For the Skiddaw group of hills, see Skiddaw Group
25-754: The Skiddaw Group is a group of sedimentary rock formations named after the mountain Skiddaw in the English Lake District . The rocks are almost wholly Ordovician in age ( Tremadoc through Arenig to Llanvirn epochs ) though the lowermost beds are possibly of Cambrian age. This rock sequence has previously been known as the Skiddaw Slates , the Skiddaw Slates Group and the Skiddavian Series. Its base
50-614: A group must not be defined by fossil taxonomy. Navajo Sandstone The Navajo Sandstone is a geological formation in the Glen Canyon Group that is spread across the U.S. states of southern Nevada , northern Arizona , northwest Colorado , and Utah as part of the Colorado Plateau province of the United States . The Navajo Sandstone is particularly prominent in southern Utah, where it forms
75-459: A group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into supergroups . Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying the stratigraphy of large regions. Geologists exploring a new area have sometimes defined groups when they believe the strata within the groups can be divided into formations during subsequent investigations of
100-822: A wacke sandstone which is the rough equivalent of the Watch Hill Formation, itself a wacke sandstone as is the Loweswater Formation. Within the Central Fells are the Buttermere Formation and the overlying Tarn Moor Formation. These are matched by the Murton Formation (grey slates and thin sandstones) and the Kirkland Formation (mudstones with tuffs and lavas) at Cross Fell. The Buttermere Formation
125-849: Is also well known among rockhounds for its hundreds of thousands of iron oxide concretions . Informally, they are called "Moqui marbles" and are believed to represent an extension of Hopi Native American traditions regarding ancestor worship ("moqui" translates to "the dead" in the Hopi language). Thousands of these concretions weather out of outcrops of the Navajo Sandstone within south-central and southeastern Utah within an area extending from Zion National Park eastward to Arches and Canyonland national parks. They are quite abundant within Grand Staircase–Escalante National Monument. The iron oxide concretions found in
150-713: Is interpreted as an olistostrome . The Tarn Moor and Kirkland Formations contain some volcaniclastic rocks. The inlier to the south at Black Combe contains the wackes of the Knott Hill Formation. The group underlies the Borrowdale Volcanic Group in the southern and central Lake District and the Eycott Volcanic Group in the northern part of the district. The Kirkland Formation has provided fossils of Dichograptus octobrachiatus and Heminectere rushtoni . The sequence
175-489: Is not exposed but in its main outcrop area, it is considered to be in excess of 5,000 metres (16,000 ft) thick though less elsewhere. It consists largely of mudstones and siltstones with subordinate wacke -type sandstones . Their main occurrence is within the northern and central fells of the Lake District, either side of the major ENE-WSW aligned Causey Pike Fault , but inliers are found at Black Combe in
200-708: The 'Navajo Country' of the southwestern United States . The two major subunits of the Navajo are the Lamb Point Tongue (Kanab area) and the Shurtz Sandstone Tongue (Cedar City area). The Navajo Sandstone was originally named as the uppermost formation of the La Plata Group by Gregory and Stone in 1917. Baker reassigned it as the upper formation of Glen Canyon Group in 1936. Its age was modified by Lewis and others in 1961. The name
225-480: 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
250-466: The Navajo Sandstone exhibit a wide variety of sizes and shapes. Their shape ranges from spheres to discs; buttons; spiked balls; cylindrical hollow pipe-like forms; and other odd shapes. Although many of these concretions are fused together like soap bubbles, many more also occur as isolated concretions, which range in diameter from the size of peas to baseballs. The surface of these spherical concretions can range from being very rough to quite smooth. Some of
275-401: 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
SECTION 10
#1732773285288300-439: The Navajo Sandstone while deeply buried, reducing fluids , likely hydrocarbons , dissolved these coatings. When the reducing fluids containing dissolved iron mixed with oxidizing groundwater , they and the dissolved iron were oxidized. This caused the iron to precipitate out as hematite and goethite to form the innumerable concretions found in the Navajo Sandstone. Evidence suggests that microbial metabolism may have contributed to
