UNIVERSITY OF UTAH COLLEGE OF MINES AND EARTH SCIENCE

Quantitative Study of The Parowan Gap, From Lower

Jurassic to Present: Iron County Utah.

Michael Starkie

23rd May 2014

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Table of Contents

1. Abstract 3

2. Introduction 6

3. Geological Settings 8

4. Rock Unit Descriptions 9

a. Navajo Sandstone (Jn) Lower Jurassic 9

b. Carmel Formation (Jc) Middle Jurassic 10

c. Straight Cliffs Formation (Ksc) Late Cretaceous 11

d. Iron Springs Formation (Kis) Late Cretaceous 14

e. The Conglomerate of Parowan Gap (Kpg) Late Cretaceous to Paleocene 16

f. Grand Castle Conglomerate (Kgc) Late Cretaceous to Paleocene 16

g. The Claron Formation (Tc) Paleocene-Eocene 17

h. Volcanic (Oligocene) 20

i. Landslides (Qls), Colluvium (Qfo), and Valley Fill (Qal) Quaternary 21

5. Depositional Environments 21

6. Structural Description and Timing Relationship 24

7. Geological History and Discussion 27

8. Conclusion 31

Acknowledgments 33

References 34

Appendix 35

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1. Abstract

The Parowan Gap is a nearly three mile long canyon apart of the Red Hills, located to the west

of the town of Parowan, in Iron County Utah. Parowan Gap contains strata as old as the Lower

Jurassic, and up to the present day. The Lower Jurassic Navajo Sandstone (Jn) is the oldest

lithofacies found in the mapped area (Appendix: 1a). It represents the largest known desert in

geological history (Boggs, 2012). Evidence for this is found in the preserved grain falls, grain flows,

and cross bedding features that are still preserved in its fractured, weathered surface. The Navajo

Sandstone (Jn) can be as thick as thick as 300-600 m within the Colorado Plateau, but within the

Parowan Gap it is only about 100 m thick (Threet, 1963).

The Navajo Sandstone (Jn) is followed by the carbonate deposits of a shallow marine

environment of the Middle Jurassic Carmel Formation (Jc). The Carmel Formation (Jc) was

deposited as a result of the Cordilleran Highlands that were to the west, which rose to great heights

causing the eastern foredeep basin to subside. Warm shallow waters had moved into the area as the

basin became lower. The Carmel Formation (Jc) contains deposits of limestone, evaporates, and

sandstone (Hintze & Kowallis, 2009; Stokes, 1986). Algal deposits preserved some of the bedding

structures that were destroyed by later thrusting events. Other bedding features still found include

ripple marks, and micrites. The Carmel can reach thicknesses of 150 m, but only a few meters are

exposed in the Parowan Gap (Threet, 1963).

During the late Cretaceous, the surrounding area of the Parowan Gap experienced the first of

several thrusting events. The Sevier Orogeny pushed from the west creating highlands that stretched

from present day Mexico to Alaska. As a result of the highlands to the west, the North American

Seaway flooded the low-lying area to the east of the highlands in the foredeep basin, from the Gulf

of Mexico to Alaska. Deposits of shallow marine and marshy swamps are found; the Straight Cliffs

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Formation (Ksc) represents the deposits during this time (Hintze & Kowallis, 2009; Stokes, 1986).

Nearly 400 m of Straight Cliffs Formation (Ksc) is exposed in the Parowan Gap. Found in the

Straight Cliffs Formation (Ksc) are deposits of sandstone, limey sandstone, coal deposits, and

marine fossils such as oysters. The Straight Cliffs Formation (Ksc) is deposits of a prograding beach

and near-shore marine environments.

As the Sevier Highlands pushed farther inland, the Carmel Formation (Jc) and the Straight Cliffs

Formation (Ksc) were thrusted up, and overturned in a geosyncline. The geosyncline was later

eroded down, and all that remains are the over turned beds of the Carmel Formation (Jc) and the

steeply dipping beds of the Straight Cliffs Formation (Ksc). Geopedal indicators found in the

Carmel Formation (Jc) confirm this.

The Iron Springs Formation (Kis) of the Late Cretaceous contains records of stacked alluvial

channels that flowed to the east from the Sevier Highland from the west. The Iron Springs

Formation (Kis) is approximately 20 m of exposed sandstones and channel cuts in the Parowan

Gap. The Iron Springs Formation (Kis) contains footprints of Dinosaurs such as a single hadrosaur

footprint found in a block that had fallen from the cliffs in the Parowan Gap. The Iron Springs

formation (Kis) is mostly made of medium-to-fine grain sandstones with intermittent volcanic tuff

deposits. The deposits of the Iron Springs Formation (Kis) are that of a prograding beach

environment.

Near the boundary of the Cretaceous and the Paleocene, the Conglomerate of Parowan Gap

(Kpg) was deposited. It is roughly 4-5 m thick; composed of rounded quartzite clasts 5-20 cm in

size. The Conglomerate of Parowan Gap (Kpg) represents alluvial fan deposits of large detritus shed

from the Sevier Highlands. During deposition of the Conglomerate of Parowan Gap (Kpg), another

thrusting event piggybacked the conglomerate over the Iron Springs Formation (Kis). It was later

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eroded down, and contained in a small portion within the Parowan Gap area before the Grand

Castle Conglomerate (Kgc) was deposited on top. The Conglomerate of Parowan Gap (Kpg) also

sits on top an angular unconformity of the Straight Cliffs Formation (Ksc). Meaning the Straight

Cliffs Formation was uplifted, overturned and eroded down before the Conglomerate of Parowan

Gap was deposited on top of it. The Grand Castle Conglomerate (Kgc) is approximately 35 m of

conglomerate topped with 4 m mottled limestone. Like the Conglomerate of Parowan Gap (Kpg),

the Grand Castle Conglomerate (Kgc) represents alluvial fan deposits, followed by shallow marine

or lacustrine limestone.

After the thrusting events of the Sevier and Laramide Highlands, and the waters retreated from

the North American Interior Seaway, large interior fresh water lakes filled the low lying areas. These

were Lake Flagstaff and Lake Claron (Stokes, 1986). The Claron Formation (Tc) was deposited at

this time. Approximately 15-20 m is exposed of the Claron Formation (Tc) in the Parowan Gap. It is

composed of conglomerates near its basal unit, gray lacustrine limestones with interfingering alluvial

conglomerates in the middle, and topped with medium-grain sandstones near the top units. The

Claron Formation (Tc) often has a distinct deep red color.

During the Oligocene, the Farallon Plate which was being subducted under the North American

plate at a steep oblique angle separated from the mass of the Farallon Plate in a slab pull. About 40

Ma intrusive mantle material began to make its way to the surface in Northern Utah as a result of

the slab pull (Hintze & Kowallis, 2009). Approximately 20-30 Ma, the intrusive material made its

way to southern Utah. The result was massive volcanic events. The Parowan Gap area has three

volcanic tuffs from three separate events. The Brian Head Tuffaceous Sandstone (Tbh) is a white

volcanic ash. It is weakly consolidate, and highly brittle. Next is the Wah Wah Springs Tuff (Tnw)

that was deposited on top of the Brian Head Tuff (Tbh). The Wah Wah Springs Tuff (Tnw) is a

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crystalline volcanic tuff. The last is the Isom Tuff (Ti). This is a strongly welded tuff devoid of

crystalline structures. The deposits found in the Parowan Gap are a result of heavy and dense

volcanic material from the Isom Tuff (Ti) and the Wah Wah Springs Tuff (Tnw) being deposited on

top of the weaker Brian Head Tuff; it is believed to have caused a massive landslide. An odd thrust

fault found near the west entrance of the Parowan Gap, on the north side of the highway that runs

through the canyon, pushed the odder Carmel Formation (Jc) on top of the much younger Claron

Formation (Tc). This thrust was believed to have been the result of this massive landslide

(Appendix: 1a).

