Stratigraphic Architecture and Avulsion Deposits of a Low Net- Sand Content Fluvial Succession: Lower Wasatch Formation, Uinta Basin

Home , Crevasse splay, Sedimentary structures

STRATIGRAPHIC ARCHITECTURE AND AVULSION DEPOSITS OF A LOW NET- SAND CONTENT FLUVIAL SUCCESSION: LOWER WASATCH FORMATION, UINTA BASIN

by Kassandra L. Sendziak

A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of

Mines in partial fulfillment of the requirements for the degree of Master of Science (Geology).

Golden, Colorado

Date ______

Signed: ______Kassandra L. Sendziak

Signed: ______Dr. David R. Pyles Thesis Advisor Golden, Colorado

Date ______

Signed: ______Dr. John D. Humphrey Professor and Head Department of Geology and Geological Engineering

ABSTRACT

This study documents the stratigraphic architecture of channel and floodplain strata of low net-sand content fluvial deposits in outcrops of the lower Wasatch Formation, Desolation

Canyon, Uinta Basin, Utah. The lower Wasatch Formation has a net sand-content of 0.27 and contains predominantly floodplain strata (79% in the field area). Three types of crevasse splays are recognized in this field area based on their physical relationship to adjacent channel-belt strata. Associated coeval splays are laterally adjacent and are physically connected to a channel-belt element, indicating that the crevasse splay was deposited coeval with the channel fill. Unassociated splays are spatially isolated from channel-belt elements and are interpreted to represent a failed avulsion. Associated non-coeval splays underlie the channel-belt element and are interpreted to be genetically related to the overlying channel-belt element, and therefore are a record of a successful avulsion.

Three distinct types of associated non-coeval splays are identified in this study area based on physical, observable characteristics: type I, type II, and type III. A conceptual model is proposed that describes longitudinal changes in associated non-coeval splay deposits where type I, type II, and type III splay units represent proximal, medial, and distal positions in splay deposits relative to the source channel, respectively. Decreases in the following characteristics of splays occur with increased distance from the source channel: (1) thickness of splay unit, (2) thickness and abundance of splay beds, (3) net-sand content, (4) grain size, and (5) erosion.

The occurrence of floodplain and channel-belt strata in a vertical transect through the outcrop are evaluated to: (1) determine whether the dominant avulsion style is aggradational or incisional, and (2) relate channel story type (i.e. downstream versus lateral accreting) to avulsion style. The correlation between the abundance of splay beds and the abundance of overlying channel-belt elements is interpreted to indicate that the succession resulted from predominantly aggradational avulsion processes. The occurrence of splay beds below channel-

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belts containing predominantly downstream-accreting stories is interpreted to indicate that these channels resulted from predominantly aggradational avulsion processes. The lack of splay

beds below channel-belts containing predominantly lateral-accreting stories is interpreted to

indicate that these channels resulted from predominantly incisional avulsion processes.

TABLE OF CONTENTS

ABSTRACT ...... III

LIST OF FIGURES ...... VI

LIST OF TABLES ...... VII

ACKNOWLEDGEMENTS ...... VIII

CHAPTER 1 INTRODUCTION ...... 1

3.1 Lithofacies...... 9 3.2 Architectural and Hierarchical Fluvial Classification ...... 9

CHAPTER 4 ARCHITECTURE OF THE LOWER WASATCH FORMATION ...... 17

4.1 Channel-Belt Architecture ...... 17 4.1.1 Channel-Belt Elements ...... 17 4.1.2 Channel-Belt Stories ...... 18 4.2 Floodplain-Belt Architecture ...... 20 4.2.1 Floodplain-Belt Elements ...... 20 4.2.2 Floodplain-Belt Stories ...... 20

CHAPTER 5 CREVASSE SPLAY TYPES ...... 26

CHAPTER 6 DISCUSSION ...... 31

6.1 Spatially Varying Characteristics of Associated Non-Coeval Splays (i.e. Avulsion Complexes) ...... 31 6.2 Upward Trends: Relationship between Floodplain and Channel-Belt Elements 33

CHAPTER 7 APPLICATIONS ...... 40

CHAPTER 8 FUTURE WORK ...... 43

CHAPTER 9 CONCLUSIONS...... 44

REFERENCES CITED ...... 46

SUPPLEMENTAL FILES ...... 52

LIST OF FIGURES

Figure 2.1 Location map of the Uinta Basin and chronostratigraphic chart of basin fill ...... 6 Figure 2.2 Topographic map of the study area ...... 7 Figure 2.3 Photographs of the study area ...... 8 Figure 3.1 Quantitative data of the lower Wasatch Formation in the field area ...... 13 Figure 3.2 Lithofacies photographs ...... 14 Figure 3.3 Three-level hierarchical classification scheme ...... 15 Figure 4.1 Examples of downstream accreting channel-belt stories and elements ...... 22 Figure 4.2 Examples of laterally accreting channel-belt stories and elements ...... 23 Figure 4.3 Example of crevasse channel story ...... 24 Figure 4.4 Examples of crevasse-splays and floodplain-fine deposits ...... 25 Figure 5.1 Field example and schematic diagram of an associated coeval splay ...... 28 Figure 5.2 Field examples and schematic diagram of associated non-coeval splays...... 29 Figure 5.3 Field examples and schematic diagram of unassociated splays...... 30 Figure 6.1 Field example and schematic diagram of type I splays ...... 35 Figure 6.2 Field example and schematic diagram of type II splays...... 36 Figure 6.3 Field example and schematic diagram of type III splay s ...... 37 Figure 6.4 Schematic of spatially varying characteristics of associated non-coeval splays .38 Figure 6.5 Upward trends of the lower Wasatch Formation ...... 39 Figure 7.1 Gamma Ray signatures of associated non-coeval spaly types ...... 42

LIST OF TABLES

Table 3.1 Lithofacies descriptions ...... 14

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ACKNOWLEDGEMENTS

There are many people with whom this project would not have been possible. I am particularly grateful for the guidance of my advisor Dr. David Pyles. The knowledge and enthusiasm he shares for the scientific method have made me a better scientist, geologist, and critical thinker. I would also like to thank other members of my committee: Dr. Rick Sarg, committee-chair, for his support and guidance regarding coursework, research, and my future as a geologist; Dr. Bryan Bracken, for his time in and out of the field, mentoring, and support

throughout this project; and Dr. Matthew Pranter, for his guidance and encouragement.

I would like to express my greatest gratitude to Grace Ford. This project would not have

started nor been completed without her encouragement and extraordinary mentoring in and out

of the field. I wish to acknowledge Chelsea Philippe for her assistance in getting us safely down

the river and through many days in the field, I might not have survived without her. Additional

field assistance from Neil Sharp is also greatly appreciated. I would like to thank other

members of the CoRE team for their support throughout this project: Jane Stammer, Jeremiah

Moody; Greg Gordon; Charlie Rourke, Linda Martin, and Cathy Van Tassel. Finally, I would like

to thank my parents, Linda and Walter Sendziak, most of all. Without their support I would have

never made it through these countless years of school.

The majority of funding for this research was provided by the Chevron Center of

Research Excellence. Additional funding was provided by the Timothy & Barbara Bartshe

Fellowship, Robert L. Burch Fellowship, Devon Scholarship, and Colorado School of Mines

Department of Geology and Geologic Engineering.

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CHAPTER 1

INTRODUCTION

Fluvial deposits host significant amounts of hydrocarbons, but characterization of these reservoirs (i.e. sandstone geometry, distribution, and connectivity) is challenging (Leeder, 1978;

Allen, 1978; Bridge and Leeder, 1979; Mackey and Bridge, 1995; Heller and Paola, 1996,

Pranter and Sommer, 2011). Reservoir characterization is especially difficult in low net-sand

content fluvial successions where the discontinuity of the channel-belts results in internally

heterogeneous reservoirs (Pranter et al, 2009; Pranter and Sommer, 2011). Knowledge of the

distribution and dimensions of channel-belt strata is crucial to characterizing connectivity in low

net-sand content fluvial reservoirs (Pranter et al., 2009). The term ‘channel-belt’ is defined

herein as deposits associated with channel processes including channel bar and channel fill

deposits. Coarse-grained floodplain deposits, such as crevasse-splay deposits, also impact

connectivity of channel-belts (Pranter et al., in press). Despite the abundance of floodplain

strata in low net-sand content fluvial systems and the potential role that floodplain strata has in

sandstone-body connectivity, research has focused primarily on the architecture of channel-

belts, the exceptions are Bown and Kraus (1987), Kraus and Aslan (1993), Smith (1990, 1993),

and Willis and Behrensmeyer (1994). Even fewer studies describe the relationship between

floodplain strata and the associated channel-belt strata (e.g. Kraus and Gwinn, 1997; Kraus and

Wells, 1999; Mohrig et al., 2000; Jones and Hajek, 2007).

