Beachrock

Beachrock is a friable to well-cemented sedimentary rock that consists of a variable mixture of gravel-, sand-, and silt-sized sediment that is cemented with carbonate minerals and has formed along a shoreline. Depending on location, the sediment that is cemented to form beachrock can consist of a variable mixture of shells, coral fragments, rock fragments of different types, and other materials. It can contain scattered artifacts, pieces of wood, and coconuts. Beachrock typically forms within the intertidal zone within tropical or semitropical regions. However, Quaternary beachrock is also found as far north and south as 60° latitude.[1][2]

Reunion Saint-Leu Beachrock
Beachrock along Réunion island seashore
Reunion Saint-Leu Beachrock(detail)
Detail showing fragments of coral and shells

Overview

Beachrock units form under a thin cover of sediment and generally overlie unconsolidated sand. They typically consist of multiple units, representing multiple episodes of cementation and exposure. The mineralogy of beachrocks is mainly high-magnesium calcite or aragonite. The main processes involved in the cementation are : supersaturation with CaCO3 through direct evaporation of seawater,[3] groundwater CO2 degassing in the vadose zone,[4] mixing of marine and meteoric water fluxes[5] and precipitation of micritic calcium carbonate as a byproduct of microbiological activity.[6]

On retreating coasts, outcrops of beachrock may be evident offshore where they may act as a barrier against coastal erosion. Beachrock presence can also induce sediment deficiency in a beach and out-synch its wave regime. Because beachrock is lithified within the intertidal zone and because it commonly forms in a few years, its potential as an indicator of past sea level is important.

Cementation and position of beachrock

Beachrocks are located along the coastline in a parallel term and they are usually a few meters offshore. They are generally separated in several levels which may correspond to different generations of beachrock cementation. Thus, the older zones are located in the outer part of the formation when the younger ones are on the side of the beach, possibly under the unconsolidated sand. They also seem to have a general inclination to the sea (50 – 150). There are several appearances of beachrock formations which are characterized by multiple cracks and gaps. The result from this fact is an interruptible formation of separated blocks of beachrock, which may be of the same formation.

The length of beachrocks varies from meters to kilometers, its width can reach up to 300 meters and its height starts from 30 cm and reaches 3 meters.

Following the process of coastal erosion, beachrock formation may be uncovered. Coastal erosion may be the result of sea level rise or deficit in sedimentary equilibrium. One way or another, unconsolidated sand that covers the beachrock draws away and the formation is revealed. If the process of cementation continues, new beachrock would be formed in a new position in the intertidal zone. Successive phases of sea level change may result in sequential zones of beachrock.

See also

References

  1. ^ Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, J.A., eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN 0-922152-76-4
  2. ^ Scholle, P.A., D.G. Bebout, and C.H. Moore (1983) Carbonate Depositional Environments. Memoir no. 33. Tulsa, Oklahoma, American Association of Petroleum Geologists. 708 pp. ISBN 978-0-89181-310-1
  3. ^ Scoffin, T.P. & Stoddart, D.R. 1983. Beachrock and intertidal sediments, Chemical Sediments and Geomorphology. Academic Press, Inc.
  4. ^ Hanor, J.S. 1978. Precipitation of Beachrock Cements: Mixing of Marine and Meteoric Waters Vs. Co2-Degassing.
  5. ^ SCHMALZ, R.F. 1971. Formation of beachrock at Eniwetok Atoll.
  6. ^ Neumeier, U. 1998. The role of microbial activity in early cementation of beachrocks (intertidal sediments). PhD Thesis, University of Geneva. Terre et Environment (12).
Al Khor Island

Al Khor Island (Arabic: جزيرة الخور‎), also known as Jazirat bin Ghanim and Purple Island, is an island located in the municipality of Al Khor on the northeast coast of Qatar. It accommodates the only archaeological site in the country attributable to the second millennium BC. There are four main periods of occupation on the island, dating from as early as c. 2000 BC to as late as 1900 AD. The island is best known for being the site of operation of a Kassite-controlled purple dye industry in the second millennium BC.

