Fine Scale 3D Architecture of a Deepwater Channel Complex, Carbon County, South-Central Wyoming
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Transcript of Fine Scale 3D Architecture of a Deepwater Channel Complex, Carbon County, South-Central Wyoming
UNIVERSITY OF OKLAHOMA
GRADUATE COLLEGE
FINE SCALE 3D ARCHITECTURE
OF A DEEPWATER CHANNEL COMPLEX,
CARBON COUNTY, SOUTH-CENTRAL WYOMING
A THESIS
SUBMITTED TO THE GRADUATE FACULTY
In partial fulfillment of the requirements for the
degree of
Master of Science
(Geology)
By
Staffan Kristian Van Dyke
Norman, Oklahoma
2003
FINE SCALE 3D ARCHITECTURE
OF A DEEPWATER CHANNEL COMPLEX,
CARBON COUNTY, SOUTH-CENTRAL WYOMING
A THESIS APPROVED FOR THE
SCHOOL OF GEOLOGY AND GEOPHYSICS
BY
Chair:
Dr. Roger Slatt
Member:
Dr. Douglas Elmore
Member:
Dr. Roger Young
© Copyright by STAFFAN KRISTIAN VAN DYKE 2003
All Rights Reserved
ACKNOWLEDGEMENTS
I would like to extend an overwhelming appreciation and special thanks to my
advisor, Roger Slatt, for guiding me through this project as well as giving me
invaluable insight over the course of writing this thesis and during my 3 year stay at
the University of Oklahoma. Thanks for believing in me, Roger.
I would also like to extend appreciation to my committee members, Douglas
Elmore and Roger Young. They have not only provided valuable insight into the
project, but have also been very understanding with all the problems encountered at
the end of thesis writing. I thank Ozzie Ilaboya for all the help and advice regarding
GOCAD™, without whom, none of this would have been possible.
All teachers and fellow graduate students at the University of Oklahoma are
also thanked, and their memory will forever be burned into my conscious – thanks for
everything. A particular thanks goes to my field assistants, Andria Parker and Ash
Hall.
Lastly, I would like to thank my family, Gene, Astrid, and Tor Van Dyke.
This work is dedicated to them, in particular, to my mother for being the best mom in
the world and always being there for me when I needed somebody. I love you mom
and you will always be number one in my book.
TABLE OF CONTENTS
Acknowledgements…………………………………………………………….……..iv
Table of Contents…………………………………………………………………......v
List of Figures……………………………………...……………………………….....x
List of Appendices......................................................................................................xiii
Abstract…………………………………………………………………………...…xiv
CHAPTERS PAGE
1.
INTRODUCTION…………………………………………………………………….1
Research Objectives…………………………………………...………1
Significance……………………………………………………...…….1
Location of Study Area and Description of Outcrop………..……..….3
Geologic Overview……………………………………….….……..…6
Lithostratigraphy and Sequence Stratigraphy………………………..10
Lewis Shale Petroleum System……………………………….……...12
Previous Studies……………………………………………………...13
Data Collection………………………………………………………15
Data Analysis………………………………………………………...18
3-Dimensional GOCAD™ Model…………………………………...19
2. LITHOFACIES DESCRIPTION…………………………………………….…..20
Introduction…………………………………………………………..20
Lithofacies Types………………………………………………….....20
Lithofacies 1 (F1): Structureless to Cross-Bedded
Sandstone with Water-Escape Structures……………............22
Physical Description…………………………………….…...22
Hydrodynamic Interpretation…………………………….......23
Lithofacies 2 (F2): Structureless Sandstone
without Water-Escape Structures…………………….............24
Physical Description…………………………………………24
Hydrodynamic Interpretation………………………………...25
Lithofacies 3 (F3): Cross-Bedded Sandstones
without Water-Escape Structures ……………........................27
Physical Description…………………………………………27
Hydrodynamic Interpretation………………………………...28
Lithofacies 4 (F4): Parallel to Subparallel Laminae……....................28
Physical Description…………………………………………28
Hydrodynamic Interpretation………………………………...30
Lithofacies 5 (F5): Rippled or Climbing-Ripple Sandstone…............30
Physical Description…………………………………….…...30
Hydrodynamic Interpretation…………………………...……31
Lithofacies 6 (F6): Shale or Mudstone……………………................32
Physical Description…………………………………………32
Hydrodynamic Interpretation………………………………...33
Lithofacies 7 (F7): Shale-Clast Conglomerates……………...............34
Physical Description…………………………………………34
Hydrodynamic Interpretation………………………………...36
Lithofacies 8 (F8): Slump Beds……………………………...............37
Physical Description…………………………………………37
Hydrodynamic Interpretation………………………………...38
3. ENVIRONMENT OF DEPOSITION AND FACIES RELATIONSHIPS..……..39
Introduction……………………………………………………………..........39
Interpretations………………………………………………………………..40
E1: Non-sinous (Straight) leveed-channel environment……………………..42
Interpretation…………………………………………………………42
Facies Relationship…………………………………………………..42
E2: Outer-side of sinuous channel bend………….……………….................43
Interpretation…………………………………………………............43
Facies Relationship………………………………………............…..44
E3: Inner-side of sinuous channel bend…………………………............…...45
Interpretation…….……………………………………............……...45
Facies Relationship……………………………………............……..46
E4: Proximal levee………………………………..……………….................47
Interpretation……………………………………………............……47
Facies Relationship………………………………………............…..50
E5: Distal levee…………………………………………………............……51
Interpretation…………………………………………............….…...51
Facies Relationship……………………………………............……..52
4. 3D MODEL DESCRIPTION AND INTERPRETATION…………………..…...53
Introduction…………………………………………………………………..53
Viewing the Data……………………………………………............……….55
Channel-Fill Sandstone 1……………………………………............….........58
Vertical and Lateral Geometry……………………............……..…...60
Lithologic Stacking Patterns and Locations………............……..…..61
Interpretation…………………………………………............…..…..65
Subsurface………………………………………............………..…..65
Channel-Fill Sandstone 2…………………………………............……….....71
Vertical and Lateral Geometry…………………………............….....72
Lithologic Stacking Patterns and Locations……………..............…..72
Interpretation……………………………………………..............…..74
Channel-Fill Sandstone 3……………………………………….....................74
Vertical and Lateral Geometry…………………………............….....75
Lithologic Stacking Patterns and Locations……………..............…..75
Interpretation…………………………………………............…..…..77
Channel-Fill Sandstone 4………………………………………............….....77
Vertical and Lateral Geometry…………………………….................79
Lithologic Stacking Patterns and Locations………………............…79
Interpretation…………………………………………............………81
Channel-Fill Sandstone 6………………………………………............….....83
Vertical and Lateral Geometry…………………………….................83
Lithologic Stacking Patterns and Locations…………............………85
Interpretation……………………………………………............……85
Channel-Fill Sandstone 7………………………............………………….....87
Vertical and Lateral Geometry…………………............………….....87
Lithologic Stacking Patterns and Locations………............…………88
Interpretation……………………………………............……………88
Channel-Fill Sandstone 8……………………………………............…….....90
Vertical and Lateral Geometry………………………............…….....90
Lithologic Stacking Patterns and Locations…………............………91
Interpretation…………………………………………............………93
Channel-Fill Sandstone 9……………………………………............…….....94
Vertical and Lateral Geometry……………………............……….....95
Lithologic Stacking Patterns and Locations…………............………95
Interpretation……………………………………………............……95
Channel-Fill Sandstone 10…………………………………............………...97
Vertical and Lateral Geometry………………............…………….....97
Lithologic Stacking Patterns and Locations………............…………98
Interpretation………………………………………............…………98
5. CONCLUSIONS……….…….……………………………………………….....100
6. REFERENCES CITED…………………………………………………………..105
APPENDICES………………………………………………………………………CD
FOLDER Detailed Measured Sections in Digital Format………………………DMS
Gamma-Logs of Eight Shallow Boreholes…………………………..BHGL
Copy of Thesis Text…………………………………………………THESIS
GOCAD™ Data Files……………………………………………….GOCAD
SUBFOLDER D1. Raw Data…………………………………………………RD
D2. Channel-Fill Sandstone 1……………………………….CFS01
D3. Channel-Fill Sandstone 2……………………………….CFS02
D4. Channel-Fill Sandstone 3……………………………….CFS03
D5. Channel-Fill Sandstone 4……………………………….CFS04
D6. Channel-Fill Sandstone 5……………………………….CFS05
D7. Channel-Fill Sandstone 6……………………………….CFS06
D8. Channel-Fill Sandstone 7……………………………….CFS07
D9. Channel-Fill Sandstone 8……………………………….CFS08
D10. Channel-Fill Sandstone 9……………………………….CFS09
D11. Channel-Fill Sandstone 10..…………………………….CFS10
D12. Digital Elevation Map……………………………………DEM
D13. Quickview………………………………………………….QV
LIST OF FIGURES
FIGURE PAGE
Fig. 1.01: Chronostratigraphic chart of Upper Cretaceous strata, southern
Wyoming……………………………………………………….…………… ..2
Fig. 1.02: Shaded relief map of Wyoming and Washakie
Basin………………………………….………...……………….…………….3
Fig. 1.03: Topographic map of Spine 1 and Spine 2…….……………………………5
Fig. 1.04: Spine 1 with 9 channel-fill sandstones with detailed measured
sections colored black; overlain on topographic contours (Generated in
GOCAD™ v.2.0.6, 003)……………….……………………………………...5
Fig. 1.05: Cretaceous Western Interior Seaway .……………………….……………..6
Fig. 1.06: Paleogeographic Map for Lower Maastrichtian time…..….……………….7
Fig. 1.07: Major geologic features surrounding field area..……………..…………….9
Fig. 1.08: Lewis Shale Stratigraphic Column.………………………...….………….11
Fig. 1.09: Initial work characterizing the Dad Sandstone Member..……….………..14
Fig. 1.10: Example of detailed measured section produced for thesis research ……16
Fig. 1.11: Channel-fill boundary nomenclature……..…………………………...…..17
Fig. 2.01: Classic Bouma Sequence deposits………..……………………………….21
Fig. 2.02: “Knobby” texture interpreted as weathered vertical/subvertical
dewatering pipes……………………………………………………………..22
Fig. 2.03: Dewatering pipes located at the top of Channel-fill Sandstone 1………...23
Fig. 2.04: Structureless Sandstone with geologically unrelated holes
pockmocking surface of Channel-fill Sandstone 3….……..………………...24
Fig. 2.05: Temporal and Spatial relations in flow environments.....…………………25
Fig. 2.06: Walker’s (1978) classification of deepwater deposits….…………………26
Fig. 2.07: Lowe (1982) classification of High Density Turbidity Current
(HDTC) and Low Density Turbidity Current (LDTC)………………………26
Fig. 2.08: Low-angle, high amplitude crossbedding from Channel 1……… …..…..27
Fig. 2.09: Planar laminae on outcrop exposure on Channel-fill Sandstone 6….…….29
Fig. 2.10: Planar laminae located in Channel-fill Sandstone 1……………… …...…29
Fig. 2.11: Climbing-Ripple Facies located in Channel-fill Sandstone 6………..…...31
Fig. 2.12: Climbing-ripple facies description……………………………………......32
Fig. 2.13: Shale/mudstone facies bounded by structureless sandstone facies……….33
Fig. 2.14: Stacked shale-clast conglomerates (A) interbedded with
turbidites (B) on Channel-fill Sandstone 1……..……………………………35
Fig. 2.15: Faint imbrication of shale clasts occur in Channel-fill Sandstone 1……...35
Fig. 2.16: Debris Flow Rheology……………..………………………..……….……36
Fig. 2.17: Slump beds bounded in yellow from Channel-fill Sandstone 1 “Prong.”...37
