Tag Archive for: geology

Chinle Formation (Geology of Utah’s Grand Staircase)

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Geologic Cross section of the layers of The Grand Staircase from Bryce through Zion to the Grand Canyon National Parks. Note the Navajo forms the walls of Zion Canyon.

Explore unit thickness in All-in-One App

Grand Staircase Strat Column (Link).

Exposure:

The Chinle formation can be found throughout the Colorado Plateau. From the Flanks of the Uintas to Petrified Forest National Park in Arizona.

Age:  Late Triassic.

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

Paleogeography: 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)

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: 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, 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).

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

Description:

The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In New Mexico, it is often raised to the status of a geological group, the Chinle Group. Some authors have controversially considered the Chinle to be synonymous to the Dockum Group of eastern Colorado and New Mexico, western Texas, the Oklahoma panhandle, and southwestern Kansas. The Chinle Formation is part of the Colorado Plateau, Basin and Range, and the southern section of the Interior Plains.[1] A probable separate depositional basin within the Chinle is found in northwestern Colorado and northeastern Utah. The southern portion of the Chinle reaches a maximum thickness of a little over 520 meters (1,710 ft). Typically, the Chinle rests unconformably on the Moenkopi Formation.

The Chinle Formation was probably mostly deposited in the Norian stage, according to a plethora of chronological techniques. It is a thick and fossiliferous formation with numerous named members (subunits) throughout its area of deposition.

The Chinle continues northwards into southern Utah and the Four Corners area, though it thins greatly to the northwest. A narrow band of undifferentiated purplish sediments from the lower part of the formation extend into vicinity of St. George. The formation thickens eastward into Zion National Park and Grand Staircase–Escalante National Monument. The Chinle is a prominent component of badlands and outcrops in the various national parks, monuments, and recreation areas of southeast Utah, extending in a discontinuous patchwork up to the San Rafael Swell.[24][25] The stratigraphic nomenclature used in southern Utah is also utilized in Monument Valley, where the coarse-grained lower members of the Chinle form a caprock for many famous buttes which characterize the valley.[7]

In this region, the stratigraphically lowest unit in the Chinle is usually the Shinarump Conglomerate (or Shinarump Member), which thins northward but is a reliable component of outcrops throughout the region. In several areas, a thin layer of mottled paleosols, the Temple Mountain Member, may be superimposed onto the Shinarump and underlying Moenkopi Formation.[26][25][27]

The Monitor Butte Member overlies the Shinarump and Temple Mountain members in southeast Utah and Monument Valley. This unit comprises drab and generally fine-grained sediments, equivalent to the Blue Mesa Member and Bluewater Creek Formation found further south.[25] The facies of this interval have been interpreted as overbank (distal floodplain) and lacustrine deposits. At Zion National Park, the Monitor Butte Member is replaced by a thick time-equivalent unit, the Cameron Member, which is also found in the Navajo Nation near its namesake of Cameron, Arizona. The Cameron Member is practically identical to the Blue Mesa Member, and likely represents the same depositional environment along the ancient river system responsible for the Chinle Formation. It is also distinct from the Monitor Butte Member, which has more evaporite deposits and fewer red sandy layers.[11][25]

The drab mudstone of the Monitor Butte and Cameron members are succeeded in a few areas by a thin section of massive conglomeratic sandstone, the Moss Back Member. This member represents sandy river channel deposits and is likely equivalent to part of the Sonsela Member.[25] Elsewhere, the Monitor Butte grades into the Petrified Forest Member, which in Utah includes the thin but geographically extensive Correo Sandstone Bed. The Petrified Forest Member is followed by the Owl Rock Member.[25][9] A unit of drab interbedded coarse and fine sediments, the Kane Springs beds, develops in the Paradox Basin. The Kane Springs beds are river deposits which are likely equivalent to the Owl Rock Member and the upper part of the Petrified Forest Member.[25] Finally, either the Rock Point Member or Church Rock Member overlie the Owl Rock. Some researchers feel that the Church Rock and Rock Point members may be synonymous.[28] They are complex heterolithic units, representing variously braided-river facies, lacustrine, and overbank deposits.

Modern Analog to Utah’s Middle Jurassic

Many modern analogs have been proposed for the desert ergs, sabkha’s and limestone’s of Utah’s Middle Jurassic, but we favor Africa & the Turkmenistan/Caspian Basin as it includes all the depositional environments found for this geologic period.

