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31-804: The Buildwas Formation ( Bw , BUI ), formerly called Wenlock Shale and Buildwas Beds , is a geologic formation in Shropshire , England . It preserves fossils dating back to the Silurian period . The formation is the defining formation of the Sheinwoodian age of the Wenlock epoch , the Middle Silurian. The Buildwas Formation comprises olive-green and grey calcareous mudstones and nodular to lenticular calcareous mudstones and argillaceous limestones with shell fragments present throughout. The basal part of

62-558: A complexity of inter fingering and inter bedded carbonate and siliciclastic sedimentary rocks. In addition, intense post-depositional ( diagenetic ) changes have produced a more composition variation by the alteration of limestone to dolomite and the silicification of limestone to form chert . In the western Grand Canyon region, the Fossil Mountain Member consists of fossiliferous and cherty limestone with an abundant and diverse normal- marine fossil fauna . Further east in

93-594: A geologic formation goes back to the beginnings of modern scientific geology. The term was used by Abraham Gottlob Werner in his theory of the origin of the Earth, which was developed over the period from 1774 to his death in 1817. The concept became increasingly formalized over time and is now codified in such works as the North American Stratigraphic Code and its counterparts in other regions. Geologic maps showing where various formations are exposed at

124-526: A newly designated formation could not be named the Kaibab Formation, since the Kaibab Limestone is already established as a formation name. The first use of a name has precedence over all others, as does the first name applied to a particular formation. As with other stratigraphic units, the formal designation of a formation includes a stratotype which is usually a type section . A type section

155-594: A permanent natural or artificial feature of the geographic area in which they were first described. The name consists of the geographic name plus either "Formation" or a descriptive name. Examples include the Morrison Formation , named for the town of Morrison, Colorado , and the Kaibab Limestone , named after the Kaibab Plateau of Arizona. The names must not duplicate previous formation names, so, for example,

186-626: A result, the Kaibab Limestone directly overlies the Coconino Sandstone in the Mogollon Rim region. The Kaibab Limestone directly overlies the White Rim Sandstone in northeastern Arizona and southeastern Utah. The upper contact of the Kaibab Limestone (Harrisburg Member) with the overlying Moenkopi Formation is an erosional unconformity and disconformity. Within northwestern Arizona, southeastern Nevada, and southwestern Utah this contact

217-449: Is not a valid lithological basis for defining a formation. The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region. Formations must be able to be delineated at the scale of geologic mapping normally practiced in the region; the thickness of formations may range from less than a meter to several thousand meters. Geologic formations are typically named after

248-433: Is also used informally to describe the odd shapes (forms) that rocks acquire through erosional or depositional processes. Such a formation is abandoned when it is no longer affected by the geologic agent that produced it. Some well-known cave formations include stalactites and stalagmites . Kaibab Limestone The Kaibab Limestone is a resistant cliff-forming , Permian geologic formation that crops out across

279-624: Is an erosional unconformity that in part consists of paleovalleys, as much as several hundred feet deep, and paleokarst that were eroded into the underlying Kaibab Limestone before the deposition of the Moenkopi Formation . These paleovalleys are often filled with conglomerates and breccias that are known as the Rock Canyon conglomerate. Within the Marble Canyon and eastern Grand Canyon regions and south into Verde Valley , upper contact of

310-560: Is central to the geologic discipline of stratigraphy , and the formation is the fundamental unit of stratigraphy. Formations may be combined into groups of strata or divided into members . Members differ from formations in that they need not be mappable at the same scale as formations, though they must be lithologically distinctive where present. The definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata . Formations were at first described as

341-455: Is ideally a good exposure of the formation that shows its entire thickness. If the formation is nowhere entirely exposed, or if it shows considerably lateral variation, additional reference sections may be defined. Long-established formations dating to before the modern codification of stratigraphy, or which lack tabular form (such as volcanic formations), may substitute a type locality for a type section as their stratotype. The geologist defining