Avulsion processes influence the distribution of sediment on the floodplain and the

resulting floodplain deposits (Allen, 1965; Bridge and Leeder, 1979; Mackey and Bridge, 1995;

Miall, 1996). Avulsion processes also impact channel-belt stratigraphy on a larger scale,

particularly the stacking patterns and distribution of channel-belts (Smith et al., 1989; Mackey

and Bridge, 1995; Heller and Paola, 1996). Avulsion is the ‘process by which flow diverts out of

an established river channel into a new permanent course on the adjacent floodplain’

(Slingerland and Smith, 2004, p. 259). Studies of the modern Saskatchewan River by Smith et al. (1998) and Smith and Perez-Arlucea (1994) document that during avulsion, flow from the parent channel diverts to a laterally adjacent network of crevasse channels and splays. This avulsion complex receives water and sediment during all stages of flow (Smith et al., 1989). As avulsion progresses, flow within the avulsion complex becomes concentrated into a smaller number of channels, until a single channel is sustained, and the avulsion process is complete.

Relatively few studies describe ancient avulsion deposits (e.g. Kraus and Gwinn, 1997;

Kraus and Wells, 1999; Mohrig et al., 2000; Jones and Hajek, 2007). Kraus and Wells (1998) build upon the model of Smith et al. (1998) by documenting ancient avulsion deposits termed

‘heterolithic avulsion deposits’ that underlie paleochannels in the Willwood and Fort Union

Formations. Mohrig et al. (2000) document paleochannels in the Guadalope-Matarranya system in Spain and the Wasatch Formation in western Colorado that incise directly into the floodplain, and lack underlying heterolithic avulsion deposits. To address these contrasting stratigraphic expressions of avulsion, Mohrig et al. (2000) proposes two end-member styles of avulsion. The first is termed aggradational avulsion, in which a network of crevasse splays is developed in the adjacent floodplain that is subsequently followed by the new channel (i.e. fill

then cut), a model similar to that proposed by Smith et al. (1989). The second is termed

incisional avulsion, in which the channel cuts directly into the fine-grained strata in the floodplain

and is subsequently filled with channel-belt strata (i.e. cut-then-fill model). Jones and Hajeck

(2007) also document two end-members of avulsion stratigraphy based on their observations in

the Willwood and Ferris Formations in Wyoming. The first is termed stratigraphically

transitional, where crevasse splays and other non-overbank deposits (i.e. crevasse channel and

splay deposits) are overlain by paleochannels, these are similar to deposits that result from

aggradational avulsion (sensu Mohrig et al., 2000). The second is termed stratigraphically

abrupt, where the main paleochannel stratigraphically overlies fine-grained overbank-floodplain

deposits, these are similar to deposits that result from incisional avulsion (sensu Mohrig et al.,

2000). Although the various stratigraphic manifestations of avulsion styles have been

documented, no studies describe the spatial variability within these deposits.

This study uses exceptionally well-exposed outcrops of the low net-sand content (net- sand content of 0.27, floodplain-to-total of 0.79; calculated herein) fluvial strata of the lower

Wasatch Formation to document, for the first time, how stratigraphic architecture of crevasse-

splay deposits vary with increased distance from the source channel. Furthermore, this study

relates upward patterns in the floodplain to upward patterns in the channel-belt, documenting an

association between floodplain strata, channel-belt strata, and channel-belt style. Understanding

the evolution of a fluvial succession and the relationship between floodplain and channel-belt

strata within a fluvial succession has important implications for reservoir characterization.

CHAPTER 2

GEOLOGIC SETTING AND FIELD AREA

The Uinta Basin is a foreland basin located in northeastern Utah (Figure 2.1 A) that

encompasses a total area of ~2,000 km2 (Montgomery and Morgan, 1998). The basin is bounded to the north by the Uinta uplift, to the east by the Douglas Creek Arch, to the south by the San Rafael Swell, and to the west by the Sevier thrust belt (Figure 2.1 B). The basin developed in the Latest Cretaceous Period through the Early Oligocene Epoch (Fouch, 1975;

Fouch et al., 1994a) (Figure 2.1 C).

The Uinta Basin contains up to 5,000 m of siliciclastic and carbonate strata (Fouch et al.,

1994a). These strata are interpreted to have been deposited in a range of environments

including open lacustrine, marginal lacustrine, and fluvial (Fouch, 1975). These strata

unconformably overlie Campanian strata of the Mesaverde Group (Figure 2.1 C). Formations of

the Uinta Basin fill succession are the North Horn, Wasatch, and Green River Formations

(Figure 2.1 C). The Wasatch Formation unconformably overlies the Flagstaff Formation in most

areas (Figure 2.1 C). Where it does not, Fouch (1976) referred to it as the Colton Formation.

The Colton and Wasatch Formations are time-equivalent units and the spatial extent of the

underlying Flagstaff Formation is unknown. Therefore, the term Wasatch is used herein (Ford,

2012). The Green River Formation conformably overlies the Wasatch Formation (Fouch, 1976)

(Figure 2.1 C).

The Wasatch Formation is composed of variegated shale and sandstone interpreted to

have been deposited in a fluvial environment (Spieker, 1946). The Wasatch Formation is

informally divided in to the lower, middle, and upper members based on upward changes in

lithofacies, depositional style, and net-sand content (Ford, 2012). Each of these members are

separated by regionally extensive red, compound paleosols. This study focuses on the lower

member of the Wasatch Formation, which has a net-sand content of 0.27 (calculated herein) and contains single-story and multi-story channel-bar deposits, channel-fill deposits, crevasse- channel deposits, crevasse-splay deposits, floodplain-fine deposits, and paleosols. The lower

member is interpreted to have been deposited in a floodplain-dominated fluvial succession. The

middle Wasatch Formation has a net-sand content greater than 0.75 and contains amalgamated

multi-story channel-fill deposits, crevasse-splay deposits, and floodplain-fine deposits (Ford,

2012). The upper Wasatch Formation has a net-sand content of 0.5 and contains amalgamated

multi-story channel-fill deposits, crevasse-splay deposits, and floodplain-fine deposits (Ford,

2012).

The study area is located in Desolation Canyon along the southern margin of the Uinta

Basin, where Joe Hutch Canyon and Rain Canyon intersect with the modern Green River

(Figure 2.2). The study area is 1.5 km2 and contains a complete exposure of the lower Wasatch

Formation (Figure 2.2). The depositional strike of the strata is approximately east-west, and the

dip is close to zero degrees. Vegetation is sparse and strata are exceptionally well exposed

and accessible (Figure 2.3).

A C N 500 km 25 Qf L Tc Uinta Basin 30 Legend Study Area Qal Tw Duchesne River

OLIGOCENE E & Uinta Fms UTAH 35 Outcrop Location Qal Upper part of Price L Kpru 4 40 River Formation Qal Qf GreenKt RiverTuscher Fm Formation B 110° 45

Wyoming EOCENE Qal Alluvium Qcf M TERTIARY PALEOGENE

50 CENOZOIC Tw Coalesced alluvial Sevier Thrust Belt Qcf Tg Ma fan deposit Uinta Mountains 55 E upper WasatchQf FmAlluvial fanmiddle deposit Tc lower ta Basin Sync Vernal 60 Uin line L FlagstaffTc MemberColton FormationNorth Uinta Basin Fill Succession Basin Fill Uinta Qf Horn Fm Oil Fields

Colorado

65 PALEOCENE E Flagstaff Member of Green River Formation Tfn and North Horn Formation Gas 70 Uinta Basin Fields 40° 40° Tg Green River Formation 75 Qal Wasatch Formation Tw Tw Mesaverde(undifferentiated) Group

80 MESOZOIC CRETACEOUS ° CRETACEOUS L. 111 Study Area CAMPANIAN MAAS. water Price (Figure 2.2 Qf and 2.3) Qal

Douglas Creek Arch Tfn Outcrop of Kt Kpru Uncompahgre ¯ 0 5 mi Wasatch Fm Uplift 0 5 km 0 10 20 30 miles San Rafael Swell Green River 39° 0 10 20 30 40 kilometers 110° Figure 2.1: 3: (A)A, MapLocation of Uinta of the Basin Uinta majorBasin in structural northeastern features. Utah (Ford,B, Geologic 2012). (B)map Map of fieldof the area. Uinta TheBasin Upper, documenting Middle, theand location Lower Wasatchof the study areaare mapped and major as structuralWasatch Formationfeatures (Ford, (undifferentiated) 2012). (C) Chronostratigraphic east of the river chart and Coltonof Lower Formation Cretaceous westand ofUpper the Tertiaryriver. 3A strata modified in the fromUinta Basin (modiﬁedChidsey (1980). from Fouch 3B etmodified al., 1994a; from Johnson Witkind and (1988). Roberts, 2003; Ford, 2012).

