capitol reef national park geological overview click on the button

Capitol Reef National Park

Geological Overview

Capitol Reef National Park is situated on the edge of the Colorado Plateau; a physiogeographic province centered roughly on the Four Corners area of the western US. The Colorado Plateau is characterized by a nearly complete section of sedimentary rock units ranging in age from Late Permian (~275 Ma) to Early Tertiary (~60 Ma) (Smith et al., 1963; Billingsly et al., 1987; Morris et al., 2003). Uplift and erosion began ~70-50 Ma during the Laramide orogeny (mountain building event) that created the 100 mile long, N-S striking monocline known as the Waterpocket Fold (Mathis, 2000; Morris et al., 2003). Downcutting along the monocline has created canyons and exposed the sedimentary layers that tell the paleogeographic story of the western US during the Mesozoic era. Volcanics during the Middle Tertiary (~30-20 Ma) and again in the Late Tertiary (~6.4 Ma) covered the strata with basalt and remnant black boulders can be seen throughout the park (Delaney and Gartner, 1997; Mathis, 2000; Morris et al., 2003).

The purpose of this website is to document sedimentary structures (and other outcrop scale features) and interpret depositional environments of the rock formations in Capitol Reef and other nearby areas. We examine primary sedimentary structures such as bedding, trace fossils and soft sediment deformation. Secondary (diagenetic) features are also identified such as iron and uranium precipitation by groundwaters with different chemistries. Geomorphic and weathering features like hoodoos and honeycomb weathering patterns are also highlighted.

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Click on the button below for the Stops to visit at in Capitol Reef National Park

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Geology of Capitol Reef NP

For a complete list of references please go to the References page.

A pdf version of this website is available on the Main Page Disclaimer: The information is property of the University of Utah. Unless cited, images and files found on this site have been taken or created by the Geology and Geophysics Department at the University of Utah. Any use of these images should be cited appropriately. The stratigraphic column is from: Mathis, A. C. 2000. Capitol Reef National Park and Vicinity Geologic Road Logs, Utah, in: P.B. Anderson and D.A. Sprinkel (eds.) Geologic Road, Trail, and Lake Guides to Utah’s Parks and Monuments Utah Geological Association Publication 29. http://www.utahgeology.org/uga29Titles.htm Copyright (c) 2010, Geology and Geophysics Department, The University of Utah Site Map


Capitol Reef National Park Geology


Morrison Formation

(Tidwell Member, Salt Wash Member, Brushy Basin Member)

Age:

v Late Jurassic (Kimmeridgian) 155-148 Ma

Depositional Environment: Alluvial plain, fluvial channels and floodplains with paleosols

Tectonics: Subduction to the west created a back arc rift basin (between Morrison basin and paleo Pacific Ocean). Mountain ranges (rift shoulder) to the west were source for clastic sediment Calderas in rift basin provided abundant ash fall during Brushy Basin deposition

Climate: Located ~32° N (modern southern AZ) Prevailing easterly winds (present day NE due to rotation of plate) Warm, dry climate with high evaporation

Features: Morrison Formation - 180-200 m thick

Tidwell Member (oldest) Alluvial plain – streams, overbank deposits, paleosols; locally (in Capitol Reef area) gypsiferous, hyper-saline lagoons

Varicolored mudstone with interbedded sandstone, limestone, gypsum

Salt Wash Member (middle) Fluvial channel deposits, floodplain deposits, crevasse splays

Predominately fine/medium sand - coarse sand/ pebble conglomerates; trough stratification, fining upward

Brushy Basin Member (youngest) Lacustrine/ wetlands; local fluvial channels

Varicolored mudstone

Mostly ground and surface water flowing to the east (present day NE) Losing streams with associated riparian environments prograding to the east Floodplains with paleosols; grassy savannahs

Sites Best to See it:

Stop 1-1: Exhumed paleo channels in Salt Wash Member Stop 2-1: All three members

Figure 1: Paleogeographic map of the Middle Jurassic, Page Sandstone, Carmel Formation, Entrada Sandstone, Curtis Formation, and Summerville Formation. (Blakey, 2008)

Morrison Formation

Figure 2: Channel in Salt Wash Member (outlined with dotted line).

Morrison Formation

Summerville Formation

(in San Rafael Group)

Age: Middle Jurassic

Deposited from early to late Oxfordian

time (161 - 155 Ma) (Wilcox, 2007).

Depositional Environment: Marginal marine and tidal One unconformably-bound, transgressive-regressive (T-R) sequence, marine and marginal-marine (Wilcox, 2007).

Paleogeography: A major transgression of the Late Jurassic seaway drowned the eolian sand sea of the Entrada Sandstone. Subsequent regressive paleoflow was to the northeast into the Late Jurassic interior seaway (Kocurek & Dott,

1983, Blakey 2008).

Tectonics: Deposition was in a retroarc to craton-margin basin as the region

drifted north (Kocurek & Dott, 1983).

Climate: Arid

With paleolatitude range of 5 to 25 degrees north, the paleoclimate was intensely hot and arid (Kocurek & Dott, 1983).

Features: The Summerville is noted for its thin red beds of rippled sandstones and mud cracks, overprinted with secondary gypsum veins. The Jurassic "J3" unconformity, a regional surface of erosion atop the Entrada Sandstone, marks the basal bounding surface of the Curtis-Summerville T-R sequence. A thin, lower Curtis transgressive systems tract is the finest grained facies of the Curtis Formation topped by a maximum flooding surface. Thick middle and upper Curtis represents a highstand systems tract reflected in upward coarsening cycles from marine shelf to tidal channels to shoreface. The upper sequence is tidal flat, reddish-brown mudstones and evaporites of the Summerville Fm topped by the "J5" unconformity, the upper sequence bounding surface and the contact with overlying Morrison Formation (Wilcox, 2007).


Stop 1-2: View the Curtis-Summerville Formations and bounding unconformities in distant cliffs at Goblin Valley State

Park.

Stop 1-3: Summerville gypsiferous mudstones outcrop along Highway 24 west of Hanksville.

Stop 4-1: For close inspection of Curtis Formation tide-generated sedimentary structures see the East I-70 road cut where

the most impressive tidal features, sigmoid-shaped tidal bundles occur.



Figure 2: View of the Morrison Formation, the Summerville Formation, the Curtis Formation, and the Entrada Formation.


Curtis Formation


Age:

Deposited from early to late Oxfordian

time (161 - 155 Ma) (Wilcox, 2007).

Depositional Environment: Marine and marginal-marine tidal flat. Comprises one unconformably-bound, transgressive-regressive (T-R) sequence (Wilcox, 2007).

Paleogeography: A major transgression of the Late Jurassic seaway drowned the eolian sand sea of the Entrada Formation. Subsequent regressive paleoflow was to the northeast into the Late Jurassic interior seaway (Kocurek & Dott, 1983).

Tectonics: Deposition was in a retroarc to craton-margin basin as the region

drifted north (Kocurek & Dott, 1983).

Climate: With paleolatitude range of 5 to 25 degrees north, the paleoclimate was both hot and arid (Kocurek & Dott, 1983).

Features: The Curtis Formation shows a variety of nearshore sedimentary structures (e.g. horizontal bedding -> beach, rhythmites and sigmoidal bundles -> tidal). The Jurassic "J3" unconformity, a regional surface of erosion atop the Entrada Formation, marks the basal bounding surface of the Curtis-Summerville T-R sequence. A thin, lower Curtis transgressive systems tract is the finest grained facies of the Curtis Formation topped by a maximum flooding surface. Thick middle and upper Curtis deposits represent a highstand systems tract reflected in upward coarsening cycles from marine shelf to tidal channels to shoreface envirionments. The upper sequence is tidal flat, reddish-brown mudstones and evaporites of the Summerville Formation topped by the "J5" unconformity, the upper sequence bounding surface and the contact with overlying Morrison Formation (Wilcox, 2007).


Stop 1-2: View the Curtis-Summerville Formations and bounding unconformities in distant cliffs at Goblin Valley State

Park.

Stop 1-3: Summerville gypsiferous mudstones outcrop along Highway 24 west of Hanksville.

Stop 2-1: San Rafael Group overlook

Stop 4-1: For close inspection of Curtis Formation tide-generated sedimentary structures see the East I-70 road cut where

the most impressive tidal features, sigmoid-shaped tidal bundles occur.


Curtis Formation

Figure 2: View of the Morrison Formation, the Summerville Formation, the Curtis Formation, and the Entrada Formation.

Curtis Formation

Entrada Sandstone


Age:

Upper Jurassic, 80 and 140 ma

Depositional Environment: Eolian, sabkha, and tidal flat. The Entrada Sandstone preserves terrestrial environments. Within the field trip area, the deposits generally indicate a high water table with some dunes (wet eolian) present. The bedding contains sandstone laminations, sand lenses with some lenses starved and encased in mud. This environment is broadly interpreted as a tidal regime (tidal flat) in this region.

Paleogeography: In the Upper Jurassic, the

supercontinent, Pangea, was beginning to break up with North American and Eurasia pulling apart from South America. Utah was closer to the equator with eastern Utah as a dry Sahara-like desert, with shallow seas that intermittently covered the area (Blakey 2008).

At around 170 Ma, the Goblin Valley State Park area was a wide tidal flat between the sea to the north and continental mountains and hills to the west. Tidal channels migrated across the tidal flats, routing flowing water to the open sea. Coastal sand dunes also covered parts of the tidal flats. Oscillatory tide motions were a dominant force in the deposition of this area. Silts, sands, and clays were primarily sourced from erosional debris shed from granitic highlands of Northwestern Utah and then were re-deposited in seas, shorelines, river channels, and playas.

Tectonics: Goblin Valley State Park is near the edge of a regional system of faults that cut across the San Rafael Swell (Fillmore 2000, Milligan 2003). Several sets of microfaults divide the Entrada Sandstone into yard sized rhombohedral blocks. The blocks exhibit reduced grain size, decreasing porosity and permeability within the fractures. In Goblin Valley only small-scale fractures with small offsets may be visible.

Climate: warm and arid

Features: The dark reddish color of the Entrada Sandstones comes mainly from the mineral hematite (an iron oxide and principal ore of iron) staining the


Figure 2: These goblins form in flat-lying, fine-grained sandstone beds that are interbedded and underlain by shale and siltstone. Joints within the Entrada are conduits for erosion along zones

Entrada Sandstone

sandstone. This is the same formation that makes up the natural arches of Arches National Park in southeastern Utah. A synthesis of the Entrada Sandstone is given in Carr and Kocurek (1993).