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372-403: Is most likely that the high-frequency changes in sea level were caused by glacial sea level oscillations during this time period. Early paleontological studies of the Kaibab Limestone firmly established its age on the basis of the abundant fossils that it and the underlying Toroweap Formation contain. On the basis of its brachiopod and siliceous sponge faunas, it was initially concluded that it

403-613: The Kaibab Plateau , which is on the north side of Grand Canyon in Coconino County, Arizona . In his definition of the Kaibab Limestone formation, no type locality was designated. He also designated the Kaibab Limestone as the upper formation of the Aubrey Group, a now-abandoned stratigraphic unit. In 1921, Bassler and Reeside revised Darton's work and defined the Harrisburg Member of the Kaibab Limestone. In his 1938 monograph on

434-505: The Toroweap Formation and Kaibab Limestone of northern Arizona, McKee split Darton's original Kaibab Limestone into the currently recognized Kaibab Limestone and Toroweap Formation. He also revised Kaibab Limestone's lower contact and divided it into informal (descending) alpha, beta and gamma members. Later in the 1970s, its upper contact was revised and its areal extent were defined. Also, unsuccessful attempts were made to raise

465-700: The U.S. states of northern Arizona , southern Utah , east central Nevada and southeast California . It is also known as the Kaibab Formation in Arizona, Nevada, and Utah. The Kaibab Limestone forms the rim of the Grand Canyon . In the Big Maria Mountains , California , the Kaibab Limestone is highly metamorphosed and known as the Kaibab Marble . The Kaibab Limestone was named by Darton in 1910 for

496-622: The Coconino Plateau region, the lithology , mineralogy , and fauna of the Fossil Mountain Member changes drastically where it grades laterally into sandy dolomite and dolomite that contains a restricted-marine fossil fauna and subordinate amounts of sandstone . The Harrisburg Member, which forms the uppermost cliffs and receding ledges along both north and south rims of the Grand Canyon, consists of an assemblage of gypsum , dolomite, sandstone, redbeds , chert, and minor limestone. Within

527-472: The Grand Canyon region, the Kaibab Limestone overlies gypsum and contorted sandstones of the Toroweap Formation. Originally, geologists interpreted the lower contact of the Kaibab Limestone to be an unconformity based on the presence of local intraformational breccias and erosional surfaces. However, additional research has concluded that these local intraformational breccias and erosional surfaces are

558-433: The Kaibab Limestone have also been largely removed by erosion. The Kaibab Limestone contains the abundant fossils of Permian invertebrates and vertebrates . The invertebrate fossils found within the Kaibab Limestone include brachiopods , conodonts , corals , crinoids , echinoid spines, mollusks , hexactinellid and other sponges , trilobites , and burrows of callanassid shrimp . The fossil cephalopods found in

589-498: The Kaibab Limestone include giant football-sized nautiloids . Fossil shark teeth , which represent a diverse assemblage of chondrichthyans , occur within the Kaibab Limestone of Arizona. The complex intercalation of carbonate and clastic sediments within the Kaibab Limestone reflects the deposition of sediments within a gently sloping continental margin during a period of frequent, high-frequency sea level changes. Relatively minor changes in sea level caused major lateral shifts in

620-542: The Kaibab Limestone with the Moenkopi Formation is an erosional disconformity. This disconformity exhibits little relief and is identified by marked differences in color, topography, and rock types between tan, ledge-forming, calcareous sandstones and of the Kaibab Limestone and red, slope-forming siltstones of the Moenkopi formation. The unconformity and disconformity are inferred to represent most of Permian time (including

651-470: The Leonardian) and part of Early Triassic time. Although the Moenkopi Formation overlies the Kaibab Limestone, its redbeds have been removed almost entirely by erosion because they are less resistant to erosion than the strata of the Kaibab Formation. As a result, the Kaibab Limestone forms the surface of many of the vast plateaus that border the Grand Canyon. Within these plateaus, the uppermost beds of