.

Paleogeography or Depiction of Utah during Middle Jurassic

Paelogeography of the Triassic and Early Jurassic. Deposition of the Kayenta, Wingate/Moenave, Chinle & Moenkopi Formations in a prograding sequence. (Deltaic mountains extremely unlikely. Blakey, 2008)

What is the Grand Staircase?

The Grand Staircase is a unique and extensive exposure of Earth’s history, showcasing over 200 million years of sedimentary rock layers. Geologists often liken these layers to a “book,” allowing for a detailed study of the Earth’s past, including changes in climate and environment.

The major sedimentary rock units exposed in the Grand Canyon range in age from 200 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world.

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[flickr_tags user_id=”95435349@N04″ tags=”chinle, navajo”]

Wingate/Moenave Sandstone (Geology of Utah’s Grand Staircase)

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Geologic Cross section of the layers of The Grand Staircase from Bryce through Zion to the Grand Canyon National Parks. Note the Navajo forms the walls of Zion Canyon.

Explore unit thickness in All-in-One App

Exposure:

The Wingate is exposed throughout the state of Utah, especially visible in Capital Reef and Glen Canyon NRA. In the Southwest corner it transitions into and interfingers with the Moenave Fm which has a strong lacustrine component.

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. 

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.         
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

Description:

Wingate Sandstone is particularly prominent in southeastern Utah, where it forms attractions in a number of national parks and monuments. These include Capitol Reef National Park, the San Rafael Swell, and Canyonlands National Park.

Wingate Sandstone frequently appears just below the Kayenta Formation and Navajo Sandstone, two other formations of the Glen Canyon group. Together, these three formations can result in immense vertical cliffs of 2,000 feet (610 meters) or more. Wingate layers are typically pale orange to red in color, the remnants of wind-born sand dunes deposited approximately 200 million years ago in the Late Triassic.

Long dated to the Early Jurassic only, fossils (including a phytosaur skull) and other evidence indicate that part of the Wingate Sandstone is as old as Late Triassic in age. The upper part of the formation, which laterally interfingers with the Moenave Formation to the west, is Early Jurassic in age

The Moenave was deposited on an erosion surface on the Chinle Formation following an early Jurassic uplift and unconformity that represents about ten million years of missing sedimentation. Periodic incursions of shallow seas from the north during the Jurassic flooded parts of Wyoming, Montana, and a northeast–southwest trending trough on the Utah/Idaho border. The Moenave was deposited in a variety of river, lake, and flood-plain environments, near the ancient Lake Dixie.

The oldest beds of this formation belong to the Dinosaur Canyon Member, a reddish, slope-forming rock layer with thin beds of siltstone that are interbedded with mudstone and fine sandstone.[4] The Dinosaur Canyon, with a local thickness of 140 to 375 feet (43 to 114 m), was probably laid down in slow-moving streams, ponds and large lakes. Evidence for this is in cross-bedding of the sediments and large numbers of fish fossils.

The upper member of the Moenave is the pale reddish-brown with a thickness of 75 to 150 feet (23 to 46 m) and cliff-forming Springdale Sandstone. It was deposited in swifter, larger, and more voluminous streams than the older Dinosaur Canyon Member. Fossils of large sturgeon-like freshwater fish have been found in the beds of the Springdale Sandstone. The next member in the Moenave Formation is the thin-bedded Whitmore Point, which is made of mudstone and shale. The lower red cliffs visible from the Zion Human History Museum (until 2000 the Zion Canyon Visitor Center) and the St. George Dinosaur Discovery Site, discovered on February 26, 2000, are accessible examples of this formation.

Modern Analog to Utah’s Middle Jurassic

Many modern analogs have been proposed for the desert ergs, sabkha’s and limestone’s of Utah’s Middle Jurassic, but we favor Africa & the Turkmenistan/Caspian Basin as it includes all the depositional environments found for this geologic period.

.

Paleogeography or Depiction of Utah during Middle Jurassic

Paelogeography of the Triassic and Early Jurassic. Deposition of the Kayenta, Wingate/Moenave, Chinle & Moenkopi Formations in a prograding sequence. (Deltaic mountains extremely unlikely. Blakey, 2008)

What is the Grand Staircase?

