The Neslen Formation near Harley Dome, Book Cliffs, Utah

Copyright

By

Ashlyn Victoria Murphy

2017

The Thesis Committee for Ashlyn Victoria Murphy

Certifies that this is the approved version of the following thesis:

Paleoenvironmental reconstruction of a heterogeneous, tidally

influenced reservoir analogue: The Neslen Formation near

Harley Dome, Book Cliffs, Utah

APPROVED BY

SUPERVISING COMMITTEE:

Supervisor:

Ron Steel

Co-Supervisor:

Peter Flaig

Charles Kerans




by

Ashlyn Victoria Murphy

Thesis

Presented to the Faculty of the Graduate School of

The University of Texas at Austin

in Partial Fulfillment

of the Requirements

for the Degree of

Master of Science in Geological Sciences

The University of Texas at Austin

August 2017

Dedication

I dedicate this thesis to my husband, Kevin Murphy, whose unwavering support and sacrifice for

my dream made this thesis possible. I would also like to dedicate this thesis to my father, Clark

Boswell, my mother, Robyn Boswell, and my sister Macy Sharp.

v

Acknowledgements

I would first like to thank my supervisor Dr. Peter Flaig for his patience, guidance, support, and

encouragement throughout the completion of the thesis project. I am truly a better geologist due to your instruction

in the field, guidance in grant writing, step-by-step teaching during my facies analysis, and constant encouragement.

I would also like to thank Drs. Steel and Kerans for their assistance as committee members and for their comments

to improve this thesis. My gratitude extends to Dr. Stephen Hasiotis, Emily Marino, and Rebecca Jones for their

insight and assistance during my field work and post field discussions. Additional thanks to Dr. Jacob Covault for

ideas, insight, and grant edits which helped provide partial funding for this project. Other additional thanks go to

Yawen He who was always willing to teach and answer my questions about reservoir modeling. This project was

supported in part by the Quantitative Clastics Laboratory at the Bureau of Economic Geology and the Jackson

School of Geosciences, UT Austin. Additional funding for this project was provided through grants from

ExxonMobil’s Global Geoscience Recruiting Grant program, Jackson School of Geosciences at the University of

Texas at Austin, the American Association of Petroleum Geologists, and the Geological Society of America.

Kevin Murphy, thank you for your willingness to do whatever it takes so that I can fulfill my dream. Your

unconditional love and encouragement during these past few years is the reason I have been able to come back to

school and study what I love.

Mom and Dad, thank you for your consistent support and love and for always reminding me that I can

finish strong.

Grandpa, thank you for getting an undergraduate degree in geology so that you may share your interest

with me as I was growing up. Without you I would not have known that geology was my passion and I am forever

grateful to you for that.

Lastly, I want to thank my sister, Macy Sharp, for sitting through another one of my graduations.

vi

Abstract




Ashlyn Victoria Murphy, M.S. Geo. Sci.

The University of Texas at Austin, 2017

Supervisor: Ron Steel

Co-Supervisor: Peter Flaig

A sedimentologic, ichnologic, and architectural analysis of the upper Sego and Neslen fms

(Campanian) along the Book Cliffs near Harley Dome, UT document a paleoenvironmental

evolution from wave and tidally-modified deltaic deposits of the upper Sego Fm to tidally

influenced estuarine deposits of the Neslen Fm. Paleoenvironments of the upper Sego include tidal

barforms and interdistributary bays while those of the Neslen include distal to proximal tidal-

fluvial channels, sandy and muddy tidal flats, and floodplains.

A total of 28 trace fossil forms were identified in the upper Sego and Neslen fms including

14 fully marine traces, 11 facies breaking traces, (those traces that can exist in fresh, brackish, or

marine salinities), 1 freshwater trace, and 2 continental traces. Ichnology was critical for refining

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paleoenvironmental interpretations and was used to distinguish between deposits of distal tidal-

fluvial channels and proximal tidal-fluvial channels, and tidal flats and floodplains. The

Teredolites ichnofacies was used as an indicator of marine flooding events.

Neslen sandbodies preserve inclined heterolithic stratification in point bars of estuarine

tidal-fluvial channels. In contrast to recent studies, bayhead deltas and deltaic deposits were not

identified in the Neslen near Harley Dome. Carbonates that include stromatolites and oolites are

identified for the first time in the Neslen. The predominance of distal to proximal tidal-fluvial

channels and tidal flats, abundant marine ichnology, the recurrence of the Teredolites ichnofacies

and carbonates, and the lack of bayhead delta or wave-modified deposits suggests deposition

within a distal, yet protected estuarine environment.

The Neslen Fm near Harley Dome provides an analogue for a heterolithic, paralic reservoir

system. Due to the heterogeneity that is evident at multiple scales within tidally influenced

systems, the outcrops of the Neslen Fm in the Harley Dome, UT area provide an analogue to

examine the distribution of various heterogeneities and facies in estuarine deposits that could

ultimately affect reservoir performance.

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Table of Contents

List of Tables.…………………………………………………………………………………….xi

List of Figures.…………………………………………………………………………………...xii

Chapter 1 Introduction of Project…………...…………………………………………………......1

Chapter 2: The Sego-Neslen Formation Transition (Campanian) near Harley Dome, Utah: An

Analogue for Tidally Influenced, Heterolithic, Paralic Reservoir Systems……………….3

Introduction………………………………………………………………………………..4

Regional Stratigraphic Setting and Previous Work……………………………………....13

Methods…………………………………………………………………………………..15

Facies Analysis…….……………………………………………………………………..19

Facies Association I (FA-I): Distal Tidal-Fluvial Channel…………...…………..19

Description……………………………………………………………….19

Interpretation……………………………………………………………..23

Facies Association II (FA-II): Tidal Flat…………………………………………29

Facies Association IIa & IIb (FA-IIa, FA-IIb): Sandy & Muddy Tidal Flat………29

Description……………………………………………………………….31

Interpretation……………………………………………………………..32

Facies Association IIc (FA-IIc): Distal Estuary…………………………………..31

Description……………………………………………………………….31

Interpretation……………………………………………………………..31

Facies Association III (FA-III): Proximal Tidal-Fluvial Channel………………..38

Description……………………………………………………………….38

Interpretation……………………………………………………………..38

Facies Association IV (FA-IV): Floodplain……………………………………...44

Facies Association IVa (FA-IVa): Levee-Splay-Swamp Margin………………...44

Description……………………………………………………………….44

Interpretation……………………………………………………………..44

Facies Association IVb (FA-IVb): Swamp……………………………………….45

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Description……………………………………………………………….45

Interpretation……………………………………………………………..45

Facies Association IVc (FA-IVc): Paleosol……………………………………...45

Description……………………………………………………………….45

Interpretation……………………………………………………………..46

Facies Association IVd (FA-IVd): Lake-Pond…………………………………...46

Description……………………………………………………………….46

Interpretation……………………………………………………………..46

Facies Association V (FA-V): Tidal Barform…………………………………….49

Description……………………………………………………………….49

Interpretation……………………………………………………………..49

Facies Association VI (FA-VI): Interdistributary Bay……………………………50

Description……………………………………………………………….50

Interpretation……………………………………………………………..50

Discussion………………………………………………………………………………..54

Combining Ichnology and Sedimentology to Refine Paleoenvironmental

Interpretations……………………………………………………………………54

Paleoenvironmental Evolution of the upper Sego to Neslen Formations at Harley

Dome……………………………………………………………………………..59

Sequence Stratigraphic Framework for the upper Sego and Neslen fms………...63

Regional Comparative Analysis of the Neslen Fm………………………………65

Implications for Reservoir Modelers………………….…………………………66

Conclusions………………………………………………………………………………68

Chapter 3: Future Studies in the Neslen Formation………………………………………………70

Appendix A: Detailed Composite Measured Sections: Harley Dome area, Utah…………………72

Appendix B: Paleocurrent Data…………………………………………………………………..73

Appendix C: Measured Sections with Paleocurrents: Harley Dome area, Utah…………………..74

Appendix D: Detailed Fence Diagram: Harley Dome area, Utah………………………………...75

Appendix E: Drone Videos: Harley Dome area, Utah……………………………………………76

x

Appendix F: 2D Geocellular Modeling Study of the Neslen Formation………………………….77

Appendix G: WTF Geocellular Model and Facies Distribution…………………………………..78

References………………………………………………………………………………………..79

xi

List of Tables

Table 2.1: Facies of the upper Sego and Neslen Formations near Harley Dome, UT……….21

Table 2.2: Facies associations (paleoenvironments) of the upper Sego and Neslen

Formations near Harley Dome, UT……………………………………………....22

Table 2.3: Dominant salinity of trace fossils found in the Sego and Neslen Formations near

Harley Dome, UT………………………………………………………………...54

xii

List of Figures

Figure 2.1: Regional paleogeography of the study area and modern basin geography. A.

Approximate location of the study area in northeastern Utah along the Campanian

paleoshoreline of the Cretaceous Western Interior Seaway. The location of the

study area is shown by the black box (Roberts and Kirschbaum, 1995; Willis and

Gabel, 2003; Painter et al., 2013). Modified from Prather (2016). B. Modern-day

geography of Laramide age basins and uplifts of northeastern Utah and

northwestern Colorado. Modified from Gomez-Veroiza and Steel

(2010)……………………………………………………………………………...7

Figure 2.2: Ammonite biostratigraphy and generalized lithostratigraphy for the Uinta, Piceance

Creek, and Sand Wash Basins of northeastern Utah and northwestern Colorado

(Konishi, 1959; Gill and Hail, 1975; Hettinger and Kirschbaum, 2002; Gomez and

Steel, 2010). Red box indicates the interval examined in this study. Modified from

Burton et al. (2016) and Prather (2016). ………………………...............................8

Figure 2.3: Map of the study area and the relative location of additional studies on the Neslen

Formation (black boxes) in the Book Cliffs, Utah. Modified from Shiers et al.

(2014)……………………………………………………………………………...9

Figure 2.4: Map of the Harley Dome, UT area including the location of all measured sections

and fence diagram (see Fig. 2.8, Appendix A, and Appendix B) constructed along

line A-A’.……………………….………………………...……………………...10

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Figure 2.5: A. Interpreted photomosaic from East Canyon showing the formations and

formation members found in the outcrop belt. B. Interpreted photomosaic in East

Canyon showing the two lowermost sandbodies at the base of the Neslen Fm

separated by finer grained deposits……………………………………………….11

Figure 2.6: A. Interpreted photo from East Canyon outcrop belt showing inclined heterolithic

stratification (white dashed lines) in sandbodies overlying coal and other fine

grained deposits. B. Interpreted photo from San Arroyo outcrop belt showing

multiple scour surfaces within one sandbody interpreted as a distal tidal-fluvial

channel (San Arroyo Canyon, 68 m). Sandbody in B is a potential candidate for a

deeply incised tidal channel or incised valley. Person for scale (white oval),

approximately 1.5 m……………………………………………………………...12

Figure 2.7: Legend for Figure 2.8 and Appendix A, C and D…………………………………17

Figure 2.8: Simplified version of the four composite measured sections and cross-section of the

top of the upper-Sego and Neslen deposits near Harley Dome, UT. Diagram

includes interpreted depositional environments and their correlation across the four

measured sections. Measured section locations and distances between outcrops are

included. Location of cross-section is shown on Fig. 2.4. I1 and I2 are addressed in

the paleoenvironmental evolution section of the discussion. A detailed version of

this figure is located in Appendix D………………………………………………18

Figure 2.9: Orthophoto of the basal Neslen showing dimensions of the lower two sandbodies

interpreted as distal tidal-fluvial channels. Orthophoto also shows the relationship

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between deposits of distal tidal-fluvial channels (FA-I), tidal flats (FA-II), and

floodplain (FA-IV) within outcrops along East Canyon………………………….25

Figure 2.10: Predominant facies, sedimentary structures, and inclusions found in distal tidal-

fluvial channels (FA-I) of the Neslen Fm. Images include A. Organic-rich lag

consisting of carbonaceous rip-up clasts at the base of FA-I; B. Mud-rich lag

consisting of mud chips and mud rip-up clasts at the base of FA-I exhibiting some

soft sediment deformation; C. F-11 containing combined flow ripple cross-

laminated sandstone with abundant mud drapes and double mud drapes; D. F-8

combined flow ripple cross-laminated sandstone; E. Wood fragments in the lag at

the base of FA-I; F. F-14 small to large scale trough cross-stratified sandstone

within FA-I. Shovel (50 cm) for scale. Pocket knife (9 cm) for scale……………..26

Figure 2.11: Trace fossils found in the Neslen within distal tidal-fluvial channels (FA-I). A.

