Misplaced Pages

#720279

49-815: The Grand Canyon Supergroup uncomformably overlies the Vishnu Basement Rocks but was never subjected to metamorphism. The units of the Supergroup were faulted and then tilted from 10 to 15 degrees. A section of the Unkar Group members is visible north of Grand Canyon Village , on the South Rim; specifically at the intersection of the Bright Angel Fault and the Grandview–Phantom Fault (which cuts through Phantom Creek), on

98-623: A tuff at the top of the Walcott Member is 729.0 ± 0.9 Ma. These ages also indicate that the vase-shaped microfossils-bearing Walcott Member is between 751 and 729 Ma. The types of fossils found and sedimentary strata comprising the Chuar Group are indicative of its deposition within a low-energy marine embayment. During the deposition of the Chuar Group, this embayment was influenced by tidal and wave processes, infrequent large storms, microbial activity and carbonate precipitation, and

147-405: A fault as oblique requires both dip and strike components to be measurable and significant. Some oblique faults occur within transtensional and transpressional regimes, and others occur where the direction of extension or shortening changes during the deformation but the earlier formed faults remain active. The hade angle is defined as the complement of the dip angle; it is the angle between

196-582: A fault hosting valuable porphyry copper deposits is northern Chile's Domeyko Fault with deposits at Chuquicamata , Collahuasi , El Abra , El Salvador , La Escondida and Potrerillos . Further south in Chile Los Bronces and El Teniente porphyry copper deposit lie each at the intersection of two fault systems. Faults may not always act as conduits to surface. It has been proposed that deep-seated "misoriented" faults may instead be zones where magmas forming porphyry copper stagnate achieving

245-489: A fault plane, where it becomes locked, are called asperities . Stress builds up when a fault is locked, and when it reaches a level that exceeds the strength threshold, the fault ruptures and the accumulated strain energy is released in part as seismic waves , forming an earthquake . Strain occurs accumulatively or instantaneously, depending on the liquid state of the rock; the ductile lower crust and mantle accumulate deformation gradually via shearing , whereas

294-408: A fault's age by studying soil features seen in shallow excavations and geomorphology seen in aerial photographs. Subsurface clues include shears and their relationships to carbonate nodules , eroded clay, and iron oxide mineralization, in the case of older soil, and lack of such signs in the case of younger soil. Radiocarbon dating of organic material buried next to or over a fault shear

343-427: A hanging wall or foot wall where a thrust fault formed along a relatively weak bedding plane is known as a flat and a section where the thrust fault cut upward through the stratigraphic sequence is known as a ramp . Typically, thrust faults move within formations by forming flats and climbing up sections with ramps. This results in the hanging wall flat (or a portion thereof) lying atop the foot wall ramp as shown in

392-484: A major fault. Synthetic faults dip in the same direction as the major fault while the antithetic faults dip in the opposite direction. These faults may be accompanied by rollover anticlines (e.g. the Niger Delta Structural Style). All faults have a measurable thickness, made up of deformed rock characteristic of the level in the crust where the faulting happened, of the rock types affected by

441-400: A manner that creates multiple listric faults. The fault panes of listric faults can further flatten and evolve into a horizontal or near-horizontal plane, where slip progresses horizontally along a decollement . Extensional decollements can grow to great dimensions and form detachment faults , which are low-angle normal faults with regional tectonic significance. Due to the curvature of

490-421: A non-vertical fault are known as the hanging wall and footwall . The hanging wall occurs above the fault plane and the footwall occurs below it. This terminology comes from mining: when working a tabular ore body, the miner stood with the footwall under his feet and with the hanging wall above him. These terms are important for distinguishing different dip-slip fault types: reverse faults and normal faults. In

539-464: A reverse fault, the hanging wall displaces upward, while in a normal fault the hanging wall displaces downward. Distinguishing between these two fault types is important for determining the stress regime of the fault movement. Faults are mainly classified in terms of the angle that the fault plane makes with the Earth's surface, known as the dip , and the direction of slip along the fault plane. Based on

SECTION 10

#1732764655721

588-422: Is a horst . A sequence of grabens and horsts on the surface of the Earth produces a characteristic basin and range topography . Normal faults can evolve into listric faults, with their plane dip being steeper near the surface, then shallower with increased depth, with the fault plane curving into the Earth. They can also form where the hanging wall is absent (such as on a cliff), where the footwall may slump in

637-423: Is a zone of folding close to a fault that likely arises from frictional resistance to movement on the fault. The direction and magnitude of heave and throw can be measured only by finding common intersection points on either side of the fault (called a piercing point ). In practice, it is usually only possible to find the slip direction of faults, and an approximation of the heave and throw vector. The two sides of

686-544: Is defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault. A special class of strike-slip fault is the transform fault when it forms a plate boundary. This class is related to an offset in a spreading center , such as a mid-ocean ridge , or, less common, within continental lithosphere , such as the Dead Sea Transform in the Middle East or