Joint or fracture patterns in the Entrada Sandstone create initial weak zones that become enlarged over time. Joints intersections are susceptible to weathering because of increased surface to area volume ratio. These joints weather quickly, creating spherical-shaped goblins, from spheroidal weathering (Milligan 2003). Interbedded and underlying shale and siltstone beds are capped by the sandstone beds. The soft shale and siltstone beds help create the smooth shaped pedestals in Goblin Valley State Park.


Stop 1-2: Goblin Valley State Park

of weakness, and subsequent spheroidal weathering.

Entrada Sandstone

Carmel Formation


Age:

Middle Jurassic, 160 Ma

Depositional Environment: Sabkha (and supratidal) to marine

Paleogeography:

Frequent, but short-lived sea level fluctuations during the Middle to Late Jurassic caused periodically flooding from shallow extensions of the ocean. Flooding deposited gypsum, sand, and limey silt in depressed blocks of land that were bordered by parallel faults (grabens), and were periodically covered by sea water. Evaporites were deposited from repeated flooding during this time.

Tectonics:

Stable, some volcanism with subduction to the west.

Climate:

Arid

Features: The Carmel Formation is composed of 200 to 1,000 feet (60 to 300 m) of reddish-brown siltstone, mudstone and sandstone that alternates with whitish-gray gypsum and fossil-rich limestone in a banded pattern. Fossils include marine bivalves and ammonites. The Carmel formation contains massive limestone beds in varying shades of gray, but also contains brittle limestone beds that weather into hard angular chips. The limestone beds can also be sandy and some contain ripple marks. Various types of soft sediment deformation also characterize the Carmel Formation. Typical Carmel exposures occurs as a series of low cliffs and steep slopes. In some areas, the Carmel Formation forms a resistant cap and slows the erosion of the underlying Navajo Sandstone.


Stop 2-2: Carmel Formation


Figures 2-3: Soft Sediment Deformation features in the Carmel Formation on Hwy 24 heading east between the visitor’s center and the east park boundary. Soft sediment deformation forms

shifting, and displacement of sediments, possibly from escape of water from below, and/or from sediment loading (denser bed sinking into a less dense bed). Soft sediment deformation is an important process because it records rapid deposition, fluid movement, or tectonism prior to lithification. Various styles of soft sediment deformation are commonly associated with evaporite minerals.

Carmel Formation

Page Sandstone


Age:

Middle Jurassic

Depositional Environment: Eolian

Paleogeography: In the Middle Jurassic, Utah lay closer to the equator creating an arid, eolian environment (Blakey 2008). Sedimentation was controlled by sea level, climate and tectonics. The Sundance sea entered the area from the north due to a global sea level rise. This was a time of subsidence most likely due to a sag next to west lying Nevadan highlands. The Page Sandstone is confined to the south

central portion of Utah and north central regions of Arizona. Narrowing of the seaway in northern Utah encroached and inundated onto the Page Sandstone erg to cease the eolian deposition.

Tectonics: In the Middle Jurassic, parts of Utah were in a period of mountain-building phase. Tectonic activity, like the Nevada Orogeny, was centered in the northeast portion of Nevada and volcanic highlands were located to the south and southwest. Folding and thrusting from the orogeny led to subsidence and a foreland basin.

Features: The Page Formation was a large dune field (erg/eolian system) ranging from northern Arizona, in the Middle Jurassic, that extended northward across a band within Utah to Wyoming (Fillmore 2000). It was separated to the west by a tidal-flat/sabkha complex and then the Sundance seaway. The Sundance seaway expanded and extended southward and eastward and as it retreated, the Page erg followed and expanded over the sabkha sediments. Page Sandstone and the Carmel Formation comprise a mix of marine, sabkha, fluvial systems of the Carmel (marinal marine and marine) and eolian deposits of the Page Sandstone.


Stop 2-3: Navajo Waterfall


Page Sandstone

Navajo Sandstone

(in Glen Canyon Group)

Age: Early Jurassic

The Navajo Sandstone is dated as Early Jurassic, although precise dating is typically difficult due to a lack of age diagnostic fossils, a common problem in eolian deposits.

Depositional Environment: Eolian (wind blown) The Navajo Sandstone was deposited in an eolian environment composed of large sand dunes, similar to portions of the modern Sahara Desert. In an eolian environment there are two primary types of deposits: 1) dunes, typified by large-scale trough cross stratification; and 2) interdunes, which are the flat lying areas between dunes.

Paleogeography: The Navajo Sandstone represents an enormous erg, a large sand sea. This sand sea extended over most of Utah as well as parts of New Mexico, Arizona, Colorado and Wyoming. Though the deposits are known by different names in different areas, they were all a part of this major erg system. At this time, the modern Colorado Plateau region was at very low

latitude, approximately 10o north of the equator (Blakey 2008). The Colorado Plateau region was located near the western edge of Laurentia, the western-most portion of North America (not having accreted to the rest of the continent by then). By the Early Jurassic, Pangaea had begun to break up. Detrital zircon geochronology indicates that the Navajo erg received some sediment from the Appalachian Mountains via a continental scale river system similar to the modern Mississippi River. (Dickinson and Gehrels 2003; Rahl et al.2003) To the south and west of the erg were mountains of the nascent Cordilleran Arc, while to the east lay to the platform of central North America and the remnants of the Ancestral Rocky Mountains. Directly adjacent to the south and west of the erg lay the fluvial facies of the Kayenta Formation.

Tectonics: Although the Navajo Sandstone was not deformed by the active tectonics, it did form in a basin that was a result of the regional tectonics. As the mountains to the south and west were uplifting a flexural basin was formed from the added mass of the new mountain range. The subsidence of this basin created room for the sand to be deposited in. This also caused deceleration of the regional winds due to a decrease in the pressure gradient, which caused the sand being transported by the wind to be deposited in the erg (Kocurek 2003).

Climate: arid

The climate in the Colorado Plateau region during deposition of the Navajo Sandstone was very dry (classified as hyper-arid). Due to the mechanics of global

atmospheric circulation, large desert, such as the Arabian Desert, are typically located around 25-30o north and south of the equator in the trade wind belt. Because of the Navajo location on the western side of the Laurentian landmass, easterly trade winds were very dry by the time that they reached the Colorado Plateau region

at approximately 10o north latitude, delivering little rain all to the region (Kocurek and Dott 1983, Loope et al. 2004).

Dunes require strong winds to form. Winter monsoon winds blowing from the northwest seem to be counter to the northeasterly winds typically present at the low latitudes at which the Navajo Sandstone was deposited. Studies of modern low latitude atmospheric circulation shows that low latitude, low-pressure systems

can cause monsoon winds that undergo a 900 change in direction as they approach latitudes within 100 of the equator. These observations explain how dune fields formed by northwesterly winds could develop at a latitude where northeasterly winds are expected. During the summer a lighter cross equatorial monsoon wind blew from the southwest modifying the dune shapes (Loope et al. 2004).

Features: The Navajo Sandstone is most notable for its excellently preserved, large-scale trough cross strata recording lee-face deposition on the subareial sand dunes (Kocurek and Dott 1983). Two types of internal stratification are common in the cross strata: grain flow strata and wind ripple strata. Grain flow strata form as avalanches of sand grains slump down the lee faces of the dunes. They primarily form during periods when the wind is blowing in the dominant dune forming direction. These strata can be recognized most easily by their downslope pinch outs towards the toe of the dune. Wind ripple strata leave thin, inversely graded “pin stripe” laminae, formed by ripples superimposed on the much larger sand dunes. In some cases, wind ripples at the toe of the dune and form aprons or plinths of reworked sand. In Capitol Reef National Park there are two primary eolian deposits, the Navajo Sandstone and the Wingate Sandstone. Since they were formed in the same depositional environment the two formations on might think these should look fairly similar. However, the two formations weather quite differently. The Navajo tends to weather into smooth rounded domes and cliffs, whereas the Wingate tends to from very blocky, vertical cliffs. The Navajo also has a tendency to sometimes have weathered pockets from a process called honeycomb weathering. In general, the Wingate tends to be red in color, and the Navajo is typically more white in the field trip area. This is most likely the result of higher permeability in the Navajo, permitting higher fluid flow and diagenetic bleaching of the rock.

Sites Best to See it: Stop 2-3 - Navajo Waterfall Stop 2-4 - Navajo Sandstone Soft Sediment Deformation

Stop 3-3 - Grand Wash Trail

Figure 1: Paleogeographic map of the Early Jurassic, Wingate Sandstone, Navajo Sandstone, and Kayenta Formation. (Blakey, 2008)

Navajo Sandstone

Figure 2: A modern dune field at White Sands National Monument shows analogous eolian features to the Navajo Sandstone. Note the smaller wind ripples superimposed on the larger dunes in the foreground. The flat, lightly vegetated low spot in the middle of the picture is an interdune area.

Figure 3: This paleogeographic reconstruction of the western US during the Early Jurassic (Kocurek and Dott,1983 p. 106) shows the Navajo Sandstone and correlative eolian units, the Nugget and the Aztec, covering parts of Utah, Wyoming, Colorado, Arizona, Nevada, New Mexico and California. To the south and west lie mountains of the nascent Cordilleran Arc and the Mogollon Highlands, while to the east lay the North American platform and the remnants of the Ancestral Rocky Mountains.

Figure 4: Seasonal climate reconstructions (Loope et al., 2004 p. 317) showing the primary wind direction for the Navajo Sandstone.

Figure 5: Figure from Loope et al., 2004 (p. 318) showing reorientation of trade winds to westerlies at low latitudes due to regional low-pressure regimes driving monsoon systems.

Figure 6: This image shows the large-scale trough cross bedding that is characteristic of the Navajo. These cross strata are the preserved lee faces of sand dunes that were present in the erg when the Navajo was deposited. Trough cross strata can be seen to cut down into lower layers, indicating that

Figure 7: This is a picture of grain flow strata in the Navajo Sandstone. As you look along the bedding you can see how individual layers expand and pinch out. This is due to the avalanche nature of the grain flow strata. Laterally some parts of the avalanche will be thicker than

Navajo Sandstone

the wind that formed the dunes also caused them to scour into previous dune deposits. It is also possible to see the pock marked weathering pattern, common to the Navajo sandstone, called honeycomb weathering.

others, while at their edges and in a down slope direction the individual flows must pinch out where they come to an end.

Figure 9: Since both the Wingate and Navajo Sandstones are eolian formations present in Capital Reef National Park, and are nearly adjacent formations with only the Kayenta formation separating them, it is important to be able to tell them apart. This photo shows the Wingate in the midground with the Navajo in the center background, on the skyline, and is good for highlighting the differences between the two formations. The Wingate tends to weather in shear, vertically jointed cliffs, while the Navajo tends to weather in rounded domes. The Wingate tends to be red from iron oxide staining, though as can be seen in the center midground the Wingate can also be bleached, while the Navajo is almost always a light, bleached color.