Fig. 3.01: Enviroments of Deposition (E) 1-5 contained within
a leveed-channel system ………......……………………..………………….39
Fig. 3.02: Situations leading to different flow behaviors…………..………….……..40
Fig. 3.03: Planform view of flow movement within a leveed-channel system……....41
Fig. 3.04: Flow movement within a sinuous channel-bend...…………..……………41
Fig. 3.05: 3D seismic horizon slice……………………..…………………………....44
Fig. 3.06: Sinuous submarine channel-fill deposit localities………………………...45
Fig. 3.07: Oblique depositional strike view of Channel-fill Sandstone 1…………....46
Fig. 3.08: Environments of deposition of Channel-fill Sandstone 4………………....48
Fig. 3.09: Proximal levee with convoluted bedding and climbing ripples
associated with Channel-fill Sandstone 4……………………..……………..49
Fig. 3.10: Proximal levee with nice set of climbing ripples associated
with Channel-fill Sandstone 4…………………………………….…………50
Fig. 3.11: Distal levee deposits from Channel-fill Sandstone 4…...…..…….………51
Fig. 4.01: 3D GOCAD™ model of Dad Sandstone Member,
Lewis Shale; “Prong” region of Channel-fill Sandstone 1
circled in red; brown represents “Outcrop Plane,” while other colors
represent “Outcrop Face” of the nine channel-fill sandstones..……..…….…55
Fig. 4.02: Planview basemap of nine stacked channel-fill sandstones...…….....……57
Fig. 4.03: Channel-fill Sandstone 1 location in Field Area...……………...…..…….58
Fig. 4.04: Locations of detailed measured sections on
Channel-fill Sandstone 1 (1.01 – 1.22) ……...……………………………...59
Fig. 4.05: Plan view map of surface outcrop dimensions of
Channel-fill Sandstone 1 …………………………………………………….60
Fig. 4.06: “Prong;” located in the eastern region of Channel-fill……………………62
Fig. 4.07: Shale-clast conglomerate facies found in northern-most
portions of Channel-fill Sandstone 1 model……..…………………………..63
Fig. 4.08: Western-most flank of Channel-fill Sandstone 1 ends at MS# 1.0.1.… …64
Fig. 4.09: Boreholes (1-8) with locations of dip (green; 5-3-6)
and strike (white; 1-2-3-4) cross-sections, located on eastern
flank of Channel-Fill Sandstone 1 ………………………...………………...66
Fig. 4.10: Example of gamma-ray log from Borehole 1…...……………….………..67
Fig. 4.11: Dip cross-section of Boreholes 5-3-6 of Channel-Fill Sandstone 1…....…68
Fig. 4.12: Strike cross-section of Boreholes 1-2-3-4 of Channel-Fill Sandstone 1.…69
Fig. 4.13: Electro-Magnetic Induction and GPR (3-B to 3-B’)
carried out on eastern flank of Channel-Fill Sandstone 1….……………...…70
Fig 4.14: Ground-Penetrating Radar facies located in the subsurface
of Channel-Fill Sandstone 1 …………………………………….…….…….71
Fig. 4.15: Location and number of detailed measured sections (black)
with outcrop dimensions (red) on Channel-fill Sandstone 2………..…….…71
Fig. 4.16: F7, shale-clast conglomerates and F3, crossbedded sandstone,
located on Channel-fill Sandstone 2…..……………………………..………73
Fig. 4.17: Location and number of detailed measured sections (black)
with outcrop dimensions (red) on Channel-fill Sandstone 3…………..…….74
Fig. 4.18: Diagnostic facies of Channel-fill Sandstone 3...………………….....……76
Fig. 4.19: Location of Channel-fill Sandstone 4 on Spine 1……………..……....…77
Fig. 4.20: Location and number of detailed measured sections(black)
with outcrop dimensions (red) on Channel-fill Sandstone 4………….…..…78
Fig. 4.21: Diagnostic facies located on Channel-fill Sandstone 4.………………..…80
Fig. 4.22: Amalgamated channel-fills CFS 4a and CFS 4b,
comprising Channel-fill Sandstone 4………...................................................82
Fig. 4.23: Location and number of detailed measured sections (black)
with outcrop dimensions (red) on Channel-fill Sandstone 6……………….83
Fig. 4.24: Diagnostic facies of Channel-fill Sandstone 6.……………………….…85
Fig. 4.25: Amalgamated channel-fills CFS 6a and CFS 6b,
comprising Channel-fill Sandstone 6…........................................................86
Fig. 4.26: Location and number of detailed measured sections (black)
with outcrop dimensions (red) on Channel-fill Sandstone 7…………….…87
Fig. 4.27: Diagnostic facies of Channel-fill Sandstone 7…...……………………...89
Fig. 4.28: Location and number of detailed measured sections (black)
with outcrop dimensions (red) on Channel-fill Sandstone 8…………….…90
Fig. 4.29: Diagnostic facies of Channel-fill Sandstone 8…...…………………...…92
Fig. 4.30: Location and number of detailed measured sections (black)
with outcrop dimensions (red) on Channel-fill Sandstone 9…………….…94
Fig. 4.31: Diagnostic facies of Channel-fill Sandstone 9…………………………..96
Fig. 4.32: Location and number of detailed measured sections (black)
with outcrop dimensions (red) on Channel-fill Sandstone 10….………..…97
Fig. 4.33: Diagnostic facies Channel-fill Sandstone 10...………………………….99
Fig. 5.01: First generation conceptual model representing channel-fill
sandstones in 3D space (no channel sinuosity recorded)………………….101
Fig. 5.02: Second-generation diagram representing channel-fill
sandstone sinuosity………………………………………………………..102
LIST OF APPENDICES
APPENDIX (LOCATED ON ATTACHED CD) FOLDER
A. Detailed Measured Sections in Digital Format………………………DMS
B. Gamma-Logs of Eight Shallow Boreholes………………………….BHGL
C. Copy of Thesis Text……………………………………….………THESIS
D. GOCAD™ Data Files…………………………………….……....GOCAD
SUBFOLDER
D1. Raw Data…………………………………………………RD
D2. Channel-Fill Sandstone 1……………………………….CFS01
D3. Channel-Fill Sandstone 2……………………………….CFS02
D4. Channel-Fill Sandstone 3……………………………….CFS03
D5. Channel-Fill Sandstone 4……………………………….CFS04
D6. Channel-Fill Sandstone 5……………………………….CFS05
D7. Channel-Fill Sandstone 6……………………………….CFS06
D8. Channel-Fill Sandstone 7……………………………….CFS07
D9. Channel-Fill Sandstone 8……………………………….CFS08
D10. Channel-Fill Sandstone 9……………………………….CFS09
D11. Channel-Fill Sandstone 10..…………………………….CFS10
D12. Digital Elevation Map……………………………………DEM
D13. Quickview…………………………………………………QV
ABSTRACT
Nine channel-fill sandstones comprise a 255ft thick stratigraphic succession in
the deepwater Dad Sandstone Member, Lewis Shale, Wyoming. This succession has
been characterized by measuring 121 closely-spaced outcrop stratigraphic sections,
decimeter-scale GPS-tracing (Global Positioning System) of bed boundaries, drilling
and gamma-logging of 8 shallow boreholes, ground-penetrating radar (GPR), and
electro-magnetic induction (EMI) behind the outcrops. A 3D facies and architectural
model was built using GOCAD TM
.
Each channel-fill sandstone is separated by thin-bedded, very fine
sandstone/mudstone strata. Channel facies include structureless sandstone with fluid
escape structures, structureless sandstone without fluid escape structures, rippled to
climbing rippled sandstone, parallel to subparallel laminated sandstone, cross-bedded
sandstone, shale-clast conglomerate, thin-bedded sandstone/mudstone, and slumped
beds. In separate channel-fill sandstone, these facies can be complexly interbedded,
but there is a tendency for shale-clast conglomerates to comprise the base and one
side of a channel-fill, whereas cross-bedded sandstones comprise the opposite side.
Massive/fluid escape structured sandstones typically occupy the top of these
successions. Proximal to distal levee beds occur adjacent to some of the channel
sandstones.
This distribution of facies, coupled with GPR data, suggests the sandstones
filled sinuous channels. The shale-clast conglomerates are thought to be the product
of slumping of adjacent levee walls from the steeper channel margin, and the cross-
bedded sandstones are interpreted to be in-channel bar or dune forms. These channels
probably fed sand into the deeper basin contemporaneously with levee formation; the
channel-fill sandstones represent the product of later backfilling episodes. The
slumped and erosive nature of some channel margins support this interpretation.
This 3D outcrop characterization provides an excellent, scaled analog for
leveed channel reservoirs. The complex vertical stratigraphy indicates individual
channel sandstones can be mutually isolated reservoirs. The complex internal channel
sandstone distribution indicates internal reservoir fluid flow will also be complex. A
figure illustrating the relation of channel-fill sandstone sinuosity relative to one
another in outcrop has also been created.
Chapter 1
INTRODUCTION
Research Objectives
This thesis research has two main objectives. The first objective is to
document the 3-dimensional surface geometry of nine submarine slope channel
sandstones in outcrops of the Lewis Shale through detailed measured sections and
computer modeling via GOCAD™. The second objective is to correlate channel
facies in 3-D space in order to better document reservoir-scale features of leveed-
channel deposits and their lateral continuity and vertical connectivity. This research
study also attempts to better understand the reservoir aspect of the petroleum system,
i.e., the Dad Sandstone Member of the Upper Cretaceous Lewis Shale in southern
Wyoming (Fig. 1.01).
Significance
The study of submarine slope channel deposits is of great importance for
many different reasons: (1) documenting the facies scale character of channel-fill
sandstones, (2) reservoir characterization for better field development planning, (3)
understanding the progressive evolution of sinuous submarine channels, and (4)
determining the active mechanisms that force sinuosity. This thesis will not solve all
of these problems, but will offer insight into better understanding and documenting
these factors. It is also hoped that the resultant 3D model and its correlations will
help to shed light on expected lateral continuity and vertical connectivity of reservoir
scale facies in analog fields located within other deepwater sinuous channel systems,
such as those found in the deepwater Gulf of Mexico and offshore West Africa.
With the real-scale, outcrop-based 3-dimensional GOCAD™ model, fluid
flow simulation can also be performed and compartmentalization within channel
reservoirs can be modeled. The 3-D model will impact future work on reservoir
characterization within other submarine slope channel complexes around the world.
It is necessary to solve the unknowns in these types of problems by developing better
depositional models from outcrop work, which will have direct bearing on new field
development solutions in the future.
Fig. 1.01: Chronostratigraphic chart of Upper Cretaceous strata, southern Wyoming (Modified
after Schell, 1973).
Location of Study Area and Description of Outcrop
The study area outcrops along the Sierra Madre Uplift in the eastern portion of
the Washakie Basin, south-central Wyoming, Carbon County, within Sections 24 and
25 of T16N R92W (Fig. 1.02). From the town of Baggs, which is located 3 miles
north of the Wyoming-Colorado border, the outcrop can be easily accessed by
traveling 23.5 miles north on Hwy. 789 and approximately 4 miles east on a dirt road
(to the west of the dirt road is a metal quanset hut). The study area is a resistant ridge
referred to as Spine 1, which trends ENE-WSW. Spine 1 and another ridge to the
southeast, called Spine 2, are separated from one another by a 0.5 mile wide modern
floodplain (Fig, 1.03). Spine 2 trends E-W.
Fig. 1.02: Shaded relief map of Wyoming and Washakie Basin (Modified after Sterner,
1997).