735-545: Is dominate in all of these members. Thick (meter-scale) basal dolomite beds define the Tanner and Jupiter members. In case of the Jupiter Member, the basal dolomite bed is stromatolitic . The Carbon Canyon Member contains stromatolite bioherms . The Kwagunt Formation is composed of sandstones, siltstones, shales , carbonates, cherts , and ironstones . These strata have been subdivided, in ascending order, into

784-543: Is often critical in distinguishing active from inactive faults. From such relationships, paleoseismologists can estimate the sizes of past earthquakes over the past several hundred years, and develop rough projections of future fault activity. Many ore deposits lie on or are associated with faults. This is because the fractured rock associated with fault zones allow for magma ascent or the circulation of mineral-bearing fluids. Intersections of near-vertical faults are often locations of significant ore deposits. An example of

833-572: Is overlain by silicified oolites, chert beds, black shales. A pair of meter-scale dolomite beds ( upper and lower dolomite couple ) occur in the upper Walcott along with early diagenetic dolomite nodules up to 1 m (3.3 ft) in diameter. The mudrocks of the Galeros and Kwagunt formations are normally interbedded with meter-thick sandstone and dolomite beds. The mudrocks are typically gray to black when freshly exposed and weather to reddish or greenish colors. The fresh gray to black colors of

882-492: Is particularly clear in the case of detachment faults and major thrust faults . The main types of fault rock include: In geotechnical engineering , a fault often forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel , foundation , or slope construction. The level of a fault's activity can be critical for (1) locating buildings, tanks, and pipelines and (2) assessing

931-425: Is the cause of most earthquakes . Faults may also displace slowly, by aseismic creep . A fault plane is the plane that represents the fracture surface of a fault. A fault trace or fault line is a place where the fault can be seen or mapped on the surface. A fault trace is also the line commonly plotted on geologic maps to represent a fault. A fault zone is a cluster of parallel faults. However,

980-762: The Alpine Fault in New Zealand. Transform faults are also referred to as "conservative" plate boundaries since the lithosphere is neither created nor destroyed. Dip-slip faults can be either normal (" extensional ") or reverse . The terminology of "normal" and "reverse" comes from coal mining in England, where normal faults are the most common. With the passage of time, a regional reversal between tensional and compressional stresses (or vice-versa) might occur, and faults may be reactivated with their relative block movement inverted in opposite directions to

1029-560: The Chuar Group is well constrained between as being 729 and 782 Ma by Re-Os and U-Pb ages. First, U–Pb dating of detrital zircons from basal beds of the underlying Nankoweap Formation indicates it to be less than 782 Ma. Second, Re–Os ages from organic-rich carbonates in the upper Galeros Formation and marcasite nodules in the lower Kwagunt Formation yielded ages of 757.0 ± 6.8 and 751.0 ± 7.6 Ma, respectively. Finally, an U–Pb age obtained from CA-ID-TIMS analysis of zircons recovered from

SECTION 20

#1732764655721

1078-538: The Grand Canyon Supergroup , overlain by the thin, in comparison, Sixtymile Formation , the top member of the multi-membered Grand Canyon Supergroup. The outcrop of the Chuar Group strata is limited to exposures along the western bank of the Colorado River in a 150 km (58 sq mi) area of the eastern Grand Canyon, Arizona. The strata of the Chuar Group have been subdivided into

1127-657: The seismic shaking and tsunami hazard to infrastructure and people in the vicinity. In California, for example, new building construction has been prohibited directly on or near faults that have moved within the Holocene Epoch (the last 11,700 years) of the Earth's geological history. Also, faults that have shown movement during the Holocene plus Pleistocene Epochs (the last 2.6 million years) may receive consideration, especially for critical structures such as power plants, dams, hospitals, and schools. Geologists assess

1176-605: The Carbon Butte, Awatubi, and Walcott members. The Carbon Butte Member consists largely of sandstone interbedded with carbonates and, locally, ironstones. The Awatubi Member consists of a distinctive zone of stromatolitic bioherms at its base overlain by grey, green, and black organic-rich siltstones and shales, some of which contain marcasite nodules. The base of the Walcott Member consists of a distinctive meter-scale laminated dolomite bed (the Flakey dolomite ). The Flakey dolomite

1225-530: The Colorado River on the Tonto Platform. The three units of the Tonto Group are Muav Limestone , upon Bright Angle Shale, upon Tapeats Sandstone. The Tapeats is a thin cliff-former unit found along Granite Gorge and its side canyons forming a flat surface in locales not dramatically affected by faulting, up-warping (domes), or down-warping. The Isis Temple with Cheops Pyramid formation contains