Figure 10: This is a picture of wind ripple strata in the Navajo Sandstone. Wind ripple strata are typically very thin, parallel laminated strata that are formed as the wind moves sand up and over the dune. If the wind ripples are being blown by winds in the primary dune forming direction then they will collect at the crest of the dune until they have built up a steep enough slope to avalanche down the lee face of the dune. This process forms grain flow strata but no direct evidence of the wind ripples are preserved. If the wind is blowing in a direction where the wind ripples do not collect at a dune crest and become grain flows then wind ripples can be preserved. This can happen if the wind is blowing in a secondary direction and wind ripples are carrying sand across the face that is normally the lee slope. This can also happen when the wind is blowing in the primary direction on dune faces that are not on the lee slope of the dune. See Kocurek et al., 2007 for a good explanation of where to expect to find wind ripple strata preserved on a dune. If wind ripples are being preserved over the course of a full year then seasonal variations in wind strength will lead to slight variations in the grain size of the sand carried. This alternation in grain size is reflected in the eolian deposit as slight variations in the way the outcrop weathers, giving a ribbed texture to the weathered rock.

Navajo Sandstone

Kayenta Formations


Age:

Early Jurassic, 199.6 million years ago to 175.6 million years ago

Depositional Environment: Fluvial (river) environment

Paleogeography: The Wingate erg was reworked by river currents in the time period when the Kayenta formation was being deposited.

Tectonics:

Climate: Seasonal climate, rainy summers and dry winters

Features: The Kayenta Formation is Jurassic in age and makes up the middle third of the three-part section that make up the Glen Canyon Group. The Wingate Sandstone is below the Kayenta, while the Navajo Sandstone is above it. The Kayenta Formation is about 350 feet thick and range in color from red, to maroon, to brown (Mathis, 2000). The Kayenta is composed of sandstones, siltstones, and conglomerates that interbed (or alternate) within each other (Bates et al., 1984). At the top of the Kayenta, where it meets the Wingate, and the bottom of the Kayenta, where it meets Navajo, are contacts that are gradational (Mathis, 2000). Due to this, sometimes it is challenging to differentiate between the Wingate and the Kayenta formations but there are some clues that might aid in discerning the two. The Wingate Sandstone is eolian in origin meaning it was formed/deposited by the wind. In contrast, the Kayenta formation represents a fluvial (pertaining to a river) environment (Bates et al., 1984). According to Friz 1980, the rivers that formed the Kayenta were traveling in a westward to southwestward direction. In the Kayenta, there are small cross-beds (layers of sediment that are tilted at an angle) in contrast to the Navajo and Wingate, which have large cross-beds (Morris et al., 2003). Cross-beds that look like lenses (lenticular) often are indicative of the Kayenta. The Wingate fractures vertically, while the Kayenta fractures horizontally. This fracturing is readily apparent in “the castle” rock structure seen at the Visitors Center of the park (Figure 1). The Kayenta usually weathers as low cliffs and ledges (Morris et al., 2003).


Stop 2-7: “The Castle”


Kayenta Formation

Figure 2: “The castle” rock structure is north of the Visitors Center of the park. The Wingate (upper light tan colored rock) fractures vertically, whereas the Kayenta (reddish brown, overlying the Wingate as shown to the far right of the Wingate in the background) breaks horizontally.

Kayenta Formation

Wingate Sandstone


Age: Early Jurassic

The Wingate Sandstone is dated to the Earliest Jurassic, though precise dating of eolian deposits is typically difficult (see discussion in Navajo Sandstone).

Depositional Environment: Eolian (wind blown)

The Wingate Sandstone was deposited in an eolian environment made up of large sand dunes, similar to portions of the modern Sahara Desert. See Navajo Sandstone discussion for details that apply to the Wingate Sandstone as well.

Paleogeography: The Wingate Sandstone erg (a large sand sea) originally

lay at very low latitude, centered approximately 10o north of the equator. Like the Navajo Sandstone, its sediment source was at least partly from the Appalachian

Mountains (Dickenson and Gehrels 2003).

Directly adjacent to the south and west of the erg lay the erg margin facies of the Moenave Formation (Blakey et al. 1988, Blakey 1989, 2008, Clemmensen et al. 1989) . Tectonics:

The basinal area (created by tectonism) was subsiding significantly enough to provide enough accommodation space to capture and accumulate eolian sediment (Kocurek and Dott 1983).

Climate: Dry /Arid

Similar to the Navajo Sandstone, the climate in the Colorado Plateau region during deposition of the Wingate sandstone would have been very dry, classified as hyper-arid (Kocurek and Dott 1983, Loope et al. 2004). Features: The Wingate tends to from very blocky, vertical cliffs, likely related to different grain sizes and cementation compared to the younger (overlying) Navajo Sandstone. Because of the cliff weathering and smooth vertical faces, it is often difficult to see and access sedimentary structures in the Wingate Sandstone. It contains large-scale cross stratification characteristic of dunes and shows internal grain fall, grain flow, and wind ripple strata. Further, the desert varnish, iron oxide staining and weathering pattern of the Wingate Sandstone commonly obscures the trough cross stratification.

For further information on desert varnish see stop 2-6 (Petroglyphs). For more information on grain flow and wind ripple strata see the Navajo Sandstone page.


Stop 2-6 - Petroglyphs

Stop 2-7 - The Castle

Stop 3-1 - Wingate Sandstone


Wingate Sandstone

Figure 2: This is a map of the paleogeography of the western US during the deposition of the Wingate sandstone from Blakey, 1989 (p. 392). This map shows the Wingate Sandstone covering parts of Utah and Arizona and extending into Colorado and New Mexico. To the south and west of the primary Wingate erg are the erg margin facies of the Moenave Formation. It was originally believed that fluvial channels in the Moenave Formation carried sediment from source areas in the south to the northwest of the erg, from where the sediment could be blown into the dune field. Recent detrital zircon work has proved that much of the sediment was transported from eastern North America to the northwest of the Wingate erg to be transported by the wind into the dune field.

Figure 3: Figure from Loope et al., 2004 (p. 317) showing the primary wind direction for the Wingate Sandstone.

Figure 4: Figure from Loope et al., 2004 (p. 318) showing reorientation of trade winds to westerlies at low latitudes due to regional low-pressure regimes driving monsoon systems.

Wingate Sandstone

Figure 5: Though it is hard to see elsewhere in the park because of the desert varnish, iron oxide staining, and weathering, the Wingate does have large-scale trough cross strata common to sand dunes. These trough cross strata are visible when you can get very close to the rock, such as at the Petroglyphs stop. It is also possible to see the pock marked weathering pattern, common to the Navajo sandstone, called honeycomb weathering.

Figure 6: Since both the Wingate and Navajo Sandstones are eolian formations present in Capital Reef National Park, and are nearly adjacent formations with only the Kayenta formation separating them, it is important to be able to tell them apart. This photo shows the Wingate in the midground with the Navajo in the center background, on the skyline, and is good for highlighting the differences between the two formations. The Wingate tends to weather in shear, vertically jointed cliffs, while the Navajo tends to weather in rounded domes. The Wingate tends to be red from iron oxide staining, though as can be seen in the center midground the Wingate can also be bleached, while the Navajo is almost always a light, bleached color.

Wingate Sandstone

Chinle Formation

(Shinarump Conglomerate Member, Monitor Butte Member, Owl Creek Member)

Age:

Late Triassic

Depositional Environment: Non-marine fluvial channels, floodplains, paleosols, marshes, and small lakes.

Paleogeography/Tectonics: The Chinle Formation was deposited during the Late Triassic when the supercontinent Pangea had landmass on both sides of the equator. Utah lay at the paleolatitude of 15° N. On the western margin of the continent (the approximate location of California today) and in southern Arizona into Mexico, subduction complexes

contributed the volcanic ash to the bentonitic beds in the Chinle Formation (Prochnow et al., 2006.) East of Utah, the Uncompahgre highlands was a sediment source for Chinle deposits. (Prochnow et al., 2006)

Climate: The beginning of Chinle deposition was dominated by wet environments such as stream systems, lakes, wetlands, and deltaic distributary channels. Eventually the climate shifted and dryer environments prevailed such as seasonal stream systems and floodplains. By the end of the Chinle time, eolian deposits (sand dunes) indicate arid conditions.

Features: · Uranium-rich conglomeratic sandstones in the Shinarump Member.

This resistant basal unit is typically white, yellow, or gray in color. Sandstone structures within this subfacies include lenticular internal scour surfaces, large trough cross beds, and some horizontal laminations. The sandstone grades laterally into siltstone and mudstone lenses which contain organic carbon fragments as well as carbonized plant fossils (Dubiel, 1987). The Shinarump Member is a coarse-grained conglomeratic sandstone that represents a widespread fluvial channelbelt.

· Colorful variegated mudstones and bentonitic sediments in the Monitor Butte Member are gentle slope formers of the characteristic Chinle “badlands”. There is a gradational contact between the Shinarump and overlying Monitor Butte Member which is purple, yellow, and white mottled sandy siltstone and sandstone. This unit is known as the purple mottled unit (PMU), the color variations occur from different concentrations of iron bearing minerals (Dubiel, 1987). This unit contains lungfish burrows and represents a fluctuating water table which formed oxidizing and reducing environments which redistributed the iron in the sediments (Dubiel, 1987), along with fragments of plant material. The black mudstone has abundant conchostracans, fish scales, fragments of fish bone, and lenses of coal. This unit represents lacustrine marsh bog and wetland environments. Limestone, bentonitic sandstone, and siltstone occur above the coal units. Overall, the Monitor Butte Member was an extensive system of fluvial (stream) and deltaic distributary channels and splays, lacustrine (lake), prodelta and deltaic deposits (Dubiel,

Figure 1: Paleogeographic map of the Late Triassic, Chinle Formation. (Blakey, 2008)

Chinle Formation

1987).

· Carbonized and Petrified Wood in the Monitor Butte Member. Above the Moss Back Member, lavender and brown variegated mudstone and sandstone of the Petrified Forest Member (Dubiel, 1987 has bentonites (volcanic ashes), thin lenses of carbonate nodule conglomerate, and sandy units with large scale internal scour surfaces and large trough cross-stratification. Important fauna include abundant vertebrate remains, gastropods, lungfish tooth plates, and unionid thin shelled bivalves. This unit represents fluvial sandstone and floodplain mudstones and laterally restricted marsh mudstones. It was deposited by sinuous streams and had many avulsion (redirection of the stream) events. The Petrified Forest Member interfingers with pink and green limestone and red to orange siltstone of the Owl Rock Member. The limestone has mottled coloration and contains lungfish burrows and ostracodes. This indicates lacustrine basins and lacustrine margin deposition (Dubiel, 1987).