This region nicely exposes all 3 successive components of a complete
Lowstand Systems Tract in one place (Witton, 2000); from the base of the outcrop,
there are two sheet sandstones (basin floor fans) overlain by nine leveed channel-fill
sandstones (the subject of this thesis) and then an interval of predominantly mudstone
(prograding complex).
Sinuous leveed-channel systems are formed in the deepwater regions of the
ocean basins. Those described in this text are found on the slope. They are
aggradational channels, i.e., the channel depression is a result of levee aggradation.
Upon sea level rise, these vacant channel depressions become backfilled with
sediment. The channel related sediments are referred to as channel-fill sandstones.
The processes involved with the deposition of channel-fill sandstones are
thought to resemble those of subaerial fluvial systems. Many of the geological
features recognized in subaerial fluvial systems are also recognized in submarine
leveed-channel systems. These features include: 1) inner-side, point-bar style
deposits, 2) outer-side cut-bank style erosion, 3) proximal levee regions, and 4) distal
levee regions.
Nine of these channel-fill sandstones have been identified as comprising Spine
1 and are the main focus of the research (Fig. 1.04). Originally, Witton (2000)
identified 10 separate channel-fill sandstones, but due to more in-depth work using
GPS and GOCAD™ v.2.0.6, sandstone boundaries mapped in 3D space indicate her
Channel-fill Sandstone #5 is actually the western part of Channel-fill Sandstones #2
and #4. As the nomenclature was already deeply entrenched in most of her work, I
have retained the original 1 – 10 designations. Channel-fill Sandstone #5 is no longer
present.
Fig. 1.03: Topographic map of Spine 1 and Spine 2 (from Slatt, 2003).
Fig. 1.04: Spine 1 with 9 channel-fill sandstones with detailed measured sections colored
black; overlain on topographic contours (Generated in GOCAD™ v.2.0.6, 2003)
Geologic Overview
This geologic overview has been modified from Pyles (2000) and Witton
(2000). During the Cretaceous, the Western Interior portion of the United States was
inundated with an elongate, relatively shallow epeiric seaway known as the Western
Interior Seaway (Fig. 1.05). The Western Interior Seaway was bounded on the west
by an active Cordilleran highland, through the modern day states of New Mexico,
Colorado, Wyoming, and Montana, and to the east by the Canadian Shield (Molenaar
and Rice, 1988). It stretched from the Gulf of Mexico to the Northern Boreal Sea
(Krystinik, 1995).
Fig. 1.05: Cretaceous Western Interior Seaway (Reproduced from Witton, 2000)
This Cordilleran Highland system was the main source of terrigenous material
to the Western Interior Cretaceous basin. Due to varying rates of sedimentation and
crustal loading throughout the basin at the time, varying rates of subsidence occurred.
The western portion of the Washakie Basin records thick sequences of marine and
non-marine clastic sediments interfingering with one another, thus representing
marine transgressions and regressions that occurred during late Cretaceous time.
Weimer (1960) indicated four major transgressions and regressions in the
early Upper Cretaceous. This was supported by his work of tracing the main
interfingerings of marine and non-marine clastic sediments, which represented the
paleo-shorelines. Kauffman (1977) suggested ten major transgressions and
regressions. Wiemer’s fourth transgressive-regressive cycle matched Kauffman’s
ninth transgressive-regressive cycle.
Fig. 1.06: Paleogeographic Map for Lower Maastrichtian time (After McGookey et al., 1972)
The final transgression and regression of the late Cretaceous was known as the
Bearpaw transgressive-regressive cycle. It was during this last phase that the Lewis
Shale was deposited in south-central Wyoming (Fig. 1.06). Deposition was largely
controlled by sediment supply, intrabasin tectonics, and eustacy. Active deltas from
the north-northeast and those projecting eastward from the Washakie basin (Hale,
1961) channeled sediments into deeper regions of the basin, particularly those similar
to regions as the study area location. At the time of sediment deposition in the
location of the study area, the water depth was calculated to be as deep as 1450 ft.
based on the decompacted relief of individual clinoforms from Pyles (2000) regional
cross section.
In the lower Maastrichtian, west of the study area, was the Sevier Orogenic
Belt, contained within the Cordilleran Highlands. This was a classic fold-thrust belt
resulting when the Farallone oceanic plate subducted under the continental plate. Just
east of the fold-thrust belt was the foreland basin, and most of Wyoming was
contained within this basin at the time.
During the Laramide Orogeny (Campanian to Paleocene) and its associated
uplifts, the foreland basin was segmented into many local sub-basins, including the
Washakie basin (McMillen and Winn, 1991). The Washakie basin is part of the
Greater Green River Basin, which itself is a product of horizontal compression and
fragmentation of the craton that occurred during the Laramide orogeny (Baars et al.,
1988). Figure 1.07, provided by Baars et al. (1988), shows that the basin is bounded
to the north by the Wamsutter Arch, to the east by the Sierra Madre Uplift, to the
south by the Cherokee Arch, and to the west by the Rock Springs Uplift.
Fig. 1.07: Major geologic features surrounding field area (Baars et al., 1988).
As relative sea-level began to rise, the Lewis Shale was deposited onto a
muddy slope; as sea-level deepened considerably in middle to late Lewis time,
sedimentation into the basin was mainly sourced from deltaic systems. During most
of the early Maastrichtian, basin subsidence rates outlasted rates of sedimentation;
this was due to either 1) subcrustal loading and subcrustal cooling caused by the low
angle subduction of the oceanic crust of the Farallone plate, 2) thermal decay and
crustal contraction, 3) supracrustal loading, or 4) stress-induced subsidence as a result
of tectonic loading (Cross and Pilger, 1978).
Lithostratigraphy and Sequence Stratigraphy
The Lewis Shale Formation can be broken into three informal members: the
Lower Shale Member, the Dad Sandstone Member, and the Upper Shale Member
(Fig. 1.08). The Lewis Shale was formally named by Cross and Spencer (1899) for
exposed thick marine sequences (Gill et al., 1970). The type locality is found east of
Mesa Verde National Park in Fort Lewis, southwestern Colorado. Originally the
name was meant to designate rocks deposited during a regression and transgression of
Campanian age in the San Juan Basin. Later, the name was mistakenly extended to
include rocks of younger regressive- transgressive cycles not even recorded in the San
Juan basin. This nomenclature is inherently wrong and is very confusing, but has
become entrenched in the literature.
Fig. 1.08: Lewis Shale Stratigraphic Column (from Slatt, 2003).
Both the underlying Almond Formation and the overlying Fox Hills
Sandstone interfinger with the Lewis Shale on a regional scale (Gill et al., 1970). The
Lower Shale Member comprises several hundred feet of black shale, while the Dad
Sandstone Member is composed of interbedded shale and sandstone, ranging in
thickness from 300 to 700 feet. The upper shale member is generally dark to olive
gray, silty to sandy, nonresistant, and locally contains fossiliferous limestone or
siltstone concretions (Gill et al., 1970).
McMillen and Winn (1991) studied well log and seismic reflection data. They
concluded that the Lower Shale Member was deposited as part of a 3rd
order
transgressive systems tract, while the Dad Sandstone Member and the Upper Shale
Member were deposited as part of the ensuing 3rd
order highstand systems tract.
Pyles’ (2000) work, the most comprehensive to date, detailed the region within a
fourth-order sequence stratigraphic framework. Pyles showed that although the
broader, more extensive third-order cycle existed, there in fact are many fourth-order
cycles of aggradation and progradation within the 3rd
order cycle. This work showed
the valuable use and wealth of knowledge gained from a high-order sequence
stratigraphic framework approach to an area.
Lewis Shale Petroleum System
Three major components to any petroleum system are: 1) source, 2) reservoir,
and 3) trap/seal. The source is defined as strata of high organic carbon (C) content; a
high total-organic-carbon (TOC) percentage is necessary for the generation of
kerogen, the precursor to hydrocarbons. If hydrocarbons are generated, there must be
a reservoir to house them. The reservoir can be any lithology with porosity and
permeability, e.g., limestone, sandstone, and siltstone. In order for these
hydrocarbons to be trapped, they must collect under some sort of trap or seal.
Stratigraphically this component is usually an impermeable lithology that seals the
hydrocarbons, or in structural traps, confines the hydrocarbons by a variety of means,
e.g. fault seals.
The Lewis Shale within south-central Wyoming is an unconventional gas
reservoir with an estimated 24 TCF of gas in place, with 10.7 TCF recoverable
(Doelger and Barlow, 1997). The Federal Energy Regulatory Commission designated
the formation as a tight gas sand (Winn et al., 1985). As of 1997, only 6% of the total
reserves had been produced, thus leaving much room for new unconventional
development concepts to exceed the production capabilities of reservoirs.
There is a third-order condensed section near the top of the Lower Lewis
Shale comprised of organic-rich shale known as the Asquith Marker; it ranges in
thickness from thirty to eighty feet. It is generally believed by most who work this
region, that the Asquith Marker is the most likely source-rock of the Lewis Shale
Petroleum System (Slatt, Lewis Consortium field notes, 2001).
The reservoir-prone lithology of the Lewis Shale petroleum system is the Dad
Sandstone Member. The hydrocarbon seals for this petroleum system consist of
bentonite clays and shales (Slatt, Lewis Consortium field notes, 2001).
Previous Studies
In 2000, work was completed in the field area by Elizabeth Witton (Witton,
2000). Her work characterized the field area by delineating the northernmost ridge,
Spine 1, into its constituent parts: the lowermost two sheet sandstone bodies, the
originally interpreted 10 separate channel sandstone bodies, and fourteen units within
the overlying prograding complex (Fig. 1.09). Her work, which included outcrop
interpretation and descriptions, was instrumental in setting up the basis for this
research. Witton classified four separate lithofacies: A) continuous thick-bedded
sandstones, B) discontinuous thick-bedded sandstones with rip-up clasts, C) thin-
bedded sandstones, and D) thin-bedded, laminated mudstones and shale.
Her work also involved the recognition of facies in a borehole image log from a
well drilled through the same stratigraphic interval about 8 miles away. This work
was accomplished by first describing detailed measured sections of the outcrop to
recognize and categorize the four different facies. The facies were then correlated to
sedimentary features identified on the image log. More recently, Slatt et al. (2002)
and Pyles and Slatt (2002) have provided evidence suggesting the channel sandstones
are leveed-channel deposits similar to those that produce hydrocarbons in many
deepwater settings (Abreau, 2002).
Fig. 1.09: Initial work characterizing the Dad Sandstone Member (Witton, 2000)
Data Collection
The succession of the nine stacked leveed channel-fill sandstones was
characterized by 121 closely-spaced, detailed, measured sections, dm-scale GPS-
tracing of bed boundaries, outcrop gamma-logging with a handheld scintillometer,
drilling/gamma-logging of 8 shallow boreholes, ground-penetrating radar (GPR)
behind outcrop, and Electro-Magnetic Induction (EMI). The GPR and EMI data were
not used in this thesis as they form parts of other thesis research at University of
Oklahoma. Lateral variations within each channel-fill sandstone were noted in the
field and at these points detailed measured sections were emplaced and described.
Enough detailed measured sections were completed so that all lateral variations
within each channel-fill sandstone outcrop were recorded.
The sections were measured using a Brunton Compass and a Jacob Staff. This
method was carried out for each channel-fill sandstone, with measured sections
ranging from as many as 26 for Channel-fill Sandstone 1 to as few as 6 for smaller
channel-fill sandstones, such as Channel-fill Sandstone 9 (Fig. 1.10). These
measured sections range in thickness from 2ft to 34ft. All 121 detailed measured
sections are cataloged on the CD in Appendix A.