The Grand Staircase is a unique and extensive exposure of Earth’s history, showcasing over 200 million years of sedimentary rock layers. Geologists often liken these layers to a “book,” allowing for a detailed study of the Earth’s past, including changes in climate and environment.

The major sedimentary rock units exposed in the Grand Canyon range in age from 200 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world.

[flickr_tags user_id=”95435349@N04″ randomize=”true” margins=”4″ pagination=”numbers” tags=”navajo” max_num_photos=”9″]

[flickr_tags user_id=”95435349@N04″ tags=”chinle, navajo”]

Kayenta Formation (Geology of Utah’s Grand Staircase)

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Geologic Cross section of the layers of The Grand Staircase from Bryce through Zion to the Grand Canyon National Parks. Note the Navajo forms the walls of Zion Canyon.

Explore unit thickness in All-in-One App

Exposure:

The Kayenta is exposed throughout the state of Utah, but is especially visible in Zion National Park, Capital Reef and Glen Canyon NRA.

Age:  Early Jurassic, 199.6 million years ago to 175.6 million years ago.

Depositional Environment: Fluvial (river) environment

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

Tectonics: The earliest uplift of the Navadaplano and Island arcs (Sierra Navadas) begin to create a rain shadow in early Jurassic (late Kayenta?) times.

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).

“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.

Description:

The red and mauve Kayenta siltstones and sandstones that form the slopes at base of the Navajo Sandstone cliffs record the record of low to moderate energy streams. Poole (1997) has shown that the streams still flowed toward the east depositing from 150 to 210 m (500 to 700 ft) of sediment here. The sedimentary structures showing the channel and flood plain deposits of streams are well exposed on switchbacks below the tunnel in Pine Creek Canyon.

In the southeastern part of Zion National Park a stratum of cross bedded sandstone is found roughly halfway between the top and bottom of the Kayenta Formation. It is a “tongue” of sandstone that merges with the Navajo formation east of Kanab, and it shows that desert conditions occurred briefly in this area during Kayenta time. This tongue is the ledge that shades the lower portion of the Emerald Pool Trail, and it is properly called Navajo, not Kayenta.

Fossil mudcracks attest to occasional seasonal climate, and thin limestones and fossilized trails of aquatic snails or worms mark the existence of ponds and lakes. The most interesting fossils, however, are the dinosaur tracks that are relatively common in Kayenta mudstone.

These vary in size, but all seem to be the tracks of three-toed reptiles that walked upright, leaving their tracks in the muds on the flood plains. Unfortunately, so far no bone materials have been found in Washington County that would enable more specific identification.

Apparently during Kayenta time Zion was situated in a climatic belt like that of Senegal with rainy summers and dry winters at the southern edge of a great desert. The influence of the desert was about to predominate, however, as North America drifted northward into the arid desert belt.

In Southeast Utah, most sections that include all three geologic formations of the Glen Canyon group the Kayenta is easily recognized. Even at a distance it appears as a dark-red, maroon, or lavender band of thin-bedded material between two thick, massive, cross bedded strata of buff, tan, or light-red color. Its position is also generally marked by a topographic break. Its weak beds form a bench or platform developed by stripping the Navajo sandstone back from the face of the Wingate cliffs. The Kayenta is made up of beds of sandstone, shale, and limestone, all lenticular, uneven at their tops, and discontinuous within short distances. They suggest deposits made by shifting streams of fluctuating volume. The sandstone beds, from less than 25 millimetres (1 in) to more than 3 metres (10 ft) thick, are composed of relatively coarse, well-rounded quartz grains cemented by lime and iron. The thicker beds are indefinitely cross bedded. The shales are essentially fine-grained, very thin sandstones that include lime concretions and balls of consolidated mud. The limestone appears as solid gray-blue beds, a few inches to a few feet thick, and as lenses of limestone conglomerate. Most of the limestone lenses are less than 8 metres (25 ft) long, but two were traced for nearly 150 metres (500 ft) and one for 500 metres (1,650 ft).

Modern Analog to Utah’s Middle Jurassic

Many modern analogs have been proposed for the desert ergs, sabkha’s and limestone’s of Utah’s Middle Jurassic, but we favor Africa & the Turkmenistan/Caspian Basin as it includes all the depositional environments found for this geologic period.