Angoumian

The Angoumian is a geological group restricted to the northern Aquitaine Basin in France. The group consists of two fossiliferous limestone formations deposited during the Turonian.

Bermuda Triangle

The Bermuda Triangle, also known as the Devil's Triangle or Hurricane Alley, is a loosely defined region in the western part of the North Atlantic Ocean where a number of aircraft and ships are said to have disappeared under mysterious circumstances. Most reputable sources dismiss the idea that there is any mystery.

The vicinity of the Bermuda Triangle is amongst the most heavily traveled shipping lanes in the world, with ships frequently crossing through it for ports in the Americas, Europe and the Caribbean islands. Cruise ships and pleasure craft regularly sail through the region, and commercial and private aircraft routinely fly over it.

Popular culture has attributed various disappearances to the paranormal or activity by extraterrestrial beings. Documented evidence indicates that a significant percentage of the incidents were spurious, inaccurately reported, or embellished by later authors.

Bimini

Bimini is the westernmost district of the Bahamas and comprises a chain of islands located about 80 kilometres (50 mi) due east of Miami. Bimini is the closest point in the Bahamas to the mainland United States and approximately 210 km (130 mi) west-northwest of Nassau. The population is 1,988 as of the 2010 census.

Bimini Road

The Bimini Road, sometimes called the Bimini Wall, is an underwater rock formation near North Bimini island in the Bahamas. The Road consists of a 0.8 km (0.50 mi)-long northeast-southwest linear feature composed of roughly rectangular to subrectangular limestone blocks. Various claims have been made for this feature being either a wall, road, pier, breakwater, or other man-made structure. However, credible evidence or arguments are lacking for such an origin.

Cementation (geology)

Cementation involves ions carried in groundwater chemically precipitating to form new crystalline material between sedimentary grains. The new pore-filling minerals forms

"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 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 or silica phases like cristobalite, iron oxides, and clay minerals, but other mineral cements also occur.

Cementation 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 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 the matrix, which is either sparry (prominently composed of cement) or micritic (prominently composed of mud).

Coastal geography

Coastal geography is the study of the constantly changing region between the ocean and the land, incorporating both the physical geography (i.e. coastal geomorphology, geology and oceanography) and the human geography (sociology and history) of the coast. It includes understanding coastal weathering processes, particularly wave action, sediment movement and weather, and the ways in which humans interact with the coast

Coquina

Coquina () is a sedimentary rock that is composed either wholly or almost entirely of the transported, abraded, and mechanically-sorted fragments of the shells of molluscs, trilobites, brachiopods, or other invertebrates. The term coquina comes from the Spanish word for "cockle" and "shellfish".For a sediment to be considered to be a coquina, the particles composing it should average 2 mm (0.079 in) or greater in size. Coquina can vary in hardness from poorly to moderately cemented. Incompletely consolidated and poorly-cemented coquinas are considered grainstones in the Dunham classification system for carbonate sedimentary rocks. A well-cemented coquina is classified as a biosparite (fossiliferous limestone) according to the Folk classification of sedimentary rocks.Coquinas accumulate in high-energy marine and lacustrine environments where currents and waves result in the vigorous winnowing, abrasion, fracturing, and sorting of the shells, which compose them. As a result, they typically exhibit well-developed bedding or cross-bedding, close packing, and good orientation of the shell fragments. The high-energy marine or lacustrine environments associated with coquinas include beaches, shallow submarine raised banks, swift tidal channels, and barrier bars.

Crassula moschata

Crassula moschata, commonly known as the Shore Stonecrop, Musky Stonecrop, or Musky Crassula, is a hairless, mat-forming, succulent, perennial herb. It is widespread on the subantarctic and cool temperate shores of the Southern Ocean.