The Red Hills west of the town of Parowan, Utah are a horst once part of the Colorado Plateau.

They separated from the Colorado Plateau as a result of Basin and Range Extension which began 17

Ma (Hintze & Kowallis, 2009; Threet, 1963). Tectonics forces changed on the west coast as the last

of the Farallon Plate was subducted under the North American Plate. This allowed the western

portion of the North American Plate, which was under compressional stresses for millions of year,

to begin to extend westward. The westward extension continues to this day. The Red Hills are still a

tectonically active area. Normal faults can be found throughout the Parowan Gap area. These

normal faults offset some of the formations as much as 30 m. The Parowan gap is also under going

active erosion. Weathering, ice wedging, and biological forces are actively breaking down the rocks.

Numerous landslides and colluviums are found throughout the mapping area; a result of active

erosional process.

2. Introduction

The area of study is the nearly three mile long Parowan Gap (Appendix 1a). The Parowan

Gap is part of the larger Red Hills of Iron County, west of Parowan, Utah. The Red Hills is a horst

that separated from the Colorado Plateau, forming the adjacent Cedar Valley; a result of Basin and

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Range extension which started approximately 17 Ma. The Parowan Stream meandered through the

canyon forming the cliff walls and exposing the strata before Basin and Range extension began. As

the range moved west the stream was subsequently diverted away from the Parowan Gap area.

The Parowan Gap consists of several rock units. The oldest unit is the Lower Jurassic

Navajo Sandstone (Jn); followed by the Carmel Formation (Jc) (Middle Jurassic); the Straight Cliff

Formation (Ksc) (Late Cretaceous); Iron Springs Formation (Kis) (Late Cretaceous); Parowan Gap

Conglomerate (Kpg) (possibly Late Cretaceous to Paleocene?); the Grand Castle Conglomerate

(Kgc) (possibly Late Cretaceous to Paleocene?); and the Claron Formation (Tc) (Paleocene-Eocene).

The Parowan Gap also contains several volcanic units all occurring during the Oligocene. They are

the weakly cemented Brain Head Tuffaceous Sandstone and Tuff Breccia (Tbh), the Wah Wah

Springs Tuff (Tnw), and the strongly welded tuff of the Isom Formation (Ti). There are also

numerous Quaternary landslides, colluvium, and valley fill in the region too. The region has been

faulted, thrusted up, and overturned during the Sevier Orogeny in the Late Cretaceous, and then

dropdown and portions eroded by normal faulting from Basin and Range extension starting in the

Miocene.

The goal of this project was to map the region surrounding the Parowan Gap in order to

better understand the dynamics of the thrusting events resulting from the Sevier Orogeny, and the

later extension of the Basin and Range, and how both events affected the various lithofacies. It was

also pertinent to understand the environmental conditions of each lithofacies during the time of

their deposition. The mapping consisted of determining the contacts between formations, the

relationship between formations (unconformities), descriptions of each lithofacies, and any

geological hazards such as landslides or faults. Tools used were the Parowan Gap 7.5 Minute

Topographic Quadrangle enlarged by 200% (Appendix: 1a), and a Brunton Hand Transit.

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3. Geologic Settings

During the Lower Jurassic, the area surrounding the Parowan Gap was a foredeep basin east

of the Cordilleran Highlands which were to the west. The Cordilleran Highlands would create the

largest know desert in geological record, spanning nearly 7 states (Appendix: 4a) (Blakey, 2011;

Boggs, 2012) . Towards the Middle Jurassic, the area surrounding the Parowan Gap was flooded by

the Sundance Seaway which approached from the north (Appendix: 4b). Southern Utah was near the

southern most margin of the Sundance Seaway (Blakey, 2011). Deposits of this area are both

limestone and sandstone, which confirms that the mapped area was near the southern shore of the

Sundance Seaway.

During the Late Cretaceous, tectonic forces pushed the land up resulting in the Sevier

Orogeny. The area of Parowan Gap was just to the east of the highlands, in a foreland basin (Hintze

& Kowallis, 2009). At this time too, the North American Interior Seaway which stretched from the

Gulf of Mexico to Alaska was to the east of the area. Detritus shed from the Sevier Highlands were

transported east to the inland sea. Deposits of the Straight Cliffs Formation (Ksc) are not found any

farther west, putting the Parowan Gap as the western most margin of the North American Interior

Seaway (Appendix: 4c) (Blakey, 2011; Hintze & Kowallis, 2009).

From the Paleocene through to the Miocene, the Indian Peak Volcanic Center which lay to

the west of the Parowan Gap would see intense volcanic activity (Hintze & Kowallis, 2009). Thick

deposits of ash, tuff, and welded tuff would be deposited in the area surrounding the Parowan Gap

(Hintze & Kowallis, 2009). Parowan Gap also sits south-southeast from the Marysvale Volcanic

Center, which may have also contributed to the deposits of volcanic material (Hintze & Kowallis,

2009). The Indian Peak Volcanic Center is responsible for the Isom Formation (Ti) and Wah Wah

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Springs Tuff (Tnw); where the Marysvale Volcanic Center is believed to have formed the Brian

Head Tuffacesous Sandstones and Ash deposits (Tbh).

The Parowan Gap currently is on western margin of the Colorado Plateau. It is also on the

eastern margin of the Basin and Range Providence. Over the last 17 Ma, the Parowan Gap has since

been removed from the Colorado Plateau and has slowly moved westward as a result of Basin and

Range extension. Extension was caused by a shift in plate tectonics on the west coast of North

America causing a shift in stresses from compression to extensional. The extension westward

thinned the crust as much as 100 % its original thickness (Hintze & Kowallis, 2009). Normal faults

can be found throughout the area, offsetting formation several meters. The Parowan Gap has

experienced several normal faults cutting through and offsetting the formations as much as 30 m.

This process is still ongoing. The area of the Red Hills is a very active tectonic area. It will continue

to move westward. Along with being tectonically active, the Parowan Gap is also undergoing active

erosional forces. Weathering, ice wedging, and biological forces are actively breaking down the rock

units. The area of the Parowan Gap contains numerous landslides, colluvium deposits, and valley fill;

all evident forms of erosion.

