Grus (geology)

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Grus sand and granitoid GrusSand.JPG
Grus sand and granitoid

Grus is an accumulation of angular, coarse-grained fragments (particles of sand and gravel) resulting from the granular disintegration by the processes of chemical and mechanical weathering of crystalline rocks (most notably granitoids) generally in an arid or semiarid region. [1] Grus sand, when cemented into a sandstone, will form an arkose.

Within a European context most of the saprolite mantles of Late Cenozoic age are made up grus, contrasting with Mesozoic and Early Cenozoic saprolites made up of kaolinitic and ferrallitic material. [2]

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Sandstone Type of sedimentary rock

Sandstone is a clastic sedimentary rock composed mainly of sand-sized silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.

Regolith A layer of loose, heterogeneous superficial deposits covering solid rock

Regolith is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestrial planets and moons.

Ironstone

Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron ore compound from which iron (Fe) can be smelted commercially. Not to be confused with native or telluric iron, which is very rare and found in metallic form, the term ironstone is customarily restricted to hard, coarsely banded, non-banded, and non-cherty sedimentary rocks of post-Precambrian age. The Precambrian deposits, which have a different origin, are generally known as banded iron formations. The iron minerals comprising ironstones can consist either of oxides, i.e. limonite, hematite, and magnetite; carbonates, i.e. siderite; silicates, i.e. chamosite; or some combination of these minerals.

Spheroidal weathering

Spheroidal weathering is a form of chemical weathering that affects jointed bedrock and results in the formation of concentric or spherical layers of highly decayed rock within weathered bedrock that is known as saprolite. When saprolite is exposed by physical erosion, these concentric layers peel (spall) off as concentric shells much like the layers of a peeled onion. Within saprolite, spheroidal weathering often creates rounded boulders, known as corestones or woolsack, of relatively unweathered rock. Spheroidal weathering is also called onion skin weathering,concentric weathering,spherical weathering, or woolsack weathering.

Bedrock Lithified rock under the regolith

Bedrock in geology is solid rock that lies under loose softer material (regolith) within the crust of the Earth or another terrestrial planets.

Arkose Type of sandstone containing at least 25% feldspar

Arkose is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose.

Parent material is the underlying geological material in which soil horizons form. Soils typically inherit a great deal of structure and minerals from their parent material, and, as such, are often classified based upon their contents of consolidated or unconsolidated mineral material that has undergone some degree of physical or chemical weathering and the mode by which the materials were most recently transported.

Geology of Europe

The geology of Europe is varied and complex, and gives rise to the wide variety of landscapes found across the continent, from the Scottish Highlands to the rolling plains of Hungary. Europe's most significant feature is the dichotomy between highland and mountainous Southern Europe and a vast, partially underwater, northern plain ranging from England in the west to the Ural Mountains in the east. These two halves are separated by the Pyrenees and the Alps-Carpathians mountain chain. The northern plains are delimited in the west by the Scandinavian Mountains and the mountainous parts of the British Isles. The southern mountainous region is bounded by the Mediterranean Sea and the Black Sea. Major shallow water bodies submerging parts of the northern plains are the Celtic Sea, the North Sea, the Baltic Sea and the Barents Sea.

Lavaka Type of gully, formed via groundwater sapping

Lavaka, the Malagasy word for "hole", usually found on the side of a hill, is a type of erosional feature common in Madagascar. However, lavakas have also been found in South Africa, the Democratic Republic of the Congo, and South Carolina, and similar landforms have been found in Brazil, the Great Plains of the U.S., and Eswatini. They are most common in tropical regions between the Cancer and Capricorn latitudes, especially the Central Highlands of Madagascar, where approximately one metre thick laterites develop on steep terrains in a monsoonal climate. Lavakas form where these hard laterites overlie thick saprolite, on steep slopes, in areas that have a hot dry season and a warm wet season.

Sand Granular material composed of finely divided rock and mineral particles

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Saprolite Chemically weathered rock

Saprolite is a chemically weathered rock. Saprolites form in the lower zones of soil profiles and represent deep weathering of the bedrock surface. In most outcrops its color comes from ferric compounds. Deeply weathered profiles are widespread on the continental landmasses between latitudes 35°N and 35°S.