6 Rose Diagram of Sediment 0 1 2 3 Transport Directions mi 0 2.5 5 km x = 16° N Joe Hutch Canyon lower Wasatch Formation

middle Wasatch Formation ¯

Alluvium Alluvium lower Wasatch n = 25 Formation

Figure 2.3 D middle Wasatch Formation

Figure 2.3 B Supplemental Files A-1 & A-2

Main Field Area Figure 2.3 C

Green River lower Wasatch Formation Alluvium Rain Canyon

Figure 2.2: Topographic and geologic map of the ﬁeld area showing location of outcrops studied in this research. Sediment transport direction and the locations of photopanels in Figure 2.3 are also shown.

7 A SW NE Middle Wasatch Middle Wasatch

Lower Wasatch Lower Wasatch 250 m Lower Wasatch

B SW Middle Wasatch NE

Lower Wasatch 250 m

C NW SE D SE NW 250 m 150 m

Figure 2.3: (A) Photograph of the exposures of the study area documenting the contact between the lower and middle members of the Wasatch Formation. (B) Photograph of the main study area. (C) Photograph of the southern part of the study area. (D) Photograph of the northern part of the study area. See Figure 2.2 for locations of photographs in B, C, and D.

CHAPTER 3

DATA AND METHODOLOGY

In order to address the goals of this study, the following data were collected:

1) forty-eight stratigraphic columns totaling 1,040 m that record grain size and

physical and biogenic sedimentary structures at a centimeter-scale resolution

(Supplemental File A-1);

2) paleocurrent measurements (n = 25) collected from channel margins, flutes, 3D

trough cross-beds, and 3D ripple laminations (Figure 2.2 and Supplemental File A-

2);

3) high-resolution Gigapan photopanels which are used to document stratal

boundaries (Figure 2.3 and Supplemental Files A-2); and

4) thickness measurements (n=98) of stratal units, widths cannot be defined as the

orientation of the outcrop is parallel to paleoflow of most units (Figure 3.1, and

Supplemental File A-3).

3.1 Lithofacies

This study uses Gressley’s (1938) definition of lithofacies as those observable, physical, chemical, and biological properties of rock that collectively permit objective description (Cross

and Homewood, 1997). Ten lithofacies are documented in the field area. A detailed description

and interpretation of each is included in Table 3.1. Photographic examples of each lithofacies

are included in Figure 3.2.

3.2 Architectural and Hierarchical Fluvial Classification

There are two prevailing methods for describing and classifying fluvial strata: Allen’s (1983) hierarchical surfaced-based approach, and Miall’s (1985) architectural-element analysis.

Building upon the work of McKee and Weir (1953) and Brookfield (1977), Allen (1983) proposes

a method in which first-, second-, and third-order bounding surfaces, which are determined by

stratal terminations and superposition, are used to define a hierarchy of strata. This method has many strengths; however, it does not account for the internal or external geometry of stratal units or sedimentary processes. For example, variations in channel-belt architecture (e.g. lateral-accreting bars and downstream-accreting bars) and sedimentary process (e.g. suspension versus tractive deposition) are not considered. These characteristics are important because they have implications for continuity of sandstone units within channel-belts, connectivity between stratigraphically adjacent channel-belts, porosity, and permeability.

Additionally, this method is difficult to apply to floodplain strata. For example, crevasse-splay

sandstone beds have approximately parallel bounding surfaces. As a result each stratal boundary is a first-order surface, regardless of the size or timespan of deposition of the units.

Furthermore, bedding in floodplain strata is difficult to correlate due to poor exposure and

bioturbation, rendering this technique inadequate.

Building upon the work of Fisk (1944), Beerbower (1964), and Allen (1983), Miall’s (1985)

method for describing and classifying fluvial strata is based on the division of fluvial strata into

eight architectural elements: (1) channels, (2) gravel bars and bedforms, (3) sandy bedforms,

(4) foreset macroforms, (5) lateral-accretion deposits, (6) sediment-gravity-flow deposits, (7)

laminated-sand sheets, and (8) overbank fines. These elements are differentiated by the nature

of their bounding surfaces, external and internal geometry, and scale (i.e. width and thickness).

This method does not integrate sedimentary processes, timespan of deposition, or temporal

context. For example, channel elements are not distinguished by their fill type (e.g. mud versus

gravel) or sedimentary process (e.g. suspension versus tractive deposition). Furthermore,

lateral-accretion elements, for example, are deposited over a longer time scale than sandy

bedforms. Lastly, lateral-accretion elements can be composed of sandy or gravelly bedforms,

allowing one element to be composed of others, thus nullifying the hierarchical concept.

Although the fluvial classification methods of Allen (1983) and Miall (1985) provide a good foundation for describing fluvial successions, they do not adequately incorporate characteristics that are essential in understanding reservoir properties.

This study utilizes the method proposed by Ford (2012), which builds upon components of

the surface-based hierarchical approach of Allen (1983) and the architectural-element approach

of Miall (1985) (Figure 3.3). Ford’s (2012) methodology for describing fluvial successions is

based on physical, observable characteristics and is constrained by lithofacies associations,

external geometry, nature of bounding surfaces, and cross-cutting relationships. In this method,

fluvial strata are divided into a three-level hierarchy (stories, elements, and archetype) that

incorporates channel-belt and floodplain strata (Figure 3.3).

Stories are the lowest hierarchical level and the fundamental building blocks of the

classification scheme (Figure 3.3). Building upon the work of Feofilova (1954), Potter (1967),

Jackson (1975), and Friend (1983), Ford (2012) defines stories as meso-scale strata formed

from genetically related beds or bedsets produced by the migration, fill, or overbank discharge

of a single fluvial channel. The thickness of stories scales to bank-full discharge and flood-

stage water depth. Stories associated with channels are: (1) downstream accreting, (2) lateral

accreting, (3) erosionally-based fine-grained fill, and (4) fine-grained fill associated with lateral

accretion. Stories associated with floodplains are: (1) crevasse channels, (2) crevasse splays,

and (3) floodplain fines. Stories stack to build elements, the second hierarchical level (Figure

3.3).

Ford (2012) defines an element as a macro-scale lithosome produced by channel

migration and overbank discharge of a single fluvial channel. Elements are separated by

floodplain fines and/or paleosols, except when eroded by younger elements. Elements are

divided into two classes (Figure 3.3): channel-belt and floodplain-belt. Elements that are

composed of one story are referred to as single-story elements whereas those composed of more than one story are referred to as multi-story elements, following the terminology of

Feofilova (1954), Potter (1967), and Gibling (2006). Elements stack to build an archetype, the largest hierarchical level (Figure 3.3).

Ford (2012) defines an archetype as a macro-scale feature consisting of a channel-belt

element and the genetically related floodplain-belt element. Archetypes are divided into two

classes based on the predominant channel-belt architectural style: those composed

predominantly of downstream accreting stories (referred to as braided archetypes) and those

composed predominantly of lateral accreting stories (referred to as meandering archetypes).

The boundaries between stratigraphically adjacent archetypes document abandonment and an

abrupt shift in the location of the axis of deposition, which is interpreted as a record of avulsion

(Figure 3.3).