4. Rock Unit Descriptions

a. Navajo Sandstone (Jn) (Lower Jurassic) The Navajo Sandstone crops out in Parowan Gap at the western end of the Canyon

(Figure: 4.a). It makes up the prominent twin-peaks at the west entrance at the narrowest portion. It

is where the Parowan Gap gets its “Gap” from. It is approximately 150 m thick, composed primarily

of quartz arenite sandstone. The sandstone in some portions is highly fractured by volcanic

landslides and faulting. The sandstone has also under gone hydrothermal alteration which destroyed

most bed form structures. The Navajo Sandstone is a medium-grain quartzite. The Navajo

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Sandstone has a desert patina of dark brown with a hint of red on weathered surfaces. On a fresh

surface, the Navajo Sandstone has a bright light white-to-yellowish color, which sparkles in direct

sunlight.

b. Carmel Formation (Jc) (Middle Jurassic)

The Carmel Formation crops out 3-4 m along the Carmel Thrust Fault in contact with the

Straight Cliffs Formation (Ksc). The Carmel Formation in the Parowan Gap contains both a light

gray limestone and a fine-grain brown sandstone. The limestone had become heavily fractured from

faulting. It was first fractured, then thrusted up. The fractures have been folded in “S” and “Z”

shape folds (Figure: 4.b). Bedding laminations have been preserved in the form of horizontal algal

deposits. Laminations are 2 cm thick. Within the outcrop are geopedal indicators which show the

beds have been thrusted up, and over turned in this area. It is dipping steeply to the west at

approximately 50°. The limestone contains fossils of brachiopods, and crinoids. This classifies the

limestone as a fossiliferous biomicrite.

In other areas of the Parowan gap, the Carmel Formation limestone is far less fractured. It

tends to fracture along its bedding plane in sheet like separations. Another feature to identify the

Figure 4.a: Navajo Sandstone (Jn) cliffs covered

in Native American petroglyphs at the western

entrance of the Parowan Gap, Parowan, Utah.

(Picture is facing north).

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Carmel Limestone is that it often contains manganese-oxide dendrites. They are dark gray tree-like

branches along bedding planes.

c. Straight Cliffs Formation (Ksc) (Late Cretaceous)

The Straight Cliffs Formation is prominent steeply dipping overturned fins near the middle

of the canyon (Figure: 4.c.1). They dip steeply towards the west about 60°-70°. The Straight Cliffs

are bound between then Iron Springs and Carmel Thrust Faults. The Straight Cliffs become more

steeply dipping the farther east along contact. There are four fins in total. The fins represent

different depths of a marine environment, with the middle fin being the deepest, and the lower and

upper fins being shallower. Total thickness observed for the Straight Cliffs Formation was

approximately 400 m.

The basal deposit is the western most fin which contact with the Carmel Formation. Here

2-2.5 m thick medium-grain tan sandstone crops out. The rocks have been fractured and have been

filled with calcium carbonate veins. Above this is a 3-4 m sandy conglomerate. This contains pebbles

3-5 cm in size. The matrix is similar sandstone to the lower sandstone bed. It is medium-grain tan

sandstone. It is dominantly matrix with pebble spaced in clumps with a large portion of matrix

separating clumps.

Figure 4.b: Carmel Limestone of the Carmel

Formation (Jc). This portion sits along the Carmel

Straight Cliff Thrust Fault in Parowan Gap,

Parowan, Utah. Notice the folding of the unit.

(Ruler in for scale)

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The middle fins begin with 2 m thick medium-grain sandstone that contains trough-cross

bedding 2-3 cm thick, and pebbles lags are 3-5 cm thick. It is followed by 0.5 - 1 m planner

laminated medium-grain sandstone bed, with laminations 2-3 cm thick. Next is 1 m planner

laminated medium-fine grain tan sandstone. This bed is highly weathered, and contains soft

sediment deformation and elongated iron concretions (Figure: 4.c.4). The laminations that are

preserved are approximately 2-3 cm. The last portion of this fin is 3 m thick medium-coarse tan

sandstone. This sand stone also contains soft sediment deformation and elongated iron concretions,

along with tangential trough-cross bedding and parallel lamination that are approximately 2-3 cm

thick.

The next fin, near an abandoned coal mine, begins with 4 m thick medium-fine grain

sandstone with calcium carbonate cement. It is a tan sandstone that is fining upwards with

preserved oyster beds (Figure: 4.c.2), with some representation of oyster burrows. The tangential

cross-bedding transition into planner lamination as the strata becomes younger. This is followed by

8 m of unexposed bedding before 3-4 m fine-grain sandstone-to-silty. It is the fine sandstone that

has weathered brown with a hint of red; a fresh surface is light tan. Within the sandstone is a 75 cm

bed of silty sandstone. The cement is also a calcium carbonate and effervesces with acid. There is

nearly 100 m of unexposed strata till the next fin.

The top of the Straight Cliffs Formation begins with 4 m medium-grain planner laminated

sandstone. This bed contains ripple marks 1-2 cm in size, followed by 3 m of unexposed rock. This

is followed by 2-3 m of planner laminated (2-3 cm) medium-grain sandstone. This is again followed

by 5 m of unexposed rock. Near the top is 2-3 m of medium-grain tangential cross-bedded

sandstone with 2-5 cm thick pebble lags. This is followed by 0.5 m planner laminated medium-grain

sandstone. Last is a 0.5 m of oyster coquina (Figure: 4.c.3). The oysters are approximately 5 cm long

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shells and are densely pack by fine-grain grayish sandstone. The oysters are aligned in the same

bedding plane, but the oysters are oblong and in place in all direction, including in the x, y and z

axes.

Figure 4.c.1: Straight Cliffs Formation (Ksc) in

Parowan Gap, Parowan Utah. This is the North side

of the canyon. Notice the steep angle the beds are

dipping

Figure 4.c.2: Oyster beds in the middle section of

the Straight Cliffs Formation (Ksc), in Parowan

Gap, Parowan, Utah.

Figure 4.c.3: Oyster coquina in the middle section of

the Straight Cliffs Formation (Ksc) in the Parowan

Gap, Parowan, Utah.

Figure 4.c.4: Elongated iron concretion of tree

bark in the middle section of the Straight Cliffs

Formation (Ksc) in Parowan Gap, Parowan, Utah.

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d. Iron Springs Formations (Kis) (Late Cretaceous)

The Iron Springs Formation has approximately 35 m of exposed units (Figure: 4.d.2). The

Iron Springs Formation is dipping slightly to the north-northeast at approximately 9°-15°. A block

that had fallen from the cliffs contains a single hadrosaur footprint. In the lowest visible unit is 1 m

thick fine-grain sandstone that is light brown in color. Bedding is planner laminated with beds 1-3

cm thick. Thin layers of silt are interbedded within the sandstone bedding (no more than 15% silt to

85% sand). There is a 50 cm silty layer that sits above which contains large amount of volcanic ash.

It is a fine mixture of white colored rock with a “boulder” or “blocky” appearance. A 50 cm fining

upward medium-to-medium-fine grain sandstone sits on top the tuffaceous sandstone layer. Above

many of these tuffaceous layers is a medium-fine grain sandstone layers which contains flute and

load casts structures.

The middle unit begins with 50 cm of a dark brown with a hint of red, medium-grain

sandstone. This also contains multiple channel cuts approximately 5 cm wide and 15 cm long. The

channel cuts are filled with course sand with some pebbles (> 3 mm). Above this bed is 1 m thick

planner laminated sandstone with bedding 2-3 cm fining upward. This bed is a brown color with

scattered iron concretions (2-5 cm) throughout. Several of the concretions formed from a mineral

replacement of ancient tree bark buried within the Iron Springs Formation at the time of deposition.

These concretions are often seen as cylindrical or elongated. Near the top of this bed (~ 25 cm) is

another tuffaceous sandstone. This is followed by a 1.5 m of planner laminated medium-fine grain

sandstone bed with laminations 2-3 cm thick, topped with 25 cm tuffaceaous sandstone. This is then

followed by 1.5 m medium tangential trough-cross bedded brown sandstone that contains 2-3 cm

concretion. Another 25 cm thick tuffaceous sandstone layer sits atop the sandstone. The last bed of

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the middle unit is 1 m thick fine sandstone that is a continuation of the fining upward trend with a

25 cm thick tuffaceous sandstone bed at the top.