Ophiomorpha (Op) within a bed of F-8; B. Bergaueria (Be) on the underside of F-

14; C. Diplocraterion (Di) within a bed of F-8; D. Siphonichnus (Si) within a bed

of F-11; E. Teichichnus (Te) within a bed of F-11; F. Rhizocorallium (Rh) within a

bed of F-11; G. Teredolites (Td) burrowed log within a bed of F-11; H. Tetrapod

swim tracks (TST) on the underside of F-11. Shovel (50 cm) for scale. Pocket knife

(9 cm) for scale. Lens cap (6 cm) for scale..………………………………………27

Figure 2.12: Interpreted outcrop image and corresponding drafted measured section in East

Canyon that shows the relationship of deposits of distal-tidal fluvial channels (FA-

I), tidal flats (FA-II), and floodplain (FA-IV). White bar on image corresponds with

location of drafted measured section.…………………………………………….32

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Figure 2.13: Predominant facies, sedimentary structures, and inclusions found in tidal flats (FA-

II) of the Neslen Fm including A. Sigmoidal crossbedding (F-9) within FA-IIa

(sandy tidal flats); B. Flaser, wavy, and lenticular bedded siltstone (F-6); C. FA-IIb

(muddy tidal flats) comprising interbedded sandstone and mudstone; D. Flat-topped

ripples at the top of FA-IIa (sandy tidal flats); E. Interbedded sandstone and

mudstone within FA-IIb (muddy tidal flat) with Skolithos (Sk); F. Punch down

structure on a trampled surface that shows FA-IIa (sandy tidal flat) injected into

FA-IIb (muddy tidal flat). Shovel (50 cm) for scale. Pocket knife (9 cm) for scale.

Lens cap (6 cm) for scale..…………………………………………......................33

Figure 2.14: Trace fossils found in tidal flats (FA-II) within the Neslen Fm. Including A.

Planolites (Pl) and other trace fossils within a highly bioturbated bed of F-6; B.

Teichichnus (Te) and other trace fossils within F-6; C. Rhizocorallium (Rh) within

F-8; D. Skolithos (Sk) within F-11; E. Trampled surface, likely dinosaur footprints;

F. Thalassinoides (Th) burrow network on the underside of F-8. Shovel (50 cm) for

scale. Pocket knife (9 cm) for scale. Lens cap (6 cm) for scale……………………34

Figure 2.15: Carbonate deposits found within the Neslen Fm. Including A. Stromatolite; B.

Stromatolite block with ooids on the surface; C. Skeletal-rich deposit with shells

and other skeletal fragments; D. Close-up of shell half within skeletal-rich deposits.

Pocket knife (9 cm) for scale. Lens cap (6 cm) for scale………………………….35

Figure 2.16: Photomicrographs of carbonate deposits found in the Neslen Fm in East Canyon

and Middle Canyon near Harley Dome, UT. A. Stromatolite showing algal

amalgamation and carbonate cement; B and C. Ooids found on the surface of

stromatolites in outcrop; D. Broken skeletal fragments found in the skeletal hash

xvi

deposit; E. Gastropod shell found in the skeletal hash deposit; F. Broken skeletal

fragments found in the skeletal hash deposit. Locations for each photomicrograph

are shown in Figure 2.15………………………………………………………….37

Figure 2.17: Interpreted outcrop image and corresponding drafted measured section in Middle

Canyon including deposits of tidal flats (FA-II), proximal tidal-fluvial channels

(FA-III), and floodplain (FA-IV). White bar on image corresponds with location of

drafted measured section.………………………………………………………...40

Figure 2.18: Predominant facies and sedimentary structures found in proximal tidal-fluvial

channels (FA-III) of the Neslen. A. Soft-sediment deformation in a bed of F-14; B.

Large-scale trough cross-stratification (F-14); C. Low-angle planar laminations (F-

8). Shovel (50 cm) for scale………………………………………………………41

Figure 2.19: Trace fossils found in the Neslen within proximal tidal-fluvial channels (FA-III).

A. Fuerisichnus (Fu) on the underside of a bed of F-14; B. Teredolites (Td) burrows

in a log within a bed of F-14; C. Rhizoliths (Rz) within a bed of F-4; D. Plant imprint

on a bedding contact of F-14. Shovel (50 cm) for scale. Pocket knife (9 cm) for

scale. Lens cap (6 cm) for scale. Finger for scale…………………………………42

Figure 2.20: Floodplain sub-facies associations including A. Levee-splay complex (FA-IVa); B.

Paleosol with rhizolith (Rz); C. Interbedded swamp (FA-IVb) and levee-splay (FA-

IVa) deposits. Shovel (50 cm) for scale. Lens cap (6 cm) for scale. White bar on

image C corresponds with location of drafted measured section…………………48

xvii

Figure 2.21: A. Outcrop image of the upper Sego in East Canyon showing the locations of Fig.

2.19B and Fig. 2.19C; B. Hummocky cross-stratification (F-15); C. Rhizocorallium

trace fossil in a bed of F-8. Shovel (50 cm) for scale. Pocket knife (9 cm) for scale.

……………………………………………………………………………………52

Figure 2.22: A. Teredolites ichnofacies in Middle Canyon; B. Teredolites ichnofacies in East

Canyon; C. Teredolites burrows on a log; D. Teredolites burrows in place of what

was once a log; E. Teredolites burrows in place of a log; F. Single Teredolites

within coal classified as an ichnofacies. Pocket knife (9 cm) for scale. Lens cap (6

cm) for scale……………………………………………………………………...58

Figure 2.23: Paleoenvironmental reconstruction of the Neslen Fm near Harley Dome, UT. Flood

and ebb tide directions are based on paleocurrent data shown in the rose diagram

from the Neslen Fm (n = 157). Tidal barforms of the reworked tidal deltas of the

upper Sego are also shown. Modified from Emery and Myers (1996)……………62

1

Chapter 1: Introduction of Project

This thesis contains a high-resolution, multiproxy sedimentologic, ichnologic, and stratal

architecture study of the transition between the Campanian upper Sego and Neslen formations

(fms) exposed along the Book Cliffs in the Harley Dome area of the Uinta Basin, Utah. The

primary focus of this thesis is the examination of the Neslen Formation (Fm) and is presented as a

stand-alone manuscript in the 2nd chapter of this thesis.

Chapter 2 integrates outcrop-based sedimentologic, ichnologic, and stratal architecture

analyses to describe and interpret deposits of the upper Sego and Neslen fms in four canyons (East,

Middle, Bryson, San Arroyo) in the Book Cliffs of UT near Harley Dome. The Harley Dome

outcrops comprise facies, ichnology, and architectural elements of an estuarine mixed fluvio-tidal

paralic system. The deposits of the upper Sego and Neslen fms represent the transition from tidally-

modified deltaic deposits to estuarine deposits, and thus provide an ancient outcrop analogue to

identify an estuarine system in the rock record and build a sequence stratigraphic framework.

Because the stratigraphy discussed herein is shallow-marine to continental transitional, ichnology

played a crucial role in the interpretation of flooding surfaces and refinement of

paleoenvironments, and therefore the importance of examining ichnology is highlighted in this

thesis. The deposits in the four canyons are described, interpreted, and correlated, and

paleoenvironmental interpretations of the Neslen Fm near Harley Dome are presented in a spatio-

temporal paleoenvironmental reconstruction. These interpretations are ultimately compared-

contrasted to those documented in three studies of the Neslen Fm undertaken southwest of the

Harley Dome area, 58 km from the study area by Shiers et al. (2014), 57 km from the study area

by Olariu et al. (2015), and 70 km from the study area by Aschoff et al. (2016). The Neslen Fm

2

can serve as an estuarine reservoir analogue and thus resultant sandbody geometries and internal

heterogeneity scale and distribution within estuarine paleoenvironments is discussed.

The goals of this thesis are to: 1) identify paleoenvironments and clarify 3D architectural

element geometries for the Sego-Neslen transition at Harley Dome, focusing on the Neslen, Fm,

to produce a spatio-temporal paleoenvironmental reconstruction based on stratigraphy, ichnology,

and stratal architectures; 2) place the upper Sego and Neslen fms into a sequence stratigraphic

framework, 3) compare-contrast the data set and these resultant interpretations with other

published research on Sego-Neslen transitional stratigraphy previously described from the Book

Cliffs region (Shiers et al. 2014; Olariu et al. 2015; Aschoff et al. 2016) to provide a revised,

regional framework; and 4) discuss the reservoir elements of the Neslen Fm including sandbody

geometries and heterogeneities to aid reservoir modelers of estuarine petroleum systems.

3

Chapter 2: The Sego-Neslen Formation Transition (Campanian) near Harley

Dome, Utah: An Analogue for Tidally Influenced, Heterolithic,

Paralic Reservoir Systems

INTRODUCTION

The Book Cliffs near Harley Dome and the Utah-Colorado border (Fig. 2.1) preserve Late

Cretaceous (Campanian) strata of the Mesaverde Group (Fig. 2.2) including fluvial-distributive to

shallow-marine strata of the Castlegate Sandstone (Castlegate), Buck Tongue of the Mancos Shale,

Sego Sandstone Member of the Mancos Shale (Sego), Neslen Formation (Fm), and Bluecastle

Tongue of the Castlegate (Konishi, 1959; Gill and Hail 1975; Hettinger and Kirschbaum 2003;

Gomez and Steel 2010; Burton et al. 2016; Allen and Pranter 2016). This study focuses solely on

the transition from the uppermost Sego to the Neslen Fm near Harley Dome, UT.

The Neslen Fm records deposition along a low relief coastal plain and associated shallow-

marine systems along the western shore of the Cretaceous Western Interior Seaway (Fig. 2.1)

(Aschoff and Steel 2011; Shiers et al. 2014; Olariu et al. 2015; Aschoff et al. 2016). The position

of the Neslen Fm within a sequence stratigraphic framework is still debated. Some workers place

the Neslen within the transgressive systems tract (TST), with a transgressive lag in the basal Neslen

(Yoshida et al. 1996), while others place a sequence boundary is in the middle to upper Neslen

(McLaurin and Steel 2000; Hettinger and Kirschbaum 2002). Others suggest that the Neslen is not

in the TST but rather the lowstand systems tract (LST) and therefore no sequence boundary exists

within the Neslen Fm (Willis 2000). The most recent sequence stratigraphic interpretation places

the lower Neslen in the TST and the upper Neslen in the highstand systems tract (HST), with a

maximum flooding surface in the upper-middle Neslen (Shiers et al. 2017). In general, the Neslen

Fm is typically placed within the TST with variable interpretations of the location of the

transgressive lag.

4

In transgressive systems along embayed coastlines, estuaries are common features rather

than tidal deltas like those of the Sego Fm (Van Wagoner 1991; Dalrymple et al. 1992; Willis and

Gabel 2003; Olariu et al. 2015). Estuaries are defined as the seaward portions of drowned incised

valleys that receive sediment from both marine and fluvial sources, and contain deposits often

exhibiting a mix of wave, tide, and/or fluvial influence (Dalrymple et al. 1992). Environments

associated with estuaries include washover fans, flood-tidal deltas, central estuary basin, bayhead

deltas, tidal flats, tidal sand bars, lagoons, floodplains, and tidal-fluvial channels (Dalrymple et al.

1992).

Recent studies of the Neslen focus on Book Cliffs strata 50-70 km southwest of Harley

Dome near Floy Canyon (Fig. 2.3; Olariu et al. 2015), Crescent Canyon (Fig. 2.3; Shiers et al.

2014), and Coal Canyon (Fig. 2.3; Aschoff et al. 2016). Although Neslen sediments are described

at these select outcrops (Shiers et al. 2014; Olariu et al. 2015; Aschoff et al. 2016), no multi-proxy,

high-resolution sedimentologic, ichnologic, and stratal architecture study has been employed to

the east in the Harley Dome area. This study describes and interprets the heterogeneous deposits

of the Neslen near Harley Dome to update the regional depositional framework for the Neslen Fm,

and provides reservoir modelers with an analogue for a tidally influenced paralic system.

Outcrops along four canyons in the Harley Dome area (Middle, East, Bryson, and San

Arroyo) (Fig. 2.4) examined for this study contain heterolithic deposits that include sandstones

with inclined heterolithic stratification comprising alternating sand-rich laminae and thin mud

drapes. Sand-rich intervals are separated by intervals of finer-grained mudstone, siltstone,

pedogenically modified sediments, and coal (Fig. 2.5). Inclined heterolithic stratification (IHS,

Fig. 2.6) is defined as large-scale, lithologically heterogeneous siliciclastic sedimentary

successions whose strata are inclined in the original depositional angle and exhibit initial dips of

5

1°-36° (Thomas et al. 1987). Some of these Neslen sandstones, but not all, have erosional bases,

and most contain numerous internal scour surfaces within sandstone packages (Fig. 2.6).

Sandbodies in the Harley Dome area that appear grossly similar to those described from other

Neslen outcrop belts have been interpreted as point bars of fluvial channels (Shiers et al. 2014;

Olariu et al. 2015; Aschoff et al. 2016), while others are interpreted as bayhead deltas (Shiers et

al, 2014; Olariu et al. 2015; Aschoff et al. 2016). Because these different depositional systems

(channels, deltas) imply inherently different plan view geometries for reservoir modelers, an

outcrop study that includes sedimentologic, ichnologic, and architecture analyses is employed to

correctly identify the depositional systems responsible for deposits of the Neslen Fm near Harley

Dome.

Not only is outcrop characterization essential for reservoir modeling to define large-scale

stratigraphic architectures, but the multiple scales of heterogeneity that exist within tidal-fluvial

systems are difficult to distinguish from subsurface data alone. Through an outcrop study such as

this, the distribution of facies within reservoir analogues can be established, and characteristics

such as grain size, sorting, and variation in lithology can be tested for its effect on reservoir

performance (Richardson et al. 1978; Lasseter et al. 1986, Thomas et al. 1987; Tyler and Finley

1991; Hartkamp-Bakker and Donselaar 1993; Willis and White 2000; Pranter et al. 2007).

