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41-416: The Pottsville Formation consists of a gray conglomerate , fine to coarse grained sandstone , and is known to contain limestone , siltstone and shale , as well as anthracite and bituminous coal. It is considered a classic orogenic molasse . The formation was first described from a railroad cut south of Pottsville, Pennsylvania . The relationship to the term "Pottsville" and actual lithologic units

82-603: A karst terrain , a collapse breccia may form due to collapse of rock into a sinkhole or in cave development. Collapse breccias also form by dissolution of underlying evaporite beds. Fault or tectonic breccia results from the grinding action of two fault blocks as they slide past each other. Subsequent cementation of these broken fragments may occur by means of the introduction of mineral matter in groundwater . Igneous clastic rocks can be divided into two classes: Volcanic pyroclastic rocks are formed by explosive eruption of lava and any rocks which are entrained within

123-522: A cobble conglomerate. Conglomerates are deposited in a variety of sedimentary environments . In turbidites , the basal part of a bed is typically coarse-grained and sometimes conglomeratic. In this setting, conglomerates are normally very well sorted, well-rounded and often with a strong A-axis type imbrication of the clasts. Conglomerates are normally present at the base of sequences laid down during marine transgressions above an unconformity , and are known as basal conglomerates . They represent

164-560: A conglomerate are in contact with each other, it is called an orthoconglomerate. Unlike paraconglomerates, orthoconglomerates are typically cross-bedded and often well-cemented and lithified by either calcite , hematite , quartz , or clay. The differences between paraconglomerates and orthoconglomerates reflect differences in how they are deposited. Paraconglomerates are commonly either glacial tills or debris flow deposits. Orthoconglomerates are typically associated with aqueous currents. Conglomerates are also classified according to

205-600: A group, the Pottsville may encompass the following formations depending on the state in which it occurs: Connoquenessing Formation, Curwensville Formation, Elliott Park Formation, Gurnee Formation, Hance Formation, Homewood Formation or Homewood Sandstone, Mercer Formation, New River Formation, Olean Conglomerate or Olean Formation, Pocahontas Formation, Schuylkill Formation, Sharon Formation or Sharon Sandstone, Sharp Mountain Formation, Tumbling Run Formation. The Pottsville

246-578: A known impact crater, and/or an association with other products of impact cratering such as shatter cones , impact glass, shocked minerals , and chemical and isotopic evidence of contamination with extraterrestrial material (e.g., iridium and osmium anomalies). An example of an impact breccia is the Neugrund breccia , which was formed in the Neugrund impact . Hydrothermal breccias usually form at shallow crustal levels (<1 km) between 150 and 350 °C, when seismic or volcanic activity causes

287-734: A meter in size and which form layers in the caldera floor. Some clasts of caldera megabreccias can be over a kilometer in length. Within the volcanic conduits of explosive volcanoes the volcanic breccia environment merges into the intrusive breccia environment. There the upwelling lava tends to solidify during quiescent intervals only to be shattered by ensuing eruptions. This produces an alloclastic volcanic breccia. Clastic rocks are also commonly found in shallow subvolcanic intrusions such as porphyry stocks, granites and kimberlite pipes, where they are transitional with volcanic breccias. Intrusive rocks can become brecciated in appearance by multiple stages of intrusion, especially if fresh magma

328-419: A mixture composed of varying amounts of silt, sand, and clay, known as matrix . If the individual gravel clasts in a conglomerate are separated from each other by an abundance of matrix such that they are not in contact with each other and float within the matrix, it is called a paraconglomerate. Paraconglomerates are also often unstratified and can contain more matrix than gravel clasts. If the gravel clasts of

369-407: A mixture of rounded and angular gravel clasts are sometimes called breccio-conglomerate. Conglomerates contain at least 30% of rounded to subangular clasts larger than 2 mm (0.079 in) in diameter, e.g., granules , pebbles , cobbles , and boulders . However, conglomerates are rarely composed entirely of gravel-size clasts. Typically, the space between the gravel-size clasts is filled by

410-415: A shoreline. Finally, conglomerates are often differentiated and named according to the dominant clast size comprising them. In this classification, a conglomerate composed largely of granule-size clasts would be called a granule conglomerate; a conglomerate composed largely of pebble-size clasts would be called a pebble conglomerate; and a conglomerate composed largely of cobble-size clasts would be called