The top unit of the Iron Springs Formation in the Parowan Gap begins with a 2.5 m layer of

weathered medium-grain light brown sandstone that fines upward. Due to the weathering, any bed

forms are difficult to see; however, it appears to contain some tangential trough-cross bedding. It is

than followed by a 2 m unexposed layer followed by 70 cm medium-fine grain light brown

sandstone with a few concretions. this is then followed by 4 m unexposed outcrop. The next layer is

a 3.5 m bed of fine brown-reddish sandstone. This sandstone is weathered and contains fluid escape

structures. This is followed by 2 m of unexposed strata. A 1.5 m channel-cut, filled with medium-

fine grain light brown sandstone. This layer also contains a few silty lenses approximately 2 m thick.

Beds are parallel laminated with thickness 5-8 cm. On top of this layer is 1 m tuffaceous sandstone.

It is topped by another 3 m of unexposed strata followed by a 1.5 m of pinkish medium-fine

sandstone with fine laminations (> 1 cm). The contact between the Iron Springs Formation (Kis)

and the Grand Castle Conglomerate (Kgc) is a 0.5 m purple to amber red paleosol; a disconformity.

Figure 4.d.1: Contact between the Iron

Springs Formation (Kis) and the Grand Castle

Conglomerate (Kgc). In Parowan Gap,

Parowan, Utah

Figure 4.d.2: Iron Spring Formation (Kis).

Notice the different layers seen in the

weathered layers. More weathered layer has

finer material with tuffaceous ash deposits.

Located in Parowan Gap, Parowan, Utah.

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e. The Conglomerate of Parowan Gap (Kpg) (Late Cretaceous to Paleocene)

The Conglomerate of Parowan Gap sits at an angular unconformity atop the over turned

beds of the Straight Cliffs Formation (Ksc), and blow the Grand Castle Conglomerate (Kgc). The

Conglomerate of Parowan Gap is approximately 4-5 m thick. Its distinguished features are that it is

almost entirely made of rounded quartzite clasts 5-20 cm in diameter, with few clasts larger than 20

cm. The quartzite clasts range in color from red, purple, and tan. The matrix is made of course sand

and pebbles (~1-2 cm). The conglomerate is poorly shorted. The weathered surface is a dark brown

with a hint of red. The noticeable difference between the Conglomerate of Parowan Gap and the

Grand Castle Conglomerate (Kgc) is its color and the material making up the matrix. Like the other

conglomerates, the Conglomerate of Parowan gap is cliff forming.

f. Grand Castle Conglomerate (Kgc) (Late Cretaceous to Paleocene)

The Grand Castle Conglomerate at the basal unit is a light gray to tan color with a slight hint

of red. The clasts making up the conglomerate are much larger at the base, decreasing in size

upwards. Clasts are 20-50 cm at the base to as large as boulders (Figure: 4.d.1). The clasts are mostly

rounded quartzite in a variety of colors. Higher in section, the clasts become smaller, and are made

of quartzite, limestone, and chert. The clasts are rounded and are poorly sorted. The matrix is coarse

sand. Within the Grand Castle Conglomerate are 1-2 m sand lenses made of coarse tan sandstone.

Some of these sand lenses can be as big as 3-4 m.

The cliffs of the Grand Castle Conglomerate are prominent along the North side of the

canyon towards the east entrance (Figure: 4.f). They rise approximately 20-25 m, then slopes slightly

in 4 m of unexposed rock before rising another 5-6 m. Like the other conglomerates, the Grand

Castle Conglomerate is cliff forming. The further up the Grand Castle Conglomerate, the clasts

become smaller in a fining upward sequence. The outcrops also become progressively redder

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towards the contact with the Claron Formation (Tc). Near the contact with the Claron Formation

(Tc), the clasts go from primarily quartzite clasts, to clasts that have an “ear wax” and “dark purple”

appearance. Clasts of chert and limestone are near the contact too. The top 2-3 m of the Grand

Castle Conglomerate is a reddish-purple mottled limestone with patches of white. This is an

important paleosol horizon that marks the boundary between the Claron Formation (Tc) and the

Grand Castle Conglomerate (Kgc). This limestone is heavily bioturbated and no longer contains

visible bed forms. The Grand Castle Conglomerate dips at a low angle towards the north-northeast.

g. The Claron Formation (Tc) (Paleocene-Eocene)

The Claron Formation sits on top of the Grand Castle Conglomerate (Kcg). It is also

dipping slightly at 10°-15° to the north-northeast. The basal units are medium-grain sandstone that

is a deep red color, approximately 1.5 -2 m thick. This sandstone has bits of litho-fragments (>1

mm). There are bits of white, black, and tan fragments. It is followed by approximately 3 m of

unexposed rock before a prominent cliff surface. The base of the cliff has a 0.5 m thick layer of a

Figure 4.f: Large Cliff face of the

Grand Castle Conglomerate (Red

Facies). It sits on top the tan

colored Iron springs Formation

(Kis). Located in Parowan Gap,

Parowan, Utah.

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light tan to white fine-grain sandstone-silt layer with no distinct bedding. Where it makes contact

with a 6 m tall conglomerate layer is an erosional scoured surface.

The conglomerate is approximately 6 m thick (Figure: 4.g.1). The matrix is deep red coarse

sand and pebbles. It is made of poorly sorted rounded clasts (10-15 cm), with clasts as big as 20

cm+. It is an extraformational conglomerate made of clasts of limestone, chert, and a variety of

colored quartzite. Within the conglomerate, are sand lenses that are anywhere from 0.5 m to 1.5 m

thick. They are spaced randomly throughout the conglomerate. They are made of medium-coarse

tan sandstone. Some have a tangential trough cross bedding that are 3-5 cm thick, other sand lenses

have parallel lamination 3-5 cm thick.

The top unit of the Claron Formation is limestone beds with outcrops 1-2 m thick. It is a

medium gray limestone with fossils of bivalves within it (biomicrite) (Figure: 2.g.2). Some

laminations 3-5 cm thick are preserved from algae. Walking along strike with the limestone, fingers

of conglomerate appear. These conglomerates are made of clasts 10-15 cm. The clasts are rounded

and poorly sorted. Clasts are composed mostly of quartzite, but limestone clasts are present. The

matrix is made of limey sandstone. Within the conglomerate are sandstone lens 0.5-1 m thick. They

are made of coarse tan sandstone with trough-cross bedding and some parallel laminated beds 2-3

cm thick. The limestone beds are the margins of the conglomerates with pebbles ~5 cm within

them, along with what appears to be bedding planes. Theses limestone beds and conglomerate beds

alternate frequently along the same line. They are most likely alluvial fan or stream deltas apart of a

lacustrine environment.

Atop the gray limestone, is a deep purple-to-reddish limestone approximately 1-1.5 m thick.