1274-911: The Duppa, Carbon Canyon, Jupiter, and Tanner members of the Chuar Group often contain organic-walled microfossils, including filaments, colonial forms, and both smooth-walled and ornamented vesicles. A morphological group of organic microfossil, called vase-shaped microfossils , occur within the Walcott and Awatubi members of the Kwagunt Formation along with the enigmatic, circular, macroscopic, organic-walled fossil Tawuia ( Churnia circularis ), and phosphatic scale microfossils. The vase-shaped microfossils are likely presentatives of either arcellinid testate amoebae , acritarchs , or some of both. Finally, organic chemicals, biomarkers , characteristic of dinoflagellates have been reported. The age of

1323-645: The East Kaibab Monocline. Fault (geology) In geology , a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth 's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as the megathrust faults of subduction zones or transform faults . Energy release associated with rapid movement on active faults

1372-503: The Galeros Formation (lower) and the Kwagunt Formation (upper) using the base of the prominent, thick sandstone unit. The Galeros Formation consists of a series of meter-scale sedimentary cycles composed of interbedded mudrocks , siltstones , and sandstones , frequently capped by dolomite beds . These strata have been subdivided, in ascending order, into the Tanner, Jupiter, Carbon Canyon, and Duppa members. Dolomite

1421-704: The Grand Canyon Supergroup members. The Isis Temple and Cheops Pyramid formation is a part of the Shinumo Quartzite 'island' and made up of the bottom three Unkar Group members. They were overlain at the Great Unconformity , onto Tapeats Sandstone (named for the bottom unit of the marine transgression series consisting of sandstone–(conglomerates)–shale–limestone laid down by the Tapeats Sea ), and are evident along

1470-645: The North Rim (at the north side of Granite Gorge). The majority of the Grand Canyon Supergroup geologic members are found in the south and southwest stretch of the Colorado River starting from Marble Canyon , traverses the southeast perimeter of the Kaibab Plateau , and flows northeasterly entering Granite Gorge and regions of the Vishnu Basement Rocks. Here, the river leaves the last of the Unkar Group 's lower-unit members behind. Other sections of

1519-810: The Tapeats is still the defining cliff unit at the Great Unconformity between the paleozoic Tapeats Sandstone and the basement geology below. However, the entire east of the Kaibab Plateau is an uplifted side of the East Kaibab Monocline . The down-dropped east side of the Kaibab Plateau is defined by the south-flowing Colorado River. Colorado sits below the East Rim, where the Little Colorado River enters from

Grand Canyon Supergroup - Misplaced Pages Continue

1568-785: The Unkar Group reappear downstream due to the general faulting of the Grand Canyon. The units of the Grand Canyon Supergroup in increasing age: Chuar Group Unkar Group The Chuar Group of the Grand Canyon Supergroup has yielded a few Neoproterozoic fossils. Its dolomite beds contain at least six different types of stromatolites . In some of the gray and black mudrocks, paleontologists have found an abundance of organic microfossils , including vase-shaped microfossils (VSMs) likely presentative of arcellinid testate amoebae , acritarchs , "Sphaerocongregus variabilis ", and organic chemicals characteristic of dinoflagellates . Finally,

1617-807: The bottom three members, a virtual quartzite 'mountain island' in the Tapeats Sea. (Tapeats Sandstone was deposited only around Shinumo Quartzite monadnocks .) The formation is a fault -block section located north of Granite Gorge and the intersection of Phantom Creek with the Bright Angel Canyon (which is also the intersection of the Bright Angel and Grandview–Phantom faults ). The dimensions of this block are approximately 3.5 mi by 2.0 mi, with slopes of multi-colored Hakatai Shale and Bass Formation (shown as reddish, yellowish, and lavender). The Apollo Temple formation occurs at

1666-403: The brittle upper crust reacts by fracture – instantaneous stress release – resulting in motion along the fault. A fault in ductile rocks can also release instantaneously when the strain rate is too great. Slip is defined as the relative movement of geological features present on either side of a fault plane. A fault's sense of slip is defined as the relative motion of the rock on each side of

1715-436: The direction of slip, faults can be categorized as: In a strike-slip fault (also known as a wrench fault , tear fault or transcurrent fault ), the fault surface (plane) is usually near vertical, and the footwall moves laterally either left or right with very little vertical motion. Strike-slip faults with left-lateral motion are also known as sinistral faults and those with right-lateral motion as dextral faults. Each

1764-601: The east-southeast. Other sub-faults intersect it north and south of Little Colorado. Even further to the extreme northeast, at the Marble Canyon (Marble Platform), four parallel faults (2 sets of 2 – including the Eminence Fault), run parallel to the side of the Paria Plateau, striking northeasterly, resulting in the Colorado River's sharp turn to the southwest. The river then turns due-south – running down