Examining the transition into the Neslen Fm from the upper Sego in the Harley Dome area

is important because: 1) the study area contains shallow-marine to continental transitional

stratigraphy with complex architectural elements and fluctuating ichnology, therefore a combined

sedimentologic, ichnologic, and architectural analysis is the best way to identify and refine

interpretations of depositional systems, each of which imply different sandbody-shale geometries;

2) the Neslen was once a producing natural gas reservoir in the eastern and southeastern Uinta

6

Basin (Keighin 1979; Pitman et al. 1987) and refining the Neslen reservoir analogue near Harley

Dome could improve recovery in nearby petroleum fields; 3) sandbody-shale geometries and

internal architectures from such analogues as the Neslen can be used to refine reservoir models of

tidally influenced distributive-paralic-shallow-marine systems in general; and 4)

paleoenvironmental interpretations of the Neslen from this study can be compared and contrasted

to those presented by Shiers et al. (2014), Olariu et al. (2015), and Aschoff et al. (2016) to refine

the regional paleoenvironmental model for the upper-Sego and Neslen fms.

The purpose of this manuscript is therefore to: 1) describe the facies, ichnology and

architectural elements found within upper Sego-Neslen fms in outcrops in the Harley Dome area;

2) place the upper Sego and Neslen fms into a sequence stratigraphic framework; 3) identify

paleoenvironments and provide a spatio-temporal paleoenvironmental reconstruction for the study

area; 3) compare these results to previous studies of the upper Sego-Neslen fms in the Book Cliffs

to refine the regional model of the Neslen Fm, and 4) discuss the implications for regional

paleoenvironmental reconstructions of the Neslen Fm and for reservoir models of tidally

influenced fluvial-distributive-shallow-marine coastal systems.

7

Figure 2.1: Regional paleogeography of the study area and modern basin geography. A. Approximate location of the study area in

northeastern Utah along the Campanian paleoshoreline of the Cretaceous Western Interior Seaway. The location of the study

area is shown by the black box (Roberts and Kirschbaum, 1995; Willis and Gabel, 2003; Painter et al., 2013). Modified from

Prather (2016). B. Modern-day geography of Laramide age basins and uplifts of northeastern Utah and northwestern Colorado.

Modified from Gomez-Veroiza and Steel (2010).

8

Figure 2.2: Ammonite biostratigraphy and generalized lithostratigraphy for the Uinta, Piceance Creek, and Sand Wash Basins

of northeastern Utah and northwestern Colorado (Konishi, 1959; Gill and Hail, 1975; Hettinger and Kirschbaum, 2002; Gomez

and Steel, 2010). Red box indicates the interval examined in this study. Modified from Burton et al. (2016) and Prather (2016).

9

Figure 2.3: Map of the study area and the relative location of additional studies on the Neslen Formation (black boxes) in the

Book Cliffs, Utah. Modified from Shiers et al. (2014).

10

Figure 2.4: Map of the Harley Dome, UT area including the location of all measured sections and fence diagram

(see Fig. 2.8, Appendix A, and Appendix B) constructed along line A-A’.

11

B

Figure 2.5: A. Interpreted photomosaic from East Canyon showing the formations and formation members found in the outcrop

belt. B. Interpreted photomosaic in East Canyon showing the two lowermost sandbodies at the base of the Neslen Fm separated

by finer grained deposits.

A

12

B

Figure 2.6: A. Interpreted photo from East Canyon outcrop belt showing inclined heterolithic

stratification (white dashed lines) in sandbodies overlying coal and other fine grained deposits.

B. Interpreted photo from San Arroyo outcrop belt showing multiple scour surfaces within one

sandbody interpreted as a distal tidal-fluvial channel (San Arroyo Canyon, 68 m). Sandbody in

B is a potential candidate for a deeply incised tidal channel or incised valley. Person for scale

(white oval), approximately 1.5 m.

A

IHS

FA-II

FA-I

FA-III

13

REGIONAL STRATIGRAPHIC SETTING AND PREVIOUS WORK

The Late Cretaceous (Campanian) upper-Sego and Neslen fms are members of the

Mesaverde Group (Fig. 2.2) deposited in a retroarc foreland basin within east-southeastward

prograding clastic wedges shed from the Sevier orogenic belt to the west (Jordan 1981; Hettinger

and Kirschbaum 2003; Willis and Gabel 2003; Aschoff and Steel 2011; Burton et al. 2016). Upper-

Sego and Neslen strata are exposed within the Laramide-type uplifts in the Uinta Basin of eastern

Utah and western Colorado (Fig. 2.1). The Neslen Fm (Fig. 2.2) is traditionally interpreted as

tidally-influenced fluvial-distributive and shallow-marine deposits emplaced along what was

likely a rugose southwest-northeast trending coastline of the Cretaceous Western Interior Seaway

(CWIS). The Neslen is underlain by the upper Sego (Willis and Gabel 2003; Hettinger and

Kirschbaum 2003; Aschoff and Steel 2011; Shiers et al. 2014; Burton et al. 2016) (Fig. 2.5). The

upper Sego is the equivalent of the middle Iles Sandstone, located to the east in the Piceance Basin

of Colorado, and contains the ammonite Baculites scotti, indicating deposition at approximately

76 MA. (Fig. 2.2) (Gill and Hail 1975; Hettinger and Kirschbaum 2003; Gomez-Veroiza and Steel

2010; Kirschbaum and Spear 2012; Burton et al. 2016). The upper Sego is dominated regionally

by trough-cross stratification; is highly bioturbated, containing such fully marine traces as

Ophiomorpha, Siphonichnus, and Thalassinoides; and is typically interpreted as deposits of tidal

bars within tidally influenced deltas, tidally-modified fluvial deposits, and deposits of fluvial

distributary channels (Van Wagoner 1991; Willis and Gabel 2003; Olariu et al. 2015). The base of

the overlying Neslen Fm is typically defined as the first appearance of coal, representing a shift

from regression to transgression (Kirschbaum and Hettinger 2004; Olariu et al. 2015). Because

carbonaceous deposits such as coal typically are laterally discontinuous, the stratigraphic level of

the base of the Neslen Fm above the Sego is inconsistently interpreted throughout the Book Cliffs.

14

The presence of the ammonite Didymoceras nebrascense indicates that the Neslen Fm was

deposited at approximately 76 MA. (Gill and Hail 1975; Hettinger and Kirschbaum 2003; Burton

et al. 2016).

Recent work on the Neslen includes outcrop studies between Floy Wash and Crescent

Canyon, UT (Shiers et al. 2014), at Floy Canyon, UT (Olariu et al. 2015), and at Coal Canyon, UT

(Aschoff et al. 2016) (Fig. 2.3). Shiers et al. (2014) subdivided the Neslen into three distinct coal

bearing zones, a methodology similar to that employed by Gualtieri (1991), Hettinger and

Kirschbaum (2003), Kirschbaum and Hettinger (2004), and Cole (2008). Shiers et al. (2014)

describe the lowermost zone, the Palisade Zone, as dominated by fine grained floodplain deposits

and coal, with deposits of small sinuous fluvial channels, tidally influenced fluvial channels, and

overbank deposits. The overlying Ballard Zone is dominated by coal, recording raised pear mires

and rare ribbon-like distributary channel deposits and levees. The stratigraphically highest

Chesterfield Zone, is further divided into lower and upper zones. The lower Chesterfield Zone is

dominated by large fluvial point bar deposits of narrower ribbon-style distributary channels.

Channel size increases upward in the lower Chesterfield Zone with incision at the larger channel

bases (Shiers et al. 2014). The upper Chesterfield Zone comprises deposits of highly amalgamated

high-energy fluvial channels, and common overbank sandstones (Shiers et al. 2014). Olariu et al.

(2015) identified seven depositional environments in the upper Sego and Neslen fms at Floy

Canyon, UT. Olariu et al. (2015) interpreted the upper Sego to include deposits of tidal bars and

dunes within an estuary mouth, muddy tidal flats, overbank fines, lagoons, and tidal-fluvial

channels. The Neslen Fm includes deposits of muddy tidal flats, bay-head deltas, lagoons, tidal-

fluvial channels, and overbank. Olariu et al. (2015) describe the Neslen Fm as dominated by

inclined heterolithic stratification (IHS) and interpret 5-8 m thick sandbodies as deposits of tidally

15

influenced point bars within tidal-fluvial channels. This interpretation is based on the presence of

brackishwater trace fossils, common mud drapes, tidal rhythmites, bidirectional ripples and cross-

stratification, and lateral accretion surfaces. Aschoff et al. (2016) divided the upper Sego and

Neslen fms into four lithofacies associations: 1) sandy, fluvial-dominated, tide-influenced, wave-

affected deposits that include tidally influenced subaerial distributary channels, proximal mouth

bars, terminal distributary channels, tide-reworked delta front turbidites, distal delta front slumps,

and proximal prodelta; 2) heterolithic, fluvial-dominated, tide-influenced and wave-affected

deposits including prodelta and medial delta front turbidites; 3) heterolithic, tide-dominated,

fluvial-influenced and wave-affected deposits that include sandy tidal flats, distal mouth bars,

muddy tidal flats, wave-reworked proximal delta front, and abandoned delta front; and 4) muddy,

distal bayhead delta and bay-fill deposits found in the central basin or distal central basin.

METHODS

Sections were recorded in Middle Canyon, East Canyon, Bryson Canyon, and San

Arroyo Canyon (Fig. 2.4), an area covering approximately 70 km2. Measured sections began 2-

35 m below the assumed upper Sego-Neslen transition, which was based on a facies change from

deltaic to estuarine deposits and the presence of coal. Measured sections were terminated at or

above the Neslen-Bluecastle Tongue transition, defined by a consistent lack of marine or

brackish water traces and a predominance of architecturally blocky sandbodies generally lacking

IHS and containing thicker packages of coarser grained material than those of the Neslen Fm.

Stratigraphic columns include lithology, grain size, contacts, sedimentary structures, bed

thickness, trace fossils, bioturbation index, flora, and fauna.

16

Paleocurrent directions (n=157) were recorded from trough cross-stratification, ripple

cross-lamination, and parting lineation/primary current lineation and plotted as rose diagrams

using GeoOrient software.

High resolution photomosaics were recorded with a Nikon D 800 SLR camera and 200-

400 mm Nikkor lens on a GigaPan robotic panhead. Panoramas and photomosaics were stitched

together using GigaPan EFX Stitch software. Photomosaics were used in an architectural

analysis to examine vertical and lateral variations in stratigraphy, pinpoint architectural elements,

and clarify outcrop stacking patterns. A DJI Phantom 4 Pro drone with a 20 megapixel camera

and an 8.8-24 mm lens was used to record a matrix of laterally and vertically continuous photos

along select outcrop belts. Photos were uploaded into AgiSoft software to create 3D point clouds

that were converted into a tiled mesh and orthomosaics. The 3D imagery produced in AgiSoft

provided quantitative data on sandbody width, thickness, and area, and also provided additional

information on the variability of sandbody and shale geometries in the Neslen in 2D-3D space

(Fig. 2.9).

17

Figure 2.7: Legend for Figure 2.8 and Appendix A, C and D.

18

Figure 2.8: Simplified version of the four composite measured sections and cross-section of the

top of the upper-Sego and Neslen deposits near Harley Dome, UT. Diagram includes interpreted

depositional environments and their correlation across the four measured sections. Measured

section locations and distances between outcrops are included. Location of cross-section is

shown on Fig. 2.4. I1 and I2 are addressed in the paleoenvironmental evolution section of the

discussion. A detailed version of this figure is located in Appendix D.

A

I1

I2

19

FACIES ANALYSIS

The Upper Sego and the Neslen fms in the Harley Dome area are broken down into 16

distinct facies (Table 2.1) based on lithology, sedimentary structures, grain size, and upper and

lower contacts. These facies are combined into 6 facies associations based on vertical and lateral

facies relationships, facies stacking patterns, and trace fossils (Table 2.2). Facies associations

exclusive to the upper Sego include: Tidal Barforms (FA-V) and Interdistributary Bays (FA-VI).

Facies associations of the Neslen Fm record deposition in Distal Tidal-Fluvial Channels (FA-I),

Tidal Flats (FA-II), and Proximal Tidal-Fluvial Channels (FA-III) along associated Floodplains

(FA-IV).