This limestone is similar to the mottled limestone seen in the Grand Castle Conglomerate (Kgc). It

also has a mottled appearance with no discerning bed forms. This sits below a 3 m sandstone

19

exposure. The sandstone is tan medium-grain sandstone. The lower 1.5 m has tangential cross-

bedding with bedding thickness 2-3 cm. The top 1.5 m has planner laminations (Figure: 4.g.3).

h. Volcanic (Oligocene)

Towards the western entrance of the Parowan Gap, lie three separate volcanic events. The

first event was the Brian Head Tuffaceaous Sandstone (Tbh) (~33 Ma) representing a basal surge

Figure 4.g.1: Conglomerate with sand lenses within

the Claron Formation (Tc) in Parowan Gap,

Parowan, Utah.

Figure 4.g.2: Gray limestone in the Claron

Formation (Tc) in the Parowan Gap, Parowan,

Utah.

Figure 4.g.3: Laminated medium-grain sandstone bed

in the Claron Formation (Tc) in Parowan Gap,

Parowan, Utah.

20

deposit. Cross-bedding can also be found in the small exposures. It is a weakly compacted white ash

with bits of none-volcanic litho-fragments in it. It is very brittle, and crumbles in your hand. Only

small outcrops of the Brian Head Tuff are exposed.

Deposited directly on top of the Brain Head Tuff (Tbh) is the Wah Wah Springs Tuff (Tnw)

(~30 Ma). The Wah Wah Springs Tuff (Tnw) is a dark pinkish volcanic rock that contains euhedral

crystals of mica, biotite and plagioclase (Figure: 4.h.2). In direct sunlight, the Wah Wah Springs Tuff

(Tnw) sparkles. Looking at adjacent hills, the Wah Wah Springs Tuff (Tnw) is dipping shallowly to

the northwest. It is weakly welded together and breaks much easier than the Isom Tuff (Ti).

The youngest aged volcanic rocks are the Isom Tuff (Ti) (~27 Ma). The Isom Tuff (Ti) is

dark gray with a hint of red and purple in it (Figure: 4.h.1). The Isom Tuff (Ti) also is devoid of

visible crystals, which is another way to distinguish it from the Wah Wah Springs Tuff (Tnw). The

Isom Tuff (Ti) contains fiamme which are lens shaped holes that align themselves parallel to each

other. From the fiamme, a strike and dip can be taken from an in place outcrop. The fiamme are

approximately 3-4 cm on a good exposure. The Isom Tuff is also strongly welded together, and is

hard to break.

The last volcanic unit is a combination of the threes volcanic tuffs. It is a Volcanic

Conglomerate (Qcv). It is distinguished by rounded clasts, and mixed volcanic rocks together

without any order. The clasts are not yet cemented together, and resemble colluvium deposits.

21

i. Landslides (Qls), Colluvium (Qfo) and Valley Fill (Qal) (Quaternary)

Numerous landslides and colluviums are found throughout the mapping area. The

Landslides (Qls) tend to preserve the orientation of the formations within the slide area, like

throwing a ball of mud on the ground. The landslides often appear to be tear-dropped shaped, with

the narrowest part at the top, and splay out at the bottom. The colluviums (Qfo) are inactive alluvial

fans. They tend to cover any exposed strata. The composition of the colluviums is a mixture of

different clasts from the surrounding formations. The clasts are usually very angular, ranging in size

as small as a pebble to as large as several meter diameter boulders. The matrix is coarse loose sand.

Finally, the Valley Fill (Qal) is all the material, rocks, and sediment that has eroded and transported

to the canyon floor.

5. Depositional Environments

Figure 4.h.1: Isom Tuff (Ti) with Fiamme.

Located in Parowan Gap, Parowan Utah.

Figure 4.h.2: Wah Wah Tuff (Tnw). Notice

the crystals of biotite and mica. Located in

Parowan Gap, Parowan, Utah.

22

The Navajo Sandstone (Jn) is the oldest of the formations in the Parowan Gap area, having

been deposited in the Lower Jurassic. The Navajo in this region is typically reddish medium-grain

well sorted quartz arenite sandstone (Biek, et al., 2009). It often is cliff forming and a prominent

feature on the western end of the Parowan Gap. In the Lower Jurassic, the environment was arid

caused by a rain shadow effect of the Cordilleran Highlands to the west. The area of Parowan, Utah

was a large desert environment consisting of an erg made of large sand dunes (Blakey, 2011). These

dunes migrated from the northwest towards the south-southeast; taken from cross bedded

measurements throughout Utah and the surrounding states (Hintze & Kowallis, 2009; Fillmore,

2011).

The Carmel Formation (Jc) (Middle Jurassic) is a direct result of the rise of the Cordilleran

Highlands to the west and a slow settling of the back bulge basin (the area to the east of the

highlands). Sea water from off the cost of the Canada/US border flooded in and filled the basin with

shallow warm water; called the Sundance Seaway (Hintze & Kowallis, 2009). The limestones in the

region are often found with layers of evaporates such as gypsum (Hintze & Kowallis, 2009). The

Carmel Formation (Jc) limestone found in Parowan Gap has been mined for such evaporates,

having been formed in a shallow marine carbonate setting.

The Straight Cliffs Formation (Ksc) (Late Cretaceous) contains a record of the eastern most

margin of the North American Interior Seaway. The Straight Cliffs Formation (Ksc) in Parowan

Gap contains interbedded medium-fine sandstones with silty layers. The cement binding much of

the sandstones layer contains calcium carbonate, indicative of warm shallow water. Overall, the

Straight Cliffs Formation (Ksc) is that of a prograding beach and near shore environment.

The Iron Springs Formation (Kis) (Late Cretaceous) is composed primarily of cross bedded

medium-to-fine grain sandstones, with a fining upward sequence. Within the Iron Springs

23

Formation (Kis) are numerous coarse-grain channel cuts. The sequence of deposition of the Iron

Springs Formation (Kis) is that of a braided river system and its flood plain (Biek, et al., 2009). In

the Iron Springs Formation (Kis) is a record of several volcanic events preserved as alternating

volcanic tuff beds.

The Conglomerate of Parowan Gap (Kpg) (Late Cretaceous-Paleocene) and the Grand

Castle Conglomerate (Kgc) (Late Cretaceous-Paleocene) are remnants of erosion of the Sevier

Highlands. They are conglomerates with intermixed sand lenses. Although these two conglomerates

are different in appearance, they are both made of mostly rounded second generation quartzite

clasts. They represent alluvial fan deposits shed from the Sevier Highlands. A change is deposition

occurs near the top of the Grand Castle Conglomerate (Kgc) when a several meter thick bioturbated

limestone is deposited on top.

The Claron Formation (Tc) (Paleocene-Eocene) is composed of several different rock units.

The basal unit is an extraformational conglomerate. Then a light gray limestone with fingers of

conglomerates that contain channel cuts > 1 m thick. Near the top of the Claron is calcareous

medium-fine sandstone that contains parallel laminations and trough-cross bedding. The Claron

Formation (Tc) over much of southern Utah, are deposits of lacustrine, and alluvial deposition

(Biek, et al., 2009).

The volcanic deposits near the western entrance of the Parowan Gap were deposited during

the Oligocene. The oldest of the units is the Brian Head Tuff (Tbh) (~30-36 Ma) which the extract

origins are unknown; however, some have suggested the Brian Head Tuff (Tbh) may have come

from the Marysville Volcanic Center in Central Utah. This was followed by the Wah Wah Springs

Tuff (Tnw) (~30 Ma.) and the Isom Tuff (Ti) (~ 27 Ma.). The heavier and denser tuffs of the Wah

24

Wah Springs (Tnw) and Isom Tuff (Ti) were deposited on the weaker Brian Head Tuff (Tbh). This

resulted in a slope failure and massive landslides which ran into the remnant of the Sevier Highlands.

