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41-637: The Lusitanian Basin results from the opening of the North Atlantic Ocean due to Mesozoic extension. Throughout the complete formation of the basin, from the Late Triassic to the Cretaceous , five distinct phases can be defined, with four stages of rifting activity: The most significant faults and salt structures throughout the Lusitanian Basin trend north-northeast, parallel to the elongation of

82-470: A thin section using a method like the Gazzi-Dickinson Method . This yields the relative percentages of quartz, feldspar, and lithic grains and the amount of clay matrix. The composition of a sandstone can provide important information on the genesis of the sediments when used with a triangular Q uartz, F eldspar, L ithic fragment ( QFL diagrams ). However, geologist have not been able to agree on

123-478: A sandstone goes through as the degree of kinetic processing of the sediments increases. Dott's (1964) sandstone classification scheme is one of many such schemes used by geologists for classifying sandstones. Dott's scheme is a modification of Gilbert's classification of silicate sandstones, and it incorporates R.L. Folk's dual textural and compositional maturity concepts into one classification system. The philosophy behind combining Gilbert's and R. L. Folk's schemes

164-459: A set of boundaries separating regions of the QFL triangle. Visual aids are diagrams that allow geologists to interpret different characteristics of a sandstone. For example, a QFL chart can be marked with a provenance model that shows the likely tectonic origin of sandstones with various compositions of framework grains. Likewise, the stage of textural maturity chart illustrates the different stages that

205-445: A twofold classification: Cement is what binds the siliciclastic framework grains together. Cement is a secondary mineral that forms after deposition and during burial of the sandstone. These cementing materials may be either silicate minerals or non-silicate minerals, such as calcite. Sandstone that becomes depleted of its cement binder through weathering gradually becomes friable and unstable. This process can be somewhat reversed by

246-837: Is a distinction that can be recognized in the field . In turn, the distinction between an orthoquartzite and a metaquartzite is the onset of recrystallization of existing grains. The dividing line may be placed at the point where strained quartz grains begin to be replaced by new, unstrained, small quartz grains, producing a mortar texture that can be identified in thin sections under a polarizing microscope. With increasing grade of metamorphism, further recrystallization produces foam texture , characterized by polygonal grains meeting at triple junctions, and then porphyroblastic texture , characterized by coarse, irregular grains, including some larger grains ( porphyroblasts .) Sandstone has been used since prehistoric times for construction, decorative art works and tools. It has been widely employed around

287-573: Is caused by basement-influenced faulting. Resultant of diapirism leading to the formation of salt pillows, the Lusitanian Basin can be divided into seven different sub-basins: The Lusitanian basin Triassic to Cretaceous rocks provided thousands of fossils, from plants, microfossils, invertebrates and vertebrates. The most productive formations are the Late Jurassic Lourinhã Formation , Alcobaça Formation , and Montejunto Formation and

328-546: Is composed of quartz or feldspar , because they are the most resistant minerals to the weathering processes at the Earth's surface. Like uncemented sand , sandstone may be imparted any color by impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Because sandstone beds can form highly visible cliffs and other topographic features, certain colors of sandstone have become strongly identified with certain regions, such as

369-523: Is likely formed during eogenesis. Deeper burial is accompanied by mesogenesis , during which most of the compaction and lithification takes place. Compaction takes place as the sand comes under increasing pressure from overlying sediments. Sediment grains move into more compact arrangements, ductile grains (such as mica grains) are deformed, and pore space is reduced. In addition to this physical compaction, chemical compaction may take place via pressure solution . Points of contact between grains are under

410-431: Is redeposited in the unstrained pore spaces. Mechanical compaction takes place primarily at depths less than 1,000 meters (3,300 ft). Chemical compaction continues to depths of 2,000 meters (6,600 ft), and most cementation takes place at depths of 2,000–5,000 meters (6,600–16,400 ft). Unroofing of buried sandstone is accompanied by telogenesis , the third and final stage of diagenesis. As erosion reduces