Residuum is often used to refer to the soil and subsoil that forms as the result of long weathering over carbonate rocks bedrock. It is defined primarily as “the unconsolidated weathered at least partly, mineral material that has accumulated as consolidated rocks disintegrated in place. It is a type of soil parent material which has formed in place of origin. This distinguishes residuum from most other types of parent material. Parent material is classified by mode of transport.

Geology of Germany Overview of the geology of Germany

The geology of Germany is heavily influenced by several phases of orogeny in the Paleozoic and the Cenozoic, by sedimentation in shelf seas and epicontinental seas and on plains in the Permian and Mesozoic as well as by the Quaternary glaciations.

Nubbin (landform) Small and gentle hill consisting of a bedrock core dotted with rounded residual blocks

In geomorphology a nubbin is a small and gentle hill consisting of a bedrock core dotted with rounded residual blocks. The blocks derive from disintegrated and weathered bedrock layers. In particular it is assumed that the boulders of the nubbins are the remnants of the outer one or two exfoliation shells that weathered underground, albeit some weathering can continue to occur once the boulders are exposed on surface.

The geology of Western Sahara includes rock units dating back to the Archean more than two billion years old, although deposits of phosphorus formed in the Mesozoic and Cenozoic have helped to prompt the current Moroccan occupation of most of the country.

Geology of Madeira

Madeira began to form more than 100 million years ago in the Early Cretaceous, although most of the island has formed in the last 66 million years of the Cenozoic, particularly in the Miocene and Pliocene. The island is an example of hotspot volcanism, with mainly mafic volcanic and igneous rocks, together with smaller deposits of limestone, lignite and other sediments that record its long-running uplift.

The geology of Malawi formed on extremely ancient crystalline basement rock, which was metamorphosed and intruded by igneous rocks during several orogeny mountain building events in the past one billion years. The rocks of the Karoo Supergroup and newer sedimentary units deposited across much of Malawi in the last 251 million years, in connection with a large rift basin on the supercontinent Gondwana and the more recent rifting that has created the East African Rift, which holds Lake Malawi. The country has extensive mineral reserves, many of them poorly understand or not exploited, including coal, vermiculite, rare earth elements and bauxite.

The geology of Uganda extends back to the Archean and Proterozoic eons of the Precambrian, and much of the country is underlain by gneiss, argillite and other metamorphic rocks that are sometimes over 2.5 billion years old. Sedimentary rocks and new igneous and metamorphic units formed throughout the Proterozoic and the region was partially affected by the Pan-African orogeny and Snowball Earth events. Through the Mesozoic and Cenozoic, ancient basement rock has weathered into water-bearing saprolite and the region has experienced periods of volcanism and rift valley formation. The East Africa Rift gives rise to thick, more geologically recent sediment sequences and the country's numerous lakes. Uganda has extensive natural resources, particularly gold.

The geology of Eswatini formed beginning 3.6 billion years ago, in the Archean Eon of the Precambrian. Eswatini is the only country entirely underlain by the Kaapvaal Craton, one of the oldest pieces of stable continental crust and the only craton regarded as "pristine" by geologists, other than the Yilgarn Craton in Australia. As such, the country has very ancient granite, gneiss and in some cases sedimentary rocks from the Archean into the Proterozoic, overlain by sedimentary rocks and igneous rocks formed during the last 541 million years of the Phanerozoic as part of the Karoo Supergroup. Intensive weathering has created thick zones of saprolite and heavily weathered soils.

The geology of Mississippi includes some deep igneous and metamorphic crystalline basement rocks from the Precambrian known only from boreholes in the north, as well as sedimentary sequences from the Paleozoic. The region long experienced shallow marine conditions during the tectonic evolutions of the Mesozoic and Cenozoic, as coastal plain sediments accumulated up to 45,000 feet thick, including limestone, dolomite, marl, anhydrite and sandstone layers, with some oil and gas occurrences and the remnants of Cretaceous volcanic activity in some locations.

References

  1. Robert L. Bates and Julia A. Jackson (editors) (1984). Dictionary of Geological Terms (3rd edition).CS1 maint: uses authors parameter (link)
  2. Migoń, Piotr; Lidmar-Bergström, Karna (2002). "Deep weathering through time in central and northwestern Europe: problems of dating and interpretation of geological record". Catena. 49: 25–40.