6. Structural Description and Timing Relationship

There are three noticeable relationships among the formation. (1) Those that have a high

angle westward dip and are overturned; (2) those with shallow dips eastward; and (3) those deposited

on top of everything else. Beginning at the oldest faults, we start with the two thrust faults near the

middle of the Parowan Gap; the Carmel-Straight Cliffs Thrust, and the Straight Cliffs-Iron Springs

Thrust. The older of the two is the Carmel-Straight Cliffs Thrust Fault. Approximately in the Late

Cretaceous, this thrust pushed the older Carmel Formation (Jc) and the Navajo Sandstone (Jn) over

the younger Straight Cliffs Formations (Ksc). The Carmel Formation (Jc) is all that had not

weathered away. It is overturned, indicated by geopedals seen in the limestone of the formation.

Fractures in the limestone, which occurred before the thrusting event, have been extremely ductile

in “S” and “Z” folds (Figure: 8). This thrust fault continues out of the mapping area along the

Straight Cliffs Formation (Ksc) to the south, but this thrust fault dies out to the north, once it makes

contact with the Conglomerate of Parowan Gap (Kpg). This gives an age for the thrust. It is older

than the Conglomerate of Parowan Gap (Kpg) and younger than the deposits of the Carmel

Formation (Jc) limestone. This thrusting event overturned the beds of the Carmel Formation (Jc)

and Straight Cliffs Formation (Ksc) in a geosyncline, which weathered down to show only the

overturned beds. The deposition of the Conglomerate of Parowan Gap (Kpc) was then deposited

after this, on top of an angular unconformity of the Straight Cliffs Formation (Ksc).

The next thrusting event is related to the last; meaning it is part of the same event, just at

different times, because the thrust reactivated. This is along the Straight Cliffs Formation (Ksc) and

the Iron Springs Formation (Kis). The Conglomerate of Parowan Gap (Kpg), which had already

25

been deposited, or in the process of being deposited, piggybacked on top of this thrust as it rode on

top of the Iron Springs Formation (Kis). At this time as well, The Grand Castle Conglomerate (Kgc)

was being deposited on top of the Conglomerate of Parowan Gap (Kpc), and on top of the Iron

Springs Formation (Kis). All this was a result of the formation of the Sevier Orogeny during the

Late Cretaceous.

The Parowan Gap contains several normal faults. The normal faults can be attributed to the

Basin and Range extension. Starting at the east entrance of the Parowan Gap and working westward;

there are approximately 9 normal faults. The first two faults encountered (again starting east and

working west) are two normal faults that truncate each other. They dropped down the east side,

lowering the younger Claron Formation (Tc) down past the older Grand Castle Conglomerate (Kgc)

and the Iron Springs Formation (Kis). There is approximately 7 m of offset at these faults. On the

north side of the mapped area, the fault continues in a straight line; however, on the south side, the

faults bend and follow up a drainage until out of the mapped area (Appendix: 1a). The apparent dip

of this fault is approximately 76°.

The next normal fault drops the western side of the contact between the Claron Formation

(Tc) and the Grand Castle Formation (Kgc). Approximate offset is 13 m. This fault can be walked-

out down the drainage on the north side, but is lost and not found once it reaches the valley fill

(Qal) (Appendix:1a) and is not visible on the south side; however, it can inferred that it continues to

the south side of the valley.

There is a small normal fault just to the east on the north side of the mapped area near the

middle of the mapped area (Appendix: 1a). Total offset is approximately 7 m dropping the east side

of the fault. This fault was only found at the Grand Castle Conglomerate (Kgc) and Iron Springs

26

Formation (Kis) contact on the north side of the canyon. It dies off and is concealed in the valley fill

(Qal) and is not seen on the south side of the canyon.

In the Straight Cliffs Formation (Ksc), there are two parallel normal faults. They are seen on

both the north and south side of the canyon. The faults are offsetting the Straight Cliffs Formation

(Ksc), Conglomerate of Parowan Gap (Kpg), and the Grand Castle Conglomerate (Kgc). The

eastern on the two faults has a larger offset of approximately 30 m, and the western normal fault has

an offset of approximately 13 m. These normal faults tend to follow the weak bedding plans of the

overturned Straight Cliffs Formation (Ksc). There apparent dips can be taken from the dips of the

Straight Cliffs Formation (Ksc) fins. Apparent dips for these faults are approximately 65°-70°.These

faults drop down the western side of the faults.

Within the Claron Formation (Tc), approaching the western entrance of the Parowan Gap,

contains two normal faults. These faults are striking at different angles. They will truncate to the

north outside our mapping area, and spread farther out from each other to the south. The western

side of each fault drops down. Total offset can be seen comparing the different rock units of the

Claron Formation (Tc). It is approximately 10 m. Dips taken where slickenlines and slickensides are

found; this puts both faults dipping approximately 67°-77°.

The last set of normal faults runs on either side of the steep slopes of the Navajo Sandstone

(Jn). The normal fault which runs along the western margin of the Navajo Sandstone (Jn) is inferred,

but because it is the western margin of the Red Hills horst of the Basin and Range, we know it

should be there. The normal fault branches off and is on the east side of the Navajo Sandstone (Jn).

A dip of slickenlines within the Navajo Sandstone (Jn) puts the eastern normal fault dipping

eastward approximately 49°. Offset is difficult to see since it is Navajo Sandstone on, Navajo

Sandstone (Jn).

27

The last fault, and bit of an anomaly, it is a thrust fault on the north side of the canyon, just

to the east of the Navajo Sandstone (Jn). This thrust fault had pushed limestone of the Carmel

Formation (Jc) on top of the much younger limestone of the Claron Formation (Tc). Exactly how

this thrust occurred is a mystery; however, it could have formed as a result of massive volcanic

landslides from the Oligocene aged volcanism being deposited on weak ash flows.

7. Geological History and Discussion

The Jurassic lasted for 62 Ma from 206-144 Ma (Fillmore, 2011). The Lower Jurassic

introduced a change in environments. The land became increasingly arid (Blakey, 2011). The lush

wetlands of the Chinle and Ankareh Formations were exchanged for a desert environment. The

Lower Jurassic saw the largest known desert in geologic record (Hintze & Kowallis, 2009; Fillmore,

2011; Boggs, 2012; Stokes, 1986). The Navajo Sandstone (Jn) covered much of modern day Utah,

Nevada, Arizona, Idaho, Wyoming, Colorado, and the southern portion of California(Figure: 9b)

(Boggs, 2012). It extended for more than 265,000 km2, which is 2.5 times the size of the modern

outcrop (Boggs, 2012). The sand thickens westward as windblown coarse sediments blew from the

northwest (Hintze & Kowallis, 2009; Stokes, 1986; Fillmore, 2011) (Appendix: 4a). The desert was a

result of a rain shadow effect caused by the highlands to the west. As they rose, the clouds loaded

with moisture from the oceans unloaded this moisture on the mountains and dry arid air blew into

the back basin. The source of the sand is thought to have come from the northwest coast. As sea

level receded, it left large expanses of beach sand exposed that was blown into the erg (Fillmore,

2011). However, once sea level rose, other sources were needed for sand. It would have come from

the flood plains of the Chinle Formation, and from the Ancestral Rockies, along with the highlands

to the west (Fillmore, 2011). The Navajo Sandstone (Jc) in Southern Utah can reach thicknesses of

2000-2500 ft (Hintze & Kowallis, 2009).