Stop 2-9: Chimney Rock and Fault Stop 2-10: Twin Rocks

Stop 3-2: Oyler Mine

Chinle Formation

Moenkopi Formation

(Black Dragon Member, Sinbad Limestone, Torrey Member, Moody Canyon Member)

Age:

Lower Triassic to possibly lower Middle Triassic

Depositional Environment: Tidal (also with nearshore, shallow marine, and some floodplain)

Paleogeography: The Moenkopi Formation was deposited along the western portion of the United States (Figure 1). Tectonics:

Very little tectonic activity was occurring during the time of deposition.

Climate: During the initial deposition of the Moenkopi Formation, the climate was rather hot and dry, then during the later

members (the Sinbad Limestone through the Moody Canyon Members) the climate progressively got wetter, but it was likely still arid (Blakey, 1973).

Features: The Moenkopi Formation preserves extensive ancient tidal and nearshore deposits. Continental conditions were located to the east, and marine conditions to the west. Four different members of the Moenkopi were deposited in the Capitol Reef region. The lowest Black Dragon Member was deposited under marine conditions preserving a shallowing upwards sequence, capped by beach sands and fluvial (river) deposits. Cyclic alternation of supratidal (above the ocean level) to subtidal (below ocean the level) deposits resulted in interbedded (alternating) mud and sand beds throughout much of the Moenkopi (Blakey, 1973).

Following the Black Dragon Member, the Sinbad Limestone Member was deposited under shallow marine conditions before clastic sedimentation resumed in the overlying Torrey Member. The final member, The Moody Canyon Member, was deposited under widespread, uniform, low-energy marine conditions, producing a generally "structure-less" mudstone (Blakey, 1973).

The Moenkopi Formation typically contains abundant thinly bedded mudstones and sandstones (Figures 2 and 3) with a large variety of ripple marks (Figures 4 and 5), and some trace fossils (impressions from animals in the sediment) (Figures 6 and 7). Secondary gypsum veins cut through this formation (Figure 8 and 9).


Stop 2-3 - Navajo Waterfall Stop 2-4 - Navajo Sandstone Soft Sediment Deformation

Stop 3-3 - Grand Wash Trail

Figure 1: Paleogeographic map of the Early Triassic, Moenkopi Formation. (Blakey, 2008)

Moenkopi Formation

Figure 2: Outcrops along the side of Hwy 24 showing the backside of The Castle. Lines have been added to show the contacts between the various formations visible at this stop.

Figure 3: Thinly laminated, alternating sandstone, siltstone and mudstone beds are typical of the Moenkopi Formation.

Figure 4: Current ripples “cast” from a sandstone bed.

Figure 5: Complex ripples from a sandstone bed.

Moenkopi Formation

Figure 6: Bioturbation where worms burrowed through the mud leaving U-shaped burrows.

Figure 7: Vertebrate "smears". This is where a small reptile swimming through the body of water scraped its claws through the mud on the bottom.

Figure 8: Gypsum veins running throughout the upper Moenkopi Formation directly underlying a Pleistocene Terrace.

Figure 9: Close up of the secondary gypsum veins showing the irregularity of the vein pattern.

Moenkopi Formation

Kaibab Limestone

Age:

Early Permian, 250 million years ago

Depositional Environment: Shallow Marine Shelf Deposit

Paleogeography: Sediment deposition was influenced by the Uncompahgre Uplift (ancestral Rocky Mountains), but by the end of the Permian, the Uncompahgre mountains had been worn down and was not longer a major sediment source.

Tectonics: Collision of the Gondwana Plate with the Northern Plate resulted in the

Uncompahgre highland.

Climate: Warm current winds

Features: The Kaibab Limestone is composed of impure cherty limestone and dolomite that interfinger with the White Rim Sandstone below it (Mathis, 2000). The Kaibab rocks range in color from gray, buff, and brown, to yellow/brown dolomite. Some sandy, carbonate beds are very fossiliferous (Condon, 1997). Invertebrate fossils include brachiopods, pelecypods, gastropods, crinoids, and bryozoans. The Kaibab formation in Capitol Reef National Park is only 0-200’ thick and but thickens to 300-500’ in the Grand Canyon (Morris, 2003). The difference in thickness is attributed to erosion. The environmental setting for the Kaibab Limestone was a shallow marine shelf deposit that represents the time of maximum eastward transgression of the Kaibab Sea (Condon, 1997). The Kaibab Sea began to withdraw by the Middle Permian, which left these sediments exposed to be subject to erosion (Condon, 1997). The Kaibab Limestone is visible at the Goosenecks Overlook in Capitol Reef National Park.


Stop 2-8: Goosenecks Overlook as seen at Panorama Point

Figure 1: Paleogeographic map of the Middle Permian, Kaibab Formation. (Blakey, 2008)

Permian Rocks

White Rim Sandstone

(in Cutler Group)

Age:

Early Permian, 280 million years ago

Depositional Environment: Coastal dune field (eolian with some marine transgressions)

Paleogeography: Sediment deposition was affected by the Uncompahgre uplift , but by the end of the Permian the Uncompahgre mountains had been worn down and was not longer a major sediment source.

Tectonics: The collision of the Gondwana Plate with the North American Plate resulted

in the Uncompahgre highland.

Climate: Warm

Warm current winds

Features: The White Rim Sandstone is the upper member of the Permian Cutler Croup of rocks. The White Rim Sandstone gets its name from the white color that is due to bleaching from hydrocarbons (organic compounds). This formation often creates a white band found along canyon rims where it is often relatively thin. The White Rim Sandstone is a cliff-forming formation consisting of fine- to coarse-grained sandstone (Condon, 1997). This sandstone commonly displays large scale, high-angle cross-beds (dipping sediment layers) deposited by wind blown dunes. The thickness of this formation ranges from 5 to 75 feet thick (Morris, 2003). The depositional environment that this was deposited in was a coastal dune field that was intermittently flooded by marine water resulting is some reworking of sediments (Komola and Chan, 1988). The White Rim Sandstone can be viewed from the Goosenecks Overlook at the bottom of Sulphur Creek Canyon in Capitol Reef National Park.


Stop 2-8: Goosenecks Overlook as seen at Panorama Point

Figure 1: Paleogeographic map of the Middle Permian, Kaibab Formation. (Blakey, 2008)

Permian Rocks

Stops to visit at in Capitol Reef National Park

Day 1 Day 2 Day 3 Day 4

Stop 1-1

Inverted Channels

Stop 1-2

Goblin Valley State Park

Stop 1-3

Summerville Formation Stop

Stop 2-1

San Rafael Group Overlook

Stop 2-2

Carmel Formation

Stop 2-3

Navajo Waterfall

Stop 2-4

Navajo Sandstone Soft Sediment Deformation

Stop 2-5

Hickman Bridge Hike

Stop 2-6

Petroglyphs

Stop 3-1

Wingate Sandstone

Stop 3-2

Oyler Mine

Stop 3-3

Grand Wash Trail

Stop 3-4

Moenkopi Formation

Stop 3-5

Slickrock Divide

Stop 4-1

Curtis Formation

Stops at Capitol Reef and Surrounding Areas

Stop 2-7

The Castle

Stop 2-8

Panorama Point

Stop 2-9

Chimney Rock and Fault

Stop 2-10

Twin Rocks

Stop 2-11

Iron Mineralization along Fault

Stops at Capitol Reef and Surrounding Areas

Stop 1-1

Inverted Channels

Exhumed channels in Salt Wash Member of the Jurassic Morrison Formation

Location: N of I-70W on Rt. 24 (exit 149). Turn right (N) on Rt. 24 exit. Park when road turns to dirt.

GPS Location:

38o 55.545' N

110o 22.711' W

Ages:

Late Jurassic (155-148 Ma)

Rock Units: Morrison Formation: Salt Wash Member of the Jurassic Morrison Formation; Cretaceous Burro Canyon Formation (possible).

Features Present: Exhumed channels of the Salt Wash Member (Fig. 1) exhibiting trough cross bedding (Fig. 2) and fining upward sequences (Fig. 3). Large clasts are mostly chert.

Depositional Environment: Fluvial system flowing to the east (Turner and Peterson, 2004).

Interpretation: Resistant channel sandstones were surrounded by soft shales (floodplain deposits). As the area was uplifted and erosion occurred, the soft shales eroded more easily exposing the more resistant, cemented channel sandstones These are excellent examples of channel sandstones that analogous to features imaged on Mars (Williams et al., 2007).

Other: Exhumed channels on top of high cliffs are probably Cretaceous Burro Canyon Formation channels (Fig. 4).

Figure 1: Exhumed Salt Wash channels outlined in dotted lines.

Figure 2: Trough cross bedding in Salt Wash Member (outlined with dotted lines). This view is along strike of flow (~70°).

Stop 1-1

Figure 3: Fining upward in trough cross bed sequence. Tick marks on top of card = 1 cm. Grain size becomes smaller (along arrow) due to reduction of energy in river flow through channel.

Figure 4: Exhumed Burro Canyon Formation (?) channels (top of cliffs adjacent to road). This formation is coarser grained than the Salt Wash Member.

Stop 1-1

Stop 1-2

Goblin Valley State Park

Jurassic Entrada “earthy facies” – Goblin Valley

Location:

24 miles south of I-70 on Highway 24

GPS Location:

38o 33.855' N

110o 42.184' W

Ages: Late Jurassic (80 and 140 ma)

Rock Units:

“layer-cake” geology of several units (in descending order) Morrison Formation


Curtis Formation

Entrada Sandstone (making up the “goblins”)

Features Present:

The Entrada Sandstone is made up of reddish-brown sandstones and mudstones comprising some of the typical redrock country of the Colorado Plateau, principally colored by the mineral hematite (an iron oxide and principal ore of iron). This formation lies between gray cliff-making rocks below and white massive beds above (Curtis Formation). The Entrada Sandstone is the same formation that erodes to arches, spires and hoodoos in Arches National Park (southeast Utah) and in Cathedral Valley in Capitol Reef National Park.

The dark red, fine-grained Entrada sandstone beds are generally less than a meter thick with some thin whispy white bands. The formation also includes thin sheets and small masses of gypsum, lenticular beds of gypsiferous shale, some calcareous shales, and small scattered red and green clay rip-up clasts.

The formation is up to 425 vertical feet of flat lying sandstones beds interpreted to be tidal flat deposits with some climbing ripples, and some mudstone rip-up lags. Some beds are remarkably massive. Sandstone beds typically form the cap of the goblins, underlain by softer horizontal layered pedestals of siltstone and mudstone. The Entrada formation readily disintegrates from weathering and erosion. Joint or fracture patterns in the Entrada Sandstone create initial weak zones that are enlarged by weathering (e.g. spheroidal weathering) to created the round-shaped goblins.