Facies Association I (FA-I): Distal Tidal-Fluvial Channels (upper Sego and Neslen fms)

Description

FA-I (Table 2.2) is a fining-upward succession (0.5-12 m thick) with an erosional base that

exhibits inclined heterolithic stratification in outcrop. FA-I is dominated by small to large-scale

trough cross-stratified sandstone (F-14) or combined-flow ripple cross-laminated very-fine to fine-

grained sandstone with common mud-drapes, abundant double mud-drapes, mud rip-ups, and rare

mud balls (F-11) at the base. The succession fines-upward into very-fine to upper fine-grained

combined-flow ripple cross-laminated sandstone (F-8) and is typically capped by carbonaceous

shale (F-2) or structureless siltstone (F-4). FA-I rarely contains very-fine to fine-grained

structureless sandstone (F-7) and very-fine to fine-grained planar-laminated sandstone (F-9). Mud

drapes (2-20 inches thick) occur on inclined heterolithic stratification. Mud rip-up clasts and mud

balls are commonly found in lags above the erosional base and soft-sediment deformation is also

20

common. Sandbodies are typically 5-12 m thick and can be exposed as either heterolithic sheets

that extend for 100s to 1000s of m laterally, or can occur as arcuate channel-forms only 10s of m

wide. Carbonaceous material in the form of organic drapes, rip-up clasts, logs, and sticks are found

within the sandbodies as well as in the fine-grained facies capping the succession. Trace fossils

include Arenicolites (Ar), Asterosoma (As), Bergaueria (Be), Chondrites (Ch), Conichnus (Co),

Cylindrichnus (Cy), Diplocraterion (Di), Lockeia (Lo), Macaronichnus (Ma), Ophiomorpha (Op),

Palaeophycus (Pa), Planolites (Pl), Rhizocorallium (Rh), Siphonichnus (Si), Skolithos (Sk),

Teredolites (Td), dinosaur footprints, and tetrapod swim tracks.

21

Table 2.1: Facies of the upper Sego and Neslen Formations near Harley Dome, UT.

Facies Sedimentary Structures and Grain

Size

Color Upper/Lower Contacts Bed Thickness

Range

Diagnostic Features

F-1 Coal brown, black Base: Sharp

Top: Sharp to erosional

Thickest: 2.1 m

Thinnest: 5 cm

Common amber and

sulphur; can have

higher silt/sand content;

breaks blocky or in thin

sheets

F-2 Carbonaceous Shale brown, gray, black Base: Sharp, rarely

gradational


Thickest: 6 m (1.4)

Thinnest: 2 cm

Thinly laminated to

fissile, sulphur halos

common, can be flaser,

wavy, and lenticular

bedded

F-3 Structureless to rooted mudstone brown, red brown, gray,

black

Base: Sharp, rarely

gradational


Thickest: 2 m

Thinnest:10 cm

Abundant organics,

rounded nodular

weathering

F-4

Structureless to rooted siltstone

brown, gray, black Base: Sharp to erosional,

rarely gradational

Top: Sharp to erosional,

rarely gradational

Thickest: 3.6 m

Thinnest: 5 cm

Abundant organics, can

be thinly laminated

and/or interbedded with

mudstone or sandstone

F-5 Combined-flow current- rippled cross-

laminated siltstone

brown, gray, black Base: Sharp

Top: Sharp to erosional,

rarely gradational

Thickest: 2.1 m

Thinnest: 2 cm

Abundant organics, can

be thinly laminated

and/or interbedded with

sandstone, may contain

mud drapes

F-6

Flaser, wavy, and lenticular bedded

siltstone

brown, red brown, gray,

black

Base: Sharp

Top: Sharp, rarely

gradational

Thickest: 2.5 m

Thinnest: 5 cm

Isolated very-fine sand

lenses within silt

F-7 Very-fine to fine-grained structureless

sandstone

tan Base: Sharp to erosional,

rarely gradational


Thickest: 50 cm

Thinnest: 5 cm

Commonly heavily

bioturbated or

sideritized

F-8 Very-fine to upper fine-grained

combined- flow ripple cross-laminated

to planar-laminated sandstone

tan Base: Sharp to erosional


Thickest: 40 cm

Thinnest: 10 cm

Soft sediment

deformation common,

can be thinly laminated

and interbedded with

siltstone, rare syneresis

cracks

F-9 Very-fine to upper fine-grained low-

angle planar-laminated to sigmoidal-

bedded sandstone



Thickest: 60 cm

Thinnest: 10 cm

Mud-rich or organic-

rich lags common at

basal contact

F-10 Very-fine to fine grained current ripple

cross laminated sandstone



Thickest: 20 cm

Thinnest: 5 cm

Organic or mud-rich

lags common, mud-

drapes rare

F-11 Very-fine to fine grained combined-

flow ripple cross-laminated sandstone

with abundant mud drapes and mud

chips



Thickest: 1.9 m

Thinnest: 10 cm

Abundant mud drapes

and double mud drapes

and/or mud chips,

organics common

F-12 Wave rippled very-fine to upper fine-

grained sandstone



Thickest: 70 cm

Thinnest: 10 cm

Abundant mud drapes

and double mud drapes,

abundant organics

F-13 Climbing ripple cross-laminated very

fine- grained sandstone

tan Base: Erosional

Top: Erosional

Thickest: 20 cm

Thinnest: 5 cm

Trampled surfaces

common

F-14

Small to large-scale trough cross-

stratified to tabular cross-stratified

sandstone



Thickest: 2 m

Thinnest: 10 cm

Common mud or

organic drapes or

ripples on cross-beds,

mud rip-ups common

F-15 Hummocky cross-stratified sandstone

(Sego only)

tan Base: Sharp

Top: Gradational

Thickest: 3 m

Thinnest: 10 cm

Many Op burrows at

base and along

bounding surfaces

F-16 Carbonate white Base: Sharp

Top: Sharp

Thickest: 30 cm

Thinnest: 15 cm

Stromatolites and ooids;

rare in section

22

Table 2.2: Facies associations (paleoenvironments) of the upper Sego and Neslen Formations

near Harley Dome, UT.

Facies

Associations

Inclusive Facies Diagnostic Features Ichnology Relationship to

other FA

FA-I:

Distal Tidal-Fluvial

Channels

F-2, F-3, F-4, F-5,

F-6, F-7, F-8, F-9,

F-10, F-11, F-12,

F-13, F-14

Erosionally based, IHS, fining-

upward successions 0.5-12 m

thick. Dominated by F-14 (0.2-

1.5 m) and F-11 (0.1-0.5 m) at

the base, fining-upward into F-8

(0.1-1 m), and capped by F-2, F-

3, F-4, F-5, F-6. F-7 and F-9 rare

in section. Mud drapes and

double mud drapes common.

Lags of mud balls and mud chips

common. Some soft-sediment

deformation and carbonaceous

material.

Ar, As, Be, Ch, Co,

Cy, Di, Lo, Ma, Op,

Pa, Pl, Rh, Si, Sk,

Td,Te, Th,

Dinosaur

Footprints,

Tetrapod Swim

Tracks

Overlies FA-IIa, FA-

IIb, FA-III, FA-IVa,

FA-IVb, FA-IVc,

FA-IVd, FA-VII,

FA-VIII.

Underlies FA-IIa,

FA-IIb, FA-III, FA-

IVa, FA-IVb, FA-

IVc, FA-IVd, FA-V,

FA-VII, FA-VIII.

FA-II: Tidal Flats

FA-IIa:

Sandy Tidal Flats

F-4, F-6, F-7, F-8,

F-9, F-11

Dominated by F-11 (0.05-0.2 m)

and F-8 (0.05-0.2 m). Commonly

interbedded with F-4 (0.05-0.1

m) and F-6 (0.05-0.1 m). F-7

(0.03 m) rare. Mud drapes and

carbonaceous material common

with rare soft-sediment

deformation. Sheet-like

geometry.

As, Co, Cy, Lo, Op,

Pl, Rh, Sk, Td, Th,

Dinosaur Footprints

Overlies FA-I, FA-


FA-IVb, FA-IVc.

Underlies FA-I, FA-


FA-IVb.

FA-IIb:

Muddy Tidal Flats

F-2, F-3, F-4, F-5,

F-6

Dominated by F-4 (0.05-0.5 m),

F-5 (0.05- 0.5 m), and F-6 (0.1-

0.75 m). Carbonaceous material

common with rare sulphur,

amber, mud drapes and double

mud drapes. Sheet-like geometry.

Cy, Op, Pa, Ph, Pl,

Rh, Sk, Td, Te, Th,

Dinosaur Footprints

Overlies FA-I, FA-

IIa, FA-IIc, FA-IVa,

FA-IVb, FA-IVc,

FA-VIII.

Underlies FA-I, FA-

IIa, FA-III, FA-IVa,

FA-IVb, FA-IVc.

FA-IIc:

Distal Estuary

F-16 Solely F-16 (0.2-0.4 m).

Carbonate deposits in the form of

stromatolites, oolites, and skeletal

hash.

None Overlies FA-IVb.

Underlies FA-IIb,

FA-IVd.

FA-III:

Proximal Tidal-Fluvial

Channels

F-3, F-4, F-5, F-6,

F-7, F-8, F-9, F-10,

F-11, F-13, F-14

Erosionally based, IHS, typically

fining-upward packages 0.5 to 20

m thick. Dominated by F-14 (0.2-

2 m), F-8 (0.3-0.75 m), F-10 (0.1-

1.5 m), and F-11 (0.05-1 m),

fining-upward into F-4, F-5, and

F-6. F-7, F-9, and F-13 rare. Mud

drapes, double mud drapes, and

soft-sediment deformation

common. Lags of mud balls and

mud chips. Carbonaceous

material rare.

Cy, Pl, Td (in logs),

Dinosaur Footprints

Overlies FA-I, FA-

IIa, FA-IIb, FA-IVa,

FA-IVb, FA-IVc,

FA-IVd.

Underlies FA-I, FA-

IIa, FA-IVa, FA-IVb,

FA-IVc, FA-IVd.

FA-IV: Floodplain

FA-IVa:

Levee-Splay, Swamp

Margin

F-2, F-3, F-4, F-5,

F-7

Commonly coarsening-upward

successions 0.3-2 m thick of F-2,

F-4, F-5, and rarely capped by F-

7. F-3 is also rare. Carbonaceous

material common with rare

siderite.

Dinosaur Footprints Overlies FA-I, FA-

IIa, FA-IIb, FA-III,

FA-IVb, FA-IVc.

Underlies FA-I, FA-


FA-IVb, FA-IVc,

FA-IVd.

23

Table 2.2 continued: Facies associations (paleoenvironments) of the upper Sego and Neslen

Formations near Harley Dome, UT.

FA-IVb:

Swamp

F-1, F-2, F-3 Dominated by F-1 (0.1-1.5 m)

with rare F-2 (0.1-0.5 m) and F-3

(0.1 m). Carbonaceous material

common with F-1 containing

sulphur and amber.

Td Overlies FA-I, FA-


FA-IVa, FA-IVc,

FA-IVd.

Underlies FA-I, FA-

IIa, FA-IIb, FA-IIc,

FA-III, FA-IVa, FA-

IVc, FA-IVd.

FA-IVc:

Paleosol

F-3, F-4, F-6, F-7 Dominated by F-3 containing

rhizoliths. Rhizolith bearing F-4,

F-5, F-6, and F-7 rare. Paleosols

range from 0.5-2 m thick.

Carbonaceous material and wood

abundant. Nodular weathering

common.

None Overlies FA-I, FA-


FA-IVb, FA-IVd,

FA-VIII.

Underlies FA-I, FA-


FA-IVa, FA-IVb,

FA-IVd.

FA-IVd:

Lake-Pond

F-2, F-4, F-5, F-6 Dominated by F-6 (0.4-2.5 m)

with carbonaceous material

abundant. F-2, F-4, and F-5 rare.

Rare organic lentils in F-6.

None Overlies FA-I, FA-

IIa, FA-IIc, FA-III,

FA-IVa, FA-IVb,

FA-IVc.

Underlies FA-I, FA-

III, FA-IVb, FA-IVc.

Facies Associations Exclusive to the upper Sego

FA-V:

Tidal Barforms

F-3, F-4, F-5, F-6,

F-7, F-8, F-9, F-10,

F-11, F-14, F-15

Dominated by F-14 (0.5-2.5 m)

with F-3, F-4, F-5, F-6, F-7, F-8,

F-9, F-10, F-11, and F-15 rare.

Rare mud drapes, mud chips, and

mud balls.

As, Cy, Op, Pa, Pl,

Rh, Sch, Si, Sk, Te,

Th

Overlies FA-I, FA-

VI.

Underlies FA-I, FA-

IIb, FA-VI.

FA-VI:

Interdistributary Bay

F-4, F-5 Dominated by F-5 (0.5-0.6 m)

and F-4 (0.7 m) with mud drapes

common and rare siderite.

As, Cy, Pa, Pl, Te Overlies FA-V.

Underlies FA-V.

Interpretation

Concave up, erosionally based, sandbodies with trough cross-stratification, mud chip and

mud ball lags, mud drapes, abundant double mud drapes, and marine to brackish-water trace fossils

that thin and fine-upward into finer-grained facies have been interpreted as tidal-fluvial channels

(Dalrymple et al. 1992; Shiers et al. 2014; Olariu et al. 2015). These channels are not interpreted

as deposits of distributary channels because they are part of a transgressive estuarine system and

were not distributing sediment to a delta (Dalrymple et al. 1992; Shiers et al. 2014; Olariu et al.