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682-550: The essential geologic time markers, based on their relative ages and the law of superposition . The divisions of the geological time scale were described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries. Geologic formations can be usefully defined for sedimentary rock layers, low-grade metamorphic rocks , and volcanic rocks . Intrusive igneous rocks and highly metamorphosed rocks are generally not considered to be formations, but are described instead as lithodemes . "Formation"

713-539: The formation consists of grey-green rubbly mudstones, containing comminuted shell debris and overlies the mottled green, grey and purple mudstones of the Rubery Formation with a 1 metre (3.3 ft) thick transition in colour and upward decrease in number of hard siltstone beds. The top of the Buildwas Formation shows a gradational increase in thickness of beds and a number of limestone beds, where it grades into

744-522: The formation is expected to describe the stratotype in sufficient detail that other geologists can unequivocally recognize the formation. Although formations should not be defined by any criteria other than primary lithology, it is often useful to define biostratigraphic units on paleontological criteria, chronostratigraphic units on the age of the rocks, and chemostratigraphic units on geochemical criteria, and these are included in stratigraphic codes. The concept of formally defined layers or strata

775-512: The formation to group rank and divide it into several formations. In 1982, Warren Hamilton renamed it as the Kaibab Marble and determined its areal extent for California. In 1991, Sorauf and Billingsley subdivided the Kaibab Limestone into (ascending) Fossil Mountain Member (new) and Harrisburg Member. They designated the strata comprising McKee's alpha (or upper) member as the Harrisburg Member and

806-588: The overlying Barr Limestone Formation . The thickness of the formation ranges from 22 to 40 metres (72 to 131 ft), with the thinnest outcrops occurring near Walsall thickening towards Wenlock Edge. The type section of the formation was defined by Barrett in 1989 along the left (north) bank of Hughley Brook, 200 metres (660 ft) southeast of Leasows Farm and 500 metres (1,600 ft) northeast of Hughley Church. The formation has provided fossils of Eodictyonella capewellii . Formation (geology) A formation must be large enough that it can be mapped at

837-519: The position of supratidal, subtidal, and shallow-marine environments during the deposition of the Kaibab Limestone. The shifting sea levels and associated depositional environments brought about a complex interlayering of different types of carbonate and clastic sediments in the strata that comprise the Kaibab Limestone. The gently sloping continental margin on which the Kaibab Limestone accumulated, extended seaward from northern Arizona to southern Nevada, at times exceeding 200 miles (125 km) in width. It

868-483: The result of collapse following the dissolution of evaporite deposits within the upper part of the Toroweap Formation. As a result, this contact is inferred to be conformable or only locally a disconformity . South and east of the Grand Canyon, the evaporites and contorted sandstones ( sabkha deposits) of Toroweap Formation interfinger with and are replaced by cross-bedded sandstones of the Coconino Sandstone . As

899-484: The strata comprising McKee's beta (or middle) member as the Fossil Mountain Member. The Fossil Mountain Member was named for Fossil Mountain along the south rim near the Bass Trail . McKee's gamma member is considered to be part of the Fossil Mountain Member. Later research has further redefined the regional extent of the Kaibab Limestone. The Kaibab Limestone is an assemblage of sedimentary rock types. It consists of

930-643: The surface are fundamental to such fields as structural geology , allowing geologists to infer the tectonic history of a region or predict likely locations for buried mineral resources. The boundaries of a formation are chosen to give it the greatest practical lithological consistency. Formations should not be defined by any criteria other than lithology. The lithology of a formation includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures , fossils regarded as rock-forming particles, or other organic materials such as coal or kerogen . The taxonomy of fossils

961-432: The surface or traced in the subsurface. Formations are otherwise not defined by the thickness of their rock strata, which can vary widely. They are usually, but not universally, tabular in form. They may consist of a single lithology (rock type), or of alternating beds of two or more lithologies, or even a heterogeneous mixture of lithologies, so long as this distinguishes them from adjacent bodies of rock. The concept of

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