Trimble ™ GPS units were used to delineate 3-D geometry of outcrops and to
accurately locate detailed measured sections in 3-D space. GPS “Line
Measurements” of bed boundaries were recorded in the field to best represent the 3-
dimensional nature of the outcrop (Fig. 1.11). Walking the three lines: 1) Base, 2)
Outside Top, and 3) Subsurface Top, provided two planes: 1) Outcrop Face and 2)
Outcrop Plane. “Outcrop Face” and “Outcrop Plane” were constructed in GOCAD™
allowing the raw data to portray the nine channel-fill sandstone bodies in their basic
morphological structure as seen on Spine 1 (Fig. 1.04). Along with all of the channel-
fill sandstone data, a topographic map was digitized and corrected for elevation. This
was than input into GOCAD™ as a pseudo-DEM (Digital Elevation Map).
Fig. 1.10: Example of detailed measured section produced for thesis research (located in CD as
Appendix A).
Fig. 1.11: Channel-fill boundary nomenclature
.
A handheld gamma-ray scintillometer was used to record the natural gamma
radiation of the channel-fill sandstones at all of the measured stratigraphic sections
(Slatt et al., 1995). A complete log profile of each measured section within every
channel sandstone was input into digital format for comparison with outcrop
measured sections (Appendix A). Eight shallow boreholes were also drilled and
gamma-logged for the lowermost Channel-fill Sandstone 1.
Data Analysis
Channel-fill sandstones 1 through 10 were mapped with the dm-scale Trimble
™ GPS units and detailed measured sections were completed on all nine channel-fill
sandstones. Enough of these detailed measured sections were obtained so that a very
accurate representation of all channel-fill sandstones on Spine 1 and all of their
internal facies characteristics were attained to build a 3D geologic model in
GOCAD™.
Each of the eight gamma-logged boreholes was input into digital format and
was interpreted for its internal lithology based on the merits of its gamma-log pattern
as well as cuttings from the borehole. The boreholes were then interpreted with both
strike and dip direction cross-sections, thus gaining valuable insight on the character
of subsurface facies within Channel 1 in a region where speculation was very high
and outcrop exposure very poor.
Additional work has been carried out by Dr. Roger Young and Ph.D. student
Julie Staggs who use GPR (Ground-Penetrating Radar) techniques to document the
shallow subsurface character of Channel Sandstone 1 (Young et al., in press), Dr.
Alan Witten and M.S. student Ryan Stepler used Electro-Magnetic Induction (EMI)
techniques to document the subsurface character of the sandstone and shale within the
eastern-most flank of the lowermost channel-fill sandstone. Most of Dr. Young’s and
Julie Stagg’s work on Spine 1 is focused primarily on Channel-fill Sandstone 1.
Some of their work will be incorporated within later chapters of the thesis since their
techniques have the means of tracking channel geometry in the subsurface.
3-Dimensional GOCAD ™ Model
A 3-Dimensional GOCAD ™ model has been designed to capture the
channel-fill sandstone outcrop geometry and internal fill architecture with 3-
Dimensional facies correlation through regions within the outcrop. The measured
sections were the basis for this correlation. Bed boundaries, recorded by the Trimble
™ GPS units, provide the skeletal structure for the model of the channel-fill
sandstones seen in outcrop. The detailed measured sections were input manually into
the model, whereby facies correlations were accomplished. As aforementioned,
Trimble™ GPS units were used to record X,Y,Z points in 3D space along outcrop
boundaries. After daily field work sessions, these data were retrieved and stored in
GPS Pathfinder™ on a laptop computer. Upon arrival back at the University of
Oklahoma, the files were then transferred as text (*.txt) files to GOCAD™ with
proper header format for computer recognition. The data was then capable of being
manipulated and viewed in GOCAD™. Each field day’s work was saved as a
separate file and each file contained its own cache of points in 3D space. These data
had to be meticulously sorted and classified in the GOCAD™ lab to fit points to their
proper channel boundary designations. After all points had been designated to their
proper locations and all channel boundaries had been defined, channel facies were
then input. The channel facies were then correlated to one another in 3D space.
Additional description of the model and its correlations are found in additional
chapters.
Chapter 2
LITHOFACIES DESCRIPTION
Introduction
Previous work performed by Witton (2000) and Slatt et al. (2000, 2001, and
2002) interpret Spine 1 to comprise a sinuous leveed-channel system. The steeper
side of each channel-fill sandstone was interpreted to have abundant debris flow
deposits (represented by facies F7, shale-clast conglomerate facies and the shallower
side was interpreted to contain cross-bedded sandstone) (Witton, 2000). The resultant
3D GOCAD™ model was built to test this interpretation and those offered in the text.
Lithofacies Types
Eight lithofacies were recognized in the field; they are: F1) sandstone with
water-escape structures (some cross-bedded), F2) structureless sandstone (without
water-escape structures), F3) cross-bedded sandstones (without water-escape
structures), F4) parallel to subparallel laminated sandstone, F5) rippled or climbing-
rippled sandstone, F6) shale or mudstone, F7) shale clast conglomerates, and F8)
slumped beds. With the exception of the shale-clast conglomerates (F7) and slump
beds (F8), the facies are fine-grained and well-sorted.
Fig. 2.01: Classic Bouma Sequence deposits (Modified from Jordan et al., 1993)
Three of the eight facies constitute classic Bouma Sequence deposits (Fig.
2.01); they are: F4, F5, and F6. F4, parallel to subparallel laminae is categorized as
Bouma division Tb. Rippled or climbing-rippled sandstone, F5, is interpreted as
Bouma division Tc and is the product of traction of grains along the sea bed during
lower flow regime conditions (Weimer and Slatt, in press). The final facies
categorized within the Bouma Sequence is F6, a shale or mudstone, denoted by Te.
Lithofacies 1 (F1): Structureless to Cross-Bedded Sandstone with Water-Escape
Structures
Physical Description
The structureless to cross-bedded sandstone with water-escape structures
consists of yellowish-tan, fine-grained, well-sorted sandstone. It is the second most
abundant facies. This facies exhibits primary low-angle cross-bedding in some
exposures, and in all of the exposures, secondary water-escape “knobs” (Fig. 2.02).
Water escape structures are common in the upper portions of the outcrop exposures,
particularly in Channel-fill Sandstone 1 (Fig. 2.02 and 2.03). This position within the
channel-fill facies sequence indicates that these sands may have been deposited as
liquefied/fluidized flows.
Fig. 2.02: “Knobby” texture interpreted as weathered vertical/subvertical dewatering pipes.
Fig. 2.03: Dewatering pipes located at the top of Channel Sandstone 1.
Hydrodynamic Interpretation
Sandstones with water-escape structures, such as vertical pipes, are formed by
hindered settling of sediments in a liquefied and/or fluidized flow (Weimer and Slatt,
in press). As the sediment in this facies is finally deposited, water migrates toward
the top of the flow, leaving a cavity in its pathway into which the surrounding
sediments collapse (Fig. 2.06). Because grain size varies within the deposit,
differential cementation occurs, giving rise to surficial differential weathering and the
development of the more resistant “knobs” (Slatt, personal communication, 2003).
Lithofacies 2 (F2): Structureless Sandstones without Water-Escape Structures
Physical Description
Structureless sandstone without water-escape structures are the most abundant
facies within the outcrops (Fig. 2.04). It is a yellowish-tan sandstone. This sandstone
does not exhibit any visible primary or secondary sedimentary structures. Thickness
of this facies can reach significant heights (up to 80% of the channel-fill stratigraphic
column, in some cases up to 24ft) and may represent many separate flow events.
Fig. 2.04: Structureless Sandstone with geologically unrelated holes pockmocking surface of
Channel-fill Sandstone 3.
Hydrodynamic Interpretation
Structureless sandstones are deposited in only one spatial and temporal flow
condition, steady depletive (Kneller, 1995; Fig. 2.05). Both Walker (Fig. 2.06; 1978)
and Lowe (Fig. 2.07; 1982) differentiated structureless sandstone from Bouma
division Ta. This was based on the interpretation that these sandstones tended to
exhibit: 1) water-escape structures, 2) fewer associated shale interbeds, 3) an increase
in erosionally-based and irregularly bedded sandstone, and 4) sandstone beds that are
thicker than associated beds (Weimer and Slatt, in press).
Fig. 2.05: Temporal and Spatial relations in flow environments (Modified from Kneller, 1995)
Fig. 2.06: Walker’s (1978) classification of deepwater deposits.
Fig. 2.07: Lowe (1982) classification of High Density Turbidity Current (HDTC) and Low
Density Turbidity Current (LDTC).
Lithofacies 3 (F3): Cross-Bedded Sandstones without Water-Escape Structures
Physical Description
This yellowish-tan sandstone is the third most abundant facies. These
deposits tend to manifest low-angle, high amplitude cross-bedding features (Fig
2.08). Many times it is difficult to reveal the low-angle cross-bedding in the field
because of the position of the sun.
Fig. 2.08: Low-angle, high amplitude crossbedding from Channel 1 (from Slatt, 2003).
Hydrodynamic Interpretation
Primary cross-bedding is formed by sediments that move along the seafloor as
tractive bedload. Traction can be defined as “a mode of sediment transport in which
the particles are swept along (on, near, or immediately above) and parallel to a bottom
surface by rolling, sliding, dragging, pushing, or saltation” (Jackson, 1997). Cross-
bedding is a lower flow regime feature. The low-angle nature of the cross-bedding
indicates that these features were most likely in-channel bar or dune forms (Slatt,
personal communication, 2003). The in-channel barforms are interpreted to lie on the
pointbar-equivalent side of the channel-fill system or upon the channel floor.
Lithofacies 4 (F4): Parallel to Subparallel Laminae
Physical Description
Parallel to subparallel laminae, L4, are found in yellowish-tan, fine-grained,
well-sorted sandstone (Fig. 2.09 and 2.10). The deposit was not found in abundance
in the field. This facies is characterized by parallel to subparallel bedding planes, or
laminations. It occurs within many of the stratigraphically higher channel-fill
sandstone bodies, i.e., Channels 6 – 10.
Fig. 2.09: Planar laminae on outcrop exposure on Channel-fill Sandstone 6.
Fig. 2.10: Planar laminae located in Channel-fill Sandstone 1.
Hydrodynamic Interpretation
Planar bedding occurs in both the lower and upper flow regime. It exhibits
parallel bedding. For lower flow regime deposits, the flow velocity is very low. This
is a very simple deposit, exhibiting only planar bedding in plan view and horizontal
laminae in side view.
Planar bedding, deposited in upper flow regime conditions, exhibits current
lineations due to the high flow velocity. Current lineations form as concentrations of
heavy minerals align themselves in the direction of flow. In plan view, the current
lineations are visisble, but only the laminae can be seen from the side view.
Figure 2.10 exhibits Bouma division Tb-Tc, categorizing Tb within the lower
flow regime; all F4 deposits in the field are interpreted to be lower flow regime planar
bedding.
Lithofacies 5 (F5): Rippled or Climbing-Ripple Sandstone
Physical Description
Facies F5, exhibits ripples or climbing-ripples in a yellowish-tan sandstone.
This deposit is not abundant within the outcrop exposures, however, nearly all nine
channel-fill sandstone bodies contain this facies. Channel-fill Sandstone 6 contains a
2’2” thick set of climbing-ripples (Fig. 2.11). The climbing-rippled sandstone
includes those with lee slope deposition, as well as those with lee and stoss slope
deposition (Fig. 2.12).
Fig. 2.11: Climbing-Ripple Facies located in Channel-fill Sandstone 6.