24

2015; Shiers et al. 2017). Mud drapes on inclined heterolithic stratified sandbodies are continuous

across the entire sandbody and contain rhythmic sand-mud alterations and abundant double mud

drapes, similar to typical descriptions of estuarine tidal-fluvial point bars (Thomas et al. 1987;

Ranger and Pemberton 1992; Allen 2009). Double mud drapes on combined flow ripples suggests

two slack-water periods during a flood and ebb tidal cycle, and are a characteristic feature of the

subtidal zone (Nio and Yang 1991b). Mud balls and mud clasts within sandbodies and in lags

indicate higher-energy flows that rip-up and rework mud (Martinius et al. 2001). The fining

upward successions represented as inclined heterolithic stratification in outcrop with paleocurrents

indicating flow at a high angle to the bounding surfaces record lateral accretion of channels

(Fielding 2006). Scour surfaces within the laterally extensive sheet-like sandbodies reflect

autocyclic changes and reoccupation of older channels (Hughes 2012). The high diversity and high

abundance trace fossil assemblage is classified as proximal Cruziana and Skolithos ichnofacies

and therefore indicates marine salinities (Gingras and MacEachern 2012). The presence of marine

trace fossils eliminates the classification of these deposits being of purely fluvial origin. FA-IIa

and FA-IIb (sandy and muddy tidal flats) commonly overlie and underlie FA-I. Fluvial-tidal

channels such as these can incise into tidal flats, and tidal flats typically form on the flanks of

estuaries (Weimer et al. 1982; Dalrymple et al. 1992; Hughes 2012).

25

Figure 2.9: Orthophoto of the basal Neslen showing dimensions of the lower two sandbodies interpreted as distal tidal-fluvial

channels. Orthophoto also shows the relationship between deposits of distal tidal-fluvial channels (FA-I), tidal flats (FA-II), and

floodplain (FA-IV) within outcrops along East Canyon.

26

A B

D

E F

Figure 2.10: Predominant facies, sedimentary structures, and inclusions found in distal tidal-

fluvial channels (FA-I) of the Neslen Fm. Images include A. Organic-rich lag consisting of

carbonaceous rip-up clasts at the base of FA-I; B. Mud-rich lag consisting of mud chips and

mud rip-up clasts at the base of FA-I exhibiting some soft sediment deformation; C. F-11

containing combined flow ripple cross-laminated sandstone with abundant mud drapes and

double mud drapes; D. F-8 combined flow ripple cross-laminated sandstone; E. Wood

fragments in the lag at the base of FA-I; F. F-14 small to large scale trough cross-stratified

sandstone within FA-I. Shovel (50 cm) for scale. Pocket knife (9 cm) for scale.

C

27

Figure 2.11

A B

C D

E F

G H

28

Figure 2.11: Trace fossils found in the Neslen within distal tidal-fluvial channels

(FA-I). A. Ophiomorpha (Op) within a bed of F-8; B. Bergaueria (Be) on the

underside of F-14; C. Diplocraterion (Di) within a bed of F-8; D. Siphonichnus (Si)

within a bed of F-11; E. Teichichnus (Te) within a bed of F-11; F. Rhizocorallium

(Rh) within a bed of F-11; G. Teredolites (Td) burrowed log within a bed of F-11; H.

Tetrapod swim tracks (TST) on the underside of F-11. Shovel (50 cm) for scale.

Pocket knife (9 cm) for scale. Lens cap (6 cm) for scale.

29

Facies Association II (FA-II): Tidal Flats (Neslen Fm)

FA-II (Table 2.2) is dominated by finer-grained facies including rooted siltstone (F-4),

combined-flow current-ripple cross-laminated siltstone (F-5), and flaser, wavy, and lenticular

bedded siltstone (F-6) along with coarser-grained facies including very-fine to fine-grained

combined-flow ripple cross-laminated sandstone with abundant mud drapes and mud chips (F-11)

or very-fine to fine-grained combined-flow ripple cross-laminated to planar-laminated sandstone

(F-8). FA-II is divided into three sub-facies associations: FA-IIa: Sandy Tidal Flats, FA-IIb:

Muddy Tidal Flats, and FA-IIc: Distal Estuary.

Facies Association IIa & IIb (FA-IIa): Sandy & Muddy Tidal Flats

Description

FA-IIa (Table 2.2) is dominated by very-fine to fine-grained combined-flow ripple cross-

laminated sandstone (0.05-0.2 m thick) with abundant mud drapes and mud chips (F-11), very-

fine to fine-grained low-angle planar-laminated to sigmoidal-bedded sandstone (F-9) (Fig. 2.12A),

or very-fine to fine-grained combined-flow ripple cross-laminated to planar-laminated sandstone

(0.05-0.2 m thick) (F-8) and can be interbedded with structureless to rooted siltstone (F-4) or flaser,

wavy, and lenticular bedded siltstone (F-6) (Fig. 2.12B). Very-fine to fine grained structureless

sandstone (F-7) is rare. Flat-topped ripples are rare (Fig. 2.12D). Carbonaceous material is

common in all facies and includes organic rip-up clasts, organic chips, organic drapes, leaves, and

sticks. Soft-sediment deformation is less common. FA-IIa varies in thickness from 0.25-2.0 m.

FA-IIa and IIb are both expressed as a laterally extensive sheets that may be 10s-100s m wide (Fig.

30

2.11). Trace fossils include As, Co, Cy, Lo, Op, Pl (Fig. 2.13A), Rh (Fig. 2.13C), Sk (Fig. 2.13F),

Td (Fig. 2.13D), Th (Fig. 2.13H), and dinosaur footprints (Figs. 2.12F, 2.13G).

FA-IIb (Table 2.2) is dominated by structureless to rooted siltstone (F-4), combined-flow

current-ripple cross-laminated siltstone (F-5), and flaser, wavy, and lenticular-bedded siltstone (F-

6) (Fig. 2.12B). FA-IIb ranges from 0.1-2.5 m thick. Carbonaceous material is common in the form

of organic rip-up clasts and plant debris with rare sulphur and amber. Trace fossils include Cy, Op,

Pa, Phycosiphon, (Ph), Pl, Rh, Sk (Fig. 2.12E), Td, Te (Fig. 2.13B), Th, and dinosaur footprints.

Interpretation

The predominance of sand-rich facies in FA-IIa suggests strong current action that

winnowed out finer-grained material (Weimer et al. 1982). In comparison, the dominance of finer-

grained facies in FA-IIb suggests a location closest to the high tide line (Reineck 1972). In both

FA-IIa and FA-IIb, mud drapes, interbedded sandstone and siltstone, and flaser, wavy, and

lenticular bedding suggest alternating currents and slack water, suggesting tidal influence (Reineck

and Wunderlich 1968). The high diversity and high abundance trace fossil assemblage is

characteristic of tidal flat deposits and indicates marine influence (Gingras and MacEachern 2011).

Rhizoliths and dinosaur footprints indicate some subaerial exposure with alternation between

subaqueous and subaerial environments, also characteristic of tidal flats (Weimer et al. 1982).

31

Facies Association IIc (FA-IIc): Distal Estuary (East Canyon only)

Description

Rare carbonate deposits in the form of stromatolites, oolites, and skeletal fragments are

found at two separate stratigraphic levels in East Canyon (F-16) (Fig. 2.13E). Carbonate deposits

occur above the first major sandbody of the Neslen (~53 m) (Fig. 2.8, 2.9, 2.16, Appendix A) and

near the base of the Whiskey Tango Foxtrot (WTF) sandbody (~118 m) (Fig. 2.8, 2.16, Appendix

A). Stromatolites are found as isolated carbonate lenses 1-2 m thick and 10s m wide, and are

commonly overlain by intervals of oolites (Fig. 2.15). On a micro-scale, algal-skeletal fragments

are encased in carbonate mud (Fig. 2.16).

Interpretation

Stromatolites may form in distal estuarine environments, such as in the estuaries found

along the western shore of Andros Island, Bahamas (Franҫoise and Bourrouilh 2007).

Stromatolites can even form with an influx of clastics if there are periods of clastic quiescence that

allow microbial mats to form and accrete (Weimer et al. 1982; Reineck and Gerdes 1997; Lee et

al. 2000; Draganits and Noffke 2004). The ooids encrusting the stromatolites formed from tidal

reworking of carbonate sediments (Davies et al. 1978) and can be found in distal estuarine

environments, such as the oolite deposits described in the Lower Carboniferous estuarine

Ducabroook Formation in Queensland, Australia (Parker and Webb 2008). Skeletal fragments

were deposited in this restricted marine setting either by tidal reworking or by storm events

(Wiedemann 1972).

32

Figure 2.12: Interpreted outcrop image and corresponding drafted measured section in East Canyon showing the relationship of

deposits of distal-tidal fluvial channels (FA-I), tidal flats (FA-II), and floodplains (FA-IV). White bar on image corresponds

with location of drafted measured section.

33

Figure 2.13: Predominant facies, sedimentary structures, and inclusions found in tidal flats

(FA-II) of the Neslen Fm including A. Sigmoidal crossbedding (F-9) within FA-IIa (sandy

tidal flats); B. Flaser, wavy, and lenticular bedded siltstone (F-6); C. FA-IIb (muddy tidal

flats) comprising interbedded sandstone and mudstone; D. Flat-topped ripples at the top of

FA-IIa (sandy tidal flats); E. Interbedded sandstone and mudstone within FA-IIb (muddy

tidal flat) with Skolithos (Sk); F. Punch down structure on a trampled surface that shows FA-

IIa (sandy tidal flat) injected into FA-IIb (muddy tidal flat). Shovel (50 cm) for scale. Pocket

knife (9 cm) for scale. Lens cap (6 cm) for scale.

A B

A

C

A

D

A

E

A

F

A

34

A B

C D

E F

Figure 2.14: Trace fossils found in tidal flats (FA-II) within the Neslen Fm. Including A.

Planolites (Pl) and other trace fossils within a highly bioturbated bed of F-6; B. Teichichnus

(Te) and other trace fossils within F-6; C. Rhizocorallium (Rh) within F-8; D. Skolithos (Sk)

within F-11; E. Trampled surface, likely dinosaur footprints; F. Thalassinoides (Th) burrow

network on the underside of F-8. Shovel (50 cm) for scale. Pocket knife (9 cm) for scale.

Lens cap (6 cm) for scale.

35

A B

C D

murphya

Typewritten Text

Figure 2.15

36

Figure 2.15: Carbonate deposits found within the Neslen Fm near Harley Dome. Including A.

Stromatolite; B. Stromatolite block with ooids on the upper surface; C. Skeletal-rich deposit

with shells and other skeletal fragments; D. Close-up of shell cross-section within skeletal-rich

deposits. Pocket knife (9 cm) for scale. Lens cap (6 cm) for scale.

37

A B

A

C

A

D

A

E

A

F

A

Figure 2.16: Photomicrographs of carbonate deposits found in the Neslen Fm in East Canyon

and Middle Canyon near Harley Dome, UT. A. Stromatolite showing algal amalgamation and

carbonate cement; B and C. Ooids found on the surface of stromatolites in outcrop; D.

Broken skeletal fragments found in the skeletal hash deposit; E. Gastropod shell found in the

skeletal hash deposit; F. Broken skeletal fragments found in the skeletal hash deposit.

Locations for each photomicrograph are shown in Figure 2.15.

38

Facies Association III (FA-III): Proximal Tidal-Fluvial Channels (Neslen Fm)

Description

FA-III (Table 2.2) exhibits inclined heterolithic stratification within erosionally based,

fining-upward successions (0.5- 20 m thick) dominated by small to large-scale trough cross-

stratified sandstone (F-14), very-fine to fine-grained combined-flow ripple cross-laminated to

planar-laminated sandstone (F-8), and very-fine to fine-grained combined flow ripple cross-

laminated sandstone with abundant mud drapes and mud chips (F-11). These facies fine-upward

upward into structureless to rooted siltstone (F-4), combined-flow current-ripple cross-laminated

siltstone (F-5), and flaser, wavy, and lenticular bedded siltstone (F-6). Very-fine to fine-grained

structureless sandstone (F-7), Very-fine to upper fine-grained low-angle planar-laminated to

sigmoidal-bedded sandstone (F-9), and climbing ripple cross-laminated very fine-grained

sandstone (F-13) are rare in fining-upward successions. Sandbodies can be laterally extensive (10s-

100s m wide) exhibiting sheet-like or channel-form geometries, and can exhibit deep incision (>

10 m) and multiple scour surfaces. Mud drapes, double mud drapes, soft-sediment deformation,

mud balls, mud chips, and mud rip-up lags are common. Carbonaceous material in the form of

organic drapes, logs, and other plant debris is rare. Trace fossils include Cy, Fuerisichnus (Fu), Pl,

and Td found in logs.

Interpretation

Similar to FA-I, FA-III is a concave up, erosionally based, cross-stratified sandbody with

a mud chip lag similar to tidally influenced fluvial-channels (Dalrymple et al. 1992; Shiers et al.

2014; Olariu et al. 2015). Sandbodies that compose the inclined heterolithic stratification within

FA-III thin and fine-upward into finer-grained facies with brackish water trace fossils and

39

abundant double mud drapes. FA-III are interpreted to be point bars of estuarine tidal-fluvial

channels due to the continuous mud drapes on IHS and interbedded sand and mud. FA-III is

interpreted as proximal tidal-fluvial channels rather than distal tidal-fluvial channels because FA-

III contains thinner and less abundant mud drapes on IHS than FA-I (2-5 inches thick) and a higher

sandstone/mudstone ratio (~0.7) than FA-I (~0.5-0.6). Most notably FA-III contains a lower-

diversity trace fossil assemblage, also suggesting deposition in a more proximal position near

freshwater input than FA-I (Gingras and MacEachern 2012). Deep incision created by proximal

tidal-fluvial channels is observed in San Arroyo Canyon and is interpreted as a potential incised

valley (Willis and Gabel 2003).