325-970: The Western portion of the Supercontinent Pangaea . This region was affected by annual monsoons that came about each winter when cooler winds and wind reversal occurred. Navajo Sandstone outcrops are found in these geologic locations: The formation is also found in these parklands (incomplete list): Indeterminate theropod remains geographically located in Arizona, USA. Theropod tracks are geographically located in Arizona, Colorado, and Utah, USA. Ornithischian tracks located in Arizona, USA. Ammosaurus Ammosaurus cf. major Dilophosaurus D. wetherilli Attributed trackways at Red Fleet State Park . Pteraichnus Segisaurus S. halli "Partial postcranial skeleton." Seitaad S. ruessi The Navajo Sandstone
350-668: The area. It is possible for only some of the strata making up a group to be divided into formations. An example of a group is the Glen Canyon Group , which includes (in ascending order) the Wingate Sandstone , the Moenave Formation , the Kayenta Formation , and the Navajo Sandstone . Each of the formations can be distinguished from its neighbor by its lithology , but all were deposited in
375-430: 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
400-411: The concretions are grooved spheres with ridges around their circumference. The abundant concretions found in the Navajo Sandstone consist of sandstone cemented together by hematite (Fe 2 O 3 ), and goethite (FeOOH). The iron forming these concretions came from the breakdown of iron-bearing silicate minerals by weathering to form iron oxide coatings on other grains. During later diagenesis of
425-418: 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
450-543: 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. The age of the Navajo Sandstone is somewhat controversial. It may originate from the Late Triassic but is at least as young as the Early Jurassic stages Pliensbachian and Toarcian . There is no type locality of the name. It was simply named for
475-577: The main attractions of a number of national parks and monuments including Red Rock Canyon National Conservation Area , Zion National Park , Capitol Reef National Park , Glen Canyon National Recreation Area , Grand Staircase–Escalante National Monument , and Canyonlands National Park . 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
500-540: The past also been used as units for chronostratigraphy and geochronology . These are the Rotliegend and Zechstein (both of Permian age); Buntsandstein , Muschelkalk , and Keuper ( Triassic in age); Lias , Dogger , and Malm ( Jurassic in age) groups. Because of the confusion this causes, the official geologic timescale of the ICS does not contain any of these names. As with other lithostratigraphic ranks,
525-567: The same vast erg . Not all these formations are present in all areas where the Glen Canyon Group is present. Another example of a group is the Vadito Group of northern New Mexico . Although many of its strata have been divided into formations, such as the Glenwoody Formation , other strata (particularly in the lower part of the group) remain undivided into formations. Some well known groups of northwestern Europe have in
SECTION 20
#1732773285288550-812: The south of the Lake District and at Cross Fell in the North Pennines . In the Northern Fells of the Lake District, the Skiddaw Group comprises five formations of which the earliest/lowest is the Bitter Beck Formation. This is succeeded by the Watch Hill Formation, then the Hope Beck, Loweswater and Kirk Stile Formations in ascending order. The inlier at Cross Fell comprises just the Catterpallot Formation,
575-402: 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,
600-505: Was affected by low-grade regional metamorphism and deformation associated with the Acadian Orogeny , causing the dominant fine-grained parts of the sequence to become slates . The resulting slaty cleavage is parallel to the axial plane of regional folds . Group (stratigraphy) In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form
625-526: Was originally not used in northwest Colorado and northeast Utah, where the name 'Glen Canyon Sandstone' was preferred. Its age was modified again by Padian in 1989. A 2019 radioisotopic analysis suggests that the Navajo Sandstone formation is entirely Jurassic, extending for about 5.5 million years from the Hettangian age to the Sinemurian age . The sandstone was deposited in an arid erg on
#287712