451-507: Is substantial hydrocarbon potential in this basin alone, Portugal imports 100% of its fossil fuel. There are two major petroleum systems at work within the basin—Subsalt and Suprasalt. In the subsalt petroleum system, there are Paleozoic source rocks and synrift Triassic sandstone reservoirs that are sealed by Dagorda evaporites. In the suprasalt system, the oldest source rock is the Lower Brenha formation. The best reservoirs to mention include

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492-443: Is that it is better able to "portray the continuous nature of textural variation from mudstone to arenite and from stable to unstable grain composition". Dott's classification scheme is based on the mineralogy of framework grains, and on the type of matrix present in between the framework grains. In this specific classification scheme, Dott has set the boundary between arenite and wackes at 15% matrix. In addition, Dott also breaks up

533-580: The continental lithosphere . Iceland extends across the Mid-Atlantic Ridge . The Mid-Atlantic Ridge is a divergent plate boundary, and it separates the Eurasian and North American plates. The ages of the earliest volcanic rocks from this plume lie in the late Paleocene , and both sides of the Atlantic Ocean contain these rocks. Since these rocks have been dated to the late Paleocene, this lines up with

574-583: The Coimbra dolomite and Upper Dagorda carbonates, Candieiros oolitic and bioclastic grainstones, and the fractured carbonates of the Brenha formation. Seals are tight or marly carbonates of the Brenha and overlying basal Upper Jurassic. N. Pimentel1 and R. Pena dos Reis (2016) - PETROLEUM SYSTEMS OF THE WEST IBERIAN MARGIN: A REVIEW OF THE LUSITANIAN BASIN AND THE DEEP OFFSHORE PENICHE BASIN. Journal of Petroleum Geology, Vol. 39(3), July 2016, pp 305-326. Opening of

615-486: The Cretaceous Papo Seco Formation . This includes an outstanding abundance of Jurassic mammals, and dinosaur fossils and trackways. The Lusitanian Basin is a late Triassic rift basin is filled with synrift siliciclastics and capped by post-rift evaporites . In the late Triassic, there was deposition of fluvial sand and clay that eventually evolved into deposition of shallow marine dolomites during

656-509: The Dagorda formation are the synrift continental siliciclastics of the Silves formation. Above the Dagorda formation is the post-rift carbonate shelf environment—the Coimbra dolomite, Brenha limestone , and Cardieros carbonate grainstone . A substantial unconformity , associated with significant tectonic activity, characterizes the top of the sequence. The carbonate shelf environment is still present in

697-480: The Earth, hot mantle rises to force doming of the crust. This causes thinning of the crust and lithosphere , then melting and underplating occur. Finally, there is rifting at the crest of the domed crust and volcanism occurs. In passive rifting, driven by plate tectonics, the crust and lithosphere extend as a result of plate boundary forces such as slab pull . Far field stresses thin the crust and lithospheric mantle, and hot asthenospheric mantle passively enters

738-534: The North Atlantic Ocean The opening of the North Atlantic Ocean is a geological event that has occurred over millions of years, during which the supercontinent Pangea broke up. As modern-day Europe ( Eurasian Plate ) and North America ( North American Plate ) separated during the final breakup of Pangea in the early Cenozoic Era, they formed the North Atlantic Ocean . Geologists believe

779-650: The Upper Jurassic—characterized by the Montejunto grainstone and reef facies, Cabacos organic-rich limestone (capped by anhydrite ). Above this sequence, deposition is dominated by the siliciclastics from the Meseta highlands. The Abadia formation is composed of shale, marl, siltstone, and minimal sandstone. The rest of the Upper Jurassic and Cretaceous is dominated by westward-prograding continental clastics. In