40

Figure 2.17: Interpreted outcrop image and corresponding drafted measured section in Middle Canyon including deposits of

tidal flats (FA-II), proximal tidal-fluvial channels (FA-III), and floodplain (FA-IV). White bar on image corresponds with

location of drafted measured section.

41

A

C

A

Figure 2.18: Predominant facies and sedimentary structures found in proximal tidal-fluvial channels (FA-III) of

the Neslen. A. Soft-sediment deformation in a bed of F-14; B. Large-scale trough cross-stratification (F-14); C.

Low-angle planar laminations (F-8). Shovel (50 cm) for scale.

B

A

42

A

C

A

D

A

B

A

murphya

Typewritten Text

Figure 2.19

43

Figure 2.19: Trace fossils found in the Neslen within proximal tidal-fluvial channels

(FA-III). A. Fuerisichnus (Fu) on the underside of a bed of F-14; B. Teredolites (Td)

burrows in a log within a bed of F-14; C. Rhizoliths (Rz) within a bed of F-4; D.

Plant imprint on a bedding contact of F-14. Shovel (50 cm) for scale. Pocket knife (9

cm) for scale. Lens cap (6 cm) for scale. Finger for scale.

44

Facies Association IV (FA-IV): Floodplain (Neslen Fm)

FA-IV (Table 2.2) contains finer-grained sediments including coal (F-1), carbonaceous

shale (F-2), structureless to rooted mudstone (F-3), structureless to rooted siltstone (F-4),

combined-flow current-ripple cross-laminated siltstone (F-5), flaser, wavy, and lenticular bedded

siltstone (F-6), and rare very-fine to fine grained structureless sandstone (F-7). Wood and plant

debris is abundant and marine or brackishwater trace fossils are absent. FA-IV is divided into four

sub-facies associations based on inclusive facies and facies stacking.

Facies Association IVa (FA-IVa): Levee-Splay, Swamp Margin

Description

FA-IVa (Table 2.2) is typically a coarsening-upward succession (0.3-2 m thick and 10-

100s of m wide) with carbonaceous shale (F-2) at the base. Overlying facies include structureless

to rooted siltstone (F-4) and combined-flow current-ripple cross-laminated siltstone (F-5) that is

rarely capped by very-fine to fine-grained structureless sandstone (F-7). Root traces, wood, and

plant debris is abundant. Trace fossils are limited to dinosaur footprints.

Interpretation

Thin, coarsening upward successions composed of sandstone and siltstone with finer

grained facies, abundant organic material, and root traces suggest that these record crevasse-splays

and levees on the flanks of channels or swamps, some of which are pedogenically modified

(Coleman et al. 1964; Elliott 1974; Bridge 1984; Fielding 1984; Kraus 1987; Mjøs et al. 1993;

Smith and Pérez-Arlucca 1994; Changsong et al. 1995; Rajchl and Uličnŷ 2005; Martín-Closas

45

and Galtier 2005; Flaig et al. 2011). Vertebrate footprints are common in channel marginal

environments (Laporte and Behrensmeyer 1980).

Facies Association IVb (FA-IVb): Swamp

Description

FA-IVb (Table 2.2) is dominated by 0.1-1.5 m thick and 10-100s of m wide packages of

coal (F-1) with rare carbonaceous shale (F-2) and structureless to rooted mudstone (F-3). Wood

and plant debris is abundant and sulphur and amber are rare. Trace fossils include Td in logs and

on the surface of some coals.

Interpretation

Coal and carbonaceous shale record swamps (Fielding 1985). The abundance of coal and

the position of these coals within the stratigraphy suggest that Neslen peats formed on the lower

delta plain on channel margins, abandoned crevasse-splays, and near lakes or bays (Frazier and

Osanick 1969; Donaldson et al. 1970; Fielding 1984; Fielding 1985; Fielding 2010; Cross 2012).

Facies Association IVc (FA-IVc): Paleosol

Description

FA-IVc (Table 2.2) is dominated by 0.5-2 m thick and 5-100s m wide packages of rooted

mudstone (F-3) and rooted siltstone (F-4). Rhizoliths are ubiquitous and nodular weathering, plant

debris, and wood-plant debris is also common.

46

Interpretation

Mudstone and siltstone containing rhizoliths are interpreted as pedogenically modified

deposits (paleosols). Rhizoliths, root traces from ancient plants, form during subaerial exposure,

landscape stability, and non-deposition (Kraus 1999; Ruskin and Jordan 2007; Tänavsuu-

Milkeviciene and Plink-Björklund 2009). Neslen paleosols are brown to gray in color and contain

abundant organic material, suggesting these could be classified as poorly drained gleysols that

experienced rapid burial and reducing conditions (Fanning and Fanning 1989, Retallack 2001,

Kraus and Hasiotis 2006; Flaig et al. 2013).

Facies Association IVd (FA-IVd): Lake-Pond

Description

FA-IVd (Table 2.2) is dominated by 0.4-2.5 m thick and 5-10 s of m wide packages of

flaser, wavy, and lenticular bedded siltstone (F-6) with abundant carbonaceous plant debris.

Carbonaceous shale (F-2), and combined-flow current-rippled cross-laminated siltstone (F-5) rare.

Organic rich lentils in flaser, wavy, and lenticular bedded siltstone (F-6) are less common.

Interpretation

Interbedded siltstone and carbonaceous shale with sharp, non-erosive bases lacking marine

or brackishwater trace fossils are commonly interpreted as lakes or ponds on the floodplain

(Fielding 1984; Pontén and Plink-Björklund 2007; Flaig et al. 2011; Flaig et al. 2013). Deposition

of these sediments likely occurred in low-energy settings such as depressions on the floodplain

(Pontén and Plink-Björklund 2007). These deposits are interpreted as purely freshwater due to the

47

lack of marine ichnology and their stratigraphic position below and above other strata interpreted

as floodplain deposits and paleosols (Pontén and Plink-Björklund 2007; Flaig et al. 2013).

48

Figure 2.20: Floodplain sub-facies associations including A. Levee-splay complex (FA-IVa); B. Paleosol with rhizoliths (Rz); C.

Interbedded swamp (FA-IVb) and levee-splay (FA-IVa) deposits. Shovel (50 cm) for scale. Lens cap (6 cm) for scale. White bar on

image C corresponds with location of drafted measured section.

A

B

C

49

Facies Association V (FA-V): Tidal Barforms (upper Sego Fm)

Description

FA-V (Table 2.2) is dominated by small to large scale trough cross-stratification (F-14) in

packages ranging in thickness from 0.5-2.5 m and 100s-1000s of m wide. Sandbodies of FA-V

form a sheet-like geometry. Less common in FA-V are structureless mudstone (F-3), structureless

siltstone (F-4), combined-flow current-ripple cross-laminated siltstone (F-5), flaser, wavy, and

lenticular bedded siltstone (F-6), very-fine to fine grained structureless sandstone (F-7), very-fine

to upper fine grained combined flow ripple cross laminated to planar laminated sandstone (F-8),

very-fine to upper fine grained planar laminated to sigmoidal sandstone (F-9), very-fine to fine

grained current ripple cross-laminated sandstone (F-10), and very-fine to fine grained combined

flow ripple cross laminated sandstone with abundant mud drapes and mud chips (F-11),

hummocky cross-stratified sandstone (F-15). Mud drapes, mud chips, and mud balls are rare.

Trace fossils include As, Cy, Op, Pa, Pl, Rh, Schaubcylindrichnus (Sch), Si, Sk, Te, and Th.

Interpretation

Sigmoidal and trough-cross stratified intervals such as this containing such tidal indicators

as single and double mud drapes and mud chips are interpreted as tidal barforms deposited in a

high-energy environment, such as on the front of tide-dominated deltas (Van Wagoner 1991;

Fenies and Tastet 1997; Willis 2000; Willis and Gabel 2001, 2003; Fielding 2010; Hurd et al.

2015). Sigmoidal geometries with reactivation surfaces and low-angle planar laminations indicate

bar migration with a component of tidal reworking due to strong tidal indicators such as double

mud drapes (Rossi and Steel 2016). The trace fossil assemblage is high-diversity and high-

abundance and contains both marginal-marine and fully marine traces indicating repeated influx

50

of marine water into this portion of the system (Gingras and MacEachern 2012). FA-V is

interbedded and cross-cut by FA-I, indicating that tidal channels alternated with and incised into

these barforms. The association of FA-V with surrounding distal tidal-fluvial channels and tidal

flats places these tidal bars into an estuarine system rather than a deltaic system (Rossi and Steel

2016).

Facies Association VI (FA-VI): Interdistributary Bay (upper Sego Fm)

Description

FA-IX (Table 2.2) is dominated by packages of combined-flow current-ripple cross-

laminated siltstone (F-5) and structureless siltstone (F-4) ranging in thickness from 0.5-0.7 m with

widths of 10s of m. Mud drapes are abundant while siderite is rare. Trace fossils include As, Cy,

Pa, and Te.

Interpretation

Relatively thick intervals containing F-5 and F-4 with tidal indicators such as mud drapes

are interpreted as interdistributary bay deposits (c.f. van der Kolk et al. 2015) emplaced in a lower-

energy environment where fine-grained sediment was deposited from suspension settling between

distributary channels along a delta front (Elliot 1974; Phillips 2003; Bhattacharya 2010; van der

Kolk 2015). The trace fossil assemblage is low-diversity and contains both marginal-marine and

fully marine traces indicating both brackish and fully marine salinities (Gingras and MacEachern

2012). Interdistributary bay deposits (FA-VI) are similar to tidal flat deposits (FA-II) in outcrop,

but are differentiated from FA-II because they are consistently underlain and overlain by tidal

51

barform deposits, which are interpreted to be the preserved portion of reworked delta fronts (Rossi

and Steel 2016).

52

A

C B

murphya

Typewritten Text

Figure 2.21

53

Figure 2.21: A. Outcrop image of the upper Sego in East Canyon showing the locations of

Fig. 2.19B and Fig. 2.19C; B. Hummocky cross-stratification (F-15); C. Rhizocorallium trace

fossil in a bed of F-8. Shovel (50 cm) for scale. Pocket knife (9 cm) for scale.

54

Table 2.3: Dominant salinity of trace fossils found in the Sego and Neslen Formations near

Harley Dome, UT

DOMINANT SALINITY TRACE FOSSILS

Marine Asterosoma, Bergaueria, Chondrites,

Diplocraterion, Macaronichnus,

Ophiomorpha, Phycosiphon, Rhizocorallium,

Schaubcylindrichnus, Teichichnus,

Teredolites, Thalassinoides, Treptichnus,

Zoophycos

Marine, Brackish, or Freshwater Arenicolites, Conichnus, Cylindrichnus,

Lockeia, Palaeophycus, Piscichnus,

Planolites, Siphonichnus, Skolithos, Syneresis

cracks, Tetrapod swim tracks

Freshwater Fuerisichnus

Continental Dinosaur footprints, Rhizoliths

DISCUSSION

Combining Ichnology and Sedimentology to Refine Paleoenvironmental Interpretations

Combining sedimentologic and ichnologic observations and interpretations was essential

for differentiating between marine, brackishwater, freshwater, and continental deposits in the

Harley Dome area. A total of 28 trace fossils were identified in the upper Sego and Neslen fms

near Harley Dome (Table 2.3). All trace fossils were categorized based on their predominant

salinity (Table 2.3) resulting in the identification of 14 fully marine traces, 11 facies breaking

traces (trace fossils found in marine, brackish, or freshwater deposits), 1 freshwater trace, and 2

continental traces. The most abundant trace fossils include Cy, Pl, Sk, Td, Te, and Th with Co,

dinosaur footprints, Op, Rh, rhizoliths and Si being common. Rare traces include Ar, As, Be, Ch,

Di, Fu, Lo, Ma, Pa, Ph, Pi, Sch, syneresis cracks, Tetrapod swim tracks, Tr, and Zo.

55

Ichnologic observations were critical to distinguish between 1) distal tidal-fluvial channels

(FA-I) and proximal tidal-fluvial channel deposits (FA-III); and 2) deposits of tidal flats (FA-II)

and floodplains (FA-IV). Both distal tidal-fluvial channels and tidal flats exhibit a high-abundance,

high-diversity trace fossil assemblage (Table 2.2), with most trace fossils indicative of marine

salinities and few brackishwater traces or facies breakers (Table 2.3). In contrast, proximal tidal

fluvial channels and floodplain deposits exhibit low-diversity and diminutive traces in the form of

Cy, Fu, Pl, and Td found in logs, which suggests brackish water influence. A key surface

dominated by the Teredolites ichnofacies was identified at several intervals in the Neslen. The

Teredolites ichnofacies is a proxy for a marine flooding surface.

