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56-541: The region can be divided into two different orographic zones: the mountainous southwest, formed by the Arrábida mountain range, cut by valleys and hills, with altitudes between 100 and 500 m (330 and 1,640 ft), and the remaining extensive flat areas, part of the Tagus floodplain . 38°35′N 9°00′W  /  38.583°N 9.000°W  / 38.583; -9.000 This Setúbal location article

112-463: A sedimentary carbonate rock that contains a high percentage of the mineral dolomite , CaMg(CO 3 ) 2 . It occurs widely, often in association with limestone and evaporites , though it is less abundant than limestone and rare in Cenozoic rock beds (beds less than about 66 million years in age). One of the first geologists to distinguish dolomite from limestone was Déodat Gratet de Dolomieu;

168-418: A French mineralogist and geologist whom it is named after. He recognized and described the distinct characteristics of dolomite in the late 18th century, differentiating it from limestone. Most dolomite was formed as a magnesium replacement of limestone or of lime mud before lithification . The geological process of conversion of calcite to dolomite is known as dolomitization and any intermediate product

224-434: A drop of dilute hydrochloric acid is dropped on it. This distinguishes dolomite from limestone, which is also soft but reacts vigorously with dilute hydrochloric acid. Dolomite usually weathers to a characteristic dull yellow-brown color due to the presence of ferrous iron. This is released and oxidized as the dolomite weathers. Dolomite is usually granular in appearance, with a texture resembling grains of sugar . Under

280-405: A high percentage of CaMg(CO 3 ) 2 in which natural caves or solution tubes have formed. Both calcium and magnesium go into solution when dolomite rock is dissolved. The speleothem precipitation sequence is: calcite , Mg-calcite, aragonite , huntite and hydromagnesite . Hence, the most common speleothem (secondary deposit) in caves within dolomite rock karst , is calcium carbonate in

336-544: A high-calcium limestone, such as manufacture of sodium carbonate . Dolomite is used for production of magnesium chemicals, such as Epsom salt , and is used as a magnesium supplement. It is also used in the manufacture of refractory materials . As with limestone caves , natural caves and solution tubes typically form in dolomite rock as a result of the dissolution by weak carbonic acid. Caves can also, less commonly, form through dissolution of rock by sulfuric acid . Calcium carbonate speleothems (secondary deposits) in

392-529: A marine ecosystem covered by ocean, resulting in the formation of Dolomite limestones , today being constituted by white limestone . From the Jurassic there was a movement of submersion, that formed "alternating layers of limestone, sandstone and breccia , with a clear angular unconformity on the previous limestone that ministered part of the material" . The sedimentary breccia is a valuable ornamental stone, more commonly known as Arrábida Marble . Among

448-566: A result, attempts to precipitate dolomite from seawater precipitate high-magnesium calcite instead. This substance, which has an excess of calcium over magnesium and lacks calcium-magnesium ordering, is sometimes called protodolomite . Raising the temperature makes it easier for magnesium to shed its hydration shell, and dolomite can be precipitated from seawater at temperatures in excess of 60 °C (140 °F). Protodolomite also rapidly converts to dolomite at temperatures of 250 °C (482 °F) or higher. The high temperatures necessary for

504-500: A vast area of diverse vegetation, that includes 42 types and subtypes of habitats, 10 prioritized as important for conservation. The complexity and diversity of marine habitats present in the waters of Arrábida have contributed to it being a hotspot of biodiversity, with 1400 registered species occupying the space. A stretch of road in the natural park is notable for being the scene in the 1969 James Bond film On Her Majesty's Secret Service where Tracy Bond (played by Diana Rigg )

560-453: A very high ratio of calcium to magnesium. Dolomite is used for many of the same purposes as limestone, including as construction aggregate ; in agriculture to neutralize soil acidity and supply calcium and magnesium; as a source of carbon dioxide ; as dimension stone ; as a filler in fertilizers and other products; as a flux in metallurgy ; and in glass manufacturing . It cannot substitute for limestone in chemical processes that require

616-474: Is a stub . You can help Misplaced Pages by expanding it . Serra da Arr%C3%A1bida Arrábida Natural Park ( Portuguese : Parque Natural da Arrábida ) is a protected area in Portugal . Founded in 1976, the park occupies an area of 176.41 km (68.11 sq mi), (123.30 km (47.61 sq mi) on land and 53.11 km (20.51 sq mi) at sea) covering the southernmost margin of