Hydrodynamic Interpretation
Rippled sandstone and climbing-rippled sandstone are categorized in the
uppermost division of lower flow regime deposits. Standard ripples are formed by
particles as they move by traction along the seafloor. Slowly they stack upon one
another until the angle of repose is met (28º - 30º), and at this point the sedimentary
particle is transported along the face of the lee slope, where either it remains or
continues to move. The climbing-rippled sandstone has a sedimentary input that
exceeds its sedimentary output, particularly those with lee and stoss slope deposition.
These deposits are diagnostic of a sediment-choked system and are interpreted to
occur at either the inner channel-levee margin of the channel-fill environment or in
proximal levee environments (Browne and Slatt, 2002).
Fig. 2.12: Climbing-ripple facies description.
Lithofacies 6 (F6): Shale or Mudstone
Physical Description
The shale and/or mudstone located within the channel-fill sandstones tend to
exhibit erosive tops (Fig. 2.13). This facies is colored light to dark gray and is
composed of clay-sized particles. F6 is mostly absent from many of the channel-fill
sandstone bodies, but is quite abundant within Channel-fill Sandstone 1.
Fig. 2.13: Shale/mudstone facies bounded by structureless sandstone facies.
Hydrodynamic Interpretation
Facies F6, shale and/or mudstone, is interpreted to be deposited from either
the tail-end of a turbidity current flow or as pelagic rain. The major process by which
this facies is deposited in the channel-fill environment is interpreted to be the tail-end
of a turbidity current flow. Channel-fill lithologies are comprised mainly of
sandstone facies. Since very few F6 facies are exhibited in the field, it is interpreted
that any shale and/or mudstone located in the channel-fill environment must be
deposited as the tail-end of a turbidity current as opposed to pelagic rain (not
quiescent enough in this environment for this type of deposition to occur).
Lithofacies 7 (F7): Shale-Clast Conglomerates
Physical Description
The shale-clast conglomerates of the channel-fill sandstones in Spine 1, F7
(Fig. 2.14 and 2.15), are light to dark gray in color. The shale clasts are light gray
and the matrix is dark gray or yellowish-tan. The internal architecture exhibited
within the shale clasts themselves show a thinly laminated facies. Additionally, the
shale clasts exhibit imbrication within this faices. L7 is quite abundant and is located
in almost all of the channel-fill sandstones. F7 tends to occur mainly as small, thin
deposits (usually 2-4in thick).
Fig. 2.14: Stacked shale-clast conglomerates (A) interbedded with turbidites (B) on Channel-fill
Sandstone 1.
Fig. 2.15: Faint imbrication of shale clasts occur in Channel-fill Sandstone 1.
Hydrodynamic Interpretation
The shale-clast conglomerates are interpreted to have originated as debris flow
deposits. These flows contain a high matrix strength and therefore move in a plastic,
laminar, cohesive state (Weimer and Slatt, in press). As the debris flow is
transported, the flow region is delineated into two components, the Shear Flow
Region and the Plug Flow Region (Fig. 2.16). The Shear Flow Region, located at the
basal part of the flow, generates shear stresses that overcome the matrix shear within
the flow (Weimer and Slatt, in press). It is possible that shale clasts found in the
lower regions of debris flows (i.e., in the Shear Flow Region) could have been
imbricated by these shear stresses (Fig 2.15). The Plug Flow Region contains the
major bulk-volume of sediments in transport. It tends to remain in the same position
during its entire transit, except at the flow/seawater contact where the sediments may
exhibit a decrease in velocity due to frictional forces (Weimer and Slatt, in press). In
Spine 1 deposits, shale clast conglomerates are interpreted to comprise the failed,
slumped margins of levees.
Fig. 2.16: Debris Flow Rheology (from Weimer and Slatt, in press)
Lithofacies 8 (F8): Slump Beds
Physical Description
Slump beds (Fig. 2.17) are found only in a few of the channel-fill sandstones,
but are a very diagnostic feature, helping to orient the channel-fill sandstone into its
environment within the channel system. They tend to range in thickness from 2ft to
7ft. F8 exhibits many different characteristics within their deposits, including the
parallel interbedding of sandstone and siltstone and a lower sand/shale ratio than
other lithofacies. They range in color from yellowish-tan to light and dark grey.
Fig. 2.17: Slump beds bounded in yellow from Channel-fill Sandstone 1 “Prong.”
Hydrodynamic Interpretation
Slump beds are interpreted to have formed as a coherent unit of the failed
inner-channel margin wall within a leveed-channel system. They represent the initial
flow event of any sedimentary gravity flow and exhibit high matrix strength. Due to
their high sediment concentration they move in a plastic flow state (Weimer and Slatt,
in press). This facies is closely related to the hydrodynamic interpretation of F7, but
it differs from it mainly by the fact that the deposit exhibits a coherent unit of
different beds while F7 is one bed. The interpreted slump beds contain what was
once the channel margin, comprised largely of proximal-levee facies deposits. All of
this evidence points to slump beds having been formed on the steep side of the
channel margin, or the cutbank-equivalent side of a channel-fill system.
Chapter 3
ENVIRONMENT OF DEPOSITION AND FACIES RELATIONSHIPS
Introduction
The purpose of this chapter is to categorize the facies into their environment
of deposition within a leveed-channel system. Descriptions of lithologic stacking
patterns found to occur in the field will also be included.
There are five major environments of deposition related to the leveed-channel
system (Fig. 3.01): E1) non-sinuous leveed-channel system, E2) outer-side of sinuous
channel bend, E3) inner-side of sinuous channel bend, E4) proximal levee, and E5)
distal levee.
Fig. 3.01: Enviroments of Deposition (E) 1-5 contained within a leveed-channel system.
Interpretations
Associated with each environment of deposition is a particular lithologic
stacking pattern which is diagnostic in determining its associated environment within
the channel-fill system. Kneller’s 1995 (Fig 2.05 and 3.02) diagrams were used to
develop the guidelines in interpreting these environments. Figure 3.03 and 3.04 were
also drawn to help support and guide the interpretations.
Fig. 3.02: Situations leading to different flow behaviors (Modified from Kneller, 1995).
Kneller’s (1995) (Fig. 2.05) diagrams relate the deposited facies to Bouma
divisions Ta-Te. Although these are noted in the chapter, Bouma division Ta is
classified as a separate deposit. This interpretation rests primarily on the fact that
both Walker (Fig. 2.06; 1978) and Lowe (Fig. 2.07; 1982) recognize the presence of
water-escape structures within their normally-graded to massive deposits (other than
the water-escape structures, most sandstones in F1 are structureless).
Witton (2000) interpreted the outer-side of a channel margin (E2) to contain
numerous debris flow deposits (F7). This concept was also very instrumental in
helping to guide the interpretations introduced in this chapter.
Fig. 3.03: Planform view of flow movement within a leveed-channel system.
Fig. 3.04: Flow movement within a sinuous channel-bend.
The following text in this chapter hypothesizes on the expected facies to be
found at these five environments of deposition (E1 – E5).
E1: Non-sinuous (Straight) leveed-channel environment
Interpretation:
E1 is interpreted as the straight, U-shaped portion of a sinuous channel
system. Figures 3.03 and 3.04 show that the flow out of a channel-bend, into the
straight portions of the system is interpreted to be spatially depletive (downcurrent
decrease in velocity; Fig. 3.02). Figure 2.05 shows there are three temporal
considerations to factor in with the spatial descriptions of the flows, they are: waxing
(increasing in velocity over time), waning (decreasing in velocity over time), and
steady (uniform velocity over time) (Kneller, 1995). Since the flow can do any three
of these when exiting the channel-bend, all deposits related to these three spatial-
temporal flows could be expected to be found in this non-sinuous environment.
Facies Relationship:
If the flow was to increase in velocity while exiting the channel-bend, the
expected spatial-temporal relation would be “waxing depletive.” A waxing depletive
deposit yields an inverted classic Bouma Sequence (Kneller, 1995). The expected
deposit contains Bouma divisions Te/Td, which underlie Tc, Tb, and Ta, respectively.
Relating these Bouma divisions to aforementioned facies would yield the expected
lithologic stacking pattern of (base to top): F6, F5, and F4. If there is a range in grain
size, this stacking pattern will exhibit reverse grading.
If the flow out of the channel-bend was to remain steady, the expected
lithologic stacking pattern would yield a continuous deposit of Bouma division Ta or
Tb (F4), and further downstream, Tc (F5). The last scenario is the least diagnostic of
all, waning depletive. In fact, all “waning” flows show more or less the same deposit:
a classic, normally graded Bouma Sequence (top to bottom): Ta, Tb (F4), Tc (F5),
Td, and Te (F6).
E2: Outer-side of sinuous channel bend
Interpretation:
E2 is the outer-side of a sinuous bend in a channel-fill system. Figures 3.03
and 3.04 show that the expected spatial flow in this environment is accumulative
(downcurrent increase in flow velocity), because the movement of the flow is similar
to that of water traveling down a waterslide. Since “waxing-accumulative” and
“steady-accumulative” both yield erosion within the system, the only setting that
deposition can occur is “waning-accumulative.”
Facies Relationship:
In a “waning accumulative” flow, the classic Bouma Sequence is expected to
be deoposited. Thus the lithologic stacking pattern to be recognized in the field
contains the facies (from base to top): F4, F5, and F6. Ideally, this deposit would also
be normally graded, helping to define the boundary between flow events.
Frequently bounding the facies in the lithologic stacking pattern of E2, are
shale-clast conglomerates, or F7. The process by which this facies is deposited is the
slumping of adjacent levee walls into the channel-fill axis (Fig. 3.05 and 3.06). This
is the most diagnostic facies in the set.
Fig. 3.05: 3D seismic horizon slice (photo courtesy of H. Posamentier).
Fig. 3.06: Sinuous submarine channel-fill deposit localities (modified from Peakall et al., 2000).
E3: Inner-side of sinuous channel-bend
Interpretation:
This interpretation is based mainly on field observations and personal
communication with Slatt (2003). Witton (2000) initially interpreted the outer-side of
a sinuous channel-bend to contain debris-flow deposits (shale-clast conglomerates)
concentrated at one end (Fig. 2.14 and 2.15). Field observations show that directly
opposite these deposits are large sandstones exhibiting cross-bedding features (Fig.
3.07). These large structures of low-angle, high-amplitude, cross-bedding (Fig. 2.08)
are interpreted to occur as in-channel bar or dune forms (Slatt, 2003).
Fig. 3.07: Oblique depositional strike view of Channel-fill Sandstone 1 (from Pyles and Slatt,
2002).
Additionally, Abreau et al (2002) noted that these features dominate the fill of
many submarine channels and exhibit themselves as shingled seismic reflections that
dip toward the channel axis. These features are interpreted to form as a result of the
lateral and downdip migration of the channel, with deposition of lateral accretion
beds in the inner side of the channel and erosion at the outer side of the channel
(Abreau et al, 2002; Beaubouef, 2002).
Facies Relationship:
The expected lithologic stacking pattern for E3 is simply a continuous deposit
of lateral accretion surfaces with contained cross-bedded sandstone (F3).
E4: Proximal levee
Interpretation:
E4, interpreted as the proximal levee region within the leveed-channel system,
is based on two extensive detailed measured sections taken on Channel-fill Sandstone
4 and 8 (Figs. 3. 08 - 3.10). Proximal levees are known to contain silt to very fine
grained sand because the sediments deposited in this environment originate from
overflows from the channel. These overflows tend to be finer grained than the rest of
the flow confined within the channel because larger grains are located near the base
of these flows. Significantly, dip magnitudes and orientations also vary because the
flows trend in different directions as they flow over the levee margin (Browne and
Slatt, 2002). Other facies exhibited in E4 are parallel/subparallel (F4) to
contorted/convoluted bedding planes, climbing ripples (F5, due to high sediment
input), reverse grading within associated splay deposits, and generally a higher
sand/shale ratio than distal levee facies.