Distal tidal-fluvial channels versus proximal tidal-fluvial channels.- Distal tidal-fluvial

channels and proximal tidal-fluvial channels contain similar facies and fining upward trends, and

can overlie or underlie similar deposits such as those of tidal flats (FA-II) or floodplains (FA-IV)

(Fig. 2.9, 2.15). However, distal tidal-fluvial channels and proximal tidal-fluvial channels can be

distinguished using ichnology. For example, the distal tidal-fluvial channel found at ~35 m-42 m

in the East Canyon measured section contains the fully marine traces Sch, Td, and Th, and facies

the breaking traces Co, Cy, Pl, and, Sk. The presence of fully marine traces within this channel

indicates that sedimentation likely occurred in a more distal position with waters of marine

salinities, rather than in an up-dip position dominated by brackish or freshwater. Distal tidal-fluvial

channels of the Neslen commonly underlie and incise into tidal flats, which also exhibit a suite of

fully marine traces such as Op, Td, and Th. The presence of fully marine traces in the deposits

above and below the distal tidal-fluvial channels reinforces the interpretation that these channels

were marine. Contrastingly, proximal tidal-fluvial typically contain a suite of traces including Cy,

Fu, Pl, and Td found in logs. Cy and Pl are low-abundance and commonly diminutive. Fu a

56

freshwater trace fossil, are large and abundant, indicating freshwater influence. Td, although

common in waters of marine salinities, are only present in isolated logs, indicating that the

burrowing occurred while the log was in marine water and that the log was subsequently swept

upstream. The uppermost facies in proximal tidal-fluvial channels also contain continental trace

fossils including dinosaur footprints and rare rhizoliths, indicating subaerial exposure, reinforcing

their interpretation as channels occupying more up-dip positions.

Tidal flats versus floodplain. - Tidal flats and floodplain deposits can both be fine

grained, contain abundant carbonaceous material, occur in close stratigraphic proximity to each

other, and have similar outcrop expressions. This makes distinguishing between these

paleoenvironments difficult; however, tidal flats have a high abundance, high diversity trace fossil

assemblage that includes marine, brackishwater, and continental ichnology (Gingras and

MacEachern 2011), whereas floodplain deposits only exhibit freshwater and continental trace

fossils, such as dinosaur footprints and rhizoliths (Laporte and Behrensmeyer 1980; Kraus 1999;

Ruskin and Jordan 2007; Tänavsuu-Milkeviciene and Plink-Björklund 2009). Both sandy and

muddy tidal flats of the Neslen (FA-IIa, FA-IIb), contain the trace fossils As, Co, Cy, dinosaur

footprints, Di, Lo, Op, Ph, Pl, Rh, Sk, Td, Te, and Th. This indicates both marine affinities (As, Di,

Op, Ph, Rh, Td, Te, Th) and periodic subaerial exposure (dinosaur footprints). Floodplain deposits

of the Neslen (FA-IVa, FA-IVb, FA-IVc, FA-IVd) only contain dinosaur footprints and rhizoliths,

suggesting a purely continental paleoenvironment.

Teredolites Ichnofacies.- The Teredolites ichnofacies occurs at several intervals in the

Neslen near Harley Dome including 14 m and 80 m in Middle Canyon, 43 m, 65 m, and 92 m in

East Canyon, 8 m and 40 m in Bryson Canyon, and 4 m and 60 m in San Arroyo Canyon (see

Appendix A). The Teredolites ichnofacies (Fig. 2.20) is a regionally extensive surface of

57

Teredolites burrows, made by wood-boring clams that required elevated salinities to survive, on

the surface of coal (Castagna 1961; Bromley et al. 1984; Filho et al. 2008; Cragg et al. 2009;

Didžiulis 2011). In the study area, Teredolites ichnofacies surfaces are high-abundance, with large

Teredolites burrows (Fig. 2.20A, 2.20B). Hence, the Teredolites ichnofacies records a regional

marine flooding event (Bromley et al. 1984). This differs from the Teredolites trace fossil found

in isolated logs, which are transported and are not indicative of a flooding event (Fig. 2.20C, 2.20D,

and 2.20 E). In the Harley Dome area laterally extensive, sand filled Teredolites burrows at and

near the top of a coal bed, as well as additional Teredolites burrows on the basal contact of a

sandstone above the coal are interpreted to indicate marine flooding events. The presence of

abundant Teredolites on a surface such as this indicates that waters with elevated salinities

encroached upon the area and remained long enough for wood boring clams to burrow the

underlying coal (Bromley et al. 1984). The Teredolites ichnofacies commonly occurs at the base

of distal tidal-fluvial channels and tidal flats in the Neslen Fm (Fig. 2.20). These numerous

Teredolites ichnofacies suggest that multiple, regional marine incursions occurred during Neslen

deposition in the Harley Dome area. The Teredolites ichnofacies has the potential to be a

correlatable, albeit time transgressive surface that could extend beyond the Harley Dome area,

allowing for larger-scale regionally correlations of the Neslen.

58

A B

C D

E F

Figure 2.22: A. Teredolites ichnofacies in Middle Canyon; B. Teredolites ichnofacies in East

Canyon; C. Teredolites burrows on a log; D. Teredolites burrows in place of what was once a

log; E. Teredolites burrows in place of a log; F. Single Teredolites within coal classified as an

ichnofacies. Pocket knife (9 cm) for scale. Lens cap (6 cm) for scale.

59

Paleoenvironmental Evolution of the upper Sego to Neslen Formations at Harley Dome

Deposits in the Harley Dome area record the transition from tidally influenced deltas of the

Sego to tidal-fluvial channels, tidal flats, and floodplains associated with an estuary during

deposition of the Neslen (Fig. 2.8, 2.23, Appendix A, and Appendix D). Tidally-influenced deltas

of the upper Sego Fm are evidenced by trough cross-stratified, tabular cross-stratified, and

combined flow ripple cross-laminated sandstone with abundant mud drapes and/or mud chips as

well as low-angle planar laminated to sigmoidal bedded sandstone. Hummocky cross-stratification

indicate wave influence in addition to tidal influence. The upper Sego in the Harley Dome area

contains a diverse trace fossil assemblage (11 different traces), dominated by fully marine traces

with some heavily bioturbated intervals (I.I. ≥ 4) (Droser and Bottjer 1986).

The transition from the upper Sego Fm into the Neslen Fm in the Harley Dome area is

marked by a change from deposits of tide-wave modified deltas to estuarine channels, tidal flats,

and floodplains. Directly overlying the tidal barforms of the Sego is a laterally extensive tidal flat,

a deposit typically flanking estuaries. Above the tidal flat deposits is the first coal, the traditional

marker for the basal Neslen. The transition from tidally influenced delta deposits into deposits of

tidal flats and swamps represents onset of transgression and estuary formation by flooding of a

tidal delta (Dalrymple et al. 1992). Evidence of tidal modification from potential estuary

confinement also persists into the Neslen Fm, with tidal indicators such as mud drapes, double

mud drapes, and mud lags being common. Some intervals in the Neslen contain a high-abundance,

diverse trace fossil assemblage (19 different traces) dominated by brackish traces such as Cy, Pl,

Sk, Td, Te, and Th with Co, dinosaur footprints, Op, Rh, rhizoliths and Si being common. Rare

traces include Ar, As, Be, Di, Fu, Lo, Ma, Pa, Ph, Pi, Sch, syneresis cracks, Tetrapod swim tracks,

Tr, and Zo.

60

The Neslen Fm in the Harley Dome area is interpreted to record deposits of an estuary (Fig

2.23). Two intervals within a fence diagram were chosen to capture the spatio-temporal

distribution of Neslen paleoenvironments (Fig. 2.8, 2.23). The first interval I-1 (2.8, 2.23) captures

deposits of distal-tidal-fluvial channels and tidal flats along an estuary (Fig. 2.8, 2.23, Appendix

A, Appendix D) in Middle Canyon, East Canyon, and Bryson Canyon. Paleocurrents in East

Canyon indicate paleoflow to the southeast, (134°, n=11, Appendix C). San Arroyo Canyon

deposits in I-1 are proximal tidal-fluvial channels and floodplain deposits (Fig. 2.8, 2.23, Appendix

A, Appendix B, Appendix C, Appendix D), more proximal than all other locations. This interval

(I-1) was chosen to illustrate the more distal components of the Neslen system, represented by

distal tidal-fluvial channels and tidal flats formed during the early stages of transgression. Interval

two (I-2) (Fig. 2.8, 2.23) was chosen to show the more proximal deposits of the Neslen as the

system graded into the purely fluvial deposits of the Bluecastle Tongue. I-2 in East Canyon

contains deposits interpreted as distal tidal-fluvial channels and in Middle, Bryson, and San Arroyo

Canyon as proximal tidal-fluvial channels (Fig. 2.8, Appendix C). Paleocurrents from Middle

Canyon indicate that paleoflow was to the east (90°, n=2) and those from East Canyon indicate

paleoflow to the south (182°, n=3) (Appendix B, Appendix C). The transition into the fluvial

Bluecastle Tongue of the Castlegate, is characterized by relatively thick, blocky sand packages

containing little mud and no marine or brackishwater ichnology.

Overall, the Neslen Fm at Harley Dome records the transition from distal tidally-influenced

deposits in the basal Neslen that include distal tidal-fluvial channels and tidal flats to more

proximal deposits including proximal tidal-fluvial channels and floodplain deposits to purely

fluvial channels of the Bluecastle Tongue (Fig. 2.8, 2.23). The presence of the Teredolites

ichnofacies in several intervals throughout the Neslen indicates periodic marine incursions. The

61

presence of carbonates in East Canyon indicates a more distal position within the estuary where

marine conditions exist and are more conducive for algal mat and carbonate production. The lack

of wave influence, and abundance of tidal indicators support the interpretation of the Neslen as

tidally influenced estuarine deposits protected from wave modification and typically near marine

water rather than at a more proximal position in the estuary.

62

Figure 2.23: Paleoenvironmental reconstruction of the Neslen Fm near Harley Dome, UT. Flood and ebb tide directions are based

on paleocurrent data shown in the rose diagram from the Neslen Fm (n = 157). Tidal barforms of the reworked tidal deltas of the

upper Sego are also shown. Modified from Emery and Myers (1996).

63

Sequence Stratigraphic Framework for the upper Sego and Neslen fms

The location of the upper Sego and Neslen fms within a sequence stratigraphic framework

remains controversial. This includes the systems tracts the deposits represent but also the location

of sequence boundaries within the deposits. The upper Sego is commonly placed in the LST due

to the abundance of progradational deposits of tidally influenced deltas (Van Wagoner 1991; Willis

and Gabel 2003; Olariu et al. 2015), with the Neslen Fm deposited above placed in the TST

(Yoshida et al. 1996; McLaurin and Steel 2000; Hettinger and Kirschbaum 2002; Shiers et al.

2017). In the Harley Dome, UT area in all four canyons within the study area, the upper Sego is

dominated by tidal barforms near the Sego-Neslen transition. Tidal barforms can be found either

as reworked tidal delta deposits or within estuaries (Pontén and Plink-Björklund 2009; Rossi and

Steel 2016). Deltaic tidal bars are identified based on poor sorting (grain sizes varying from very-

fine to granule), overall progradational stacking patterns, basinward dominated paleocurrents, and

vertical and lateral association with deltaic paleoenvironments (Pontén and Plink-Björklund 2009;

Rossi and Steel 2016). Estuarine tidal bars are identified based on well to very-well sorted deposits,

grain-sizes ranging from very-fine to fine, overall retrogradational stacking patterns with marine

mudstones above, landward dominated paleocurrents, and vertical and lateral association with

estuarine paleoenvironments (Pontén and Plink-Björklund 2009; Rossi and Steel 2016). In the

Harley Dome, UT area, only the upper 35 m of the upper Sego was measured and the deposits

were dominated by tidal barforms. These tidal barforms are well to very-well sorted, range in

grain-size from very-fine to upper-fine grained, and are capped by bioturbated marine mudstone

and siltstone (Appendix A, 0-35 m). Although no paleocurrent data was obtained from this interval,

shallow migration and oblique growth are interpreted from sigmoidal bedding, trough cross-

stratification, and strong tidal indicators such as double mud drapes (Willis and Gable 2003; Rossi

64

and Steel 2016). Association with estuarine paleoenvironments such as distal tidal-fluvial channels

and tidal flats suggests these tidal bars originated as deposits of the upper Sego deltas and were

reworked during rising sea level in an estuary. This places the upper Sego in the Harley Dome area

in the TST. The transgressive lag normally found between the LST and TST is not visible in the

upper Sego interval measured in East Canyon and is thus is likely to be lower in the section.

The Neslen Fm in the Harley Dome, UT area represents the continuation of the TST

observed in the upper Sego that resulted in estuarine deposits originating from flooding of deltas

at the end of the LST. The Neslen Fm is overlain by the Bluecastle Tongue of the Castlegate

sandstone, which is interpreted as preserved braided fluvial deposits. Between the upper Sego-

Neslen transition and the Bluecastle Tongue, paleoenvironments of the Neslen exhibit an overall

shallowing up, dominated by distal deposits in the lower to middle Neslen (distal tidal-fluvial

channels and tidal flats), and more proximal deposits in the middle to upper Neslen (proximal tidal-

fluvial channels and floodplain), overlain by fluvial deposits. Within this overall shallowing

pattern, there are multiple marine flooding surfaces identified by the Teredolites ichnofacies or

highly bioturbated intervals with fully marine trace fossils such as Siphonichnus or Rhizocorallium

(Appendix A, East Canyon, 82-84 m). These multiple marine flooding surfaces could represent

the maximum flooding surface (MFS) if they can be correlated regionally, but nonetheless

represent multiple periods of marine incursion within the overall transgressive Neslen. Rather than

a typical retrogradational pattern of a TST, MFS, and then the HST, the Neslen is more

aggradational within the TST, and the MFS occurs in the upper Neslen with the Bluecastle Tongue

of the Castlegate signifying the beginning of the HST.