.

Paleogeography or Depiction of Utah during Middle Jurassic

Paelogeography of the Triassic and Early Jurassic. Deposition of the Kayenta, Wingate/Moenave, Chinle & Moenkopi Formations in a prograding sequence. (Deltaic mountains extremely unlikely. Blakey, 2008)

What is the Grand Staircase?

The Grand Staircase is a unique and extensive exposure of Earth’s history, showcasing over 200 million years of sedimentary rock layers. Geologists often liken these layers to a “book,” allowing for a detailed study of the Earth’s past, including changes in climate and environment.

The major sedimentary rock units exposed in the Grand Canyon range in age from 200 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world.

[flickr_tags user_id=”95435349@N04″ randomize=”true” margins=”4″ pagination=”numbers” tags=”navajo” max_num_photos=”9″]

[flickr_tags user_id=”95435349@N04″ tags=”chinle, navajo”]

Navajo Sandstone (Geology of Utah’s Grand Staircase)

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Geologic Cross section of the layers of The Grand Staircase from Bryce through Zion to the Grand Canyon National Parks. Note the Navajo forms the walls of Zion Canyon.

Explore unit thickness in All-in-One App

Exposure:

The Navajo is exposed throughout the state of Utah, but reaches maximum thickness near Zion National Park and Red Rocks Recreation area near Las Vegas.

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.

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. 

Description:

The Navajo Sandstone is particularly prominent in southern Utah, where it forms the main attractions of a number of national parks and monuments including Arches National Park, Zion National Park, Capitol Reef National Park, Canyonlands National Park,[3] Glen Canyon National Recreation Area,[4] and Grand Staircase–Escalante National Monument.

Navajo Sandstone frequently overlies and interfingers with the Kayenta Formation of the Glen Canyon Group. Together, these formations can result in immense vertical cliffs of up to 2,200 feet (670 m). Atop the cliffs, Navajo Sandstone often appears as massive rounded domes and bluffs that are generally white in color.

Navajo Sandstone frequently occurs as spectacular cliffs, cuestas, domes, and bluffs rising from the desert floor. It can be distinguished from adjacent Jurassic sandstones by its white to light pink color, meter-scale cross-bedding, and distinctive rounded weathering.

The wide range of colors exhibited by the Navajo Sandstone reflect a long history of alteration by groundwater and other subsurface fluids over the last 190 million years. The different colors, except for white, are caused by the presence of varying mixtures and amounts of hematite, goethite, and limonite filling the pore space within the quartz sand comprising the Navajo Sandstone. The iron in these strata originally arrived via the erosion of iron-bearing silicate minerals.

Initially, this iron accumulated as iron-oxide coatings, which formed slowly after the sand had been deposited. Later, after having been deeply buried, reducing fluids composed of water and hydrocarbons flowed through the thick red sand which once comprised the Navajo Sandstone. The dissolution of the iron coatings by the reducing fluids bleached large volumes of the Navajo Sandstone a brilliant white. Reducing fluids transported the iron in solution until they mixed with oxidizing groundwater. Where the oxidizing and reducing fluids mixed, the iron precipitated within the Navajo Sandstone.

Depending on local variations within the permeability, porosity, fracturing, and other inherent rock properties of the sandstone, varying mixtures of hematite, goethite, and limonite precipitated within spaces between quartz grains. Variations in the type and proportions of precipitated iron oxides resulted in the different black, brown, crimson, vermillion, orange, salmon, peach, pink, gold, and yellow colors of the Navajo Sandstone.

The precipitation of iron oxides also formed laminae, corrugated layers, columns, and pipes of ironstone within the Navajo Sandstone. Being harder and more resistant to erosion than the surrounding sandstone, the ironstone weathered out as ledges, walls, fins, “flags”, towers, and other minor features, which stick out and above the local landscape in unusual shapes.

Modern Analog to Utah’s Middle Jurassic

Many modern analogs have been proposed for the desert ergs, sabkha’s and limestone’s of Utah’s Middle Jurassic, but we favor Africa & the Turkmenistan/Caspian Basin as it includes all the depositional environments found for this geologic period.

.

Paleogeography or Depiction of Utah during Middle Jurassic

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

What is the Grand Staircase?