Depositional Environment:

Sabkha, tidal, and nearshore ("earthy facies")

Map of Goblin Valley State Park

Stop 1-2

Figure 1: Climbing ripples in the Entrada Sandstone (climbing to the right) are overlain by parallel, flat lamination. These structures imply high sedimentation rates, and relatively high energy typical of a beach setting (parallel lamination where Froude number = 1).

Figure 2: Higher energy pulse of coarser-grained sand cut into finer-grained mud to produce the preserved mudstone rip-up clasts incorporated into the channelized sandstone.

Figure 3: Entrada goblins and hoodoos from the main parking lot on the right side of the road just past the entrance to Goblin Valley State Park. Wild Horse Butte, in the background, exposes all four rock formations (The Morrison, Summerville, and Curtis Formations, and the Entrada Sandstone).

Stop 1-2

Stop 1-3

Summerville Formation Stop

Location: Immediately west of Hanksville. Summerville Formation outcrop on the north side of Highway 24.

GPS Location:

38o 22.263' N

110o 45.064' W

Ages: Late Jurassic, deposited during early to late Oxfordian time (161 - 155 Ma) (Wilcox, 2007)

Rock Units: Summerville Formation

Features Present: The Summerville Formation consists of two generalized lithofacies including a silty mudstone/sandstone and an upper facies of more gypsiferous mudstone and sandstone (Wilcox, 2007). Intercalated chocolate red mudstones, very fine- to fine-grained sandstones, and gypsum are typical of Summerville Formation in outcrop (Figure 1). Bedding is dominantly tabular. Sedimentary structures include ripple cross lamination (Figure 2) and polygonal mudcracks filled with light-colored sand (Figure 3).

Depositional Environment: Tidal. The Summerville Formation is mud-dominated intertidal to supratidal deposits of the Jurassic epicontinental sea. The lower boundary of Summerville is gradational with upper facies of the marine Curtis Formation and indicates a gradual shallowing of sea through time. Caputo and Pryor (1991) describe the deposition of Summerville as mud rich, restricted, evaporative, hypersaline conditions. Upper Summerville, with its desiccation mud cracks and ever present evaporite stringers, represents the supratidal stage of the upward shallowing cycle in the last vestiges of the receding Jurassic seaway. Interpretation: The reddish brown silty facies and gypsiferous facies in the Summerville Formation were deposited in the supratidal stage of the upward shallowing cycle in the Curtis-Summerville regression (Caputo and Pryor, 1991). The Summerville Formation tabular sand bodies and mudstones are interpreted to represent a tidal flat environment. The presence of polygonal sand filled shrinkage cracks (Figure 3) suggests periodic subaerial exposure. Numerous thin evaporite layers formed from hypersaline waters that periodically dried up. The lack of trace fossils indicates a paucity of life possibly due to an ecologically stressed paleoenvironment. Upper Summerville in some areas is interpreted to represent a sabkha environment (Wilcox, 2007).

Stop 1-3

Figure 1: Summerville Formation outcrop on Highway 24, grain size and bed thickness tend to increase up section.

Figure 2: Gypsum stringers cut across ripple forms.

Figure 3: Vertical mudcracks filled with sand, representing polygonal desiccation cracks in the clay bed.

Stop 1-3

Stop 2-1

San Rafael Group Overlook

Location: East Park Boundary/San Rafael Group overlook, Highway 24 rest stop on north side of road.

GPS Location:

38o 17.042' N

111o 07.719' W

Ages: Late Jurassic

Rock Units: Summerville Formation

Curtis Formation

Entrada Sandstone

Carmel Formation

Features Present: Rock layers to the north are Upper Jurassic, San Rafael Group including the Carmel Formation, Entrada Sandstone, Curtis Formation, and Summerville Formation (Figure 1). The basal red sandstones and siltstones of the Entrada Sandstone are topped by the Jurassic-3 (J3) unconformity and the greenish-gray, fine-grained Curtis sandstones. Sedimentary structures within the Curtis Formation transition up section from hummocky cross stratification to trough cross stratification (Wilcox, 2007). The Curtis Formation is relatively thin here (~ 24 m) and grades upward into redish brown silty mudstones of the Summerville Formation. Top of Curtis is often marked by a color change from greenish gray to the Summerville chocolate red. The Summerville is ~ 60 m thick here and consists of intercalated fine-grained sandstone, mudstone, and gypsum. The Summerville upper contact is the Jurassic-5 (J5) unconformity, overlain by lowermost beds of the Morrison Formation which forms the caprock.

Depositional Environment: Marginal marine

The red beds of the Entrada Sandstone are underlain by Carmel Formation which typically shows soft sediment deformation (Figure 2). The Entrada Sandstone in this area was deposited in shallow water, probably in a tidal flat environment, whereas further east the Entrada transitions into an eolian environment. The Jurassic marine incursion over the Carmel deposits, transgressed generally from north to south and is characterized by basal medium to coarse sandstone that fines upward to calcareous green gray mudstone which represents the time of maximum flooding during the Curtis-Summerville cycle. Above the green gray marine mudstones, upward coarsening cycles are representative of a shoaling sea. Tidal sedimentary structures are present in the middle Curtis Formation to the north (See Stop 4 – 1 along I-70, Kreisa & Moiola 1986). Generally, more terrestrial facies occur to the south and open-marine conditions are documented to the north (Figure 3; Wilcox 2007). The upper 10 meters of Curtis and overlying Summerville Formation redbeds are intertidal mixed mud, sand flat, and tidal channel facies (Kreisa & Moiola, 1986).

Interpretation: The Late Jurassic epicontinental seaway inundated the Entrada terrestrial deposits as recorded in the J3 unconformity marking the Curtis-Summerville Formations transgressive-regressive cycle. The basal Curtis contact may show erosional scours and lenticular fill along the J3 unconformity. In a sequence stratigraphic context, the Curtis-Summerville Formations are interpreted to represent one unconformably bound, transgressive-regressive (T-R) sequence associated with the Jurassic Interior seaway. Regionally, the Curtis Formation lithofacies thin to the south and thicken toward the Jurassic seaway in the north. Lower Curtis Formation green-gray mudstones (Figure 1) are interpreted as offshore marine (below fair-weather wavebase). Middle Curtis Formation ripple-cross laminations and flaser bedding are interpreted as tidally influenced lower shoreface and estuarine-like conditions. Upper Curtis Formation horizontal laminations are interpreted as subtidal to intertidal (Wilcox, 2007). As the Curtis-Summerville shoreline migrated seaward, the Summerville Formation reddish-brown silty mudstones are interbedded with evaporites, and is interpreted as a tidal flat, sabkha environment (Figure 3).

Stop 2-1

Figure 1: The uppermost units of the San Rafael Group (from bottom to top, Entrada Sandstone, Curtis Formation, and Summerville Formation) capped by the basal conglomerate of the Tidwell Member of the Morrison Formation (Mathis, 2000).

Figure 2: Soft sediment deformation in the Carmel Formation (scale: outcrop covers several meters).

Figure 3: Middle-Late Jurassic paleogeography (Kocurek & Dott, 1983).

Stop 2-1

Stop 2-2

Carmel Formation Stop

GPS Location:

38o 17.066' N

111o 08.996' W

Ages: Middle Triassic

Rock Units: Morrison Formation

Carmel Formation

Features Present: Carmel Formation

Just off Highway 24 is a prominent angular unconformity. An angular unconformity

occurs when older sediments that generally dip at a steep angle are eroded and then overlain by younger sediments that dip at a lesser angle (typically horizontal) atop the older rocks (Boggs, 2006). In this figure, the Pleistocene terrace deposits overlie the Jurassic Carmel Formation. The Carmel Formation, composed of interbedded sandstone, siltstone, limestone, and gypsum, dips ~ 10° to the east (Mathis, 2000). The Pleistocene terrace forms the horizontal bed above the Carmel. A significant amount of time (~ 165 million years) is lost/missing in between the older tilted layers and the younger horizontal layers.

Salt Wash, Tidwell, Summerville Salt Wash Member fluvial channel sandstone overlie the thin Tidwell Member (~3 m thick). The Tidwell Member is not always present in this area. Where the member is present in the Capitol Reef area, it is interpreted as a gypsiferous, hyper-saline lagoon (Turner and Petersen, 1998) evidenced by crinkly bedding. Tidwell Member crinkly bedding. The unit is ~3 m thick. The bedding has been disrupted due to dissolution of evaporite minerals. The Morrison formation Salt Wash Member representes channel deposits, and the overlying Brushy Basin Member contains floodplain and paleosol deposits.

Stop 2-2

Figure 1: Angular unconformity with Pleistocene terrace overlying the Carmel Formation.

Stop 2-2

Stop 2-3

Navajo Waterfall

GPS Location:

38o 17.296' N

111o 09.774' W

Ages: Early - Middle Jurassic

Rock Units: Page Sandstone

Navajo Sandstone

Features Present: The waterfall overlook is a good place to view the contact between the Navajo Sandstone and the overlying Page Sandstone. Because they are of very similar lithology, the Page Sandstone and Navajo Sandstone

were not originally differentiated as separate formations. It was not until the recognition that the J-2 unconformity, subtly indicated by a lag deposit, was a disconformable surface separating the two formations that stratigraphers identified them as two separate formations. The Page Sandstone is separated into three members, which are identified below (Mathis 2000).

Across Hwy 24 from the waterfall overlook is the abandoned former channel of the Fremont River. In 1962 the Fremont River was rerouted as part of construction of Hwy 24. Exposed in the east wall of this former channel are soft sediment deformation structures in the uppermost Navajo Sandstone. In general, the upper third of the Navajo Sandstone formation contains more soft sediment deformation than lower portions. This may indicate that it was deposited in a wetter environment, or perhaps that watertable flucuations were an important factor in soft sediment deformation.


Figure 1: The Page Sandstone is subdivided into three members. The

Figure 2: This picture shows some soft sediment deformation in the east side

Stop 2-3

lowermost member, the Harris Wash Tongue, is the thickest and is composed of trough cross-bedded sands grading up into planar-bedded sands. This indicates a transition from a dune field to a sand sheet environment, which could indicate that the environment was becoming wetter through time. The next member is the recessive, shaley Judd Hollow Tongue, which records a wet, muddy flood plain environment. This would have been the wettest period during the deposition of the Page Sandstone and would have been marked by the presence of lakes, fluvial channels and an absence of sand dunes. The top member is the Thousand Pockets Tongue, composed primarily of trough cross strata that are smaller in size than the lower Harris Wash Tongue. This indicates a return to a drier environment with sand dunes, after the wet Judd Hollow interval.

of the former Fremont River channel. In the right side of the picture the bedding is trough cross stratification, fairly typical to the Navajo Sandstone. To the left side of the picture the strata are vertical, and in between the strata curve from vertical to pointing to the upper right. The origin of this soft sediment deformation is unknown, though it has been speculated that it is a fluid escape structure. Fluid escape structures do not usually leave behind vertically bedded strata, so the ultimate cause of the soft sediment is still a mystery.