A 1 Erosionally-Based Fine- Downstream F10 (<1 %) Lateral Accreting F9 (1 %) F10 (1 %) 0.8 Accreting F2 (<1 %) F3 (4 %) n = 12 Grained Fill F8 (5 %) 0.6 F3 (11 %) F8 (4 %) x = 4 m

1 f/n 0.4 m = 0-5 m n = 20 n = 36 x = 7 m 0.2 0.8 x = 7 m 0.8 F4 (13 %) m = 5-10 m m = 0-5 m F4 (17 %) 0 0 5 T 10 15 20 0.6 F7 (44 %) 0.6 F5 (22 %) F5 (19 %) F7 (51 %) f/n f/n Fine-Grained Fill Associated 1 Story 0.4 0.4 0.8 with Lateral Accretion

0.2 F6 (2 %) 0.2 0.6

F6 (5 %) f/n n = 1 0.4 x = 3 m 0 0 0.2 m = 3.2 m 0 5 10 15 20 0 5 10 15 20 T T 0 0 5 T 10 15 20 B Downstream Accreting Lateral Accreting 1 1 F9 (1 %) F10 (1 %) F10 (1 %) F3 (5 %) n = 5 n = 3 F3 (10 %) F8 (5 %) 0.8 x = 11 m F8 (5 %) 0.8 x = 13 m F4 (11 %) m = 10-15 m m = 5-20 m

0.6 0.6

f/n 0.4 F7 (35 %) F4 (27 %) f/n 0.4 F7 (52 %) F5 (25 %)

0.2 0.2 F5 (20 %)

0 0 F6 (2 %) 0 5 10 15 20 F6 (2 %) 0 5 10 15 20

Multi-story Channel-Belt Element T T 1 F10 (<1 %) 1 F9 (1 %) F10 (2 %) F3 (2%) Element n = 19 F2 (<1%) n = 2 x = 8 m F8 (5 %) x = 10 m F8 (4 %) 0.8 F3 (11 %) 0.8 m = 5-10 m m = 5-15 m

0.6 0.6 F4 (21 %) F4 (13 %) f/n f/n 0.4 0.4 F7 (48 %) F7 (47 %) F5 (9 %) F5 (18 %) 0.2 0.2 F6 (15 %)

0 0 0 5 10 15 20 F6 (3 %) 0 5 10 15 20

Single-story Channel-Belt Element T T C Fine-Grained Crevasse Channels Fill Assoiated < 1 % with Lateral Accretion Channel-Belt < 1 % Sandstone Splay Beds 27 % 6 % 21 % Erosinally-Based Fine-grained Fill Paleosols Floodplain-Belt 2 % Mudstone 1 % 73 % 79 %

Lateral Accreting 32 % Downstream Floodplain Fines Accreting lower Wasatch Fm Wasatch lower 93 % 66 %

Figure 3.1: (A) Thickness and lithofacies percentage of channel-belt stories. (B) Thickness and lithofacies percentage of channel-belt elements. (C) Percentage of various rock types and architectural components in the lower Wasatch Formation in this study area. (n = number of occurrences; x = average thickness; m = mode; f = frequency; T = thickness)

13 F1: Green or Gray Mottled Mudstone F2: Red Mottled Mudstone F3: Burrowed Sandstone F4: Laminated Sandstone

0.5 m 0.5 m 0.25 m 0.2 m

F5: Tabular Cross-Stratifed Sandstone F6: Trough Cross-Strati ed Sandstone F7: Massive Sandstone F8: Horizontally-Strati ed Conglomerate

0.25 m 0.5 m 0.4 m 0.1 m

F9: Trough Cross-Stratifed Conglomerate F10: Chert-Clast Conglomerate

0.25 m 0.2 m

Figure 3.2: Photographic examples of the ten lithofacies of the lower Wasatch Formation in the study area. Descriptions and interpretations of the lithofacies are summarized in Tale 3.1.

14 Figure 3.3: Schematic chart of the three-level hierarchical classiﬁcation used to describe the ﬂuvial architecture of the lower Wasatch Formation (Ford, 2012).

15 Facies # Facies Name Grain Size Description Interpretation Green or Gray Mottled mud Non-distinct bedding with minor burrows and granular ped structures; Post depositional bioturbation F1 Mudstone rare desiccation cracks; gradational lower contact. Gradational to resulting in deformation of sharp upper contact. sedimentary structures. Red Mottled Mudstone mud Non-distinct bedding with minor burrows, glaebules, and granular Post depositional bioturbation F2 ped structures; rare desiccation cracks.; gradational to sharp lower resulting in deformation of and upper contacts. sedimentary structures. Burrowed Sandstone very fine- to fine-grained Non-distinct bedding; horizontal and vertical burrows, vertical roots; Post depositional bioturbation F3 sandstone rare ripple laminations; sharp to erosive lower contact; sharp upper resulting in deformation of contact. sedimentary structures. Laminated Sandstone fine- to medium-grained Asymmetric unidirectional ripples; planar to wavy laminations; Lower to upper flow-regime, tractive F4 sandstone climbing ripples rare; gradational to sharp lower and upper contacts. deposition; low to high energy.

Tabular Cross-Stratified fine- to medium-grained Tabular laminations, typically <25°; gradational to sharp lower and Lower flow-regime, tractive F5 Sandstone sandstone upper contacts. deposition; high energy.

Trough Cross-Stratified fine- to medium-grained Trough laminations; undulatory lower contact; gradational to sharp Lower flow-regime, tractive F6 Sandstone sandstone upper contact. deposition; high energy.

Massive Sandstone fine- to medium-grained NA NA F7 sandstone Horizontally-Stratified granule to pebble clasts Horizontally-stratified mud-clast laminae alternating with sandstone Upper flow-regime, tractive Conglomerate in fine- to medium- matrix laminations; clasts are commonly imbricated; sharp to erosive deposition; lower flow regime with F8 grained sandstone matrix lower contact; gradational to sharp upper contact. high sediment fall out rates; very high energy.

Trough Cross-Stratified granule to pebble clasts Trough cross-stratified mud-clast laminae alternating with sandstone Upper flow-regime, tractive F9 Conglomerate in fine- to medium- matrix laminations; clasts are commonly imbricated; sharp to erosive deposition; very high energy. grained sandstone matrix lower contact; gradational to sharp upper contact. Chert-Clast Conglomerate granule to cobble clasts Non-distinct bedding; chert clasts within sandstone matrix; sharp to Cohesive flow and/or bank collapse F10 in fine- to medium- erosive lower contact; gradational to sharp upper contact. settling. grained sandstone matrix Table 3.1: Table listing descriptive characteristics and interpretation of the ten lithofacies recognized in the lower Wasatch Formation in this study area. Photographic examples of each lithofacies are documented in Figure 3.2.

CHAPTER 4

ARCHITECTURE OF THE LOWER WASATCH FORMATION

4.1 Channel-Belt Architecture

The lower Wasatch Formation, in the study area, channel-belt strata predominantly contains downstream accreting stories (Figure 3.1 and Figure 4.1). The channel-belt strata consists of 66% downstream-accreting stories, 32% lateral-accreting stories, 2% erosionally- based fine-grained fill stories, and less than 1% fine-grained fill associated with lateral accretion stories (Figure 3.1).

4.1.1 Channel-Belt Elements

The average thickness of multi-story elements containing predominantly downstream- accreting stories is 11 m (Figure 3.1). The most abundant lithofacies in these elements is

massive sandstone (Facies 7) followed by laminated sandstone (Facies 4) and tabular-cross

stratified sandstone (Facies 5) (Figure 3.1). The average thickness of single-story elements

containing predominately downstream-accreting stories is 8 m (Figure 3.1). The most abundant

lithofacies in these elements is massive sandstone (Facies 7) followed by tabular-cross stratified

sandstone (Facies 5) and laminated sandstone (Facies 4) (Figure 3.1).

The average thickness of multi-story elements containing predominantly lateral-accreting

stories is 13 m (Figure 3.1). The most abundant lithofacies in these elements is massive

sandstone (Facies 7) followed by tabular-cross stratified sandstone (Facies 5) and laminated

sandstone (Facies 4) (Figure 3.1). The average thickness of single-story elements containing

predominantly lateral-accreting stories is 10 m (Figure 3.1). The most abundant lithofacies in these elements is massive sandstone (Facies 7) followed by laminated sandstone (Facies 4)

and trough-cross stratified sandstone (Facies 6) (Figure 3.1).