820-491: The application of tetraethyl orthosilicate (Si(OC 2 H 5 ) 4 ) which will deposit amorphous silicon dioxide between the sand grains. The reaction is as follows. Pore space includes the open spaces within a rock or a soil. The pore space in a rock has a direct relationship to the porosity and permeability of the rock. The porosity and permeability are directly influenced by the way the sand grains are packed together. Sandstones are typically classified by point-counting

861-538: The basin, all Jurassic source-rocks could possibly be within the hydrocarbon generation window. However, this is not the case throughout the entire basin. This is due to the highly heterogeneous nature of basin subsidence, especially in the Late Jurassic. Around 100 exploratory wells have been drilled in the basin. 80% of these wells, from Triassic, Jurassic, and Cretaceous strata, had oil and gas shows while drilling and 27% recovered live oil or gas at surface. While there

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902-463: The basin. Both thrust faults and normal faults are observed. The thrusting observed is resultant of the basement-attached inversion movements of the pre-existing normal faults during the Miocene . Most of the faults within the basin are fairly high-angle, with some shallowing with depth observed. There is always faulting beneath salt structures and it is speculated that the movement of the salt structures

943-656: The breakup occurred either due to primary processes of the Iceland plume or secondary processes of lithospheric extension from plate tectonics . Rocks from the North Atlantic Igneous Province have been found in Greenland , the Irminger Basin , Faroe Islands , Vøring Plateau (off Norway), Faroe-Shetland Basin , Hebrides , Outer Moray Firth and Denmark . The supercontinent known as Pangea existed during

984-468: The common minerals most resistant to weathering processes at the Earth's surface, as seen in the Goldich dissolution series . Framework grains can be classified into several different categories based on their mineral composition: Matrix is very fine material, which is present within interstitial pore space between the framework grains. The nature of the matrix within the interstitial pore space results in

1025-456: The depositional environment, older sand is buried by younger sediments, and it undergoes diagenesis . This mostly consists of compaction and lithification of the sand. Early stages of diagenesis, described as eogenesis , take place at shallow depths (a few tens of meters) and are characterized by bioturbation and mineralogical changes in the sands, with only slight compaction. The red hematite that gives red bed sandstones their color

1066-407: The depth of burial, renewed exposure to meteoric water produces additional changes to the sandstone, such as dissolution of some of the cement to produce secondary porosity . Framework grains are sand-sized (0.0625-to-2-millimeter (0.00246 to 0.07874 in) diameter) detrital fragments that make up the bulk of a sandstone. Most framework grains are composed of quartz or feldspar , which are

1107-446: The different types of framework grains that can be present in a sandstone into three major categories: quartz, feldspar, and lithic grains. When sandstone is subjected to the great heat and pressure associated with regional metamorphism , the individual quartz grains recrystallize, along with the former cementing material, to form the metamorphic rock called quartzite . Most or all of the original texture and sedimentary structures of

1148-433: The greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of cement that binds the grains together. Pressure solution contributes to cementing, as the mineral dissolved from strained contact points

1189-442: The hardness of individual grains, uniformity of grain size and friability of their structure, some types of sandstone are excellent materials from which to make grindstones , for sharpening blades and other implements. Non-friable sandstone can be used to make grindstones for grinding grain, e.g., gritstone . A type of pure quartz sandstone, orthoquartzite, with more of 90–95 percent of quartz, has been proposed for nomination to

1230-429: The late Paleozoic and early Mesozoic eras and began to rift around 200 million years ago. Pangea had three major phases of breakup. The Iceland plume is a mantle plume under Iceland that carries hot material from the deep within Earth's mantle upwards to the crust. The rising hot material weakens the lithosphere, making the separation of plates easier. The flow of hot plume material creates volcanism under

1271-440: The lower and middle Jurassic. These sediments are known as the Silves, Dagorda, and Coimbra Formations. Deposition of Carbonates of the Brenha and Candieros Formations are in shelf, ramp, and sub-marine fan environments and filled the basin during the early and middle Jurassic. The carbonate formations are commonly interbedded with shale and there are local turbidite beds also present. Below the halite-bearing evaporites that compose