28

The Middle Jurassic saw a subsidence in the back bulge basin, as sedimentation increased,

and the Cordilleran Highlands to the west raised higher (Hintze & Kowallis, 2009). Waters from the

western ocean flooded in around present day British Columbia and flooded as far south as southern

Utah (Appendix:1b ) (Hintze & Kowallis, 2009; Stokes, 1986). The Sundance Seaway was shallow

and warm; leaving deposits of different evaporates such as salt, and gypsum (Stokes, 1986). The

Carmel Formation (Jc) of Southern Utah correlates to the Twin Creek Formation in Northern Utah.

Both are deposits of the Sundance Seaway. The date of the Carmel Formation (Jc), using 40Ar/ 39Ar

to date volcanic ash was approximately 182 Ma (Hintze & Kowallis, 2009). The shallow sea was

bounded by the same margins as the desert that had occupied the same area earlier (Hintze &

Kowallis, 2009; Blakey, 2011). The waters retreated and rivers would once again flow through the

region (Stokes, 1986).

Tectonic activity continued off the west coast well into the Cretaceous Period. The Sevier

Orogeny would migrate eastward from the Utah-Nevada border from Mexico to Alaska (Fillmore,

2011). The fold and thrust formed as the western North American Plate experienced compression as

the Farallon Plate continued to be subducted. The Sevier Orogeny pushed tens of kilometers

eastward, shortening the western North American Plate as much as 100 km (Fillmore, 2011). The

thrusting episodes had profound effects on the strata. It caused the land to be uplifted and tilted

steeply southwest, along with overturning the portion of the Carmel Formation (Jc), and the Straight

Cliffs Formations (Ksc) between the Carmel Thrust Fault, and the Iron Springs Thrust Fault. The

interior of Utah became a foreland basin collecting the detritus of the Sevier Highlands (Hintze &

Kowallis, 2009; Fillmore, 2011). Much of the clasts and sediments that formed the Conglomerate of

Parowan Gap (Kpg) and the Grand Castle Conglomerate (Kgc) came from alluvial deposits that

were shed off the Sevier Highlands to the west (Biek, et al., 2009). The Sevier Highlands rose steeply

during the Late Cretaceous, and shed millions of tons of debris to the east.

29

Also during the Late Cretaceous was the North American Interior Seaway. The western

most margin of the seaway was the present day Parowan Gap. This area was a swampy marsh land

and near shore environment (Biek, et al., 2009). Deposits of coal can be found in the Straight Cliffs

Formation (Ksc), which show a prograding beach environment (Hintze & Kowallis, 2009). Within

the Parowan Gap, along the Straight Cliff Formation (ksc), lies a tailing pile from an abandon coal

mine. The Sevier Highlands continued to push eastward. The Iron Springs Formation (Kis) formed

as braided rivers flowed from the Sevier Highlands from the west, to the seaway to the east. The

rivers carried heavy loads of sediment. The Iron Springs Formation (Kis) preserves a prograding

channel sequences. It is after the deposition of the Iron Spring Formation (kis), that the Sevier

Highlands push even farther eastward, overturning the Straight Cliffs Formation (Ksc) and eroding

the Iron Springs formation (Kis) to the west. The Conglomerate of Parowan Gap (Kpg) and the

Grand Castle Conglomerate (Kgc) where subsequently deposited after the first initial thrusting

event. The Conglomerate of Parowan Gap (Kpg) would piggyback over during the second thrusting

event, and eroded during the process. Then the Grand Castle Conglomerate (Kgc) would be

deposited on top, as detritus form the Sevier Highlands was transported downslope.

The North American Seaway retreated away from Utah in the Late Cretaceous as a result

of uplifting (Stokes, 1986). The land continued to be uplifted once again in the Laramide Orogeny at

the beginning of the Paleocene, which reactivated the Iron Springs Fault. The basins and lower lying

areas created by both the Sevier Orogeny and Laramide Orogeny were filled in by fresh bodies of

water. They were Lake Flagstaff, and Lake Claron (Stokes, 1986; Hintze & Kowallis, 2009). The

Claron Formation (Tc) namesake comes from Lake Claron. The Claron Formation (Tc) is made up

of conglomerates, limestones, and calcareous sandstones. The waters of Lake Flagstaff and Lake

Claron would have been warm bodies in order to produce lacustrine limestone. At its thickest, the

Claron Formation (Tc) can reach thicknesses of 1000 ft. (Hintze & Kowallis, 2009).

30

During the Oligocene, western Utah saw a period of intense volcanism. Igneous activity

moved into northern Utah about 40 Ma, and reached southern Utah about 30-20 Ma (Hintze &

Kowallis, 2009). The subduction of the Farallon plate continued up to about 40 Ma. It was being

subducted eastward but at a very oblique angle. After which, the plate broke free in a slab pull which

released the mantel into parts of continental crust that would not normally see volcanic activity so

far from the subduction zone (Hintze & Kowallis, 2009). The types of volcanoes produced were

Andean like stratovolcanoes, which produce explosive eruption (Hintze & Kowallis, 2009). Large

quantities of ash flows and tuffs blanketed the area. The main source for the volcanism that

deposited the Wah Wah Springs Tuff (Tnw) and the Isom Formation (Ti) is believed to have been

the Indian Peaks Volcanic Center near the Utah-Nevadan border which occurred between 33-20 Ma

and producing nearly 9000 feet of ash flow and tuffs (Hintze & Kowallis, 2009). The Marysvale

Volcanic Center near central Utah may have been the source for the Brian Head Tuff (Tbh), but its

source is still unclear.

The volcanic deposits seen in the Parowan Gap are believed to have been deposited as a

result of the heavier tuffs of the Wah Wah Springs (Tnw) and the Isom (Ti) being deposited on top

of the weaker Brian Head Tuff (Tbh). The result was a massive landslide. Evidence for this slide

comes from the odd thrust fault found at the western entrance of the Parowan gap. The thrust

moved Carmel (Jc) on top of Claron (Tc).

About 17 Ma, the last of the Farallon became fully subducted and the Pacific Plate made

contact with the North American Plate (Dott Jr. & Prothero, 2010). The change in tectonic

compression resulted in a stress being removed against the North American Plate and the land

slowly began to extend westward. The resulting movement created a series of normal fault block

mountains with down-dropped grabens or basins in between, along with a multitude of normal

31

faults that strike approximately north to south (Dott Jr. & Prothero, 2010). This area known as the

Basin and Range Providence is bounded by the Cascade Mountains in the north, and the northwest

desert of Mexico in the south, and from the Sierra Nevada Mountains in the west, to the Wasatch

Line in the east. The extension westward thinned the crust as much as 100 % its original thickness

(Hintze & Kowallis, 2009). Normal faults can be found throughout the area, offsetting formation

several meters. The Red Hills where the Parowan Gap is located was once part of the mountains to

the east which are a part of the Colorado Plateau. They are the eastern margin of the Basin and

Range Providence and the western margin of the Colorado Plateau. The Red Hills broke free, and

formed the typical horst and graben seen throughout the Basin and Range. The Parowan Stream

once flowed through the canyon, forming its cliff walls, and exposing the strata. As the Red Hills

pulled away from the Colorado Plateau, the stream was subsequently redirected.