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672-467: Is characterized by its nearly ideal 1:1 stoichiometric ratio of magnesium to calcium. It is distinct from high-magnesium limestone in that the magnesium and calcium form ordered layers within the individual dolomite mineral grains, rather than being arranged at random, as they are in high-magnesium calcite grains. In natural dolomite, magnesium is typically between 44 and 50 percent of total magnesium plus calcium, indicating some substitution of calcium into

728-548: Is dotted by karst cavities, that include the Gruta do Frade, known for its uniqueness, rarity, diversity and scenic beauty. From a paleontological perspective there are fossil deposits that include fragments of dinosaurs (normally sauropods ), relevant to scientific investigation, commonly associated with Cape Espichel. There are also valleys of important interest, including south of the Serra de São Francisco up to Aldeia Grande, and

784-413: Is known as dolomitic limestone . The "dolomite problem" refers to the vast worldwide depositions of dolomite in the past geologic record in contrast to the limited amounts of dolomite formed in modern times. Recent research has revealed sulfate-reducing bacteria living in anoxic conditions precipitate dolomite which indicates that some past dolomite deposits may be due to microbial activity. Dolomite

840-474: Is more varied and elevated than the one from Sesimbra to Cape Espichel . The coast, generally elevated and abrupt, is 380 metres (1,250 ft) at the Alto do Píncaro , with rare and small beaches and coves, mostly accessible by boat. From Alpertuche to Outão the coast is less elevated resulting in more beaches, such as the bay of Portinho or Chã da Anixa, a small platform only metres above the sea. But, generally,

896-536: Is named for the main geomorphological unit that covers the entire area, designated the Arrábida cordillera or massif, consisting of three subareas: This group is oriented east-northeast to west-southwest, covering an area of about 35 kilometres (22 mi) long and 6 kilometres (3.7 mi) wide, and reaching 501 metres (1,644 ft) at its highest altitude as a result of the Formosinho anticline . Arrábida

952-626: Is no consistent trend in its abundance with age, but most dolomite appears to have formed at high stands of sea level. Little dolomite is found in Cenozoic beds (beds less than 65 million years old), which has been a time of generally low sea levels. Times of high sea level also tend to be times of a greenhouse Earth , and it is possible that greenhouse conditions are the trigger for dolomite formation. Many dolomites show clear textural indications that they are secondary dolomites, formed by replacement of limestone. However, although much research has gone into understanding this process of dolomitization ,

1008-423: Is not seen to precipitate in the oceans. Likewise, geologists have not been successful at precipitating dolomite from seawater at normal temperatures and pressures in laboratory experiments. This is likely due to a very high activation energy for nucleating crystals of dolomite. The magnesium ion is a relatively small ion, and it acquires a tightly bound hydration shell when dissolved in water. In other words,

1064-419: Is resistant to erosion and can either contain bedded layers or be unbedded. It is less soluble than limestone in weakly acidic groundwater , but it can still develop solution features ( karst ) over time. Dolomite rock can act as an oil and natural gas reservoir. Dolomite takes its name from the 18th-century French mineralogist Déodat Gratet de Dolomieu (1750–1801), who was one of the first to describe

1120-416: Is secondary, formed by replacement of calcium by magnesium in limestone. The preservation of the original limestone texture can range from almost perfectly preserved to completely destroyed. Under a microscope, dolomite rhombs are sometimes seen to replace oolites or skeletal particles of the original limestone. There is sometimes selective replacement of fossils, with the fossil remaining mostly calcite and

1176-535: Is shot dead by Irma Bunt ( Ilse Steppat ) in a drive-by shooting at the end of the film. Arrábida is depicted in the video game Tom Clancy's Endwar as one of the theatres in World War III, when the U.S. Army invades Portugal in an attempt to weaken the European Federation's defences. Dolomite (rock) Dolomite (also known as dolomite rock , dolostone or dolomitic rock ) is

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1232-541: Is stained by Alizarin Red S while dolomite grains are not. Dolomite rock consisting of well-formed grains with planar surfaces is described as planar or idiotopic dolomite, while dolomite consisting of poorly-formed grains with irregular surfaces is described as nonplanar or xenotopic dolomite. The latter likely forms by recrystallization of existing dolomite at elevated temperature (over 50 to 100 °C (122 to 212 °F)). The texture of dolomite often shows that it