Fig. 3.08: Environments of deposition of Channel-fill Sandstone 4 (from Slatt, 2003).
Fig. 3.09: Proximal levee with convoluted bedding and climbing ripples associated with Channel-
fill Sandstone 4
Fig. 3.10: Proximal levee with 2-inch set of climbing ripples associated with Channel-fill
Sandstone 4
Facies Relationship:
All of the facies described above (convoluted bedding, climbing ripples, etc.)
are contained within the two detailed measured sections recorded. Along with
matching these facies, inversely-graded deposits also occur in the measured sections.
Another match is the sand/shale ratio, which is much higher here than in the
interpreted distal levee region.
E5: Distal levee
Interpretation:
Distal levee deposits contain a lower sand/shale ratio than proximal levee
deposits (Brown and Slatt, 2002). This is expected as the overbank flows typically
are depleted of energy as they reach the distal, lower gradient portions of the levee
region, depositing the finest material in the flow. The dominant facies within E5 is
continuous parallel bedding, making them more laterally extensive than the proximal
levee facies (Fig 3.11).
Fig. 3.11: Distal levee deposits from Channel-fill Sandstone 4.
Facies Relationship:
E5 contains these two diagnostic facies, where they appear on a detailed
measured section of distal-levee deposits belonging to Channel-fill Sandstone 4
(Appendix A). Comparison of the above interpretation with this measured section
shows that the grain-size of the deposits are silt and clay sized particles, typically
interbedded. Immediately apparent is the low sand/shale ratio. Parallel bedding is
the dominant facies exhibited on the measured section (Appendix A).
Chapter 4
3D MODEL DESCRIPTION AND INTERPRETATION
Introduction
The 3D model that all outcrop measurements were based upon was built in
GOCAD™ v.2.0.6 (4th
Quarter, 2002). This is a robust package of software that
allowed the raw data collected from the Trimble™ GPS units to be viewed and
manipulated in 3D space. The software was instrumental in developing the resultant
3D model (see CD) and helped guide many new interpretations of the channel-fill
sandstone boundaries.
Data was first recorded in the field with Trimble™ GPS units which recorded
the position of the interpreter as he walked actual outcrop boundaries. These data
were then transferred to a PC-based laptop with Trimble™ Pathfinder GPS Software.
This software stored the data as *.ssf files which were then exported as *.dbf files
into Microsoft™ Excel. After the X,Y,Z points were isolated into their separate
columns, an appropriately designed header format was input so the file could be
recognized in GOCAD™ v.2.0.6. At this point, the files were viewed in 3D space
and appropriate lines that represented channel boundaries (Fig. 1.11) and detailed
measured section localities could be drawn.
After all channel-fill sandstone boundaries and detailed measured section
localities were drawn, facies boundaries were delineated from the measured sections
and emplaced on the measured section lines within GOCAD™. After this task had
been carried out for all nine channel-fill sandstone bodies, correlations then
commenced along the Outcrop Face (Fig. 1.11) of each. The resultant correlations
resemble fence diagrams that float in 3D space relative to one another. Another
benefit of GOCAD™ is the ability to measure the distance between two points and
also to find the precise X,Y,Z locality of any point, whether it be a channel boundary,
facies boundary, or any other point of interest. Additionally, the data may be rotated,
tilted, slid, or zoomed-in and out.
After the model was completed, the locations of particular lithologic stacking
patterns were recognized while examining the model. Some of these stacking
patterns are diagnostic in interpreting the environment within a leveed-channel
system as stated in Chapter 3. When these stacking patterns were recognized in the
model, the related environment (E1 – E5) was assigned to that locality of the
Channel-Fill Sandstone. These observations have led to a general interpretation of
each Channel-Fill Sandstone body and its classification within the environments of
deposition of a leveed-channel system. The above-ground vertical and lateral
geometry of each Channel-Fill Sandstone was also recorded.
Each facies within the model was represented by a unique color. The
classification is as follows: (F1) Sandstone with water-escape structures: blue, (F2)
Structureless sandstone: yellow, (F3) Cross-bedded sandstone: magenta, (F4) Parallel
to sub-parallel laminated sandstone: dark-gray, (F5) Rippled or climbing-rippled
sandstone: dark-green, (F6) Shale: blue-violet, (F7) Shale-clast conglomerate: red,
and (F8) Slumped bed: white.
Fig. 4.01: 3D GOCAD™ model of Dad Sandstone Member, Lewis Shale; “Prong” region of
Channel-fill Sandstone 1 circled in red; brown represents “Outcrop Plane,” while other colors
represent “Outcrop Face” of the nine channel-fill sandstones.
Viewing the Data
Representing 3D images in 2D space has proven to be a difficult task. The
following guidelines are recommended to the reader to help view the pictures offered
in this chapter.
Each picture has a figure in the lower left corner (Fig. 4.01) denoting three
axes: X (east), Y (north), and Z (altitude). Each axis has both magnitude and
direction, i.e. it not only points in these designated directions, but the inverse of the
length of the arrow also represents the amount of tilt in that direction. This figure is
essential to orient oneself in the 3D space, as viewed in the GOCAD™ model.
Referring back to Figure 1.11, two planes are defined here: 1) the Outcrop
Face and 2) the Outcrop Plane. The “Outcrop Plane” is colored brown in all figures
(Fig. 4.01). The “Outcrop Plane” does not designate any facies described, it is simply
the top plane of each individual channel-fill sandstone.
It is handy to keep a list of the color designations for the facies, as they appear
in every figure and are denoted by their classification (F1 – F8) and are seldom re-
described. Topographic contour intervals are also labeled on every figure where they
appear; these also help to orient the reader.
In some of the figures (Fig. 4.16 and 4.17) there is a black region seen; this
region is simply the extent of the Digital Elevation Map (DEM) where there is no
elevation data; i.e. a no-data zone.
Many of the figures are encapsulated within others to help orient the reader
when viewing certain pictures. Most pictures can be related back to the planview
basemap, pointing north, which contains all nine channel-fill sandstones (Fig. 4.02).
Note that the arrow is oriented differently in different figures due to the 3 dimensional
character of the outcrop faces.
Fig. 4.02: Planview basemap of nine stacked channel-fill sandstones. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2
(yellow): structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark
gray): parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7:
(red) shale clast conglomerates, and F8: slumped beds.
Channel-Fill Sandstone 1
Fig. 4.03: Channel-fill Sandstone 1 location in Field Area. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):
structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark gray):
parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red) shale
clast conglomerates, and F8: slumped beds.
Fig. 4.04: Locations of detailed measured sections on Channel-fill Sandstone 1 (1.01 – 1.22).
F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow): structureless sandstone (without water-escape structures), F3
(magenta): cross-bedded sandstones (without water-escape structures), F4 (dark gray): parallel to subparallel laminated sandstone, F5 (dark green):
rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red) shale clast conglomerates, and F8: slumped beds.
Vertical and Lateral Geometry:
The detailed measured sections of Channel-fill Sandstone 1 can be located on
Figure 4.03 and 4.04. The lateral geometry of Channel-fill Sandstone 1 can be
characterized by measuring the distance along the Outcrop Face in its two major
trends: N-S and E-W. All detailed measured sections located on Channel-fill
Sandstone 1 are located on Figure 4.03. A N-S trending face outcrops along the
narrow side of Spine 1, on its eastern side. This measurement is 62ft (Fig. 4.05).
Any E-W trending face outcrops along the wider edge of the spine in its northern
region. This associated measurement for Channel-fill Sandstone 1 is over 600ft. (Fig
4.05) for this trend. The thickness of this channel-fill ranges from 8ft to 34ft.
Fig. 4.05: Plan view map of surface outcrop dimensions of Channel-fill Sandstone 1. F1 (blue):
sandstone with water-escape structures (some cross-bedded), F2 (yellow): structureless
sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without
water-escape structures), F4 (dark gray): parallel to subparallel laminated sandstone, F5 (dark
green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red)
shale clast conglomerates, and F8: slumped beds.
Lithologic Stacking Patterns and Locations:
In the northern region of Channel-fill Sandstone 1 are numerous shale-clast
conglomerates dipping southward (Fig. 4.06 and 4.07). Also located in the northern
region, contained within the “prong” area is a large slumped bed (Fig. 4.06).
Channel-fill Sandstone 1 is capped primarily by F1 sandstone with water-escape
structures. The crossbedded sandstone facies (F3; magenta) is shown to occur in the
southern portions of the channel-fill region. Volumetrically, in most portions of the
channel, structureless sandstone (F2) dominates the channel-fill.
In the westernmost flank of the channel-fill, sandstones show tapering out to
the last measured section, 1.0.1 (Fig. 4.08). At this location, stacking patterns involve
significant amounts of shale and/or mudstone (F6).
Fig. 4.06: “Prong;” located in the eastern region of Channel-fill Sandstone 1. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2
(yellow): structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark
gray): parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7:
(red) shale clast conglomerates, and F8: slumped beds.
Fig. 4.07: Shale-clast conglomerate facies found in northern-most portions of Channel-fill Sandstone 1 model. F1 (blue): sandstone with water-escape
structures (some cross-bedded), F2 (yellow): structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without
water-escape structures), F4 (dark gray): parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-
violet): shale or mudstone, F7: (red) shale clast conglomerates, and F8: slumped beds
Fig. 4.08: Western-most flank of Channel-fill Sandstone 1 ends at MS# 1.0.1. F1 (blue): sandstone with water-escape structures (some cross-bedded),
F2 (yellow): structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4
(dark gray): parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone,
F7: (red) shale clast conglomerates, and F8: slumped beds
Interpretation:
The large number of F7 (shale-clast conglomerate) beds in the northern region
of the channel-fill interbedded with slumped beds (F8) indicate deposition on the
outer side of a sinuous channel bend (E2; Fig. 3.06). The beds have slumped from
the channel margin/levee walls into the channel.
F3, lateral accretion surfaces (crossbedded sandstone), are located on the
southern portion of the channel-fill environment. This facies is once again very
diagnostic of its environment of deposition, in this case, it is interpreted to be located
on the inner-side of a sinuous channel bend, E3 (Fig. 3.08).
Coupled together, these two interpretations suggest the northern portion was
the steeper, cut-bank equivalent side to the channel-fill, while the southern portion
represented the tapering, feathered edge of the point-bar equivalent side of the
channel-fill.
Subsurface:
Channel-Fill Sandstone 1 was uniquely separated from the other eight
channel-fill sandstone bodies because it was the only one to include the drilling and
gamma-logging of eight shallow boreholes. The boreholes were drilled along the
eastern flank of the channel-fill sandstone (Figs. 4.09 – 4.12), Electro-magnetic
induction (EMI; Fig. 4.13) and ground-penetrating radar (GPR; Fig. 4.14) images of
the area are also shown.
The first major process carried out was the drilling of the eight shallow
boreholes (Borehole 1 – Borehole 8). While these shallow boreholes were being
drilled, the lithologic cuttings expelled from the borehole were recorded, measured,
and bagged for later analysis. After each borehole was drilled, a gamma-ray sonde
was lowered into the borehole and retrieved at a steady rate, recording the natural
gamma-radiation emitting from the lithologies in the subsurface. These
measurements were stored onto a PC-based field laptop computer. The data was then
manipulated in Microsoft™ Excel in order to create gamma-ray (cps) vs. depth (ft)
plots (Fig. 4.10).
.
Fig 4.09: Boreholes (1-8) with locations of dip (green; 5-3-6) and strike (white; 1-2-3-4) cross-
sections, located on eastern flank of Channel-Fill Sandstone 1.