Currently the Parowan Gap is still being affected by Basin and Range extension. The

region is still an active fault zone. The Red Hills are also undergoing erosion effects from wind, rain,

biological, and ice. There are numerous landslides, and colluviums throughout the area.

8. Conclusion

The Parowan Gap, located in the Red Hills west of Parowan, Utah contains strata from

the Lower Jurassic to present. These formations represent a wide range of deposition such as an

eolian erg, shallow marine, alluvial fan, lacustrine, and volcanic deposit. The Parowan Gap is also

undergoing erosional processes such as weathering and landslides to this day.

Since the Cretaceous, the Parowan Gap has undergone tectonic forces. The Farallon Plate

to the west was being subducted under the North American Plate. It was the source of much of the

forces that shaped the Parowan Gap. The Sevier Orogeny thrust up the land in a series of thrust

faults and thrusting event. These thrust not only uplifted the land, but also overturned some of the

32

bedding. The Sevier Highlands were also a source of much of the sediment fill that created the

conglomerate of both the Parowan Gap Conglomerate (Kpg), and the Grand Castle Conglomerate

(Kgc).

As the Farallon Plate continued to be subducted into the Oligocene, the plate broke free,

allowing the partially melted Farallon Plate and mantle to rise farther into the North American Plate

causing intense volcanism 20-30 Ma. These volcanic events were responsible for all the volcanic

deposits within the Parowan Gap, along with a massive landslide.

Once the last remaining segments of the Farallon Plate subducted under the North

American Plate approximately 17 Ma, the tectonic forces changed to the west. This allowed the

western part of the North American Plate, which had for millions of years been compressed, to

begin to extent westward. This was the birth of the Basin and Range Providence. As a result of the

Basin and Range, the Red Hills would break free from the Colorado Plateau forming a horst and

graben. The Basin and Range would also form a series of normal faults throughout the Parowan gap.

This is the current state of the Parowan Gap. It will continue to undergo forces related to the Basin

and Range extension for the foreseeable time.

33

Acknowledgments

I would like to personally thank the following people for their help in gathering information for this

report and for gathering information out in the field.

Dr. David Dinter

Field Partners: Heather Judd, and Taylor Wessman, along with Jon Peterson, Robyn Lyons, and

Raina Mahanes’s group who often worked with ours in the field.

Field Camp Managers: Mallory Millington and Amy Steimke

A very special “THANK YOU!” to TA Jelle Wiersma for all of his help out in the field, in camp,

and for all the countless questions he would answer.

34

References

[1] Biek, R. F., Rowley, P. D., Hayden, J. M., Hacker, D. B., Willis, G. C., Hintze, L. F., et al. (2009).

Geological Map of the St. George and East Part of the Clover Mountains 30'x60' Quadrangles, Washington and

Iron Counties, Utah. Salt Lake City: Utah Geological Survey.

[2] Blakey, R. (2011, march). Library of Paleogeography. Retrieved February 5, 2014, from Colorado

Plateau Geosystems, Inc.: cpgeosystems.com/paleomaps.html

[3] Boggs, J. S. (2012). Principles of Sedimentology and Stratigraphy (Vol. 5th). Upper Saddle River, New

Jersey: Prentice Hall.

[4] Dott Jr., R. H., & Prothero, D. R. (2010). Evolution of the Earth (Vol. 8th). New York: McGeaw

Hill.

[5] Fillmore, R. (2011). Geological Evolution of the Colorado plateau of Eastern Utah and Western Colorado.

Salt Lake City: The University of Utah Press.

[6] Google Earth. (2013, October 7). Retrieved February 5, 2014, from Google Earth:

www.googleearth.com

[7] Hintze, L. F., & Kowallis, B. J. (2009). A Field Guide to Utah's Rocks: Geologic History of Utah. Provo:

Brigham Young University.

[8] Stokes, W. L. (1986). Geology of Utah. Salt Lake City: Utah Museum of Natural History, University

of Utah.

[9] Threet, R. L. (1963). Geology of The Parowan Gap Area, Iron County, Utah. Utah Geological

Association.

* All photos and figures were created by Michael Starkie unless otherwise cited

35

Appendix 1a: Geological Map of the Parowan Gap, Parowan Utah. Original scale was 1:12,000;

however, the scale has change to fit within this report. (Top of page is north)

36

37

Normal Fault (Ball on down side)

Bedding Direction

(Cross-section)

Thrust Fault (Points on upside)

Foot Wall Thrusting

Inferred Fault

Foot Wall Dropping

50

Strike & Dip Measurement

N Cardinal Direction

80

Rake Measurement

Bedding Contact

60

Overturned Bedding

77

Fault Attitude

Appendix 1b: Legend for Map, and cross-section (Appendix:2a).

Qal Quaternary Alluvium Tc Eocene Claron Formation

Qsl Quaternary Landslide

Kgc Late-Cretaceous Grand Castle Conglomerate

Qfo Quaternary Inactive Alluvium

Kpg Late-Cretaceous Parowan

Gap Conglomerate

Qvc Quaternary Volcanic

Conglomerate

Kis Late-Cretaceous Iron Springs Formation

Ti Oligocene Isom Welded Tuff

Ksc Late-Cretaceous Straight

Cliffs Formation

Tnw Oligocene Wah Wah Springs

Tuff

Jc Middle-Jurassic Carmel

Formation

Tbh Oligocene Brian Head Tuffaceous Sandstone

Jn

Lower-Jurassic Navajo Sandstone

38

Appendix 2a: Cross section of line A’, B’, C’ on the geological map (Appendix: 1a). Original scale 1:1200; however, it has since changed to fit into report format. No vertical exageration.

39

40

Appendix 3a: Stratigraphic Column for the Parowan Gap, Parowan Utah.

41

Appendix 3b: Straight Cliffs Formation (Ksc) Stratigraphic Column in the Parowan Gap, Parowan,

Utah.

42

Limestone

. . . . . . . . .. .. .. . . . .. . . . . . . .. .. … .. .. .

Unconsolidated Sediment

. . . . . . . . . . . . . . . .

. . . . . . . .

Sandstone

Concretions

. _ . _ . _ . _ . _ . _ . _ . _ . _ . _ . . _ . _ . _ . _ . _

Silt

Angular Unconformity

Tangential Trough- Cross Bedding

Erosional Unconformity

* * * * *

Crystal Structures

Unexposed

Fiamme

Pebble Lag

Volcanic Ash

Ripple Marks

. . . . . . . . .

. . . .

. . . . .

Conglomerate

Oyster Beds / Oyster

Coquina

Planner Lamination

Appendix 3c: Stratigraphic Column Legend

43

Appendix 4a-4d: North American Paleomaps from the Lower Jurassic (~189=0 Ma) through the KT boundary (~65 Ma) (Blakey, 2011)

a: Lower Jurassic (~180 Ma) Paleomap of the desert

which the Navajo Sandstone (Jn) Formed

b: Middle Jurassic (~170 Ma) introduction of the

Sundance Seaway which deposited the Carmel

Formation (Jc)

c: Late Cretaceous (~85 Ma). Notice the Sevier

Highlands to the West and the North American

Interior Seaway to the East

d: Paleomap of North America during the KT

boundary (~65 Ma). Notice the large lakes hugging the

highlands in Utah. These are Lake Flagstaff, and Lake

Claron, to which the Claron Formation (Tc) gets its

name.