Freiha

Freiha (Arabic: فريحة‎, romanized: Furayḥah) is a small deserted village on the north western coast of the Qatar Peninsula in the Al Shamal municipality. It is located in the Zubarah region being 3 km north of Zubarah town, and was founded by the Al Bin Ali tribe , main and principal Utub tribe in the first half of the eighteenth century along with the historical town of Zubarah.The age and origin of the settlement is unknown, however excavations and historical documents suggest that it was at its peak in the 17th–18th century, almost certainly pre-dating its larger neighbour Al Zubarah. The village covers an area of approximately 50 hectares, extending for 700m north to south along the coast and approximately 200m east to west inland. It is sited around a shallow bay.

Ichnofacies

An ichnofacies is an assemblage of trace fossils that provides an indication of the conditions that their formative organisms inhabited.

Island

An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island in a river or a lake island may be called an eyot or ait, and a small island off the coast may be called a holm. A grouping of geographically or geologically related islands is called an archipelago, such as the Philippines.

An island may be described as such, despite the presence of an artificial land bridge; examples are Singapore and its causeway, and the various Dutch delta islands, such as IJsselmonde. Some places may even retain "island" in their names for historical reasons after being connected to a larger landmass by a land bridge or landfill, such as Coney Island and Coronado Island, though these are, strictly speaking, tied islands. Conversely, when a piece of land is separated from the mainland by a man-made canal, for example the Peloponnese by the Corinth Canal or Marble Hill in northern Manhattan during the time between the building of the United States Ship Canal and the filling-in of the Harlem River which surrounded the area, it is generally not considered an island.

There are two main types of islands in the sea: continental and oceanic. There are also artificial islands.

Monohydrocalcite

Monohydrocalcite is a mineral that is a hydrous form of calcium carbonate, CaCO3·H2O. It was formerly also known by the name hydrocalcite, which is now discredited by the IMA. It is a trigonal mineral which is white when pure. Monohydrocalcite is not a common rock-forming mineral, but is

frequently associated with other calcium and magnesium carbonate minerals, such as calcite, aragonite, lansfordite, and nesquehonite.

Monohydrocalcite has been observed in air conditioning systems, and in moonmilk deposits in caves, both probably formed from spray of carbonate rich fluids.

It is well known in Robe on the Limestone Coast of South Australia as a component of beach sands of Lake Fellmongery and Lake Butler,

where it is believed to be formed from algal spume. Other lacustrine deposits include Lake Issyk-Kul, Kyrgyzstan, Lake Kivu, Democratic Republic of the Congo, and Solar Lake, Sinai.

It has been reported as a significant component of the decomposition of ikaite

in the towers of the Ikka Fjord, West Greenland. It is also noted for its bizarre occurrences, which include inside the otoliths of the tiger shark,

the bladder of a guinea pig, the calcareous corpuscles of a cestode parasite, and the final stages of decomposition of the putrefying flesh of the giant saguaro cactus. These occurrences suggest

a biochemical origin is possible.

Mudflat

Mudflats or mud flats, also known as tidal flats, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A recent global analysis suggested they are as extensive globally as mangroves. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and marine animal detritus. Most of the sediment within a mudflat is within the intertidal zone, and thus the flat is submerged and exposed approximately twice daily.

In the past tidal flats were considered unhealthy, economically unimportant areas and were often dredged and developed into agricultural land. Several especially shallow mudflat areas, such as the Wadden Sea, are now popular among those practising the sport of mudflat hiking.

On the Baltic Sea coast of Germany in places, mudflats are exposed not by tidal action, but by wind-action driving water away from the shallows into the sea. These wind-affected mudflats are called windwatts in German.