The Grand Staircase is a unique and extensive exposure of Earth’s history, showcasing over 200 million years of sedimentary rock layers. Geologists often liken these layers to a “book,” allowing for a detailed study of the Earth’s past, including changes in climate and environment.

The major sedimentary rock units exposed in the Grand Canyon range in age from 200 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world.

[flickr_tags user_id=”95435349@N04″ randomize=”true” margins=”4″ pagination=”numbers” tags=”navajo” max_num_photos=”9″]

[flickr_tags user_id=”95435349@N04″ tags=”chinle, navajo”]

Page Sandstone & Templecap Fm (Geology of Utah’s Grand Staircase)

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Geologic Cross section of the layers of The Grand Staircase from Bryce through Zion to the Grand Canyon National Parks. Note the Templecap at the top of the towers of Zion Canyon.

Explore unit thickness in All-in-One App

Exposure:

The Temple Cap is exposed exclusively in the Southwest corner of Utah (atop the spires of Zion National Park), whereas the Page Sandstone stretches all the way into the center of the state. Both share similiar ages, but the Page is thicker and was formed by a separate erg, with far less marine influence. (ie. the slumping visible in the temple cap as the Sundance seaway covered the dune systems)

Age:  Middle Jurassic

Depositional Environment: Eolian, Marginal marine

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.

The Page Sandstone is subdivided into three members.  The 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.
This picture shows some soft sediment deformation in the east side 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. 

Description:

The Page Sandstone is the deposit of the Page coastal dune field during the Jurassic. It overlies and in is separated from the Navajo Sandstone by the continental-scale J2 unconformity. During the Jurassic, the adjacent Carmel Sea experienced several fluctuations in sea level, affecting the position of the water table in the Page Erg. Highstands in the Carmel are associated with high watertable elevations in the Page dune field that are tied to development of polygonally-fractured sabkha surfaces, and the preservation of some portion of underlying aeolian cross-strata. The packages of lowstand aeolian strata, bounded by sabkha deposits and/or polygonally-fractured surfaces represent parasequences within the overall transgressive succession of the Page Sandstone.


The occurrence of an extensive wet sabkha surface prohibited dune field development and this lack of wind-blown sand lead to surface deflation down to elevation of the water table. As such, each parasequence bounding surface represents a reset of the dune field pattern, and provides an opportunity to correlate stratigraphic architecture to paleo-environmental conditions

Modern Analog to Utah’s Middle Jurassic

Many modern analogs have been proposed for the desert ergs, sabkha’s and limestone’s of Utah’s Middle Jurassic, but we favor Africa & the Turkmenistan/Caspian Basin as it includes all the depositional environments found for this geologic period.

.

Paleogeography or Depiction of Utah during Middle Jurassic

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

What is the Grand Staircase?

The Grand Staircase is a unique and extensive exposure of Earth’s history, showcasing over 200 million years of sedimentary rock layers. Geologists often liken these layers to a “book,” allowing for a detailed study of the Earth’s past, including changes in climate and environment.

The major sedimentary rock units exposed in the Grand Canyon range in age from 200 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world.

[flickr_tags user_id=”95435349@N04″ randomize=”true” margins=”4″ pagination=”numbers” tags=”navajo” max_num_photos=”9″]

[flickr_tags user_id=”95435349@N04″ tags=”chinle, navajo”]

Carmel Formation (Geology of Utah’s Grand Staircase)

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Geologic Cross section of the layers of The Grand Staircase from Bryce through Zion to the Grand Canyon National Parks. Note the Carmel at the top of the Zion NP sequence.

Explore unit thickness in All-in-One App

Exposure:

Within the Grand Staircase, the Carmel Formation is best exposed in east of Capital Reef National Park just south of Goblin Valley State Park.

Age:  Middle Jurassic, 160 Ma

Depositional Environment: Full marine, shallow marine to sabkha (and supratidal)

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:

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

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.

View of the Morrison Formation, the Summerville Formation, the Curtis Formation, and the Entrada Formation.