1288-543: Is subject to high rates of evaporation. This results in precipitation of gypsum and aragonite , raising the magnesium to calcium ratio of the remaining brine. The brine is also dense, so it sinks into the pore space of any underlying limestone ( seepage refluxion ), flushing out the existing pore fluid and causing dolomitization. The Permian Basin of North America has been put forward as an example of an environment in which this process took place. A variant of this model has been proposed for sabkha environments in which brine

1344-635: Is sucked up into the dolomitizing limestone by evaporation of capillary fluids, a process called evaporative pumping . Another model is the mixing-zone or Dorag model, in which meteoric water mixes with seawater already present in the pore space, increasing the chemical activity of magnesium relative to calcium and causing dolomitization. The formation of Pleistocene dolomite reefs in Jamaica has been attributed to this process. However, this model has been heavily criticized, with one 2004 review paper describing it bluntly as "a myth". A 2021 paper argued that

1400-476: Is thermodynamically favorable, with a Gibbs free energy of about -2.2 kcal/mol. In theory, ordinary seawater contains sufficient dissolved magnesium to cause dolomitization. However, because of the very slow rate of diffusion of ions in solid mineral grains at ordinary temperatures, the process can occur only by simultaneous dissolution of calcite and crystallization of dolomite. This in turn requires that large volumes of magnesium-bearing fluids are flushed through

1456-540: The Setúbal Peninsula . One of the park's unique features is its carbonate geology mountain range, Serra da Arrábida (501 metres (1,644 ft)) which comes into contact with the ocean similarly to some locations in the Mediterranean, contrasting with the usual Portuguese coast (long sand beaches and cliffs) Three of the park's beaches—Galapinhos, Portinho da Arrábida and Figueirinha—are popular among

1512-531: The formation of dolomite helps explain the rarity of Cenozoic dolomites, since Cenozoic seawater temperatures seldom exceeded 40 °C. It is possible that microorganisms are capable of precipitating primary dolomite. This was first demonstrated in samples collected at Lagoa Vermelha , Brazil in association with sulfate-reducing bacteria ( Desulfovibrio ), leading to the hypothesis that sulfate ion inhibits dolomite nucleation. Later laboratory experiments suggest bacteria can precipitate dolomite independently of

1568-484: The forms of stalactites , stalagmites , flowstone etc., can also form in caves within dolomite rock. “Dolomite is a common rock type, but a relatively uncommon mineral in speleothems”. Both the 'Union Internationale de Spéléologie' (UIS) and the American 'National Speleological Society' (NSS), extensively use in their publications, the terms "dolomite" or "dolomite rock" when referring to the natural bedrock containing

1624-404: The greater temperatures characterizing deeper burial, if a mechanism exists to flush magnesium-bearing fluids through the beds. Mineral dolomite has a 12% to 13% smaller volume than calcite per alkali cation. Thus dolomitization likely increases porosity and contributes to the sugary texture of dolomite. Dolomite is supersaturated in normal seawater by a factor of greater than ten, but dolomite

1680-588: The importance of the natural vegetation, that includes the last vestiges of varying Mediterranean vegetation, the area was included in a planning process early on, in order to save and preserve the ecosystems. There are three convergent floral elements: In the more eastern areas, the cliffs were populated with important species of Macaronesian flora, supporting nesting species of maritime and raptor birds protected by international convention. In total there are 213 species of vertebrates: 8 amphibians , 16 reptiles , 154 birds , and 35 mammals . Arrábida concentrates

1736-625: The inhabitants of Lisbon and Setúbal . Overlooking the three beaches is the Convent of Our Lady of Arrábida, a former monastery established in the 16th century, managed today by the Fundação Oriente. The particular characteristics of the Arrábida massif, resulted (since the 1940s) in various attempts to protect the region, culminating in the creation of the Arrábida Reserve (Decree 355/71) on 16 August 1971, which covered

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1792-529: The lands are inclined, mainly along the north and south, but predominately along the coast. Slopes in these areas of the Serra da Arrábida, Serra de Ares, Serra de Riscoa and Serra de São Luís exceed 30%, including the Rasca Valley, Comenda, Alto da Madalena Valley until Portela da Sardinha and areas along the north and south of the Serra de São Francisco and Serra de Louro. The waterways of Arrábida can be grouped into two principal types: The hydrology of

1848-437: The magnesium ion is surrounded by a clump of water molecules that are strongly attracted to its positive charge. Calcium is a larger ion and this reduces the strength of binding of its hydration shell, so it is much easier for a calcium ion than a magnesium ion to shed its hydration shell and bind to a growing crystal. It is also more difficult to nucleate a seed crystal of ordered dolomite than disordered high-magnesium calcite. As

