The Newark Supergroup , also known as the Newark Group , is an assemblage of Upper Triassic and Lower Jurassic sedimentary and volcanic rocks which outcrop intermittently along the east coast of North America. They were deposited in a series of Triassic basins, the Eastern North American rift basins, approximately 220–190 million years ago. The basins are characterized as aborted rifts , with half-graben geometry, developing parallel to the main rift of the Atlantic Ocean which formed as North America began to separate from Africa. Exposures of the Newark Supergroup extend from South Carolina north to Nova Scotia . Related basins are also found underwater in the Bay of Fundy . The group is named for the city of Newark, New Jersey .
34-615: The Newark Supergroup consists largely of poorly sorted nonmarine sediments; typical rocks are breccia , conglomerate , arkose sandstone , siltstone , and shale . Most of the strata are red beds that feature ripple marks , mud cracks, and even rain drop prints; dinosaur footprints are common, though actual body fossils are very rare. Some of the strata are detailed to the level of varves , with indications of Milankovitch cycles . In preserved lake sediments, Semionotus fossils are especially common. The Newark sediments are extremely thick (up to 6 kilometers); they were deposited in
68-603: 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
102-437: A 30 t/m reduction in apparent preconsolidation pressure. Coop and Airey (2003) show that for carbonate soils, cementation develops immediately after deposition and allows the soil to maintain a loose structure. Non-recognition of cementation has resulted in construction disputes. For example, a land on a major Project is marked as glacier on contract drawings. It was so hard that it had to be detonated. The contractor claimed that
136-441: A calcium source (Chou et al. , 2010). Cementing has significant effects on the properties and stability of many soil materials. Cementation is not always easily identified and its effects cannot be easily determined quantitatively. It is known to contribute to clay tenderness and may be responsible for an apparent preconsolidation pressure. The filtration of iron compounds from a very sensitive clay from Labrador, Canada, resulted in
170-573: 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
204-734: 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
238-407: A rift valley. Coarse sediments were deposited near the eastern mountain front, while progressively finer ones were deposited farther west. Evidence suggests the climate at the time was subtropical and rainy, though divided between wet and dry months. A few organic-rich deposits suggest patchy or intermittent swamps and lakes . Accumulation of Newark sediments within the rift basins continued from
272-483: A series of half-grabens that were themselves faulted into block mountains. The beds dip to the east, while the faults dip westward. The beds are intruded by numerous dikes and sills , indicative of considerable igneous activity; a superb example is the New Jersey Palisades sill. The Newark Supergroup's lithologies and structure are the classic hallmarks of a rift valley ; the fault-blocking illustrates
306-404: 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
340-426: 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
374-458: 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
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#1732851618199408-485: 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
442-586: Is continuous in the groundwater zone, so much so that the term "zone of cementation" is sometimes used interchangeably. Cementation occurs in fissures or other openings of existing rocks and is a dynamic process more or less in equilibrium with a dissolution or dissolving process. Cement found on the sea floor is commonly aragonite and can take different textural forms. These textural forms include pendant cement, meniscus cement, isopachous cement, needle cement, botryoidal cement, blocky cement, syntaxial rim cement, and coarse mosaic cement. The environment in which each of
476-489: 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
510-406: 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
544-520: Is that minerals bond grains of sediment together by growing around them. This process is called cementation and is a part of the rock cycle. Cementation involves ions carried in groundwater chemically precipitating to form new crystalline material between sedimentary grains. The new pore-filling minerals form "bridges" between original sediment grains, thereby binding them together. In this way, sand becomes sandstone , and gravel becomes conglomerate or breccia . Cementation occurs as part of
578-654: The Minoan palace of Knossos on Crete in about 1800 BC . Breccia was used on a limited scale by the ancient Egyptians ; one of the best-known examples is the statue of the goddess Tawaret in the British Museum. Breccia was regarded by the Romans as an especially precious stone and was often used in high-profile public buildings. Many types of marble are brecciated, such as Breccia Oniciata. Cementation (geology) A brief, easy-to-understand description of cementation
612-460: The crustal extension forces in play during the breakup of Pangea during the late Triassic Period. The Appalachian Mountains had already been nearly eroded flat by the end of the period; the uplift and faulting that was the first part of the rifting provided new sources of sediment for the vast thicknesses deposited in the Newark Supergroup; the igneous intrusions are similarly diagnostic of
646-514: The diagenesis or lithification of sediments. Cementation occurs primarily below the water table regardless of sedimentary grain sizes present. Large volumes of pore water must pass through sediment pores for new mineral cements to crystallize and so millions of years are generally required to complete the cementation process. Common mineral cements include calcite , quartz , and silica phases like cristobalite , iron oxides , and clay minerals ; other mineral cements also occur. Cementation
680-486: 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
714-404: 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
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#1732851618199748-477: The bottom of grains where water droplets are held. Hardgrounds are hard crusts of carbonate material that form on the bottom of the ocean floor, below the lowest tide level. Isopachous (which means equal thickness) cement forms in subaqueous conditions where the grains are completely surrounded by water (Boggs, 2006). Carbonate cements can also be formed by biological organisms such as Sporosarcina pasteurii , which binds sand together given organic compounds and
782-454: The cements is found depends on the pore space available. Cements that are found in phreatic zones include: isopachous, blocky, and syntaxial rim cements. As for calcite cementation, which occurs in meteoric realms (freshwater sources), the cement is produced by the dissolution of less stable aragonite and high-Mg calcite. (Boggs, 2011) Classifying rocks while using the Folk classification depends on
816-427: 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
850-650: The late 1970s, the entire Newark Supergroup was assumed to be Triassic in age. A 1977 study of fossil pollen argued that the sediments actually range from the Ladinian to the Lower Jurassic . Under this hypothesis, the Supergroup was deposited over the course of 50 million years. 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')
884-431: The late Triassic into the early Jurassic . The separate basins and sub-basins of the Newark Supergroup have historically been given their own geological formations by local paleontologists. However, a study by Weems , Tanner , and Lucas (2016) proposed that the formations of the Newark Supergroup should be defined on a regional scale due to their geological uniformity over eastern North America. From youngest to oldest,
918-488: The matrix, which is either sparry (prominently composed of cement) or micritic (prominently composed of mud). Beachrock is a type of carbonate beach sand that has been cemented together by a process called synsedimentary cementation. Beachrock may contain meniscus cements or pendant cements. As the water between the narrow spaces of grains drains from the beachrock, a small portion of it is held back by capillary forces, where meniscus cement will form. Pendant cements form on
952-403: 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
986-428: 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
1020-534: The regional formations proposed by this study are: Basin-specific formations are given below: Minor basins crop out in South Carolina (Crowburg, Wadesboro basins), North Carolina (Ellerbe, Davie County basins), Virginia (Scottsburg, Randolph, Roanoke Creek, Briery Creek, Farmville , Flat Branch, Deep Run, Scottsville, Barboursville basins), Connecticut (Cherry Brook Outlier), Massachusetts (Northfield and Middleton basins), and Nova Scotia (Chedabucto Basin). Until
1054-407: 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
Newark Supergroup - Misplaced Pages Continue
1088-444: 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
1122-419: The soil was cemented during excavation as it was formed due to the clay matrix as well as the gravel. The owner concluded that this was due to the weathering of the pebbles. Proper evaluation of the material before the award of the contract could have avoided the problem. Clay particles adhere to the surfaces of larger silt and sand particles, a process called clay bonding. Eventually, larger grains are embedded in
1156-581: 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
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