Description:

The Carmel Formation consists of up to 1,000 feet (300 m) of mudrock and sandstone interbedded with limestone and gypsum. It was laid down in a shallow marine to sabkha environment,[1] into which terrigenous sediment was periodically carried. This gives the formation considerable lithological complexity.[3] The formation is underlain by the Navajo Sandstone, with the regional J-2 unconformity separating the two formations, or by the Temple Cap Formation. Portions of the Carmel Formation grade laterally eastward into the Page Sandstone.[2] The Carmel Formation in turn is overlain by the Entrada Formation.[3]

In the type area of southern Utah, the Carmel Formation is divided into the Judd Hollow Member, a basal limestone member; the Crystal Creek Member, mostly mudstone and siltstone, which grades into the Page Sandstone to the east; the Paria River Member, which is also siltstone and mudstone but is separated from the Crystal Creek Member by gypsum beds; and the Winsor Member, which is mudstone, sandstone, and siltstone separated from the Paria River by a basal limestone. Further east, the limestone marker bed pinches out, and the Winsor Member and Paria River Member become indistinguishable and are informally termed the upper member. The upper member contains volcaniclastic beds of rhyolite originating in a volcanic arc just off the edge of the Colorado Plateau.[4]

The formation preserves a Jurassic hardground, rare for North America

Modern Analog to Utah’s Middle Jurassic

Many modern analogs have been proposed for the desert ergs, sabkha’s and limestone’s of Utah’s Middle Jurassic, but we favor Africa & the Turkmenistan/Caspian Basin as it includes all the depositional environments found for this geologic period.

.

Paleogeography or Depiction of Utah during Middle Jurassic

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

What is the Grand Staircase?

The Grand Staircase is a unique and extensive exposure of Earth’s history, showcasing over 200 million years of sedimentary rock layers. Geologists often liken these layers to a “book,” allowing for a detailed study of the Earth’s past, including changes in climate and environment.

The major sedimentary rock units exposed in the Grand Canyon range in age from 200 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world.

[flickr_tags user_id=”95435349@N04″ randomize=”true” margins=”4″ pagination=”numbers” tags=”navajo” max_num_photos=”9″]

[flickr_tags user_id=”95435349@N04″ tags=”chinle, navajo”]

Likely stromatoporoid (sponge) fossil. Found in Camel Limestone near east above Orderville near Stewart Canyon. 3×5 feet in size.

Entrada Formation (Geology of Utah’s Grand Staircase)

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Geologic Cross section of the layers of The Grand Staircase from Bryce through Zion to the Grand Canyon National Parks. Note the Entrada is absent in Zion but sits atop the Carmel Fm.

Explore unit thickness in All-in-One App

Exposure:

Without a doubt the most striking exposures of the Entrada Formation are in Arches National Park. Other great exposures exist in Canyonlands, Goblin Valley State Park and Lake Powell NRA.

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 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.

View of the Morrison Formation, the Summerville Formation, the Curtis Formation, and the Entrada Formation.

Description:

At its type section at Entrada Point, located in the northern part the San Rafael Swell in Emery County, Utah,[4] the Entrada consists of red silty sandstone and lesser interbedded mudstone and is a slope-forming formation. This part of the Entrada is sometimes described as the “earthy facies”.[5] Here the Entrada is overlain by the Curtis Formation, and overlies the Carmel Formation.[4] To the south and east, the Entrada transitions to cliff-forming red or white crossbedded sandstone, sometimes called the “slickrock facies”. This is actually more typical of the Entrada as a whole, and a principal reference section including both facies was designated by Peterson in 1988 at Pine Creek, 5 kilometers (3.1 mi) north of Escalante, Utah, in the Kaiparowits Basin.[5]

At the reference section in the Kaiparowitz Basin, the Entrada is 314 meters (1,030 ft) thick and is divided into three informal members. The lower member is 113 meters (371 ft) of orange-red silty sandstone, with occasional beds of red mudstone, corresponding to the earthy facies. The middle member is 132 meters (433 ft) of red to green mudstone interbedded with red to white sandstone. The upper member is 69 meters (226 ft) of crossbedded white sandstone.[6] The white color is attributed to bleaching by organic-rich fluids from overlying beds. The formation rests on the Carmel Formation and is overlain by the Morrison Formation.[7]

In the Curtis Mountains region of northeastern Arizona, the Entrada is overlain by the Wanakah Formation.[8]

