimentation clasts; clasts are dominantly fine sand; igneous and metamorphic cobble rocks) clasts

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CHAPTER 5.

CONCLUSIONS TO DISSERTATION

5.1. Summary Conclusions and Contributions

This dissertation comprises outcrop-based studies of the Guaso I turbidite system in

Ainsa basin, Spain, and the upper Modelo Formation of eastern Ventura basin, California. Both of these deepwater depositional systems were deposited in structurally complex, confined basins, albeit in different tectonic settings. The resulting isopach patterns for each of these systems are distinct (Figure 5.1), probably due to differing spatial distributions of subsidence and basin- margin uplift. Generally, basins with more focused local subsidence and steeper basin margins

(e.g., rift, transtensional, and some salt-withdrawal minibasins) contain thicker successions of sandstone in a relatively small area. These thick successions of sandstone create an overall isopach thick, which is partly due to differential compaction. Whereas both the Guaso I and upper Modelo systems exhibit increasing depositional area and architectural diversity through time, mass-transport complexes (non-reservoir) and sand-rich strata (potential reservoir) are located in different parts (i.e., proximal vs. distal) of each basin (Figure 5.1). General results of this dissertation include documentation of stratigraphic architecture and sequential evolution of distributive submarine fans in structurally confined basins. Specific conclusions and contributions of each of the studies are described below.

5.2. Chapter 2 Conclusions and Contributions

Chapter 2 documents a fully confined, ponded fourth-order (reservoir-scale) distributive submarine fan, the Guaso I turbidite system, deposited in a deepwater basin with margins formed

171 by syndepositionally active anticlines. Isopach mapping (see Figure 5.1) reveals an axial thick that is dominated by a mass-transport complex (poor reservoir quality) in the proximal feeder system; on the basin floor, the thick comprises a succession of reservoir-quality sandstone

(mostly sandy channels and lobes). Geologic mapping, architectural analysis, and stratigraphic correlations reveal that in early stages of this depositional system, lobe elements stacked aggradationally on the relatively confined basin floor. As the system evolved, depositional area increased, and the system became more distributive. This resulted in increased compensational stacking, and increased architectural diversity, through time. Chapter 2 presents a geometric model that relates compensational stacking to effective depositional area and association of architectural elements. This model is widely applicable to turbidite systems in small, confined deepwater basins (e.g., piggyback basins, salt-withdrawal minibasins) around the world, many of which are prolific hydrocarbon reservoirs. Chapter 2 contributes a greater level of detail (i.e., at the scale of individual architectural elements in one fourth-order, reservoir-scale package) than previous studies and models for turbiditic infill of confined deepwater basins (e.g., Prather et al.,

1998; Sinclair and Tomasso, 2002).

5.3. Chapter 3 Conclusions and Contributions

Whereas the general term channel-lobe transition zone (CLTZ) applies to a range of different scales, from submarine-fan-scale to the scale of a discrete architectural element,

Chapter 3 documents an exceptionally well-exposed longitudinal transect from a channel element to its attached lobe element in a small, structurally confined deepwater basin (Ainsa basin). Paleocurrent-parallel, element-scale outcrop exposures of this quality are very rare worldwide, and this outcrop provides the opportunity for detailed documentation of the

172 stratigraphic evolution, sedimentologic features, and reservoir quality of a channel-lobe system, with particular emphasis on the CLTZ. Previous studies of the CLTZ have focused on relatively limited outcrop exposures (e.g., Vicente Bravo and Robles, 1995), or larger-scale features on the modern seafloor (e.g., Wynn et al., 2002). Chapter 3 provides recognition criteria as well as in- depth interpretations for the CLTZ, a critical morphologic region that governs sandstone continuity and flow transformations between the channel and lobe. Key conclusions of this chapter include the observation that there can be reservoir connectivity between bedsets of the channel and its basinward lobe. Erosion and internal scours generally decrease in a downcurrent direction, from the channel, through the CLTZ, to the lobe. Mean grain size and sorting change gradually, rather than abruptly, along a longitudinal profile. Sandstones of the CLTZ and lobe element are generally finer-grained and better sorted than sandstones of the genetically related channel element; this is due to the cumulative loss of coarser sediment via deposition within the channel. Building upon and modifying the build-cut-fill-spill model (Gardner and Borer, 2000;

Gardner et al., 2003), this chapter provides a four-part model describing the sequential evolution of a channel-lobe element.