451-404: A void to open along a fault deep underground. The void draws in hot water, and as pressure in the cavity drops, the water violently boils. In addition, the sudden opening of a cavity causes rock at the sides of the fault to destabilise and implode inwards, and the broken rock gets caught up in a churning mixture of rock, steam and boiling water. Rock fragments collide with each other and the sides of

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492-726: Is a sedimentary rock made up of rounded gravel -sized pieces of rock surrounded by finer-grained sediments (such as sand , silt , or clay ). The larger fragments within conglomerate are called clasts, while the finer sediment surrounding the clasts is called the matrix. The clasts and matrix are typically cemented by calcium carbonate , iron oxide , silica , or hardened clay. Conglomerates form when rounded gravels deposited by water or glaciers become solidified and cemented by pressure over time . They can be found in sedimentary rock sequences of all ages but probably make up less than 1 percent by weight of all sedimentary rocks. They are closely related to sandstones in origin, and exhibit many of

533-426: Is a breccia composed of very large rock fragments, sometimes kilometers across, which can be formed by landslides , impact events , or caldera collapse. Breccia is composed of coarse rock fragments held together by cement or a fine-grained matrix. Like conglomerate , breccia contains at least 30 percent of gravel -sized particles (particles over 2mm in size), but it is distinguished from conglomerate because

574-458: Is a breccia containing very large rock fragments, from at least a meter in size to greater than 400 meters. In some cases, the clasts are so large that the brecciated nature of the rock is not obvious. Megabreccias can be formed by landslides , impact events , or caldera collapse. Breccias are further classified by their mechanism of formation. Sedimentary breccia is breccia formed by sedimentary processes. For example, scree deposited at

615-444: Is a conglomerate that is composed largely of clasts of rounded mud chips and pebbles held together by clay minerals and created by erosion within environments such as within a river channel or along a lake margin. Flat-pebble conglomerates (edgewise conglomerates) are conglomerates that consist of relatively flat clasts of lime mud created by either storms or tsunami eroding a shallow sea bottom or tidal currents eroding tidal flats along

656-490: Is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix . The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of different origins, as indicated by the named types including sedimentary breccia, fault or tectonic breccia, igneous breccia, impact breccia, and hydrothermal breccia. A megabreccia

697-1381: Is complex. Most fundamentally, the unit may be considered a formation or a group . As a formation, the Pottsville may encompass the following members depending on the state in which it occurs: Alton Coal Member, Anthony Shale Member, Bear Run Member, Bedford Clay Bed, Boggs Member, Boyles Sandstone Member, Bremen Sandstone Member, Brookville Clay Member, Camp Branch Sandstone Member, Campbell Ledge Shale Member, Chestnut Sandstone Member, Connoquenessing Sandstone Member, Dundee Sandstone Member, Flint Ridge Clay Bed or Flint Ridge Shale Member, Harrison Member, Homewood Sandstone Member, Huckleberry Clay Bed, Kanawha Member, Lick Creek Sandstone Member, Lowellville Limestone Member, Lower Mercer Limestone Member, Massillon Sandstone Member, McArthur Member, Mercer Member, Middle Mercer Shale Member, Mount Savage Clay Bed, Olean Conglomerate Member of Olean Sandstone Member, Pine Sandstone Member, Poverty Run Member, Razburg Sandstone Member, Rocky Ridge Sandstone Member, Schuylkill Member, Sciotoville Clay Member, Shades Sandstone Member, Sharon Coal Bed, Sharon Member, Sharp Mountain Member, Straight Ridge Sandstone Member, Straven Conglomerate Member, Tionesta Clay Bed, Tumbling Run Member, Upper Mercer Limestone Member or Upper Mercer Bed, Vandusen Shale Member, Wolf Ridge Sandstone Member. As

738-489: Is intruded into partly consolidated or solidified magma. This may be seen in many granite intrusions where later aplite veins form a late-stage stockwork through earlier phases of the granite mass. When particularly intense, the rock may appear as a chaotic breccia. Clastic rocks in mafic and ultramafic intrusions have been found and form via several processes: Impact breccias are thought to be diagnostic of an impact event such as an asteroid or comet striking

779-406: Is less common in the mesothermal regime, as the formational event is brief. If boiling occurs, methane and hydrogen sulfide may be lost to the steam phase, and ore may precipitate. Mesothermal deposits are often mined for gold. For thousands of years, the striking visual appearance of breccias has made them a popular sculptural and architectural material. Breccia was used for column bases in