Nanarup Beach

Nanarup Beach is a beach in the Great Southern region of Western Australia, 20 kilometres (12 mi) east of Albany.The beach is white sand and has stairway access at the western end where Taylor Inlet discharges into the ocean. Toilets, a picnic area and a caravan park are also situated at the western end of the beach. Four-wheel drive vehicles are permitted on the beach and can drive as far as Two Peoples Bay.The beach is not patrolled by surf lifesavers and can be dangerous due to the presence of many rips along the beach. A man drowned at Nanarup in 2013 after being swept off the rocks while fishing. The area is popular for surfing, fishing and swimming.Approximately 4.2 kilometres (3 mi) in length, Nanarup has scattered beachrock reefs at the eastern end for a distance of about 1.0 kilometre (1 mi) then curves to the southwest; the remaining length is a wave dominated surf zone that extends as far as the inlet. The beach is mostly backed by scarped 40 feet (12 m) calcarenite bluffs to the east and unstable dunes to the west.The far western end of the beach has the 20 metres (66 ft) granite boulders of Islet point connected to the shore by a small tombolo forming a sheltered pool.

Sandrock

Sandrock may refer to:

Cemented sand

Adele Sandrock (1863–1937), German-Dutch actress

Helmut Sandrock (born 1956), German football administratorSand rock may refer to:

Sand Rock, Alabama, a town in the US

Sand Rock Peak (California), a mountain in California, US

Surf zone

As ocean surface waves come closer to shore they break, forming the foamy, bubbly surface called surf. The region of breaking waves defines the surf zone. After breaking in the surf zone, the waves (now reduced in height) continue to move in, and they run up onto the sloping front of the beach, forming an uprush of water called swash. The water then runs back again as backswash. The nearshore zone where wave water comes onto the beach is the surf zone. The water in the surf zone, or breaker zone, is shallow, usually between 5 and 10 m (16 and 33 ft) deep; this causes the waves to be unstable.

The Bahamas

The Bahamas ( (listen)), known officially as the Commonwealth of The Bahamas, is a country within the Lucayan Archipelago. The archipelagic state consists of more than 700 islands, cays, and islets in the Atlantic Ocean, and is located north of Cuba and Hispaniola (Haiti and the Dominican Republic), northwest of the Turks and Caicos Islands, southeast of the U.S. state of Florida, and east of the Florida Keys. The capital is Nassau on the island of New Providence. The designation of "the Bahamas" can refer either to the country or to the larger island chain that it shares with the Turks and Caicos Islands. The Royal Bahamas Defence Force describes the Bahamas territory as encompassing 470,000 km2 (180,000 sq mi) of ocean space.

The Bahamas is the site of Columbus's first landfall in the New World in 1492. At that time, the islands were inhabited by the Lucayans, a branch of the Arawakan-speaking Taíno people. Although the Spanish never colonised the Bahamas, they shipped the native Lucayans to slavery in Hispaniola. The islands were mostly deserted from 1513 until 1648, when English colonists from Bermuda settled on the island of Eleuthera.

The Bahamas became a British crown colony in 1718, when the British clamped down on piracy. After the American Revolutionary War, the Crown resettled thousands of American Loyalists in the Bahamas; they brought their slaves with them and established plantations on land grants. Africans constituted the majority of the population from this period. The slave trade was abolished by the British in 1807; slavery in the Bahamas was abolished in 1834. Subsequently, the Bahamas became a haven for freed African slaves; the Royal Navy resettled Africans there liberated from illegal slave ships, North American slaves and Seminoles escaped here from Florida, and the government freed slaves carried on US domestic ships that had reached the Bahamas due to weather. Today, Afro-Bahamians make up nearly 90% of the population.

The Bahamas became an independent Commonwealth realm in 1973 with Elizabeth II as its queen. In terms of gross domestic product per capita, the Bahamas is one of the richest countries in the Americas (following the United States and Canada), with an economy based on tourism and finance.

Yang Shouren

Yang Shouren (Chinese: 杨守仁; born 22 April 1933) is a professor in the School of Earth and Space Sciences in Peking University.

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