5.4. Chapter 4 Conclusions and Contributions

Chapter 4 documents the paleogeography and stratigraphy of a structurally confined, fault-controlled submarine fan. Outcrops of the upper Modelo Formation in the northern part of the eastern Ventura basin (EVB) comprise a longitudinal transect through a deepwater depositional system, from proximal, shallow-marine structural terraces near the San Gabriel fault, through a submarine canyon, to the basin floor and basin margin. Isopach mapping indicates that gross thickness of the upper Modelo is greatest near the interpreted mouth of a

173 submarine canyon in the feeder system. In the submarine canyon, sandstone content is low due to prevalent bypass, whereas there is a high-sandstone-content channel fairway located near the canyon-to-basin-floor transition. Relatively abrupt changes in depositional environments, distribution of lithofacies associations, and sandstone content are produced by syndepositionally active normal faults near the proximal margin of the basin. Gradual changes in distribution of lithofacies associations are produced by subtle variations in interpreted basin-floor gradients approaching the distal basin margin. Additionally, there are distinctive stratigraphic architectures and upward successions near the lateral-distal basin margin: an outwardly expanding depocenter through time is manifested as an association of channel complexes overlying lobe strata. Lobe-fringe strata are commonly thin- to medium-bedded, poorly sorted, and argillaceous, whereas channel sandstones are often thick-bedded, amalgamated, and coarser- grained. Conclusions from Chapter 4 have important implications for better understanding the architecture and distribution of reservoir quality in turbidite reservoirs originally deposited in structurally complex, fault-bounded basins of the North Sea, California, and other petroliferous regions.

5.5. References

174

Sinclair, H. D., and M. Tomasso, 2002, Depositional evolution of confined turbidite basins: Journal of Sedimentary Research, v. 72, p. 451-456.

Vicente Bravo, J.C., and S. Robles, 1995, Large-scale mesotopographic bedforms from the Albian Black Flysch, northern Spain: characterization, setting and comparison with recent analogues, in K.T. Pickering, R.N. Hiscott, N.H. Kenyon, F. Ricci Lucchi, and R.D.A. Smith, eds., Atlas of Deep Water Environments: Architectural Style in Turbidite Systems: London, Chapman & Hall, p. 216-226.

Wynn, R.B., N.H. Kenyon, D.G. Masson, D.A.V. Stow, and P.P.E. Weaver, 2002, Characterization and recognition of deep-water channel-lobe transition zones: AAPG Bulletin, v. 86, p. 1441-1462.

175

Figure 5.1. Isopach patterns for deepwater depositional systems in piggyback basins and in rift/transtensional basins. These two distinct depositional systems are shown at the same scale. A distributive deepwater depositional system comprises multiple channel-lobe elements, such as the one depicted, that build a submarine fan.

176

APPENDIX A

Measured Sections – SUPPLEMENTAL ELECTRONIC MATERIAL

Appendix A comprises measured section files and locator maps from both field areas:

Guaso I system in the Ainsa basin, and upper Modelo Formation in the eastern Ventura basin.

GuasoI_measured_section_locator_map.PDF Map documenting location of measured

sections in Ainsa basin

GuasoI_Measured_sections.PDF Drafted sections

GuasoI_Measured_sections-2.PDF Drafted sections

Modelo_Fm_measured_section_locator map.PDF Map documenting location of measured

sections in eastern Ventura basin

Modelo_Fm_measured_sections_EVB.PDF Drafted sections

177

APPENDIX B

Uninterpreted Photos – SUPPLEMENTAL ELECTRONIC MATERIAL

Appendix B includes uninterpreted photos and photopanels from the Guaso I system and the upper Modelo Formation.

GuasoI_Channel_fill_Waterfall_Canyon.PDF Uninterpreted photo

GuasoI_Lobe_bedsets_above_RioEna.PDF Uninterpreted photo

GuasoI_Lobe_bedsets_Rio_Ena.PDF Uninterpreted photo

GuasoI_RioEna_ElGradoRoad.PDF Uninterpreted photo

GuasoI_Roadside_channel_complex.PDF Uninterpreted photo

Modelo_Fm_Fustero_Point.PDF Uninterpreted photo

Modelo_Fm_TheNarrows_lower_channels.PDF Uninterpreted photo

Modelo_Fm_TheNarrows_Photopanel_2.PDF Uninterpreted photo

Modelo_Fm_TheNarrows_photopanels_1.PDF Uninterpreted photos

178

APPENDIX C

Data and Spreadsheets – SUPPLEMENTAL ELECTRONIC MATERIAL

Appendix C comprises tabular data from both field areas. These data include GPS points, strike-dip measurements, paleocurrent measurements, sample locations, and field notes.

GuasoI_GPS_points_DATA.PDF Spreadsheet

Modelo_Fm_EVB_GPS_points_DATA.PDF Spreadsheet

179

APPENDIX D

Permissions Letters – SUPPLEMENTAL ELECTRONIC MATERIAL

Appendix D includes copies of letters and emails from co-authors of the journal articles associated with Chapters 2, 3, and 4 of this dissertation. In these letters and emails, the co- authors grant permission for the use of the articles as chapters of the dissertation. Also included in Appendix D are letters from Chevron and Elsevier granting permission for the use and modification of a figure originally published in Sedimentary Geology.

Chevron_permission_letter_Prelat_et_al_2010_figure.PDF Permission letter from

Chevron

Elsevier_license_permission_for_Prelat_et_al_2010_figure.PDF Permission document from

Elsevier

Clark_authorization_letter_Mansucript.PDF Permission letter from Julian

Clark

Hoffman_permission_letter.PDF Permission letter from Matt

Hoffman

Pyles_permission_letter.PDF Permission letter from David

Pyles

180