820-571: Is often called a fanglomerate . Glaciers carry a lot of coarse-grained material and many glacial deposits are conglomeratic. tillites , the sediments deposited directly by a glacier, are typically poorly sorted, matrix-supported conglomerates. The matrix is generally fine-grained, consisting of finely milled rock fragments. Waterlaid deposits associated with glaciers are often conglomeratic, forming structures such as eskers . An example of conglomerate can be seen at Montserrat , near Barcelona . Here, erosion has created vertical channels that give

861-490: The Earth and are normally found at impact craters . Impact breccia, a type of impactite , forms during the process of impact cratering when large meteorites or comets impact with the Earth or other rocky planets or asteroids . Breccia of this type may be present on or beneath the floor of the crater, in the rim, or in the ejecta expelled beyond the crater. Impact breccia may be identified by its occurrence in or around

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902-404: The base of a cliff may become cemented to form a talus breccia without ever experiencing transport that might round the rock fragments. Thick sequences of sedimentary ( colluvial ) breccia are generally formed next to fault scarps in grabens . Sedimentary breccia may be formed by submarine debris flows . Turbidites occur as fine-grained peripheral deposits to sedimentary breccia flows. In

943-840: The characteristic jagged shapes the mountain is named for (Montserrat literally means "jagged mountain"). The rock is strong enough to use as a building material, as in the Santa Maria de Montserrat Abbey . Another example, the Crestone Conglomerate , occurs in and near the town of Crestone , at the foot of the Sangre de Cristo Range in Colorado 's San Luis Valley . The Crestone Conglomerate consists of poorly sorted fanglomerates that accumulated in prehistoric alluvial fans and related fluvial systems. Some of these rocks have hues of red and green. Conglomerate cliffs are found on

984-416: The clasts of metastable and unstable rocks and minerals, it is called either a petromict or petromictic conglomerate. In addition, conglomerates are classified by source as indicated by the lithology of the gravel-size clasts If these clasts consist of rocks and minerals that are significantly different in lithology from the enclosing matrix and, thus, older and derived from outside the basin of deposition,

1025-424: The composition of their clasts. A conglomerate or any clastic sedimentary rock that consists of a single rock or mineral is known as either a monomict, monomictic, oligomict, or oligomictic conglomerate. If the conglomerate consists of two or more different types of rocks, minerals, or combination of both, it is known as either a polymict or polymictic conglomerate. If a polymictic conglomerate contains an assortment of

1066-469: The conglomerate is known as an extraformational conglomerate. If these clasts consist of rocks and minerals that are identical to or consistent with the lithology of the enclosing matrix and, thus, penecontemporaneous and derived from within the basin of deposition, the conglomerate is known as an intraformational conglomerate. Two recognized types of intraformational conglomerates are shale-pebble and flat-pebble conglomerates. A shale-pebble conglomerate

1107-728: The domed hills of Kata Tjuta , in Australia's Northern Territory or in the Buda Hills in Hungary. In the nineteenth century a thick layer of Pottsville conglomerate was recognized to underlie anthracite coal measures in Pennsylvania. On Mars , slabs of conglomerate have been found at an outcrop named " Hottah ", and have been interpreted by scientists as having formed in an ancient streambed. The gravels, which were discovered by NASA 's Mars rover Curiosity , range from

1148-611: The east coast of Scotland from Arbroath northwards along the coastlines of the former counties of Angus and Kincardineshire . Dunnottar Castle sits on a rugged promontory of conglomerate jutting into the North Sea just south of the town of Stonehaven . Copper Harbor Conglomerate is found both in the Keweenaw Peninsula and Isle Royale National Park in Lake Superior . Conglomerate may also be seen in

1189-427: The eruptive column. This may include rocks plucked off the wall of the magma conduit, or physically picked up by the ensuing pyroclastic surge . Lavas, especially rhyolite and dacite flows, tend to form clastic volcanic rocks by a process known as autobrecciation . This occurs when the thick, nearly solid lava breaks up into blocks and these blocks are then reincorporated into the lava flow again and mixed in with

1230-403: The mesothermal regime, at much greater depths, fluids under lithostatic pressure can be released during seismic activity associated with mountain building. The pressurised fluids ascend towards shallower crustal levels that are under lower hydrostatic pressure. On their journey, high-pressure fluids crack rock by hydrofracturing , forming an angular in situ breccia. Rounding of rock fragments