In the San Juan Basin of northwestern New Mexico, the Entrada consists of upper and lower sandy members and a medial silty member, the Rehoboth Member. The Curtis Formation is sometimes absent and the Entrada then overlies Chinle Formation. It is overlain by the Todilto Formation. Southeast of Fort Defiance, Arizona, the lower sandy beds are assigned to the Iyanbito Member. Total thickness is up to 37 meters (121 ft).[8]

In the Slick Rock, Colorado area, the Entrada is divided into a “middle sandstone”, the Rehoboth Member, and the Slick Rock Member, in ascending order

Modern Analog to Utah’s Middle Jurassic

Many modern analogs have been proposed for the desert ergs, sabkha’s and limestone’s of Utah’s Middle Jurassic, but we favor Africa & the Turkmenistan/Caspian Basin as it includes all the depositional environments found for this geologic period.

.

Paleogeography or Depiction of Utah during Middle Jurassic

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

What is the Grand Staircase?

The Grand Staircase is a unique and extensive exposure of Earth’s history, showcasing over 200 million years of sedimentary rock layers. Geologists often liken these layers to a “book,” allowing for a detailed study of the Earth’s past, including changes in climate and environment.

The major sedimentary rock units exposed in the Grand Canyon range in age from 200 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world.

[flickr_tags user_id=”95435349@N04″ randomize=”true” margins=”4″ pagination=”numbers” tags=”navajo” max_num_photos=”9″]

[flickr_tags user_id=”95435349@N04″ tags=”chinle, navajo”]

Curtis Formation (Geology of Utah’s Grand Staircase)

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Geologic Cross section of the layers of The Grand Staircase from Bryce through Zion to the Grand Canyon National Parks.

Explore unit thickness in All-in-One App

Exposure:

Within the Grand Staircase, the Curtis Formation is best exposed in east of Capital Reef National Park just south of Goblin Valley State Park.

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).

View of the Morrison Formation, the Summerville Formation, the Curtis Formation, and the Entrada Formation.

Description:

The Curtis Formation is composed of shallow marine sandstone, with thin beds of mudstone and minor limestone and gypsum. The sandstone is grayish-green in color and flat bedded or cross bedded. The presence of glauconite and marine invertebrate fossils indicates it was laid down in a shallow marine environment that became hypersaline towards the end of deposition. It represents a high stand of the Sundance Sea in the Callovian

The formation was first described by Gilluly and Reeside in 1928 and named for exposures in the northeast San Rafael Reef at Curtis Point (39.126665°N 110.447615°W). Pipiringos and Imlay reassigned the Curtis as a member of the Stump Formation in 1979,[2] but this was rejected by Peterson in 1988.

Modern Analog to Utah’s Middle Jurassic

Many modern analogs have been proposed for the desert ergs, sabkha’s and limestone’s of Utah’s Middle Jurassic, but we favor Africa & the Turkmenistan/Caspian Basin as it includes all the depositional environments found for this geologic period.

.

Paleogeography or Depiction of Utah during Middle Jurassic

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

What is the Grand Staircase?

The Grand Staircase is a unique and extensive exposure of Earth’s history, showcasing over 200 million years of sedimentary rock layers. Geologists often liken these layers to a “book,” allowing for a detailed study of the Earth’s past, including changes in climate and environment.

The major sedimentary rock units exposed in the Grand Canyon range in age from 200 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world.

[flickr_tags user_id=”95435349@N04″ randomize=”true” margins=”4″ pagination=”numbers” tags=”navajo” max_num_photos=”9″]

[flickr_tags user_id=”95435349@N04″ tags=”chinle, navajo”]

Summerville Formation (Geology of Utah’s Grand Staircase)

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Geologic Cross section of the layers of The Grand Staircase from Bryce through Zion to the Grand Canyon National Parks.

Explore unit thickness in All-in-One App

Exposure:

Within the Grand Staircase, the Summerville Formation is best exposed in east of Capital Reef National Park just south of Goblin Valley State Park.

Age:  Deposited Middle Jurassic, early to late Oxfordian time (161 – 155 Ma) (Wilcox, 2007).

Depositional Environment:

Marginal marine and sabkha/tidal. One unconformably-bound, transgressive-regressive (T-R) sequence, marine (saline lacustrine?) 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:

Hot & Arid. Kocurek & Dott, 1983 suggest paleolatitude range of 5 to 25 degrees north. I disagree and suggest 25-40 degrees north within a stark rain shadow of the ancient Navadaplano, similar to current Mapmi basin in Mexico.