1904-461: The magnesium layers. A small amount of ferrous iron typically substitutes for magnesium, particularly in more ancient dolomites. Carbonate rock tends to be either almost all calcite or almost all dolomite, with intermediate compositions being quite uncommon. Dolomite outcrops are recognized in the field by their softness (mineral dolomite has a Mohs hardness of 4 or less, well below common silicate minerals) and because dolomite bubbles feebly when

1960-451: The mechanism of dolomitization, the tendency of carbonate rock to be either almost all calcite or almost all dolomite suggests that, once the process is started, it completes rapidly. The process likely occurs at shallow depths of burial, under 100 meters (330 ft), where there is an inexhaustible supply of magnesium-rich seawater and the original limestone is more likely to be porous. On the other hand, dolomitization can proceed rapidly at

2016-571: The microscope, thin sections of dolomite usually show individual grains that are well-shaped rhombs , with considerable pore space. As a result, subsurface dolomite is generally more porous than subsurface limestone and makes up 80% of carbonate rock petroleum reservoirs . This texture contrasts with limestone, which is usually a mixture of grains, micrite (very fine-grained carbonate mud) and sparry cement. The optical properties of calcite and mineral dolomite are difficult to distinguish, but calcite almost never crystallizes as regular rhombs, and calcite

2072-427: The mineral. The term dolomite refers to both the calcium-magnesium carbonate mineral and to sedimentary rock formed predominantly of this mineral. The term dolostone was introduced in 1948 to avoid confusion between the two. However, the usage of the term dolostone is controversial, because the name dolomite was first applied to the rock during the late 18th century and thus has technical precedence. The use of

2128-492: The mixing zone serves as domain of intense microbial activity which promotes dolomitization. A third model postulates that normal seawater is the dolomitizing fluid, and the necessary large volumes are flushed through the dolomitizing limestone through tidal pumping. Dolomite formation at Sugarloaf Key , Florida, may be an example of this process. A similar process might occur during rises in sea level, as large volumes of water move through limestone platform rock. Regardless of

2184-533: The natural park, expanding its coastal area and establishing the Arrábida-Espichel Marine Area, in order to support the objectives of the park, especially in the area surrounding the park. This included the region's diverse marine flora and fauna, such as the discontiguous zone of Cabo Espichel, which was included to protect coastal cliffs, endemic flora species, nesting areas for marine birds and preservation of rudimentary fossils. The park

2240-429: The night. January is the coolest month with temperatures averaging between 13–15 °C (55–59 °F) during the day and 5–8 °C (41–46 °F) during the night. These temperatures depend on altitude and proximity to the sea. The morphology of Arrábida allows a variety of microhabitats of distinct characteristics ( Mediterranean / Atlantic ), mixing species of evergreen, deciduous or semi-deciduous trees. Owing to

2296-599: The notable geomorphologic points-of-interest are the Morro de Palmela , at 232 metres (761 ft), the Montes de Azeitão , that include the Serra do Louro , at 254 metres (833 ft)) and the Serra de São Francisco 257 metres (843 ft)). Parallel to the Serra do Louro , and more to the south, is the Serra de Gaiteiros , at 226 metres (741 ft), to the southwest the Serra de São Luís , at 395 metres (1,296 ft) and to

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2352-527: The park is divided into two great basins: one to the northwest and north, and another to the south and east. Although the main waterways are in the east, between Setúbal, Palmela and the Picheleiros Valley, the ravine of Ajuda is the highest flowing waterway, and results from the confluence of the Ribeiras de Alcube e do Picheleiro, Ribeiras do Almelão and Ribeiras de Pomarinho. This basin includes

2408-584: The park. Of all these waterways within the park, only the Ribeira da Ajuda maintains its flow throughout the year. Arrábida has a Mediterranean climate with warm dry summers and mild wet winters. Its exposure to the Atlantic Ocean has a large influence over the temperature and the humidity felt throughout the year. The humid air masses that come from the Atlantic in the cooler months are confronted by

2464-427: The pore space in the dolomitizing limestone. Several processes have been proposed for dolomitization. The hypersaline model (also known as the evaporative reflux model ) is based on the observation that dolomite is very commonly found in association with limestone and evaporites , with the limestone often interbedded with the dolomite. According to this model, dolomitization takes place in a closed basin where seawater