1271-428: The overpressure of pore fluid within sedimentary basins . Hydrothermal breccias are usually formed by hydrofracturing of rocks by highly pressured hydrothermal fluids. They are typical of the epithermal ore environment and are intimately associated with intrusive-related ore deposits such as skarns , greisens and porphyry -related mineralisation. Epithermal deposits are mined for copper, silver and gold. In

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1312-416: The position of the shoreline at a particular time and are diachronous . Conglomerates deposited in fluvial environments are typically well rounded and poorly sorted. Clasts of this size are carried as bedload and only at times of high flow-rate. The maximum clast size decreases as the clasts are transported further due to attrition , so conglomerates are more characteristic of immature river systems. In

1353-407: The remaining liquid magma. The resulting breccia is uniform in rock type and chemical composition. Caldera collapse leads to the formation of megabreccias, which are sometimes mistaken for outcrops of the caldera floor. These are instead blocks of precaldera rock, often coming from the unstable oversteepened rim of the caldera. They are distinguished from mesobreccias whose clasts are less than

1394-444: The rock fragments have sharp edges that have not been worn down. These indicate that the gravel was deposited very close to its source area, since otherwise the edges would have been rounded during transport. Most of the rounding of rock fragments takes place within the first few kilometers of transport, though complete rounding of pebbles of very hard rock may take up to 300 kilometers (190 mi) of river transport. A megabreccia

1435-505: The same types of sedimentary structures , such as tabular and trough cross-bedding and graded bedding . Fanglomerates are poorly sorted, matrix-rich conglomerates that originated as debris flows on alluvial fans and likely contain the largest accumulations of gravel in the geologic record. Breccias are similar to conglomerates, but have clasts that have angular (rather than rounded) shapes. Conglomerates may be named and classified by the: The classification method depends on

1476-446: The sediments deposited by mature rivers, conglomerates are generally confined to the basal part of a channel fill where they are known as pebble lags . Conglomerates deposited in a fluvial environment often have an AB-plane type imbrication. Alluvial deposits form in areas of high relief and are typically coarse-grained. At mountain fronts individual alluvial fans merge to form braidplains and these two environments are associated with

1517-452: The size of sand particles to the size of golf balls. Analysis has shown that the pebbles were deposited by a stream that flowed at walking pace and was ankle- to hip-deep. Metamorphic alteration transforms conglomerate into metaconglomerate . Breccia Breccia ( / ˈ b r ɛ tʃ i ə / BRETCH -ee-ə or / ˈ b r ɛ ʃ i ə / BRESH -ee-ə , Italian: [ˈbrettʃa] ; Italian for 'breach')

1558-408: The thickest deposits of conglomerates. The bulk of conglomerates deposited in this setting are clast-supported with a strong AB-plane imbrication . Matrix-supported conglomerates, as a result of debris-flow deposition, are quite commonly associated with many alluvial fans. When such conglomerates accumulate within an alluvial fan, in rapidly eroding (e.g., desert ) environments, the resulting rock unit

1599-501: The type and detail of research being conducted. A sedimentary rock composed largely of gravel is first named according to the roundness of the gravel. If the gravel clasts that comprise it are largely well-rounded to subrounded, it is a conglomerate. If the gravel clasts that comprise it are largely angular, it is a breccia . Such breccias can be called sedimentary breccias to differentiate them from other types of breccia, e.g. volcanic and fault breccias. Sedimentary rocks that contain

1640-581: The void, and the angular fragments become more rounded. Volatile gases are lost to the steam phase as boiling continues, in particular carbon dioxide . As a result, the chemistry of the fluids changes and ore minerals rapidly precipitate . Breccia-hosted ore deposits are quite common. The morphology of breccias associated with ore deposits varies from tabular sheeted veins and clastic dikes associated with overpressured sedimentary strata, to large-scale intrusive diatreme breccias ( breccia pipes ), or even some synsedimentary diatremes formed solely by

1681-718: Was previously mapped in the Illinois basin as well at the Formation level, but was renamed the Tradewater Formation in 1997. A 1.3-m interval at the base of the Pottsville in the Broad Top basin in Pennsylvania contains both marine invertebrates and plant fossils of middle Morrowan age. Relative age dating of the Pottsville places it in the early to middle Pennsylvanian period Pennsylvania: Maryland: West Virginia: Ohio: Conglomerate (geology) Conglomerate ( / k ən ˈ ɡ l ɒ m ər ɪ t / )

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