Channel-belt elements have an asymmetrical bowl shape when observed in depositional strike view that is thickest in its axis and thins towards its lateral margins. In dip view, the elements have an elongate wedge or tabular shape. The lower bounding surface and lateral margins of channel-belt elements are erosional. The upper bounding surface of the elements is undulatory and conformable, except where younger strata erode into it. Channel-belt elements evolve from the migration, fill and/or abandonment of a single fluvial channel (Ford, 2012).

4.1.2 Channel-Belt Stories

Downstream-accreting stories are the most common channel-fill component in the lower

Wasatch Formation, in the study area. The most abundant lithofacies in these stories is massive sandstone (Facies 7) followed by tabular-cross stratified sandstone (Facies 5) and laminated sandstone (Facies 4) (Figure 3.1). Lenses of mud-clast or chert conglomerates occur at the base of these stories (Figure 4.1). These stories generally maintain a consistent grain size in an upward transect (i.e. blocky profile) and have an average thickness of 7 m (Figure

4.1). These stories have an asymmetrical lens shape when observed in depositional strike view that is thickest and sandiest in its axis and thins towards its lateral margins. In dip view, the stories have an elongate wedge shape that tapers in the downstream direction. The lower bounding surface of the stories is convex upward and erosional. The upper bounding surface of the stories is slightly undulatory and conformable, except where younger strata erode into it.

Sediment-transport direction is parallel to forset migration. Stories predominantly stack aggradationally (i.e. on top of one another) and/or nonsequentially (i.e. adjacent stories were not deposited in chronological order; e.g. story 1 can share a contact with story 3) (Figure 4.1). The stories are interpreted as mid-channel bars with accretion dominantly in the downstream direction (Ford, 2012).

The most abundant lithofacies in lateral-accreting stories is massive sandstone (Facies

7) followed by tabular-cross stratified sandstone (Facies 5) and laminated sandstone (Facies 4)

(Figure 3.1). These stories generally fine upwards and have an average thickness of 7 m

(Figure 4.2). These stories have a sigmoidal shape when observed in depositional strike view that is thickest in its axis and thins towards its lateral margins. In dip view, the stories have an elongate wedge shape that tapers in the upstream and downstream directions. The lower

bounding surface of the stories is erosional. The upper bounding surface of the stories is

undulatory and conformable, except where younger strata erode into it. Sediment-transport

direction is perpendicular to forset migration. Bed and bedsets within lateral accreting stories

predominantly stack sequentially (i.e. adjacent stories were deposited in chronological order;

e.g. story 1 shares a contact with story 2 but not story 3; Figure 4.2). The stories are interpreted

as side-attached bars with accretion dominantly in the lateral direction (Ford, 2012).

Erosionally-based, fine-grained fill stories consist of red mottled mudstone (Facies 2)

and burrowed sandstone (Facies 3). The average thickness of these stories is 4 m (Figure 3.1).

These stories have an asymmetrical bowl shape when observed in depositional strike view that

is thickest in its axis and thins towards its lateral margins (Figure 4.1 and 4.2). In dip view, the

stories have an elongate wedge shape that tapers in the downstream direction. The lower

bounding surface of the stories is convex upward and erosional. The upper bounding surface of

the stories is conformable, except where younger strata erode into it. The stories are

associated with downstream accreting and lateral accreting stories. The stories are interpreted

as channel-fill deposits where avulsion of the channel occurred prior to deposition of the

associated channel bars (Ford, 2012).

Fine-grained fill associated with lateral accretion stories consists of red mottled

mudstone (Facies 2). The average thickness of these stories is 3 m (Figure 3.1). These stories

have a bowl shape when observed in depositional strike view that is thickest in its axis and thins

towards its lateral margins (see Supplemental File A-2 for examples). In dip view, the sotires

have an elongate wedge shape that tapers in the downstream direction. The lower bounding

surface of the stories is conformable along the margin that is adjacent to a lateral-accretion

story and erosional on the opposite margin. The upper bounding surface of the stories is

conformable. The stories are interpreted as channel fill deposits associated with lateral

migration of a channel bar, informally referred to as mud plugs (Ford, 2012).

4.2 Floodplain-Belt Architecture

The lower Wasatch Formation containing predominantly floodplain strata (79 %) (Figure

3.1). The floodplain strata consists of 93% floodplain fines, 6% crevasse-splay beds, 1%

paleosols, and less than 1% crevasse-channel stories (Figure 3.1).

4.2.1 Floodplain-Belt Elements

Floodplain-belt elements have a wedge shape that thins away from the adjacent

associated channel-belt element. When observed in dip view, the elements have a tabular

shape. The lower bounding surface of the elements is conformable to erosional. The upper

bounding surface of the elements is conformable and undulatory, except where younger strata

erode into it. Floodplain-belt elements are built by floodplain-fill stories created from the

overbank discharge and migration of a single fluvial channel (Ford, 2012).

4.2.2 Floodplain-Belt Stories

The most abundant lithofacies in crevasse-channel stories is burrowed sandstone

(Facies 3). The stories have a symmetrical bowl shape when observed in depositional strike

view that is thickest in its axis and thins towards its lateral margins (Figure 4.3). In dip view, the

stories have a wedge shape that tapers in the downstream direction. The lower bounding

surface of the stories is unconformable. The upper bounding surface of the stories is

conformable and undulatory, except where younger strata erode into it. The stories are

interpreted as crevasse channels (Ford, 2012).

The most abundant lithofacies in crevasse-splay stories is burrowed sandstone (Facies

3). The stories have a thin tabular or lobe shape when observed in depositional strike view

(Figure 4.4). In dip view, the stories have a wedge shape that tapers in the downstream

direction. The lower bounding surface of the stories is conformable to erosional. The upper

bounding surface of the stories is conformable and undulatory to planar, except where younger

strata erode into it. The stories are interpreted as crevasse splays (Ford, 2012).

The most abundant lithofacies in the stories are red mottled sandstone (Facies 2) and

gray mottled mudstone (Facies 1). The stories have a planar to wedge shape when observed

in depositional strike and dip view (Figure 4.4). The lower and upper bounding surfaces of the

stories are conformable. The stories are interpreted as floodplain fines deposited during

flooding events (Ford, 2012).

A 20 m 20 C

B 25-F 23b-D 23e-D 23d-D 24c-L 24b-L 24a-L 23f-D 23a-D 23c-D

C m 20

Element Boundary Story Boundary Bedding Surface Truncation Downstream Accreting Lateral Accreting Erosionally-Based Fine-Grained Fill Dessication cracks C 23e-D F3

15 Mud or chert clasts F7 23d-D Bioturbation

F4 F3 Ripple laminations F7 Sandstone

23c-D Planar laminations cm 50 F4

F7 Trough cross-strati cation Cross-Stratified Trough F6: F5 10 F4 23b-D F7 Tabular cross-strati cation F8 F10 F4 Facies number F8 F7 23-D F6

F4 23a-D F7 5

F8 m 2 F4 F5 F4 F6 F9 Conglomerate 50 cm 50 50 cm 50 F10 Dessication Cracks F7: Massive Sandstone

F7 F8: Horizontally-Stratified F10F10 cm 10 MCVc F VF 0 GR Si C Sand Figure 4.1: Example of a channel-belt element (23-D) containing predominantly downstream-accreting stories. (A) Uninterpreted photopanel. (B) Line drawing based on photopanel in A (See Supplemental File A-2 for location). (C) Measured section (location shown in A and B) for downstream-accreting story with photographs of lithofacies. See Supplemental File A-2 for explanation of the naming convention.

22 A 20 m 20 20 m 20 20 m 20 C

B 36h-L 39-F 36b-L 36c-L 36d-L 38-F 37-F 36k-L m 20

L36-e 36g-L m 20 C 36f-L 36j-L 36a-L 36i-L Element Boundary Story Boundary Bedding Surface Truncation Lateral Accreting Erosionally-Based Fine-Grained Fill mud or chert clasts C 36c-L F3 F7 Bioturbation F5 F8 Ripple laminations F4 F8 10 Planar laminations Sandstone

36b-L F5 Trough cross-strati cation cm 10 F3: Burrowed Sandstone F5: Tabular Cross-Stratified Tabular F5: F8 F4: Laminated Sandstone Tabular cross-strati cation cm 10 cm 10

36-L F7 F10 Facies number F4

F5 5 36a-L F4

F7 F4

F7 Sandstone 5 cm 5 Conglomerate F6

F10 cm 10 10 cm 10 F8: Horizontally-Stratified F6: Trough Cross-Stratified Trough F6: MCVc F VF 0 GR Si C F10: Chert-Clast Conglomerate Sand Figure 4.2: Example of a channel-belt element (36-L) containing predominantly lateral-accreting stories. (A) Uninterpreted photopanels. (B) Line drawing based on photopanel in A (See Supplemental File A-2 for location). (C) Measured section (location shown in A and B) for laterally accreting story with photographs of lithofacies. See Supplemental File A-2 for explanation of the naming convention.