2520-401: The process remains poorly understood. There are also fine-grained dolomites showing no textural indications that they formed by replacement, and it is uncertain whether they formed by replacement of limestone that left no textural traces or are true primary dolomites. This dolomite problem was first recognized over two centuries ago but is still not fully resolved. The dolomitization reaction

2576-456: The question of whether this can lead to precipitation of dolomite. Dolomitization can sometimes be reversed, and a dolomite bed converted back to limestone. This is indicated by a texture of pseudomorphs of mineral dolomite that have been replaced with calcite. Dedolomitized limestone is typically associated with gypsum or oxidized pyrite , and dedolomitization is thought to occur at very shallow depths through infiltration of surface water with

2632-489: The rugged mountains resulting in abundant precipitation in November and December. In the summer, some upwelling occurs around Cabo Espichel which decreases sea temperature and increases the frequency of fogs , which are usually only present in the morning or late in the day. August is the warmest month with temperatures averaging between 24–28 °C (75–82 °F) during the day and 16–17 °C (61–63 °F) during

2688-576: The southeast the Serro do Viso at 168 metres (551 ft). Along the coast lies the Serra da Arrábida , with its highest point at 499 metres (1,637 ft) ( Formosinho ). Over the sea and abrupt cliffs are the Serra do Risco and Píncaro , the highest point along the Portuguese coast in this area, at approximately 380 metres (1,250 ft). These mountains are constituted by limestone, with frequent rocky outcroppings forming scenic cliffs. Arrábida

2744-519: The southern flanks of the mountains and cliffs of Risco. Recognizing the insufficient protection conferred on the area, Decree 622/76 was passed on 28 July 1976, creating the Parque Natural da Arrábida (PNArr). This classification envisioned the protection of the geological, forest, wildlife and landscapes, but also cultural and historical resources located within the area. Regulating decree 23/98, passed on 14 October 1998, further reclassified

2800-400: The sulfate concentration. With time other pathways of interaction between microbial activity and dolomite formation have been added to the discord regarding their role in modulation and generation of polysaccharides , manganese and zinc within the porewater. Meanwhile, a contrary view held by other researchers is that microorganisms precipitate only high-magnesium calcite but leave open

2856-422: The surrounding matrix composed of dolomite grains. Sometimes dolomite rhombs are seen cut across the fossil outline. However, some dolomite shows no textural indications that it was formed by replacement of limestone. Dolomite is widespread in its occurrences, though not as common as limestone. It is typically found in association with limestone or evaporite beds and is often interbedded with limestone. There

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2912-543: The term dolostone was not recommended by the Glossary of Geology published by the American Geological Institute . In old USGS publications, dolomite was referred to as magnesian limestone , a term now reserved for magnesium -deficient dolomites or magnesium-rich limestones. Dolomite rock is defined as sedimentary carbonate rock composed of more than 50% mineral dolomite . Dolomite

2968-616: The valleys of Barris and Alcube. Between the Serra da Arrábida and the western Montes de Azeitão, lies the Picheleiros Valley, which continues from the Ribeira da Ajuda Valley to Várzea da Comenda. There is also the Solitário Valley, between the coastal flanks of Arrábida and the Cabeços do Jaspe and Guincho, and the Vitória Valley, in the subplateau of the Serra do Risco. The coast stretching from Sesimbra to Alpertuche

3024-529: The valleys of Picheleiro, Alcube and Ajuda, and the western and southern flanks of the Serra de São Luís, as well as the western flanks of the Nico and Viso, in addition to the Ribeira de Melra, Ribeira do Vale de Cavalo and Ribeira de Mareta. Other waterways, such as the Ribeira da Corva, tributary of the Ribeira de Livramento, or the Ribeira do Calhariz, tributary of the Rio Coina, obtain their maximum flow outside

3080-567: Was created during the Jurassic and Miocene epochs, while the plains formed during the Pliocene and Quaternary periods. Ribeiro (1935) indicates that the massif began to be formed with successive movements during the Tertiary era. The same author (1937) indicated that the peninsula of Setúbal was, during the Mesozoic, covered by shallow seas. During a great part of the Jurassic, Arrábida was

3136-642: Was formed from four successive phases of rifting that resulted in the fragmentation of Laurasia and the formation of the north Atlantic . This area is unique in the Atlantic for demonstrating the western propagation of the Tethys sea and the formation of the Mediterranean, caused by the collision of the African plate and the Eurasian plate, during the Late Cretaceous . Geologically, the mountainous region

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