Stop 2-3

Stop 2-4

Navajo Sandstone Soft Sediment Deformation

GPS Location:

38o 17.059' N

111o 09.854' W

Ages: Early Jurassic

Rock Units: Navajo Sandstone

Features Present: This is another example of soft sediment deformation in the Navajo sandstone called a pop up/flower structure (Morris et al. 2003). This structure may have been caused by overpressurized pore pressures and strong ground motion (e.g., possible

Jurassic seismic activity).


Figure 1: Large Navajo Sandstone soft sediment deformation feature (“pop up/flower structure”).

Figure 2: A closer view of the “pop-up/flower structure “ shows the deformation of the cross stratification this is continuous across the top of the fold.

Stop 2-4

Stop 2-5

Hickman Bridge Hike

GPS Location:

Start of hike: End of hike:

38o 17.314' N 38o 17.481' N

111o 13.664' W 111o 14.062' W

Ages: Early Jurassic

Rock Units:

Navajo Sandstone

Kayenta Formation

Features Present: The Hickman Bridge hike is a 2 mile round trip hike to a natural bridge in the Kayenta Formation that includes several good outcrops along the way. In the distance large-scale eolian features in the Navajo Sandstone are evident.

In particular, the Hickman Bridge hike, like the Grand Wash hike, is a very good place to view eolian cross bedding even though the hike is entirely within the Kayenta Formation. Large-scale features can be seen in the Navajo formation at a distance, while other depositional features are close in the fluvial and eolian portions of the Kayenta. Besides the Mesozoic geological features, there are a good variety of modern geologic features to see. Cenozoic black andesite and basaltic andesite boulders occur in the wash that have been eroded and transported from nearby Boulder and Thousand Lake Mountains. A developing field, known as in-situ terrestrial cosmogenic nuclide (TCN) radioactive dating, allows scientists to calculate an age of how long these boulders were exposed to the surface (like a “suntan”) and therefore gives us an idea of how long they have been sitting exposed in the park (Waitt 1998). TCNs are formed by bombardment of cosmic rays from the sun and other stars. Much the same as carbon-14 is produced in the atmosphere from the interaction of cosmic rays and nitrogen-14, isotopes of helium, beryllium, carbon and aluminum, among others, are produced in rocks due to the interaction of cosmic rays and the minerals and atoms in the rock. Since cosmic rays are the only source for most of these isotopes it is possible to determine an age on the sample based on how much of the isotope is present. Further, since cosmic rays cannot penetrate very far into the Earth, these cosmogenic nuclides are only produced within the top foot or so of the Earth’s surface. This means that the age that is determined by measuring the isotopes indicates how long the rock has been exposed at the earth’s surface (e.g., Fig. 1 boulders).

Figure 1: Black, volcanic (andesite) boulders derived from Boulder Mountain and Thousand Lake Mountain are part of the Pleistocene river terraces that cut into the Navajo Sandstone. The lava flows are between 30 Ma and 6 Ma old, but the boulders themselves are recent additions to the park. Absolute age dating using in-situ terrestrial cosmogenic radionuclides (TCN) of the boulders shows that they were exposed and eroded from the volcanic cliffs during the last Ice Age.

The angularity of the boulders indicates these were not transported by streams, and recent work shows that the glaciers in the area were fairly

Figure 2: Although the Kayenta Formation is primarily fluvial and flood plain facies, some eolian deposits (this image) in the upper parts of the formation (Billingsley et al, 1987). General information on grain flow and wind ripple strata is in the Navajo Sandstone webpage.

Stop 2-5

small, so neither rivers nor glaciers are considered to be the transportation agents for these boulders. Instead, increased rainfall during the Ice Age likely led to debris flows and wet landslides that flowed down from the high mountain plateaus into the lower river valleys. Since the boulders were deposited in the valleys the rivers have continued to erode downwards leaving the boulders perch on what are called strath terraces, the former river overbank areas.

Figures 3-4: Internal wind ripple strata and the grain flow strata are distinguishable in the eolian crossbed sets. The wind ripple strata are the thin, parallel, “pin-stripe” laminations, and the grain flow strata are the thicker deposits that pinch out downdip. On close inspection with a hand lens the wind ripple laminae are inversely graded, i.e. the coarser sand grains are at the top of the laminae.

Stop 2-5

Figure 5: Hickman Bridge is a natural bridge in a white eolian unit within the upper Kayenta Formation. It is similar in appearance to, but not the same as the Navajo Sandstone. A natural bridge is similar in appearance to a natural arch, like those at Arches National Park, but is formed instead by different processes. Hickman Bridge formed when water managed to weather a small opening into the rock dividing the two drainages at the bridge at a layer of mudstone. As more water flowed through the opening it continued to grow to its modern size, with the captured stream flowing underneath. By comparison, an arch is not created by flowing water, but is formed by freeze-thaw cycles of water in the rock slowly breaking the rock down. Though the resulting features may look similar, a bridge is likely to have a relatively flat top connecting two sides of a canyon with a stream underneath, whereas an arch is more likely to be free standing on a relatively flat surface and will not be associated with a stream (Mathis, 2000).

Figure 6: Concretions. Continuing up Hickman Bridge Trail, which is within the Kayenta Formation (Jurassic in age) one may encounter cemented mineral masses called concretions. These resemble spheres, but are composed of cemented sand from later fluids that moved through the porous sandstone. These concretions have calcite cement, as tested with the HCL acid which makes them fizz. Some concretions are aligned with the fractures in the rock where there would be preferential fluid flow. Some of the concretions were truncated against from a joint/fracture.

Figure 7: Debris Flow. Just before you reach Hickman Natural Bridge you pass by a debris flow. A debris flow is a moving mass composed of rock fragments, soil, and mud, where the majority of the particles are larger than sand size (Bates et al., 1984). The clasts are a mix of chaotic sizes. The unsorted flow becomes a slurry (a mix of water and fine grains) where the large boulders “float” to the top because the finer (smaller) particles float to the bottom. Scale bar is 10 cm long.

Stop 2-5

Stop 2-6

Petroglyphs

GPS Location:

38o 17.284' N

111o 14.538' W

Ages:

Lower Jurassic

Rock Units:

Wingate Sandstone

Features Present:

Remarkable cultural features also occur in Capitol Reef National Park. The park also has a long history of human habitation. Modern indicators of habitation include the orchards and barns of the historic Fruita district, but just nearby are indicators of much older civilizations. In the Fremont River Valley, just across Hwy 24 from

some of the former orchards, are petroglyphs attributed to the Fremont Indians who occupied the area from 700 CE to 1300 CE (Mathis 2000. These petroglyphs have been carved into the desert varnish of the lowermost part of the Wingate Sandstone, just above the contact with the Chinle Formation. In most parts of the park, the Wingate Sandstone comprises inaccessible, tall cliffs. The petroglyph stop is one of the few places to get up close to the Wingate where it shows some the large cross stratification common to eolian systems.


Figures 1-2: Petroglyphs on the Wingate Sandstone are attributed to the Fremont Indians who occupied the Fremont River Valley from 700 CE to 1300 CE (Mathis, 2000).

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Figure 3: More petroglyphs attributed to the Fremont Indians.

Figure 4: On close inspection, the Wingate Sandstone shows large-scale eolian cross beds similar to the Navajo Sandstone.

Figure 5: The contact between the Chinle Formation and the overlying Wingate Sandstone is visible at the petroglyphs stop. The contact occurs at the break of slope between the overlying cliff forming Wingate Sandstone and the slope forming Chinle Formation.

Figure 6: Desert varnish gives the red to brown to black appearance of many outcrops in the desert southwest. Desert varnish is primarily made of iron and manganese oxides. It is only presenton outcrop faces that have been exposed for a long periods of time. Fresh rocks faces are free of the desert varnish, and typically have a vertically streaked appearance where water runs down the face of the outcrop.

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Stop 2-7

The Castle GPS Location:

38o 17.903' N

111o 16.338' W

Ages: Triassic - Lower Jurassic

Rock Units: Wingate Sandstone

Chinle Formation

Moenkopi Formation

Features Present: The view of the Castle from the Capitol Reef National Park Visitor Center is very popular, but the view of The Castle from the west along Hwy 24 is still spectacular. From here, one can see the dark red Moenkopi Formation and the variegated Chinle

Formation, capped by the tall cliffs of the Wingate Sandstone that have weathered into the Castle.

On the south side of the road is a good outcrop of the Moenkopi Formation in an acessible stream bed. Here there are many sedimentary structures exposed along bedding planes, such as different varieties and sizes of ripple marks (Figures 3 and 4) and trace fossils (fossils left by animal activity) including reptile "scrapes" in the mud (Figures 5 and 6).

Figure 1: View from the side of Hwy 24 showing the backside of The Castle. Lines show the contacts between the prominent formations.

Figure 2: View of The Castle from the Capitol Reef National Park Visitor Center.

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Figure 3: Wave ripples along a bedding plane surface of the Moenkopi Formation.

Figure 4: Complex ripples seen on one of the shale beds in the Moenkopi Formation.

Figure 5: Bioturbation structures where worms burrowed through the mud leaving U-shaped burrows (paired holes).

Figure 6: Vertebrate "smears". This is where a small reptile swimming through the body of water scraped its claws through the mud on the bottom. The scrapes were then cast and filled with overlying sand.

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Panorama Point

GPS Location:

38o 18.428' N

111o 17.751' W

Ages: Triassic

Rock Units:

Chinle Formation

Moenkopi Formation

Features Present: Panorama Point is a great location to view the diverse geology of Capitol Reef National Park (Figure 1). The formations of the Jurassic Glen Canyon Group are readily apparent. The red Wingate Sandstone is overlain by the

distinctly bedded Kayenta Formation ,which is then overlain by the white Navajo Sandstone. The Waterpocket Fold monocline has tilted these formations 10° to the east in this area (Mathis, 2000). A monocline is a geologic feature where the layers of sediment have been altered and compressed and resemble a stretched out “s” on its side. The monocline in Capitol Reed National Park is 100 miles long (Morris, 2003). This area of Capitol Reef National Park boasts about having the cleanest, clearest air in America. On a clear, sunny day, one can see the Henry Mountains in the distance. The tallest peak in the Henry Mountains is Mount Ellen at an elevation of 11,615 feet (Mathis, 2000). The Henry Mountains were formed 31.2-23.3 Ma (million years ago). Named by John Wesley Powell, this was the last mountain range to be mapped in the lower 48 states of America (Mathis, 2000).