23 A C 5 F3

F7 F4 F6 F4 F6 F4 F8

5 m 5 F2 MCVc F VF 0 C GR Si C Sand Mud or chert clasts Bioturbation Ripple laminations B Trough cross-strati cation F8 Facies number

C m 5

Story Boundary Bedding Surface Crevasse Channel Story Figure 4.3: Example of a crevasse channel story in this study area. (A) Uninterpreted photopanel. See Supplemental File A-2 for location (below and to the right of element 14-D). (B) Line drawing based on photopanel in A. (C) Measured section (location shown in A and B ) for crevasse channel story.

24 A B C F3 30 1 F1 m 1

25 m 25 F3 Splay Beds F2

F3 25 F2 F3 2 F2 F3 F2 F3 1 m 1 F3 F2 F3 F2 20 F3 Splay Beds F2 F1 F3

F3 F2 B F3 15 3 4 F2 F3 F2 F3 F2 F3 50 cm 50 F3

F2 cm 10

F3 10 F2: Rhizolith F1

F2 F2: Floodplain Fines 1 F3 F3 2 F3 F2

F3 F3 5 Dessication cracks F3 F2 Mud or chert clasts F1 Bioturbation F2 Rhizolith F3 F2 White Horizon MCVc F VF 0 GR Si C Sand F3 Facies Number Figure 4.4: Example of crevasse-splay and floodplain-fine stories in the study area. (A) Photographic examples of crevasse-splay and floodplain- fine stories. (B) Measured section for crevasse-splay and floodplain-fine stories (location shown in A). See Supplemental File A-2 for location (below element 23a-D). (C) Photographic examples of crevasse-splay and floodplain-fine stories and lithofacies.

CHAPTER 5

CREVASSE SPLAY TYPES

Ford (2012) identifies three types of crevasse-splay deposits based on the physical relationship between crevasse-splay(s) and adjacent channel-belt element (Figure 5.1, 5.2, and

5.3): (1) associated coeval splays, (2) associated non-coeval splays, and (3) unassociated splays. These same types of crevasse-splay deposits are identified in this study area. A description of each is included below.

Associated coeval splays are located laterally adjacent to and are physically connected to a channel-belt element, indicating that the crevasse splay was deposited coeval with the channel fill (Figure 5.1) (Ford, 2012). The widths of these crevasse splays are generally wider than that of the associated channel-belt. Associated non-coeval splay units are comprised of a succession of crevasse-splay beds that underlie the channel-belt element (Figure 5.2). The axis, or thickest part of the crevasse-splay unit, is located near the axis of the overlying channel- belt. Within an associated non-coeval splay unit, crevasse-splay beds generally thicken from one to the next in an upward succession and are commonly separated by paleosols, indicating that the crevasse splay unit was deposited over multiple flooding events. The width of associated non-coeval splay units exceeds the width of the overlying channel-belt element.

Associated non-coeval splay units are interpreted to be genetically related to the overlying channel-belt element, and therefore are a record of a successful avulsion (Ford, 2012). Smith et al. (1998), Kraus and Wells (1999), and Jones and Hajeck (2007) refer to these deposits as avulsion complexes, heterolithic avulsion deposits, and stratigraphically transitional deposits, respectively. Unassociated splay units are comprised of a succession of crevasse-splay beds that are spatially isolated from channel-belt elements (Figure 5). Within an unassociated splay unit, crevasse-splay beds generally thin from one to the next in an upward transect and are

commonly separated by paleosols. Unassociated splays are interpreted to represent a failed

avulsion (sensu Strouthamer, 2001).

A 10 m 10 m 14-D Channel bars Splay

B Channel bars Channel ll Channel ll a a’ a Floodplain nes Splay a’ Floodplain nes Channel bars Splay Cross-Section Plan View Figure 5.1: (A) Uninterpreted and interpreted photographic example of associated coeval splay from the ﬁeld area. The example is from the right margin of element 14-D (see Supplemental File A-2 for location). (B) Schematic diagram of associated coeval splay. Units are not drawn to scale.

28 A 1 10 m Channel 7-L

Splays

2 14-D Channel 10 m Splays

B 3 15 m 16-D 15-D 3 Channel 2 1 Splays

C Time 1 Channel bars Time 2 Channel ll Channel bars Channel ll b b’ Floodplain nes b’

Cross-Section Splay b Floodplain nes Splays Plan View Plan View Figure 5.2: (A) Photographic examples of associated non-coeval splays from the field area. Red line indicates division between channel-belt strata (above) and floodplain strata (below). (B) Simplified Supplemental File A-2 with location of each photographic example (A 1-3). (C) Sche- matic diagram of associated non-coeval splays. Units are not drawn to scale.

29 A 1 2 3 25 m 50 m 25 m

Splays Splays

Splays

B 25 m Splays 3 2 4 1

C Time 1 Channel bars Time 2 Channel ll c Splay c’ Floodplain nes

Floodplain nes c’ c’ Cross-Section Splay

c Plan View c Plan View Figure 5.3: (A) Photographic examples of unassociated splays from the ﬁeld area. (B) Simpliﬁed Supplemental File A-2 with location of each photographic example (A 1-4). (C) Schematic diagram of unassociated splays. Units are not drawn to scale.

CHAPTER 6

DISCUSSION

6.1 Spatially Varying Characteristics of Associated Non-Coeval Splays (i.e. Avulsion Complexes)

Associated non-coeval splay units (i.e. avulsion complexes, heterolithic avulsion deposits, and stratigraphically transitional deposits) are interpreted to be the record of a successful avulsion (Ford, 2012). Three distinct types of associated non-coeval splays are identified in this study area based on physical, observable characteristics (Figures 6.1, 6.2, and

6.3): type I, type II, and type III.

The thickness of type I splay units scale to the thickness of the overlying channel, and range from 10 to 20 m (Figure 6.1). The thickness of individual sandstone beds range from 0.1 to 3 m. The number of sandstone beds in these units ranges from 10 to 20 beds. Type I splay units have a net-sand content greater than 0.7, and grain size ranges from mud to fine-grained sand. Erosion surfaces are abundant. The amount of erosion scales to the thickness of splay beds, and range from less than 0.1 to 3 m.

The thickness of type II splay units are less than the thickness of the overlying channel, and range from 5 to 10 m (Figure 6.2). The thickness of individual sandstone beds ranges from

0.1 to 1 m. The number of sandstone beds in these splay units ranges from 5 to 15 beds. Type

II splay units have a net-sand content between 0.4 and 0.6, and grain size range from mud to very fine-grained sand. Erosion is not evident.

The thickness of type III splay units are less than the thickness of the overlying channel, and range from 1 to 3 m (Figure 6.3). The thickness of individual sandstone beds within these units is less than 0.5 m. The number of sandstone beds in these units ranges from 1 to 3 beds.

Type III splay units have a net-sand content less than 0.15, and grain size range from mud to very fine-grained sand. Erosion is not evident.

Five systematic differences are noted between type I, type II, and type III splays. First,

the thickness of the splay units and individual sandstone beds within type I splays are thicker

than those of type II, which are thicker than those of type III splays. Second, there is a broad

decrease in grain size from type I, to type II, to type III splays. Third, type I splays have a

greater net-sand content than type II, which have a greater net-sand content than type III

splays. Fourth, there is more erosion in type I splays than in type II and type III splays. Fifth,

the number of sandstone beds decreases from type I, to type II, to type III. Following this trend

a fourth type of associated non-coeval splay type could exist, one in which no sandstone beds

underlie the channel and the unit consists only of floodplain-fine deposits. However, this type IV

splay is not exposed in this study area.