Fig. 4.10: Example of gamma-ray log from Borehole 1
These plots were then positioned accordingly to their proper X, Y, Z location
and cross sections were drawn in both the dip (Fig 4.11) and strike (Fig. 4.12)
sections of the channel-fill sandstone body. Three main facies were recognized in the
subsurface, they are: 1) sandstone (interpreted as channel-fill sandstone), 2) shale-
clast conglomerates (debris-flow deposits), and 3) shale (interpreted to be deposited
outside of the channel-fill environment). The cross section interpretations were
guided by field notes and cutting samples from each borehole. The field notes were
instrumental in the interpretations because depth regions were recorded as “well” to
“poorly lithified.” These descriptions helped to guide the interpretation because the
sandstone in the subsurface showed it to be “poorly lithified,” while the shale was
found to be “well lithified” (shale-clast conglomerates fall between these two since
they comprise both lithologies).
Fig. 4.11: Dip cross-section of Boreholes 5-3-6 of Channel-Fill Sandstone 1.
Fig. 4.12: Strike cross-section of Boreholes 1-2-3-4 of Channel-Fill Sandstone 1.
Electro-Magnetic Induction techniques were carried out by Ryan Stepler and
Dr. Alan Witten (2003; Fig. 4.13). It involved a twenty-frequency (1 kHz to 20 kHz)
EMI dataset collected over a 54m by 70 m area grid and inverted for resistivity and
depth. Through Stepler’s geophysical work, EMI data correlates nicely with the
cross-section interpretations from the eight shallow boreholes (Fig 4.11 and Fig.
4.12).
Fig. 4.13: Electro-Magnetic Induction and GPR (3-B to 3-B’) carried out on eastern flank of
Channel-Fill Sandstone 1 (Blue arrow represents interpreted base of Channel-fill Sandstone
1;Stepler, 2003).
Ground-Penetrating Radar techniques were carried out by Dr. Roger Young
and Julie Staggs (2003). GPR involves high frequency radar waves penetrating the
subsurface. At bed boundaries these waves are reflected back upward where they are
recorded at a receiver on the surface. Their work identified different radar facies,
each denoting a portion of a radar profile characterizing a particular stratigraphic
facies and associated depositional features (Fig. 4.14; Young et al., 2003).
Fig 4.14: Ground-Penetrating Radar facies located in the subsurface of Channel-Fill Sandstone 1
(Young et al., in press).
Channel-Fill Sandstone 2
Fig. 4.15: Location and number of detailed measured sections (black) with outcrop dimensions
(red) on Channel-fill Sandstone 2.
Vertical and Lateral Geometry:
There are two major trends to the Outcrop Face of Channel-fill Sandstone 2,
N-S and E-W (Fig. 4.15). The N-S trend is recorded as 415ft. in length, while the E-
W trend is recorded as 360ft. in length. The detailed measured sections on Channel-
fill Sandstone 2 are found in Figure 4.15. The thickness of this channel-fill varies
from 2ft. to 10ft.
Lithologic Stacking Patterns and Locations:
In the northern regions of the interpreted channel-fill environment are
numerous shale-clast conglomerates (F7; Fig. 4.16). To the base of these deposits lies
a shale/mudstone facies (F6). Capping these two units in the northern region and
continuing south to the crossbedded facies, F3, is F2, structureless sandstone. The
southern region is dominated by lateral accretion surfaces represented by low-angle
crossbeds (Fig. 4.16).
Fig. 4.16: F7, shale-clast conglomerates and F3, crossbedded sandstone, located on Channel-fill Sandstone 2. F1 (blue): sandstone with water-escape
structures (some cross-bedded), F2 (yellow): structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without
water-escape structures), F4 (dark gray): parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-
violet): shale or mudstone, F7: (red) shale clast conglomerates, and F8: slumped beds
Interpretation:
The northern region of the channel-fill environment is dominated by facies F7,
shale-clast conglomerates (Fig. 4.16). This is a diagnostic facies of the outer-side of a
sinuous channel bend.
The southernmost region within the model shows a laterally continuous
deposit of crossbedded sandstone. Once again, this is a diagnostic facies representing
the inner-side of a sinuous channel bend.
The two previous interpretations hold that the northern region of Channel-fill
Sandstone 2 is the cut-bank equivalent side of the channel-fill system, while the
southern region is interpreted as the point-bar equivalent side of the channel.
Channel-Fill Sandstone 3
Fig. 4.17: Location and number of detailed measured sections (black) with outcrop dimensions
(red) on Channel-fill Sandstone 3.
Vertical and Lateral Geometry:
Channel-fill Sandstone 3 shows similar N-S and E-W trends as the previous
channels. The detailed measured sections on Channel-fill Sandstone 3 can be found
on Figure 4.17. The E-W trend, usually the longer of the two, is only 80ft. The N-S
trend has a length of 335ft (Fig. 4.17). Thicknesses of this channel-fill range from
4ft. to 8ft.
Lithologic Stacking Patterns and Locations:
Within Channel-fill Sandstone 3, the following facies are present (Fig. 4.19):
F6 (shale/mudstone), F1 (sandstone with water-escape structures), F2 (structureless
sandstone), and F7 (shale clast conglomerate). F7 is located on the northeastern and
southeastern portions of the channel-fill. F6 (shale/mudstone) is located at the base of
the channel and is found in the northeastern region. The northern region of the
channel-fill environment is otherwise dominated by F2 (structureless sandstone
without water escape structures), while the medial and southern regions of the
channel are otherwise dominated by F1 (sandstone with water-escape structures).
Fig 4.18: Diagnostic facies of Channel-fill Sandstone 3. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):
structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark gray):
parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red) shale
clast conglomerates, and F8: slumped beds
Interpretation:
The presence of F7 in the northeastern and southeastern regions of the
channel-fill (Fig. 4.18) are interpreted to represent the outer-side of a sinuous channel
bend (E2), or the cut-bank equivalent side. Field observations and those made in
GOCAD™ lead to the additional interpretation that Channel-fill Sandstone 3 (CFS 3)
and the overlying channel-fill sandstone, CFS 4, are amalgamated.
Channel-Fill Sandstone 4
Fig. 4.19: Location of Channel-fill Sandstone 4 on Spine 1
Fig. 4.20: Location and number of detailed measured sections (white) with outcrop dimensions (red) on Channel-fill Sandstone 4.
Vertical and Lateral Geometry:
The detailed measured sections of Channel-fill Sandstone 4 can be found on
Figure 4.19 and 4.20. There are three major trends to the Outcrop Face of Channel-
fill Sandstone 4. This indicates that this channel-fill outcrop wraps around Spine 1
from its southern slope to its northern slope. The main trend, SE-NW is 430ft. in
length. The second main trend is located in a region known as the “Eagle’s Nest.”
This face is 88ft. in length and is located on the southern slope of Spine 1 (Fig. 4.20).
The northern-slope of Channel-fill Sandstone 4 is 70ft. in length. The thickness of
this channel-fill ranges from 4ft. to 16ft.
Lithologic Stacking Patterns and Locations:
Channel-fill Sandstone 4 shows many interesting lithologic patterns located in
its southern-most flank (Fig. 4.21). Some of the facies included are F1 (sandstone
with water-escape structures), F2 (structureless sandstone), F3 (crossbedded
sandstone), F7 (shale-clast conglomerates), and F8 (slumped beds). While F1 and F2
dominate the rest of the channel-fill, they are represented equally with all other facies
at this portion of the channel-fill environment. The northernmost flank and the
eastern region of the channel-fill environment is dominated by facies F1 and F2 with
a rogue F7 facies lying near the base of the channel in the northeastern-most region
(Fig. 4.21).
Fig. 4.21: Diagnostic facies located on Channel-fill Sandstone 4. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):
structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark gray):
parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red) shale
clast conglomerates, and F8: slumped beds
Interpretation:
The southernmost flank, in the stratigraphically lower portions, shows the
dominant facies to be crossbedded sandstone (F3) and in the northern portion of the
channel-fill there resides a lone F7 facies near the base of the deposits. This
stratigraphically lower region of the channel-fill environment is interpreted to have
been a separate channel-fill system within the entire Channel-fill 4 “Complex” (Fig.
4.22). The overlying facies F8 and F7 are interpreted to be amalgamated onto the
channel-fill system of the lower region.
This interpretation holds that the stratigraphically lowest portion of the
channel-fill sandstone, denoted by CFS4a is overlain by CFS4b (Fig. 4.22). CFS4a
shows that the southern portion of the channel-fill environment was dominated by the
diagnostic facies, F3, crossbedded sandstone. This facies is interpreted to represent
the locality within the inner-side of a sinuous channel bend. The northernmost
portion of CFS4a shows F7 to be the only diagnostic facies. This facies is interpreted
to be the cut-bank equivalent side of the channel. Once again, two diagnostic facies
were used in conjunction to interpret the environments represented by the channel-
fill.
Fig 4.22: Amalgamated channel-fills CFS 4a and CFS 4b, comprising Channel-fill Sandstone 4.
CFS4b is dominated by F8 and F7 facies in the southern region of the
channel-fill. This interpretation holds that the southern region is the cut-bank
equivalent side of the channel and it eroded into the underlying crossbedded
sandstone of CFS4a to create amalgamated channel-fill deposits.
Channel-Fill Sandstone 6
Fig. 4.23: Location and number of detailed measured sections (white) with outcrop dimensions
(red) on Channel-fill Sandstone 6.
Vertical and Lateral Geometry:
The detailed measured sections of Channel-fill Sandstone 6 can be located on
Figure 4.23. Channel-fill Sandstone 6 is another channel-fill body that extends across
both slopes of Spine 1 (Fig. 4.23). It also has three major trending faces (Fig. 4.23).
The major SE-NW trend is 355ft. The secondary southern-slope trend is 105ft. in
length, while the northern-slope trend is 95ft. in length. The thickness of this
channel-fill ranges from 2ft. to 8ft.
Lithologic Stacking Patterns and Locations:
The northwestern regions of the channel-fill environment are dominated by
basal F7 units capped by F3 facies (Fig. 4.24). The western part of the medial portion
of the channel, trending NW-SE, is dominated by facies F1 and F2 with a small
portion of F5 (climbing rippled sandstone) cropping out near the top of the channel-
fill. The eastern segment of the medial portion of the channel-fill is underlain by
facies F3 and is capped by facies F1. In the southeastern-most region of the channel-
fill, F5 (rippled or climbing-rippled sandstone) is encapsulated within F1 deposits,
capped by facies F3.
Interpretation:
Two diagnostic facies occur in this channel-fill, F3 (crossbedded sandstone)
and F7 (shale-clast conglomerate). Once again, two diagnostic facies of different
channel environments are located in the same geographical region. This channel-fill
system is thus interpreted to contain two amalgamated channel-fills. The lower
region of CFS6 is interpreted as CFS6a, the lower fill, and CFS6b, the upper fill (Fig.
4.25).
Fig. 4.24: Diagnostic facies of Channel-fill Sandstone 6. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):
structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark gray):
parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red) shale
clast conglomerates, and F8: slumped beds
Fig 4.25: Amalgamated channel-fills CFS 6a and CFS 6b, comprising Channel-fill Sandstone 6.
CFS6a is interpreted to have its steep side on the northwestern-most side of
the channel-fill system with a feathered, tapering edge on the southeast. CFS6b lacks
two diagnostic facies as CFS6a, but contain plentiful F3 deposits throughout the
entire stretch of its channel-fill. The resultant interpretation holds that CFS6b was
dominated in this region by the inner-side of a sinuous channel bend (E3).
Channel-Fill Sandstone 7
Fig. 4.26: Location and number of detailed measured sections (black) with outcrop dimensions
(red) on Channel-fill Sandstone 7.