Near the parking lot at Panorama Point is a large outcrop that displays Triassic Moenkopi Formation (tidal) overlain by the greenish-grey Shinarump member (fluvial) of the Chinle Formation. In Figure 2, one can see the distinctive formations as well as the noticeable sequence boundaries. At the bottom of the outcrop, the red, layered-cake looking rock is the Moenkopi Formation. Especially noticeable on the right side of this figure on top of the Moenkopi formation are the two sequence boundaries (S1 at the bottom and S2 at the top; R. Dubiel 2010 pers. comm.) of the Shinarump (the white to tan colored rock capping the red Moenkopi). Above that is the white to green colored Chinle eroding into soft triangle-shaped mounds followed by more white/tan rock that represents a fluvial part of the Chinle Formation.

Other: Goosenecks Overlook: Optional Foot Trail

From the parking lot of Panorama Point, the 0.1mile foot trail leading you to the Goosenecks Overlook is an option for people who want to see the oldest rock formations exposed in Capitol Reef National Park (Mathis, 2000). The Goosenecks Overlook looks down into the 800 feet deep Sulphur Creek canyon. The creek has eroded the rocks in a wandering way that produced a shape that resembles that of a goose’s neck, hence the name Goosenecks Overlook (Mathis, 2000). The canyon floor exposes the Permian age rocks (250 to 290 million year old) of the Cutler Group (Morris, 2003). The most basal unit at the bottom of this canyon is the White Rim Sandstone. The White Rim Sandstone is white due to the bleaching of hydrocarbons. The White Rim Sandstone environment was eolian, a coastal dune complex subjected to periodic flooding by marine waters (Kamola and Chan, 1988). Interfingering with the White Rim Sandstone is the overlying Kaibab Limestone. The Kaibab Limestone ranges from gray, buff, brown, to yellow/brown in color (Condon, 1997). It is an impure cherty limestone and dolomite, and represents deposition in a shallow marine shelf during the maximum eastward transgression of the Kaibab Sea (Condon, 1997). On top of the Kaibab is the canyon rim forming Moenkopi Formation (red).


Chinle Formation - Fluvial and floodplains

Moenkopi Formation - Tidal

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Figure 1: View from Panorama Point.

Figure 2: The Moenkopi formation overlain by the Chinle Formation.

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Stop 2-9

Chimney Rock and Fault

GPS Location:

38o 18.935' N

111o 18.214' W

Ages: Triassic - Lower Jurassic

Rock Units:

Wingate Sandstone

Chinle Formation

Moenkopi Formation

Features Present: Erosion of the rock in the shape of a Chimney


marginal marine to non-marine

The Moenkopi Formation exhibits marginal marine to continental alluvial fans deposits and also includes deltaic, shoreline, mudflat, tidal, estuarine, sabkha (supratidal setting on arid an coastline), fluvial (river), and some minor eolian (carried by wind) deposits. The majority of the Moenkopi at this locality is largely tidal flat and floodplain. The Chinle depositional environments are fluvial and some lacustrine (lake). The Shinarump Member here is a tabular, planar-stratified, fluvial sandstone. The Shinarump has an irregular distribution and may be thick in some areas where it filled in paleovalleys, although elsewhere it can be much thinner to non-existent.

Interpretation: During the Late Triassic, the supercontinent Pangaea was symmetrically straddling the equator and Utah was located around a paleolatitude of 10° north and was continuing to shift northward entering a more subtropical zone (Dubiel et al. 1991, Dubiel 1994). The Chinle Formation as a whole is a series of fluvial-lacustrine system with a tropical monsoonal climate. This region would receive a good amount of precipitation but would be interrupted by seasonally dry periods. (Dubiel et al., 1991.) Tectonically, the Chinle was deposited in a continental back-arc basin on the west coast of Pangea.

Depositional Environment: Chinle Formation - Fluvial and floodplains

Moenkopi Formation - Tidal

Figure 1: Chimney Rock.

Figure 2: Fault view to the left of Chimney Rock. The Shinarump Member on the left side of the photograph is downdropped compared to the right side. The blue dotted line indicates the inferred location of a normal fault. The footwall is the Moenkopi Formation overlain by the Shinarump (right of photo) and the hanging wall is the Shinarump overlain by the Wingate (left of photo).

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Stop 2-10 Twin Rocks

GPS Location:

38o 19.342' N

111o 20.263' W

Ages: Triassic

Rock Units: Shinarump Conglomerate Member (Chinle Formation) Moenkopi Formation

Features Present: In the Moenkopi Formation, many varieties of ripples

along bedding planes and in cross-sectional view are present in loose rock slabs around the Twin rocks. Above the contact of the Moenkopi , mud rip -up clasts are common in the base of the Shinarump channel sandstones.

Depositional Environment: The Moenkopi Formation regionally preserves environments of shallow marine to continental alluvial fans and also includes marginal marine, deltaic, shoreline, mudflat, tidal, estuarine, sabkha (arid supratidal - above tide level), fluvial (river), and eolian (wind blown) deposits (Dubield 1994). In this locality, the deposits are largely thin-bedded tidal and floodplain deposits. The Chinle depositional environments are typically fluvial. The Shinarump Member here is a tabular planar stratified sandstone with an irregular distribution that may be thick in some areas where it filled in paleovalleys.

Interpretation: During the Late Triassic, the supercontinent Pangaea was symmetrically straddling the equator and Utah was located around a paleolatitude of 10° north and was continuing to shift northward entering a more subtropical zone. The Chinle Formation as a whole is a fluvial-lacustrine system with a tropical monsoonal climate. Meaning the region would receive a good amount of precipitation but would be interrupted by seasonally dry periods. (Dubiel, 1991.) Tectonically, the Chinle was deposited in a continental back-arc basin on the west coast of Pangea.

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Figure 1: The Twin Rocks stop shows the contact between the Moenkopi Formation and the overlying Shinarump Member of the Chinle Formation marked by the thick red lines. The far left arrow points to a slumped Shinarump boulder (not in original position). A happy grad student on the Capitol Reef National Park field trip with other equally happy students in the background.

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Stop 2-11

Iron Mineralization along Fault

GPS Location:

38o 19.434' N

111o 20.859' W

Ages: Triassic

Rock Units:

Shinarump Member of the Chinle Formation

Moenkopi Formation

Features Present: Iron oxide cementation along fault creates ~2 m wide resistant face (Fig. 1).

Interpretation: Faults create conduits along which fluids can flow more easily. The concretionary mineralization results when iron bearing reducing fluids flow along the fault, come in contact with oxidizing fluids and iron oxide precipitates (e.g., Chan et al., 2000). Clusters of spheroidal concretions are also present (Fig. 3). The cementation causes a resistant ridge that runs parallel to the highway.

Figure 1: Resistant, iron oxide mineralization along face of fault (arrow).

Figure 2: Normal fault (shown with line) with Shinarump Member of the Triassic Chinle Formation (lower left) downthrown against the Triassic Moenkopi Formation (upper right). Large tick marks on scale bar = 1 cm.

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Figure 3: Cluster of spheroidal iron oxide concretions. Large tick marks = 1 cm.

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Wingate Sandstone

GPS Location:

38o 15.452' N

111o 14.087' W

Ages: Lower Jurassic

Rock Units: Wingate Sandstone

Features Present: Although the Wingate Sandstone is typically reddish in color, due to the precipitation of iron oxides in the spaces between the

individual sand grains. This red coloration can happen with subaerial exposure at the Earth’s surface during or shortly after deposition, or even later when the rock has been buried (part of the digenetic process). Sometimes the Wingate Sandstone has a light, buff color from the bleaching of iron oxide stained sandstone. Fluids such as hydrocarbons with the ability to reduce iron oxide are critical to the bleaching process (Parry et al. 2004). Bleaching in much of the Navajo Sandstone is due to its relatively high permeability allowing fluids to flow through the rock, and is believed to indicate that the Navajo was once a significant hydrocarbon bearing formation (Beitler et al. 2003). The lack of bleaching in the Wingate Sandstone is a potential indicator that it is not as permeable to large-scale fluid flux (compared to the Navajo Sandstone). Locally areas of bleaching are present in the Wingate cliffs to the east of Scenic Dr, south of the park visitor center, in the vicinity of the Oyler Mine. In this locality, the lowermost portions of the Wingate (those directly above the Chinle Formation), appear to be bleached. A possible explanation for this bleaching is that the relatively impermeable mud-rich intervals of the Chinle Formation locally forced increased fluid flow in the lower most Wingate Sandstone. Fluids traveling downward through the Wingate Sandstone could not likely continue down into the Chinle, and would therefore have to travel along the boundary between the two formations to create a zone of increased fluid flow in the lower portions of the Wingate Sandstone.


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Figure 1: View from Scenic Dr. of the Wingate Sandstone. The lowermost portion of the Wingate Sandstone is bleached while the upper portion of the formation retains red coloration. Contacts between the bleached and unbleached portions of the Wingate and between the Wingate Sandstone and Chinle Formation are indicated by black lines.

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Oyler Mine

GPS Location:

38o 15.485' N

111o 13.895' W

Ages: Upper Triassic

Rock Units: Chinle Formation

Features Present: Uranium, carbonized wood, sandstone, conglomerate

This mine has 2 gated adits (tunnel entrances) into the sandstone. The mine

tunnel extends 108 ft long and 6.5 by 8 ft. and is currently home to the native bat population. The earliest mine claim was filed in 1901, and was of great interest because at the time was radium was worth $80,000 per gram. Uranium was not as valued yet because its industrial use was for colorant in glass and ceramic glazes, analytical reagents, and to tone photographs a red-brown color (Russell, 2008).

Depositional Environment: Fluvial channel and floodplain

Within the Chinle Formation, uranium occurs within in the lower portions in the Shinarump Conglomerate, a fluvial (river) unit. The uranium is concentrated along large elongate scours or channels within the rock formation that are cut into the underlying Moenkopi Formation. Uranium often replaces fossil material and will preferentially replace cell walls. Uraninite (a uranium oxide UO2) will replace wood cell by cell in a selective fashion so the cellular structure of the plant material is

preserved perfectly (Rosenweig, 1954).