Experimental studies and studies of modern floodplains document important spatial

trends in floodplain deposits. First, experimental and studies of modern floodplain document

that flow is fastest in the main channel, and flow velocity and shear stress diminish with

increased distance from the source channel (Sellin, 1964; Ghosh and Kar, 1975; Knight and

Shino, 1990; Shino and Knight, 1991; Willetts and Hardwick, 1993; Naish and Sellin, 1996;

Willetts and Rameshwaran, 1996; Wormleaton, 1996; Nicholas and McLelland, 1999; Patra and

Kar, 2000; and Knight and Brown, 2001). As a result, sediment transport capacity decreases

and grains are deposited in order of decreasing size away from the main channel (Stoke, 1851;

Rouse, 1950). Second, O’Brien and Wells’ (1986) study on the Clarence and Timbarra River

system documents gradual thinning of crevasse splays with increased distance from the source

channel. Finally, Allen (1970) proposes a concept in which erosion at the base of crevasse-

splay deposits is focused to areas near the source channel.

The concepts listed above are combined with the general characteristics observed in type I, type II, and type III splays to develop a conceptual model that describes longitudinal

changes in the stratigraphic characteristics of crevasse-splay deposits. In this model, type I,

type II, and type III splay units are interpreted to represent proximal, medial, and distal positions

in crevasse-splay deposits relative to the source channel, respectively (Figure 6.4). Type IV

units represent the most distal deposits and are located beyond the avulsion complex (sensu

Smith et al. 1998). Figure 6.4 describes how stratal characteristics change spatially, with

decreases in the following characteristics away from the source channel: (1) thickness of splay

unit, (2) thickness and abundance of splay beds, (3) net-sand content, (4) grain size, and (5)

erosion.

6.2 Upward Trends: Relationship between Floodplain and Channel-Belt Elements

Incisional avulsion (sensu Mohrig et al., 2000) consists of channel-belt strata that lack

underlying crevasse-splay deposits. In contrast, aggradational avulsion (sensu Mohrig et al.,

2000) implies a genetic relationship between channel-belt elements and the underlying

crevasse-splay deposits via avulsion processes. In an effort to document the avulsion style of

the lower Wasatch Formation, upward profiles are evaluated to identify correlations between

channel-belt strata and underlying crevasse-splay deposits.

The upward profiles show two intervals where channel-belt elements increase in

abundance upward (Figure 6.5 A). Each interval is underlain by intervals where crevasse-splay

beds increase in abundance, indicating an association between the abundance of channel-belt

elements and abundance of the underlying crevasse-splay beds (Figure 6.5 A). This

association is interpreted to indicate that the succession resulted from predominantly

aggradational avulsion (sensu Mohrig et al., 2000).

The relationship is strongest with channel-belt elements containing predominantly downstream-accreting stories as opposed to those containing predominantly lateral-accreting stories (Figure 6.5 A). The lack of crevasse-splay deposits beneath lateral-accreting deposits

is interpreted in two ways. First, that the floodplain strata underlying these channels are

stratigraphically abrupt (sensu Jones and Hajek, 2007), indicating that the channel-belt

elements containing predominantly lateral-accreting stories are associated with incisional

avulsion (sensu Mohrig et al., 2000). Second, floodplain-fine deposits underlying channel-belt

elements containing predominantly lateral-accreting stories are the most distal expressions of

associated non-coeval splays (i.e. Type IV). In this case the stratigraphically abrupt splays

(sensu Jones and Hajek, 2007) are simply the distal expression of stratigraphically transitional

splays (sensu Jones and Hajek, 2007). In other words, the cross-section of the exposed

channel is located beyond the limits of the sand-rich splays that are proximal to the source

channel. This interpretation implies that channel-belt elements containing predominantly

downstream-accreting stories are associated with aggradational avulsion longitudinally transfer

to channel-belt elements containing predominantly lateral-accreting stories. A regional study is

needed to test this interpretation.

A B Channel 29-D F1 Channel F2 F3 F1 20 F3 F2

F2 m 3

15 unit Splay

F3 10

splay unit C

F1 5 F3 B F2 F3 F2 F3 D Channel bars Channel ll

MCVc F VF 0 GR Si C Sand Dessication cracks Mud or chert clasts Bioturbation White Horizon Green Horizon Cross-Section F3 Facies Number Floodplain nes Splays Figure 6.1: (A) Measured section of type I splays from study area (location shown in C). (B) Photograph of type I splays (location shown in C). (C) Simpliﬁed Supplemental File A2 with location of A and B. (D) Schematic cross-section of type I splays.

35 A

Channel 7-L m 10

Splay unit B C F5 10 23-D F3 F3

F3 F3 F1 D F3 A 5

splay unit F3

F3 F2

F3 D Channel bars Channel ll

MCVc F VF 0 GR Si C Sand Dessication cracks Bioturbation Tabular cross- strati cation Cross-Section Splay Floodplain nes F5 Facies Number Figure 6.2: (A) Photograph of type II splays (location shown in C). (B) Measured section of type II splays from study area (location shown in C). (C) Simpliﬁed Supplemental File A2 with location of A and B. (D) Schematic cross-section of type II splays.

36 A

Channel 35-D m 10 5 m 5 Floodplain nes 35-D

B C Channel F8 35-D

F2 A F3 F2 B F1 Floodplain splay unit F2 5 F3 nes F2

MCVc F VF GR Si C Sand D Channel bars Channel ll Dessication cracks Bioturbation 0 White Horizon

F8 Facies Number Floodplain nes

Cross-Section Splays

Figure 6.3: (A) Photograph of type III splays (location shown in C). (B) Measured section of type III splays from study area (location shown in C). (C) Simpliﬁed Supplemental File A2 with location of A and B. (D) Schematic cross-section of type III splays.

37 Time 1 Channel bars Time 2 Channel ll

Floodplain nes d’ e’

f’

g’ Plan View Plan d

e Splay f

d Proximal Splay (Type I) d’

e Medial Splay (Type II) e’

f Distal Splay (Type III) f’ Cross-Section

Floodplain- nes Increasing distance from the source channel.

g Beyond Avulsion Complex (Type IV) g’ splay beds, (3) net-sand-content, (4) grain-size, and (5) erosion. Decreasing: (1) thickness of splay unit, (2) and abundance

Figure 6.4: Schematic diagram of spatially varying characteristics of associated non-coeval splays.

38 A Channel-Belt Floodplain- Belt Channel-Belt Floodplain-Belt Floodplain- Channel Element Downstream Lateral Element Splay Beds Fines Thickness

200

150

100 Vertical Position (m) Position Vertical 50 intervals of increasing intervals of downstream channel-belt intervals of increasing intervals of increasing increasing channel-belt lateral channel-belt splay beds 0 6040200 80 100 6040200 80 100 6040200 80 100 6040200 80 100 0 604020 80 100 604020 80 100 0 105 15 Percent (%) Percent (%) Percent (%) Percent (%) Percent (%) Percent (%) Channel Thickness (m)

B Downstream Accreting Stories Splay Beds to Crevasse Channel Channel-belt to Floodplain 220 Stories to Floodplain-Fine Net Sand Content 220 to Lateral Accreting Stories 220 Stories 220

200 200 200 200 Lateral Accreting 160 Stories 160 160 Crevasse Channel Stories 160 Channel-belt Sandstone % 120 120 Downstream Accreting 120 120 Floodplain Stories Splay beds 80 80 80 80

40 40 40 Floodplain-Fine Stories 40 Vertical Position (m) Position Vertical

0 0 0 0 6040200 80 100 6040200 80 100 6040200 80 100 6040200 80 100 Percent (%) Percent (%) Percent (%) Percent (%)

Figure 6.5 Upward trends of architectural components in the lower Wasatch Formation. Data points represent the vertical average over a 40 m thick by 600 m wide interval.

CHAPTER 7

APPLICATIONS

This thesis proposes a model that describes longitudinal changes in splay deposits. Type I, II,

and II splays can be differentiated in well logs and core by their relative high net-sand content,

sandstone bed thickness, and grain size (Figure 7.1). There is a high potential for connectivity

between adjacent sandstone beds in type I splays due to amalgamation and erosion between the sandstone beds (Figure 6.1 and 7.1). Whereas in type II and III splays, the sandstone beds

are more likely to be isolated from one another by mud (Figure 6.2, 6.3, and 7.1). Additionally,

connectivity of associated non-coeval splays with overlying channel-belt strata may enhance reservoirs where hydrocarbons are present. However, it is important to note that although the sandstone beds within type I, II, and II splays are laterally extensive, desiccation cracks are abundant. Baffles or barriers may exist within these splay beds if the desiccation cracks are filled with fine-grained sediment. Finally, the spatially varying characteristics and architecture documented in this thesis can be incorporated into reservoir models and considered when choosing exploration and development wells.