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).

View of the Morrison Formation, the Summerville Formation, the Curtis Formation, and the Entrada Formation.

Description:

The Summerville formation consists of up to 100 meters (330 ft) of red mudstone, with thin interbeds of green and red sandstone. The lower portion of the formation shows polygonal desiccation cracks and localized salt-hopper casts while the upper portion contains considerable gypsum, consistent with deposition in a sabkha on the margin of the Sundance Sea.It is exposed in the San Rafael Reef, the Waterpocket Fold, in the Henry Mountains, with additional exposures scattered across the region from the San Rafael Reef to the Paradox Basin, and in north-central New Mexico. The thin bedding is characteristic throughout the formation, but gypsum is not found in the San Juan Basin and some conglomerate is found on the south and southwestern margins of the formation. The correlation of late Jurassic beds in northwestern New Mexico with the Summerville Formation in Utah has been questioned, and it has been suggested that they be assigned to the Beclabito Formation instead.

The Summerville Formation rests conformably on the underlying Curtis Formation (Utah and western Colorado) or Todilto Formation (southwest Colorado and New Mexico) but is separated from the overlying Morrison Formation by the regional J5 unconformity.[1] It thins significantly in the Moab-La Sal area, the likely area of the divide between the marine Curtis basin to the northwest and the salina lake Todilto basin to the southeast. Here the formation is just 1.2 meters (3.9 feet) thick and rests directly on Entrada Sandstone. In many locations the Summerville is separated from the Morrison by eolian sandstones, such as the Bluff Sandstone, variously assigned to the Morrison Formation or the San Rafael Group. The Morrison Formation represents a return to more humid conditions with increased clastic input.

Modern Analog to Utah’s Middle Jurassic

Many modern analogs have been proposed for the desert ergs, sabkha’s and limestone’s of Utah’s Middle Jurassic, but we favor Africa & the Turkmenistan/Caspian Basin as it includes all the depositional environments found for this geologic period.

.

Paleogeography or Depiction of Utah during Middle Jurassic

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

What is the Grand Staircase?

The Grand Staircase is a unique and extensive exposure of Earth’s history, showcasing over 200 million years of sedimentary rock layers. Geologists often liken these layers to a “book,” allowing for a detailed study of the Earth’s past, including changes in climate and environment.

The major sedimentary rock units exposed in the Grand Canyon range in age from 200 million to 600 million years and were deposited in warm shallow seas and near-shore environments. The nearly 40 identified rock layers of Grand Canyon form one of the most studied geologic columns in the world.

[flickr_tags user_id=”95435349@N04″ randomize=”true” margins=”4″ pagination=”numbers” tags=”navajo” max_num_photos=”9″]

[flickr_tags user_id=”95435349@N04″ tags=”chinle, navajo”]

Morrison Formation (Geology of Utah’s Grand Staircase)

/in /by
Geologic Cross section of the layers of The Grand Staircase from Bryce through Zion to the Grand Canyon National Parks.

Explore unit thickness in All-in-One App

Exposure:

Within the Grand Staircase, the Morrison Formation is best exposed in Capital Reef National Park.

Age:  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

Description:

The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone, and limestone and is light gray, greenish gray, or red. Most of the fossils occur in the green siltstone beds and lower sandstones, relics of the rivers and floodplains of the Jurassic period.

It is centered in Wyoming and Colorado, with outcrops in Montana, North Dakota, South Dakota, Nebraska, Kansas, the panhandles of Oklahoma and Texas, New Mexico, Arizona, Utah, and Idaho. Equivalent rocks under different names are found in Canada.[2] It covers an area of 1.5 million square kilometers (600,000 square miles), although only a tiny fraction is exposed and accessible to geologists and paleontologists. Over 75% is still buried under the prairie to the east, and much of its western paleogeographic extent was eroded during exhumation of the Rocky Mountains.

It was named after Morrison, Colorado, where some of the first fossils in the formation were discovered by Arthur Lakes in 1877. That same year, it became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope. In Colorado, New Mexico, and Utah, the Morrison Formation was a major source of uranium ore.

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

https://web.archive.org/web/20171216143550/http://sed.utah.edu/Morrison.htm