Interpretation: During the Late Triassic, the supercontinent Pangaea was symmetrically straddling the equator and Utah was located around a paleolatitude of 10° north and was continuing to shift northward entering a more subtropical zone. The Chinle Formation as a whole is a series of fluvial-lacustrine system with a tropical monsoonal climate. Meaning the region would receive a good amount of precipitation but would be interrupted by seasonally dry periods. (Dubiel et al. 1991, and Dubiel 1994) Tectonically, the Chinle was deposited in a continental back-arc basin on the west coast of Pangea.

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Figure 1: The Geiger counter went crazy when placed near this area right next to one of the adits. The Geiger counter detects radiation given off by the “hot” yellow mineralization.

Figure 2: Two adits are mined into the Shinarump Member of the Chinle Formation. Black lines are the approximate contacts between the Moenkopi, Chinle, and Wingate Formations. The Chinle Formation is divided into the Shinarump Member, where the uranium mines are, and the overlying Monitor Butte, Petrified Forest and Owl Rock Members (lumped and not individually distinguished for labeling purposes).

Figure 3: The paleogeographic setting (Dubiel, 1994) shows the general tectonic elements of the Western Interior of Pangea.

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Grand Wash Trail

GPS Location:

Start of hike: End of hike:

38o 16.686' N 38o 15.815' N

111o 11.534' W 111o 12.943' W

Ages: Lower - Middle Jurassic

Rock Units:

Navajo Sandstone

Kayenta Formation

Features Present: The Grand Wash Trail is an excellent place to see many of the interesting

features of the Navajo Sandstone. This hike follows a narrow canyon between Scenic Dr. and Hwy 24, for 2.5 relatively flat miles.

Depositional Environments: Navajo Sandstone: Eolian

Kayenta Formation: Fluvial

Figures 1-2: Because you can get so close to the preserved dune deposits in Grand Wash, it is an excellent place to see some of the structures of the dunes. In this case it is possible to how deposits on the lee side of the dune decrease in slope as they come down to the toe of the dune, becoming tangential to the underlying flat surface. This flat surface that the dunes toe out into is called a bounding surface, and it separates packages of dune sediments that were deposited at the same time. Bounding surface are classified into one of several orders depending on how extensive they are, the extent of the surface being an indicator of how wide spread the change in deposition was. Because we did not trace this surface out to see how far it extends it is impossible to tell which order it is. A solid black line in the second picture indicates this bounding surface. There is another type of bounding surface see in this picture. It is called a reactivation surface, and indicates when a previously active dune face became active again following a period of inactivity. The period of inactivity between the two periods when the surface was active shows up due to differential erosion. This surface may only have been inactive for as short as a few months as a result of seasonal variations in wind direction. The dashed black line in the second picture indicates this reactivations surface.

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Figure 3: The Navajo Sandstone forms cliffs several hundred feet high for most of the Grand Wash hike. If you look closely at the rock you can see many layers of the stacked trough cross-stratified packages, indicating prolonged deposition in an eolian environment. To get deposits such as these, dunes and interdune flats must have been able to override previous dunes without significantly eroding them. This most likely indicates that there was was enough sand supplied to the region for new dunes to be built without cannibalizing the sand contained in older dunes.

Figure 4: Honeycomb weathering is a common feature in the Navajo Sandstone. While the direct cause of honeycomb weathering is unknown, it is believed to be a result of frost wedging, where water infiltrates the pore spaces between sand grains, freezes and as it expands during freezing slowly fractures parts of the rock off. It is interesting to note that the honeycomb weathering seems to align with the bedding of the cross strata. This may indicate that the cross strata form conduits of high permeability with increased fluid flow parallel to them, allowing more water to fill the pore spaces aligned with the cross strata, and in turn allowing for an increased frost wedging effect.

Figure 5: The Grand Wash is one of the best places in the park to see grain flow strata. See the description of the Navajo Sandstone for more information on grain flow strata.

Figure 6: Though there are few if any age diagnostic fossils in the Navajo Sandstone, that does not mean that the Navajo erg was devoid of life. In this picture, inside the dashed ellipses, are examples of rhizoliths in the Navajo Sandstone. Rhizoliths are fossilized plant roots, indicating the presence of plants in the Navajo erg.

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Figure 7: Due to the regional dip of the formations, as you approach the western mouth of the Grand Wash the Kayenta Formation makes up the lower walls of the canyon. By walking towards the west, you slowly move down section and can walk through the entire thickness of the Kayenta formation. By paying close attention to the rock you can see how the formation changed through time. In this example you can see some of the cross bedded fluvial sand common to the top of the Kayenta.

Figure 8: At the very western mouth of the Grand Wash the Wingate Sandstone is exposed as a series of cliffs that slowly climbs higher and higher into the sky due to the regional dip.

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Moenkopi Formation Stop

GPS Location:

38o 14.536' N

111o 13.460' W

Ages: Lower Triassic

Rock Units: Moenkopi Formation

Features Present: Unlike Stop 2-7, this is a good location to look at the stratigraphy (stacking of the rocks) as opposed to the surface features within individual beds. On the east side of the road (down the stream valley) are nice alternating silt and mud deposits that are characteristic of the Moenkopi Formation

(Blakey 1973). On the west side of the road, post-depositional gypsum veins run throughout the outcrop (Figures 1 and 2). Oddly, the gypsum veins stop below the top of the outcrop, possibly due to stresses upon uplift or exposure.

Depositional Environment: Tidal and floodplain, marginal marine. This portion of the Moenkopi Formation was deposited when shallow water was covered the region, laying down alternating mud and silt rich layers. The muddy layers represent quieter or deeper waters, whereas the silt represents slightly more agitate or shallower water.

Interpretation: The gypsum veins through the Moenkopi were a post-depositional feature where dissolved calcium sulfate rich waters circulated through cracks in the rock precipitating along bedding planes and microfaults.

Figure 7: Gypsum veins running throughout the upper Moenkopi Formation directly underlying a Pleistocene Terrace.

Figure 8: Close up of the gypsum veins showing the irregularity of the vein pattern.

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Slickrock Divide

GPS Location:

38o 13.463' N

111o 13.226' W

Ages: Lower Triassic

Rock Units:

Chinle Formation

Moenkopi Formation

Features Present: Slickrock Divide is a good place to get a visual overview of the Moenkopi Formation and the overlying Chinle Formation. The dip of the Moenkopi

Formation in this region is 17o to the east (Mathis, 2000).

A divide is a division between two drainage basins. Water in this region divides between Grand Wash in the north and Capitol Gorge to the south.

Figure 1: View of the Moenkopi Formation at Slickrock Divide to the north.

Figure 2: View of the Moenkopi Formation at Slickrock Divide to the south.

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Stop 4-1

Curtis Formation Stop

Location:

West flank San Rafael Swell on I-70, north

side of interstate.

Ages: Upper Jurassic

Rock Units:

Curtis Formation, upper San Rafael Group

Features Present: Curtis Formation tidal bundles occur in exposures along I-70. These are sigmoid-shaped sets of cross-strata, enclosed within mud drapes of fine-grained sediment and organic debris (Figure 1A). Fully developed, sigmoidally shaped tidal bundles are well developed at essentially one stratigraphic

horizon, but all megaripple cross-bedding in the sequence contain well-developed tidal features. Look for the associated flaser bedding and herringbone cross-bedding. The sigmoidal sets are as much as 80 cm thick and extend as much as 11 m laterally. The enclosing beds are from 0 to 8 cm thick and thicken toward the sigmoid toeset. Locally, within the toeset, two mud beds may occur, separated by thin sandstone beds. The upper surface of some sigmoidal cross-bed sets is truncated by a planar to undulatory scour surface (Kreisa & Moiola, 1986). The Curtis Formation contains a broad suite of tidally generated sedimentary structures, including flat-bedded sandstones and packages of organized tidal rhythmites (east side of the long I-70). Figures 1A, 1B and 2 illustrate the internal sedimentary structures of Curtis tidal bundles. Overall, the Curtis Formation consists of approximately 55 meters of green-gray, fine- to very fine-grained, moderately- to well sorted and weakly dolomite cemented sandstone.

Depositional Environment: Tidal, nearshore The Curtis Formation was deposited in the Jurassic shallow marine seaway that transgressed southward. Transgressive events and embayed shallow water are factors in development of shallow-marine tidal features. Curtis Formation sigmoid tidal bundles are probably formed within channels or at the margin of bars in an estuarine environment during relatively high sea level in a high-stand systems tract (Wilcox, 2007). The tidal bundles reflect increasing then waning flow velocity during a tidal episode. For instance, incoming flood tide and outgoing ebb tide are reflected by higher flow velocity while high slack water and low slack water represent low flow velocity. Pause plane surfaces marked by mud drapes of fine grained sediment represent standstill phases during the subordinate tide and slackwater (Kreisa & Moiola, 1986). A tidal origin for these sandstones is indicated by their bimodal to polymodal paleocurrent pattern.

Interpretation: Sigmoidal bundles and the regular alternating rhythmites are attributed to tidal processes. Channelized tidal flow has distinct slack-water periods that result in mud drapes like these in the Curtis Formation. Curtis tidal bundles display cyclicity that is interpreted to be in response to the lunar month, neap/spring tide fluctuations. The most complete and well-defined bundles occur during the spring phase while neap-tide bundles are less well developed. Kreisa and Moiola (1986) reported on 28 bundles with cyclic variation in thickness and sedimentary

structures. They noted that foresets developed during maximum flow of spring tides dip 25o to 28o, but neap-tide foresets are more gently

inclined (12o to 25o). Accelerating tidal currents caused the foreset lamination of bundles to steepen. Curtis sigmoid and other laterally accreted tidal bundles are believed to have formed within channels or at the margins of bars (Kreisa & Moiola, 1986). Figure 3 is repeatedly

Figure 1A

Figure 1B

Figure 1: Figure 1B, A model of internal sedimentary structures pictured in Figure 1A: 1 - A thin basal bed plus overlying, gently dipping laminations, interpreted as ACCELERATION PHASE. 2 - Topset laminations passing over a brinkpoint to foreset laminations, MAXIMUM VELOCITY. 3 - Sigmoidally curved parallel lamination, DECELERATION PHASE.

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alternating sand (some with ripple cross lamination) and mud rich beds on a scale of a few centimeters. Kreisa and Moiola (1986) interpret these features as having formed in very shallow water (probably intertidal); the flat bedded intervals formed in maximum tidal flow velocities,

and the ripple, cross lamination developed during accelerating and/or waning flow conditions.

Figure 2: (T) = topset lamination, (F) = foreset lamination, (B) = brinkpoint, (S) = sigmoidal laminations, (P) = pause plane (Kreisa & Moiola, 1986).

Figure 3: Tidal rhythmites, alternating layers of mud vs. sand rich coupled sets.

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References

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