This thesis documents that in the lower Wasatch Formation, channel-belt elements containing predominantly downstream-accreting stories are associated with aggradational avulsion (sensu Mohrig et al., 2000) based on the presence of associated non-coeval splays

(Figure 6.5). Whereas channel-belt elements containing predominantly lateral-accreting stories are associated with incisional avulsion (sensu Mohrig et al., 2000) or they are the distal expression of aggradational avulsion based on the lack of associated non-coeval splays (Figure

6.5). This relationship between channel story type (i.e. downstream or lateral accreting) and splays has implications for predictability of stratigraphic architecture of floodplain strata underlying channel-belt strata. In areas where subsurface data is limited regarding floodplain strata (e.g. low-resolution seismic or well log and/or core data are limited to the large reservoir

sandstone bodies) but channel story type is known (e.g. identify distinct upward patterns in grain size changes in downstream- and laterally-accreting stories in well log data), the architecture of

the floodplain strata can be appropriately modeled based on the relationship between channel

story type and splay type. However, identifying channel story type in the subsurface can be

difficult (Keeton, 2012).

Finally, the outcrop of the lower Wasatch Formation, documented in this study, has a

net-sand content of 0.27 and contains predominantly floodplain strata (79%) making it an

excellent analog for low net-sand content or floodplain-dominated fluvial successions. This

thesis provides quantitative data (i.e. story and element proportions, thicknesses, and facies

proportions; Figure 3.1) of architectural components that can be directly applied to reservoirs in

lower Wasatch Formation in the Uinta Basin (Fouch et al. 1994b). Additionally, the lower

Wasatch Formation is a good analog to other low net-sand content fluvial successions including

the lower Williams Fork Formation in the Piceance Basin (Pranter and Sommer, 2011) and the

Mungaroo Formation of the northwest shelf of Australia (Stoner, 2010).

Associated Non-Coeval Splays pseudo gamma ray pseudo gamma ray pseudo gamma ray pseudo gamma ray

Type I Type II Type III Type IV (no splays)

Increasing splay: (1) net sand content, (2) sandstone bed thickness, (3) grain-size, (4) connectivity between sandstone beds

Figure 7.1: Diagrammatic example of pseudo gamma ray signature of associated non-coeval splay types.

CHAPTER 8

FUTURE WORK

Recommendations for future work include:

1. A regional study in the lower Wasatch Formation and/or other low net-sand content

fluvial successions such as the lower Williams Fork that document vertical trends in

channel-belt and floodplain strata. This documentation can be used to determine if

the correlation between downstream-accreting stories and aggradational avulsion

style is limited to the lower Wasatch Formation documented in this study or if it can

be applied to the entire lower Wasatch Formation and other low net-sand content

fluvial successions.

2. A regional study in the lower Wasatch Formation that maps associated non-coeval

splays and the source channel along a longitudinal profile. This documentation

would test the spatial variability of splay deposits and could also provide additional

information such as the scale and transition between type I, II, and III splays.

3. A regional study to evaluate white paleosol horizons (facies 1) and their association

with channel-belt strata (Supplemental File A-2) to test if the abundance and location

of horizons relate to the location of channel-belt strata and more specifically channel

story type (i.e. downstream versus lateral accreting).

CHAPTER 9

CONCLUSIONS

Documentation of well-exposed outcrop from the lower Wasatch Formation in the Uinta

Basin, Utah was used to determine the following:

1. Three types of crevasse splays are recognized in this field area based on their

physical relationship to adjacent channel-belt strata. Associated coeval splays are

laterally adjacent and are physically connected to a channel-belt element, indicating

that the crevasse splay was deposited coeval with the channel fill. Unassociated

splays are spatially isolated from channel-belt elements and are interpreted to

represent a failed avulsion. Associated non-coeval splays underlie the channel-belt

element and are interpreted to be genetically related to the overlying channel-belt

element, and therefore are a record of a successful avulsion.

2. Associated non-coeval splays, interpreted to be the stratigraphic record of

aggradational avulsion processes, have physical, observable characteristics that

vary spatially along a proximal-to-distal transect relative to the source channel.

Decreases in the following characteristics of splays occur with increased distance

from the source channel: (1) thickness of splay unit, (2) thickness and abundance of

splay beds, (3) net-sand content, (4) grain size, and (5) erosion.

3. Vertical trends in floodplain and channel-belt strata can be used to: (1) determine

whether the dominant avulsion style is aggradational or incisional, and (2) relate

channel story type (i.e. downstream versus lateral accreting) to avulsion style.

4. The occurrence of splay beds below channel-belt strata, documented in the vertical

profile, is interpreted to indicate that the lower Wasatch Formation resulted from

predominantly aggradational avulsion processes.

5. The occurrence of splay beds below channel-belt elements containing predominantly

downstream-accreting stories is interpreted to indicate that these channels resulted

from predominantly aggradational avulsion processes.

6. The lack of splay beds below channel-belt elements containing predominantly by

lateral-accreting stories is interpreted to indicate that these channels resulted from

predominantly incisional avulsion processes.

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SUPPLEMENTAL FILES

The supplemental files include oversized figures that could not be included in the main thesis and include: photopanels, maps, measured sections, and data tables. The supplemental files are in the order in which they were referred to in the thesis.

A-1: Measured Sections 48 stratigraphic columns totaling 1,040 m that record grain size and physical and biogenic sedimentary structures at a centimeter-scale resolution 1.1_Reference Photopan.pdf Reference photopan indicating location of measured sections and legend for measured sections 1.2_MS Legend.pdf Legend for measured sections 1.3_MS-1.pdf Measured section 1 1.4_MS-2.pdf Measured section 2 1.5_MS-3.pdf Measured section 3 1.6_MS-4.pdf Measured section 4 1.7_MS-5.pdf Measured section 5 1.8_MS-6.pdf Measured section 6 1.9_MS-7.pdf Measured section 7 1.10_MS-8.pdf Measured section 8 1.11_MS-9.pdf Measured section 9 1.12_MS-10.pdf Measured section 10 1.13_MS-11.pdf Measured section 11 1.14_MS-12.pdf Measured section 12 1.15_MS-13.pdf Measured section 13 1.16_MS-14.pdf Measured section 14 1.17_MS-15.pdf Measured section 15 1.18_MS-16.pdf Measured section 16 1.19_MS-17.pdf Measured section 17 1.20_MS-18.pdf Measured section 18 1.21_MS-19.pdf Measured section 19 1.22_MS-20.pdf Measured section 20 1.23_MS-21.pdf Measured section 21 1.24_MS-22.pdf Measured section 22 1.25_MS-23.pdf Measured section 23 1.26_MS-24.pdf Measured section 24 1.27_MS-25.pdf Measured section 25 1.28_MS-26.pdf Measured section 26

1.29_MS-27.pdf Measured section 27 1.30_MS-28.pdf Measured section 28 1.31_MS-29.pdf Measured section 29 1.32_MS-30.pdf Measured section 30 1.33_MS-31.pdf Measured section 31 1.34_MS-32.pdf Measured section 32 1.35_MS-33.pdf Measured section 33 1.36_MS-34.pdf Measured section 34 1.37_MS-35.pdf Measured section 35 1.38_MS-36.pdf Measured section 36 1.39_MS-37.pdf Measured section 37 1.40_MS-38.pdf Measured section 38 1.41_MS-39.pdf Measured section 39 1.42_MS-40.pdf Measured section 40 1.43_MS-41.pdf Measured section 41 1.44_MS-42.pdf Measured section 42 1.45_MS-43.pdf Measured section 43 1.46_MS-44.pdf Measured section 44 1.47_MS-45.pdf Measured section 45 1.48_MS-46.pdf Measured section 46 1.49_MS-47.pdf Measured section 47 1.50_MS-48.pdf Measured section 48 A-2: Interpreted Architecture of Interpreted photopanel of the main field area lower Wasatch Formation 2.1_Main_Photopan.pdf A-3: Data Tables 3.1_Data_Tables.xlsx Includes (1) Raw data associated with each architectural story and element: thickness, associated measured sections; geographic coordinates, paleocurrent information, width, facies (2) Thickness data summarized for each story and element type (3) Facies proportions of each story and element type (4) vertical trends through succession. Sand Body B5 (14-D)