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1312-493: The much lower temperatures and pressures associated with diagenesis of sedimentary rock, but diagenesis has cemented the rock so thoroughly that microscopic examination is necessary to distinguish it from metamorphic quartzite. The term orthoquartzite is used to distinguish such sedimentary rock from metaquartzite produced by metamorphism. By extension, the term orthoquartzite has occasionally been more generally applied to any quartz-cemented quartz arenite . Orthoquartzite (in

1353-464: The narrow sense) is often 99% SiO 2 with only very minor amounts of iron oxide and trace resistant minerals such as zircon , rutile and magnetite . Although few fossils are normally present, the original texture and sedimentary structures are preserved. The typical distinction between a true orthoquartzite and an ordinary quartz sandstone is that an orthoquartzite is so highly cemented that it will fracture across grains, not around them. This

1394-638: The product of physical and chemical weathering of bedrock. Weathering and erosion are most rapid in areas of high relief, such as volcanic arcs , areas of continental rifting , and orogenic belts . Eroded sand is transported by rivers or by the wind from its source areas to depositional environments where tectonics has created accommodation space for sediments to accumulate. Forearc basins tend to accumulate sand rich in lithic grains and plagioclase . Intracontinental basins and grabens along continental margins are also common environments for deposition of sand. As sediments continue to accumulate in

1435-704: The red rock deserts of Arches National Park and other areas of the American Southwest . Rock formations composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs . Quartz-bearing sandstone can be changed into quartzite through metamorphism , usually related to tectonic compression within orogenic belts . Sandstones are clastic in origin (as opposed to either organic , like chalk and coal , or chemical , like gypsum and jasper ). The silicate sand grains from which they form are

1476-417: The sandstone are erased by the metamorphism. The grains are so tightly interlocked that when the rock is broken, it fractures through the grains to form an irregular or conchoidal fracture. Geologists had recognized by 1941 that some rocks show the macroscopic characteristics of quartzite, even though they have not undergone metamorphism at high pressure and temperature. These rocks have been subject only to

1517-622: The shoreline. The faults that trend northeast to east-northeast are fewer in number. However, they are fairly substantial—for example, the Nazare Fault. The north-trending faults are concentrated mainly in the central part of the Lusitanian Basin. These faults are a part of in important structural trend within the Estremadura Trough which highlights the Oxfordian extension within the basin. West-northwest trending faults are scattered throughout

1558-458: The surface. Volcanic anomalies are created by plate tectonics such as spreading plate boundaries or subduction zones . The location of the volcanism is governed by the stress field in the plate and the amount of melt is governed by the fusibility of the mantle beneath. Plate tectonics can explain most of the volcanism on Earth. Active rifting, such as is formed by the Iceland plume , is driven by hotspot or mantle plume activity. From deep within

1599-513: The thinned area. The upwelling of asthenosphere is not involved in the actual rifting process. The upward flow of the asthenosphere results in decompression melting , magmatic underplating and some volcanism that may occur in the rift area. Sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains, cemented together by another mineral. Sandstones comprise about 20–25% of all sedimentary rocks . Most sandstone

1640-526: The time of breakup of the North Atlantic continent, so some think it could have been a contributing factor. This theory views volcanism as the resultant of lithospheric processes rather than heat from the mantle rising up. Instead of heat coming up from deep in the mantle, volcanic anomalies come from a shallow source. Volcanism thus occurs where the crust is easier to break up because it has been stretched by lithospheric extension, allowing melt to reach

1681-612: The world in constructing temples, churches, homes and other buildings, and in civil engineering . Although its resistance to weathering varies, sandstone is easy to work. That makes it a common building and paving material, including in asphalt concrete . However, some types that have been used in the past, such as the Collyhurst sandstone used in North West England , have had poor long-term weather resistance, necessitating repair and replacement in older buildings. Because of

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