1813-589: The enigmatic circular fossils of Chuaria circularis are found at various levels within the Chuar Group. The Unkar Group of the Grand Canyon Supergroup also contians fossil stromatolites. stromatolites have been found in the dolomite beds of Bass Formation; in the transitional zone between the Hakatai Shale and Bass Formation; and from the he Comanche Point Member of the Dox Formation. Various creeks, canyons, or landforms give clues to unit locales of

1862-456: The fault and of the presence and nature of any mineralising fluids . Fault rocks are classified by their textures and the implied mechanism of deformation. A fault that passes through different levels of the lithosphere will have many different types of fault rock developed along its surface. Continued dip-slip displacement tends to juxtapose fault rocks characteristic of different crustal levels, with varying degrees of overprinting. This effect

1911-402: The fault concerning the other side. In measuring the horizontal or vertical separation, the throw of the fault is the vertical component of the separation and the heave of the fault is the horizontal component, as in "Throw up and heave out". The vector of slip can be qualitatively assessed by studying any drag folding of strata, which may be visible on either side of the fault. Drag folding

1960-576: The fault plane and a vertical plane that strikes parallel to the fault. Ring faults , also known as caldera faults , are faults that occur within collapsed volcanic calderas and the sites of bolide strikes, such as the Chesapeake Bay impact crater . Ring faults are the result of a series of overlapping normal faults, forming a circular outline. Fractures created by ring faults may be filled by ring dikes . Synthetic and antithetic are terms used to describe minor faults associated with

2009-401: The fault plane, the horizontal extensional displacement on a listric fault implies a geometric "gap" between the hanging and footwalls of the fault forms when the slip motion occurs. To accommodate into the geometric gap, and depending on its rheology , the hanging wall might fold and slide downwards into the gap and produce rollover folding , or break into further faults and blocks which fil in

Grand Canyon Supergroup - Misplaced Pages Continue

2058-427: The fault-bend fold diagram. Thrust faults form nappes and klippen in the large thrust belts. Subduction zones are a special class of thrusts that form the largest faults on Earth and give rise to the largest earthquakes. A fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault . Nearly all faults have some component of both dip-slip and strike-slip; hence, defining

2107-475: The gap. If faults form, imbrication fans or domino faulting may form. A reverse fault is the opposite of a normal fault—the hanging wall moves up relative to the footwall. Reverse faults indicate compressive shortening of the crust. A thrust fault has the same sense of motion as a reverse fault, but with the dip of the fault plane at less than 45°. Thrust faults typically form ramps, flats and fault-bend (hanging wall and footwall) folds. A section of

2156-551: The mudrocks are due to a high organic content. Some samples of these mudrocks contain high total organic carbon percentages that are as much 9.39 weight percent organic carbon. The sandstone beds often exhibit symmetrical ripple marks . These ripple marks are commonly draped with a thin veneer of mudstone with mudcracks . The Chuar Group conatins a variety of Neoproterozoic fossils. The dolomite beds contain at least six different types of stromatolites and microbially induced sedimentary structures . The gray and black mudrocks of

2205-500: The original movement (fault inversion). In such a way, a normal fault may therefore become a reverse fault and vice versa. In a normal fault, the hanging wall moves downward, relative to the footwall. The dip of most normal faults is at least 60 degrees but some normal faults dip at less than 45 degrees. A downthrown block between two normal faults dipping towards each other is a graben . A block stranded between two grabens, and therefore two normal faults dipping away from each other,

2254-412: The right time for—and type of— igneous differentiation . At a given time differentiated magmas would burst violently out of the fault-traps and head to shallower places in the crust where porphyry copper deposits would be formed. As faults are zones of weakness, they facilitate the interaction of water with the surrounding rock and enhance chemical weathering . The enhanced chemical weathering increases

2303-401: The size of the weathered zone and hence creates more space for groundwater . Fault zones act as aquifers and also assist groundwater transport. Chuar Group The Neoproterozoic Chuar Group consists of 1,600 m (5,200 ft) of exceptionally well-preserved, unmetamorphosed sedimentary strata that is composed of about 85% mudrock . The Group is the approximate upper half of

2352-474: The southeast of the Kaibab Plateau (Walhalla Plateau). The base of the largely flat-topped Redwall Limestone monolith sits upon cliffs of Muav Limestone , then Bright Angel Shale, and Tapeats Sandstone. The Nankoweap Formation is near the monolith's center of the base. The northeast side of the base merges into the overlying unit above the Nankoweap, the Chuar Group slopes. In the northeast Grand Canyon,

2401-468: The term is also used for the zone of crushed rock along a single fault. Prolonged motion along closely spaced faults can blur the distinction, as the rock between the faults is converted to fault-bound lenses of rock and then progressively crushed. Due to friction and the rigidity of the constituent rocks, the two sides of a fault cannot always glide or flow past each other easily, and so occasionally all movement stops. The regions of higher friction along

#720279