Vertical and Lateral Geometry:
The detailed measured section of Channel-fill Sandstone 7 can be located on
Figure 4.26. Channel-fill Sandstone 7 is primarily found on the northern slope of
Spine 1 and thus has only two major trends, NE-SW and E-W (Fig. 4.26). The major
E-W trending face is 430ft. in length, while the minor NE-SW trend is only 105ft.
The thickness of this channel-fill ranges from 2ft. to 10ft.
Lithologic Stacking Patterns and Locations:
Dominated in the western portions of Channel-fill Sandstone 7 (CFS7) is
facies F2, structureless sandstone and F3, crossbedded sandstone (Fig. 4.27). In the
eastern region of CFS7 is facies F8, slumped beds (Fig. 4.27). Otherwise, CFS7 is
dominated by facies F2.
Interpretation:
Since the western portion of CFS7 includes the diagnostic facies F3, this
region of the channel-fill is interpreted to be the point-bar equivalent, inner-side of a
sinuous channel bend (E3). The eastern section of CFS7 shows a slight, but
prominent facies, F8. F8 is diagnostic of cut-bank equivalent, outer-side sinuous
channel bends, E2. This interpretation yields that the eastern portion of CFS7 is the
cut-bank equivalent side of the channel-fill, while the western portion is interpreted to
be the point-bar equivalent of the fill. Field observations and those made in
GOCAD™ lead to the additional interpretation that Channel-fill Sandstone 7 (CFS 7)
and the overlying channel-fill sandstone, CFS 8, are amalgamated (Fig. 4.01)..
Fig. 4.27: Diagnostic facies of Channel-fill Sandstone 7. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):
structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark gray):
parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red) shale
clast conglomerates, and F8: slumped beds.
Channel-Fill Sandstone 8
Fig. 4.28: Location and number of detailed measured sections (black) with outcrop dimensions
(red) on Channel-fill Sandstone 8.
Vertical and Lateral Geometry:
The detailed measured sections on Channel-fill Sandstone 8 can be found on
Figure 4.28. There are two major trends associated with the Outcrop Face of
Channel-fill Sandstone 8, they are N-S and E-W trends (Fig. 4.28). The major E-W
trend is 475ft. in length, while the N-S trend is 180ft. in length. The thickness of this
channel-fill ranges from 4ft. to 12ft.
Lithologic Stacking Patterns and Locations:
Channel 8 shows some unique lithologic patterns. In the western portion of
the channel-fill system, the basal portion is dominated by facies F7, shale clast
conglomerates (Fig. 4.29). Capping these units and laterally extending to the east and
stratigraphically downward to the same plane as the F7 deposits are facies F3,
crossbedded sandstone.
In the eastern regions of the channel-fill this same type (mirror-image) of
lithologic stacking pattern exists, i.e., the shale-clast conglomerate (F7) facies resides
on the east and facies F3, crossbedded sandstone, resides on the west (Fig. 4.29).
Fig. 4.29: Diagnostic facies of Channel-fill Sandstone 8. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):
structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark gray):
parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red) shale
clast conglomerates, and F8: slumped beds
Interpretation:
These unique stacking patterns reveal an interesting interpretation. The
eastern side of CFS8 is interpreted to have a steep, cut-bank side (E2) on its eastern
flank by the diagnostic F7 facies and a shallower, point-bar side (E3) on its western
flank by the diagnostic F3 facies.
The western side of CFS8 is interpreted as the mirror image of the above
interpretation. The western flank of the western portion of CFS8 is interpreted to be
the steep, cut-bank side (E2) of the channel-fill, while the eastern flank of the western
portion is interpreted to be the shallower, point-bar (E3) side of the channel-fill.
Channel-Fill Sandstone 9
Fig. 4.30: Location and number of detailed measured sections (white) with outcrop dimensions (red) on Channel-fill Sandstone 9.
Vertical and Lateral Geometry:
The detailed measured sections of Channel-fill Sandstone 9 are found on
Figure 4.30. This is the smallest channel-fill sandstone located on Spine 1 (Fig.
4.30). Although thicknesses range from 4ft. to 8ft., the surficial lateral extent is
simply not typical for channel-fills located in this area. The two trends, NE-SW and
NW-SE, are 50ft. and 25ft., respectively.
Lithologic Stacking Patterns and Locations:
Channel-fill Sandstone 9 (CFS9) is dominated primarily by facies F2,
structureless sandstone (Fig. 4.31). In the northern region, there is a small cap of
facies F1, sandstone with water-escape structures, but there is a larger, more laterally
continuous deposit of F3, crossbedded sandstone, trending southward.
Interpretation:
The northern region of CFS9 contains the diagnostic facies, F3. Due to this
crossbedding, the northern region is interpreted to be the straight portion of the
channel (E1).
Fig. 4.31: Diagnostic facies of Channel-fill Sandstone 9. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):
structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark gray):
parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red) shale
clast conglomerates, and F8: slumped beds
Channel-Fill Sandstone 10
Fig. 4.32: Location and number of detailed measured sections (white) with outcrop dimensions
(red) on Channel-fill Sandstone 10.
Vertical and Lateral Geometry:
The detailed measured sections of Channel-fill Sandstone 10 can be found on
Figure 4.32. This is the stratigraphically highest channel-fill sandstone body. It
contains two major trends (Fig. 4.32). The first, NW-SE is 100ft. in length. The
second trend, NE-SW is 50ft. in length. The thickness of this channel-fill ranges
from 3ft. to 7.5ft.
Lithologic Stacking Patterns and Locations:
This entire channel-fill sandstone body is dominated by facies F2,
structureless sandstone. In the northwestern-most region of the channel-fill is a
prominent, 50 ft. laterally continuous deposit of facies F3, crossbedded sandstone
(Fig. 4.33).
Interpretation:
The only diagnostic facies in the channel-fill is facies F3, located in its
northern flank. This northern flank was thus interpreted to be the inner-side, point-
bar equivalent side (E3) of the channel-fill system, while the southern flank is
interpreted as the straight portion of a channel-fill (E1).
Fig. 4.33: Diagnostic facies Channel-fill Sandstone 10. F1 (blue): sandstone with water-escape structures
(some cross-bedded), F2 (yellow): structureless sandstone (without water-escape structures), F3 (magenta):
cross-bedded sandstones (without water-escape structures), F4 (dark gray): parallel to subparallel laminated
sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7:
(red) shale clast conglomerates, and F8: slumped beds.
Chapter 5
CONCLUSIONS
This research has yielded many new insights into the depositional facies and patterns of
the Dad Sandstone Member of the Lewis Shale. Although Channel-fill Sandstone 1, the
lowermost channel-fill in the complex, has been and continues to be extensively studied, the
other eight channel-fill sandstones have now been classified into their interpreted environments
of deposition as classified in this thesis: E1) non-sinuous portion of a leveed-channel system, E2)
outer-side of sinuous channel bend, E3) inner-side of sinuous channel bend, E4) proximal levee,
and E5) distal levee. The 3D GOCAD™ model and its subsequent interpretations for the
environments of deposition within each channel-fill sandstone on Spine 1 help support the
interpretation that these outcrops belong to a leveed-channel complex. Witton (2000) created a
first-generation diagram showing the channel-fill sandstones in 3D space, but this diagram lacks
channel orientation for sinuosity (Fig. 5.01)
Eight separate diagnostic facies were recognized to be contained within the nine separate
channel-fill sandstones. They are: F1) sandstone with water-escape structures (some cross-
bedded), F2) structureless sandstone (without water-escape structures), F3) cross-bedded
sandstones (without water-escape structures), F4) parallel to subparallel laminated sandstone, F5)
rippled or climbing-rippled sandstone, F6) shale or mudstone, F7) shale clast conglomerates, and
F8) slumped beds. When asymmetry of these facies was exhibited in the model, the following
interpretation of the environment led to a sinuous leveed-channel interpretation with a steep “cut
bank” side and shallower “ point bar” side.. This asymmetry of facies was not encountered in all
nine channel-fill sandstones; some lacked the diagnostic facies required to make this
interpretation, such as Channel-fill Sandstone 10, which had only structureless sandstone without
water escape structures (F2) on one side of the channel-fill system (interpreted as E1: straight
portion of a leveed-channel environment).
Fig. 5.01: First generation conceptual model representing channel-fill sandstones in 3D space (no channel
sinuosity recorded; (Modified from Witton, 2000).
Precise GPS measurements of channel-fill sandstone boundaries and the 121detailed
measured sections located throughout the study area provided the basis for the architectural
facies model in true, 3D space. The facies recorded on these measured sections were observed in
the model and recorded to their geographical location and stratigraphic position within the
channel-fill sandstone body. Certain facies were then interpreted to diagnose a particular
environment (E1 – E5) located within a channel-fill system.
Fig. 5.02: Second-generation diagram representing channel-fill sandstone sinuosity.
Based on previous interpretations by Witton (2000) and Slatt et al. (2000, 2001, and
2002), two major facies were utilized to help guide interpretations of the environments of
deposition within each channel-fill sandstone body. These two facies are: 1) debris flow deposits
(F7, shale-clast conglomerate), and 2) lateral accretion deposits (F3, crossbedded sandstone).
Debris flow deposits are interpreted to form on the outer-side of a sinuous channel bend as
internal channel margin slumps, while the crossbedded sandstone is interpreted to form on the
inner-side of a sinuous channel bend as lateral accretion bar deposits.
The 3D GOCAD™ model was instrumental in modeling the lateral distribution of facies
for recording their geographical and stratigraphic position in 3D space. After these two positions
were delineated, the appropriate environment of depositon (E1 – E5) was then categorized to its
location (Fig. 5.02). This was carried out on all nine channel-fill sandstone bodies located on
Spine 1. After this was accomplished, a clear interpretation of the stacked channel-fill sandstone
bodies and their associated environments of deposition was recognized.
The first generation model, developed by Witton (2000; Fig. 5.01) only shows the
channel-fill sandstones relative to one another and the underlying sheet sandstones. There is no
indication of sinuosity in this diagram because it is conceptual. The second generation model,
developed in this thesis research (Fig. 5.02) not only shows the channel-fill sandstones relative to
one another and the underlying sheet sandstones, but also shows the interpreted orientation of
sinuosity within each channel-fill.
This diagram (Fig. 5.02) was based on observations seen in GOCAD™ v.2.0.6. The 3D
GOCAD™ model was a success because it clearly represents each channel-fill sandstone body
relative to one another (as seen in the field), as well as including the fine-scale, architectural
nature of each. The 3D model also allows for visual manipulation in a variety of ways (rotating,
tilting, zooming-in and out, and sliding). These features allowed for better interpretations of
actual channel-fill sandstone boundaries, e.g., leading to the reinterpretation and removal of
Channel-fill Sandstone 5. It should be noted that presenting 3D material in 2D space is a
challenging task and has led to some clever tricks to help view the data.
All facies correlations and interpretations are geologically sound. They match well with
many of the interpretations introduced by Witton (2000) and Slatt et al. (2000, 2001, and 2002).
While overall the project can be considered a success, more work must still be completed
in order to better define the depositional processes related to the deposits located in the channel-
fill sandstones of Spine 1. It is anticipated that the GPR (Ground Penetrating Radar) research by
J. Staggs will confirm the sinuosity interpreted in this thesis. Other work, including the
comparison of the model to seismic data sets, is currently being carried out by Dr. Roger Slatt
and his students. Building a 3D architectural facies model of the Lewis Shale submarine slope
channel complex not only helps to better understand Lewis Shale exploration, but will also help
shed light on other deepwater channel complexes located throughout the world.
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