65

Regional Comparative Analysis of the Neslen Fm.

In order to better understand the distribution of Neslen depositional systems in the Book

Cliffs region a comparison is made to paleoenvironmental interpretations from three additional

studies that focus on the Neslen: Shiers et al. (2014), Crescent Canyon; Olariu et al. (2015), Floy

Canyon; and Aschoff et al. (2016), Coal Canyon (Fig. 2.3). In contrast to interpretations from the

studies of Shiers et al. (2014), no evidence of deposits of purely fluvial channels were documented

in the Neslen Fm at Harley Dome. In addition no deposits of delta distributary channels, mouth

bars, or other deltaic paleoenvironments such as those described by Olariu et al. and Aschoff et al.

(2016) are found in the Neslen near Harley Dome. No deposits of washover fans or bayhead deltas

as described by Shiers et al. (2014), Olariu et al. (2015), and Aschoff et al. (2016) were identified.

Each of the three prior outcrop studies of the Neslen Fm identified bayhead deltas based

on coarsening upward successions of inclined heterolithic stratification with paleoflow

measurements oriented parallel to bounding surfaces and facies breaking trace fossils (Shiers et al.

2014; Olariu et al. 2015; Aschoff et al. 2016). Although the Neslen deposits near Harley Dome do

exhibit inclined heterolithic stratification and have some architectural similarities with deposits of

deltas such as sheetlike geometries, and marine to brackishwater ichnology, sandbodies are

dominated by fining upward sequences with paleoflow at a high angle to bounding surfaces, and

multiple incision surfaces. This evidence resulted in the interpretation of inclined heterolithic

stratification as lateral accretion surfaces on point bars of tidal-fluvial channels rather than inclined

heterolithic stratification on bayhead deltas. Some deposits could be mistaken for coarsening-

upward successions because coarser-grained tidal-fluvial channels may overlie finer-grained tidal

flats that overlie coals and carbonaceous shales. These coarsening upward sequences are not

deltaic but instead record tidal flat development adjacent to swamps and incision of tidal-fluvial

66

channels into tidal flats. The distinction between tidal-fluvial channels and bayhead deltas has

important implications in terms of sandbody and shale geometries. Bayhead deltas exhibit overall

lobate geometries and are typically overlain by distributary channel deposits and underlain by

prodelta or middle estuary deposits (Aschoff et al. 2016). Tidal-fluvial channels in the Harley

Dome area are preserved as isolated arcuate channel forms that may be sinuous, or as laterally

extensive sheets if a channel complex is preserved. Tidal-fluvial channels are overlain by

floodplain deposits and underlain by tidal flats or floodplain deposits. Deposits of bayhead deltas

and tidal-fluvial channels have different geometries and associated facies, and thus should be

treated differently by reservoir modelers.

The Neslen near Harley Dome is interpreted as being on the flank or distal portion of an

estuary, rather than at the head of the estuary. This interpretation is based on the absence of

bayhead deltas, a classic head of estuary deposit, and presence of marine indicators including

marine ichnology, the marine flooding surface of the Teredolites ichnofacies, and carbonate

deposits, none of which were described by Shiers et al. (2014), Olariu et al. (2015), and Aschoff

et al. (2016). The deeply incised tidal-fluvial channel present in San Arroyo Canyon is also a

marine proximity indicator due to the presence of marine ichnology within the deposits.

Implications for Reservoir Modelers

Reservoir models of such highly heterogeneous reservoir analogues as the Neslen Fm are

crucial to improve recovery from complex paralic reservoir systems with a high mud content

(>30%). The Neslen Fm was a producing gas play in the Uinta Basin, but could also be used as an

analogue for tidally-influenced reservoir heterogeneous systems with heterolithic channel bodies

67

(IHS) such as the McMurray and Viking Fms of Alberta, and the Prince Creek-Ugnu of the North

Slope of Alaska (Reinson et al. 1988; Flaig et al. 2011; Musial et al. 2012). A major component in

tidally-influenced systems that affects reservoir quality and compartmentalization is mud content

(Pranter et al. 2007; Musial et al. 2012). Mud serves as a barrier and baffle to flow and must be

considered when predicting subsurface reservoir quality and flow characteristics (Pranter et al.

2007). The Neslen Fm contains many scales of internal heterogeneities including <10 mm small-

scale mud drapes on numerous sedimentary structures up to drapes as large as 0.5 m scale mud

drapes on IHS. The best reservoirs in the Neslen Fm outcrop analogue would be the sandy tidal

flats due to low mud content and large lateral extent (100s of m) or the laterally extensive distal to

proximal tidal-fluvial channels deposits (10s to 100s of m). Tidal fluvial channels are heterolithic,

however, which provide many barriers to flow. Floodplain deposits are non-reservoirs because

they are composed of finer grained deposits. Coals are thought to be the source of the

hydrocarbons produced from the Neslen (Pitman et al. 1987).

68

CONCLUSIONS

The Sego and Neslen Fms near Harley Dome contain tidally modified deposits that can be used as

a reservoir analogue for tidally influenced paralic systems.

Deposits of the upper Sego Fm include those of tidal barforms and interdistributary bays.

Deposits of the Neslen Fm include those of distal tidal-fluvial channels, tidal flats, proximal

tidal-fluvial channels, and floodplains.

A total of 28 trace fossils were identified in the upper Sego and Neslen fms with 14 fully

marine traces, 11 facies breaking traces, 1 freshwater trace, and 2 continental traces.

Ichnology proved critical to identifying distal vs. proximal tidal-fluvial channels, tidal flats

vs. floodplain deposits, and potential flooding surfaces. The Teredolites ichnofacies is

present in several intervals in the Harley Dome Neslen and is indicative of a marine

incursions.

Overall the Sego-Neslen system evolved from 1) wave and tide modified deltaic deposits

to 2) estuarine tidal flats and distal-tidal fluvial channels to 3) proximal tidal-fluvial

channels and floodplain deposits, and ultimately to 4) fluvial channels and floodplains of

the Bluecastle Tongue of the Castlegate.

In contrast to recent studies of the Neslen Fm, bayhead deltas and deltaic deposits were not

identified. Inclined heterolithic stratification in outcrops near the Harley Dome preserve

point bars of tidal-fluvial channels

69

Stromatolites, oolites, and shells identified in two intervals within Neslen Fm in East

Canyon and record deposition in a distal position along an estuary. This is the first time

that carbonates have been identified in Neslen

The tidal bars of the upper Sego have been interpreted as estuarine, thus placing the upper

Sego within the TST.

The aggradational stacking pattern of the Neslen Fm into the Bluecastle Tongue above

places it within the TST and the Bluecastle Tongue in the beginning of the HST. The

transgressive lag present at the transition from LST to TST is likely within the Sego, below

the studied interval. The MFS is likely represented by one of the many marine incursions

identified in the middle to upper Neslen.

Interpretations of the Neslen Fm near Harley Dome as dominated by distal to proximal

tidal-fluvial channels and tidal flats as well as the recurrence of the Teredolites ichnofacies

and the lack of bayhead delta deposits suggests a distal position along an estuary. Abundant

marine ichnology, recurring carbonates, deeply incised tidal-fluvial channels, and the lack

of wave influence and dominance of tidal indicators also supports deposition within a distal

yet protected estuarine environment

Examination of such outcrop analogues as the Neslen Fm are essential to develop accurate,

geocellular reservoir models of heterolithic, paralic reservoir systems.

70

Chapter 3: Future Studies in the Neslen Formation

Future work that could ultimately supplement the work done in Chapter 2 of this thesis on

the Neslen in the Harley Dome area of the Book Cliffs would include a geocellular reservoir model

and streamlined flow simulation to assess how the various scales of heterogeneity within the

Neslen Fm could affect reservoir performance. A similar study performed by Pranter et al. (2007)

on a fluvial point bar in an outcrop of the Williams Fork Formation in the Piceance Basin

developed a reservoir model by geostatistically populating facies and petrophysical data, and flow

simulating the model. The goal was to assess how mud-drape continuity on lateral accretion

surfaces affected reservoir performance. A modeling study such as this on the Neslen distal tidal-

fluvial channels at Harley Dome could provide a workflow from outcrop to subsurface, evaluate

the distribution of facies seen in outcrop in three-dimensions, examine sandbody and shale

geometries established from paleoenvironmental reconstruction, and identify important

heterogeneities to inform a reservoir model, which could be ultimately flow simulated to assess

the effects of increased heterogeneity on flow.

To build such a model, multiple data sets would need to be integrated to produce a

meaningful model. In the case of the Neslen Fm near Harley Dome, an outcrop of amalgamated

distal tidal-fluvial point bars, named the Whiskey Tango Foxtrot (WTF) outcrop in East Canyon,

is an ideal candidate for this study. The outcrop is well exposed, relatively easily accessed, and is

highly heterogeneous. Multiple stratigraphic sections along the entire extent of the outcrop could

be measured, including paleocurrents if possible, and plugs for porosity and permeability data

could be collected. In order to capture the three-dimensionality of the sandbody, the same interval

should be assessed similarly in nearby outcrops.

71

Reservoir model construction could be done in any 3-D geostatistical modeling software

such as Halliburton’s DecisionSpace or Schlumberger’s Petrel. Measured sections for outcrops

could be uploaded into the software and georeferenced. If subsurface data exists it could be

uploaded into the modeling software as well. Measured sections can be used to geostatistically

populate a user-defined model container with facies. These facies can then be geostatistically

populated with petrophysical data obtained from outcrop or nearby equivalent reservoir data. Once

the model is populated with porosity and permeability, a streamlined flow simulation can be run.

Multiple iterations of a flow simulation could be run to quantitatively assess how flow is affected

by multiple scales of heterogeneity. These results could then be compared to see which scale of

heterogeneity had the greatest effect on flow within this tidal-fluvial channel could be compared

and contrasted to the results of the Pranter et al. (2007) study.

Although a robust data set was not acquired, Appendix F contains a short chapter detailing

a workflow from outcrop to basic 2D geocellular facies model in Petrel of the WTF outcrop in

East Canyon. This workflow does not include any geostatistical population of facies or

petrophysical properties nor was the model run through flow simulation. It does however provide

a basic outline and workflow for a future study.

72

Appendix A

Appendix A contains drafted composite sections of the upper Sego and Neslen fms in

Middle Canyon, East Canyon, Bryson Canyon, and San Arroyo Canyon in the Harley Dome, UT

area of the Book Cliffs. These measured sections are located in a supplementary PDF on the

attached CD-ROM under the file name “Detailed Composite Measured Sections” as well as in a

large pull-out in the Thesis for higher resolution viewing of the figure.

73

Appendix B

Appendix B contains paleocurrent data recorded from trough-cross stratification, current

ripples, primary current lineation, rib and furrow, dip of bounding surfaces, and accretion

directions. Paleocurrent data includes 157 measurements taken from Middle Canyon, East Canyon,

Bryson Canyon, and San Arroyo Canyon. Raw data is shown along with rose diagrams. Vector

mean polar is the average paleocurrent angle for all values in one group and is represented by an

arrow along the outer edge of the rose diagram. Vector mean length polar is a value to

quantitatively assess the amount of variation in paleocurrent angles in that grouping. Mean length

values range from 0-1, with a value closer to 0 indicating greater variation and a value at 1

indicating no variation in paleocurrent angles in that grouping. Paleocurrent data is included as a

PDF file named “Paleocurrent Data” on included CD-ROM.

74

Appendix C

Appendix C contains detailed measured sections as in Appendix A with paleocurrent data

included as rose diagrams on the measured sections in the locations paleocurrents were measured.

Each rose diagram includes an arrow along the outer circle indicating the mean paleocurrent angle

for that grouping as well as the number of measurements included in that rose diagram (n=#).

Measured sections with paleocurrent data are included in a PDF titled “Measured Sections with

Paleocurrent Data” on the attached CD-ROM.

75

Appendix D

Appendix D includes a higher-resolution version of the fence diagram found in Figure 2.8.

This figure includes all composite measured sections with paleoenvironmental interpretations

made across the four canyons. This figure is included as a PDF on the attached CD-ROM named

“Detailed Fence Diagram”.

76

Appendix E

Appendix E includes four videos taken with the DJI Phantom 4 drone in each canyon

studied. Each video is named for the canyon in which it was filmed. These videos are included in

the attached CD-ROM as .MOV files.

77

Appendix F

Appendix includes a write-up of the first few steps of an outcrop to geocellular model

workflow mentioned in Chapter 3: Potential Future Work in the Neslen Formation. The workflow

is preliminary. This write-up is included as a PDF named “2D Geocellular Modeling Study of the

Neslen Fm” on the attached CD-ROM.

78

Appendix G

Appendix G includes high-resolution imagery of the 2D facies distribution of the WTF

outcrop drafted in Adobe Illustrator, and the geocellular model created in Petrel informed by data

from the 2D facies distribution figure. These figures are included as PDF files named “WTF

Illustrator Figure” and “WTF Petrel Model” on the attached CD-ROM.

79

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The Neslen Formation near Harley Dome, Book Cliffs, Utah

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