A subbasin or sub-basin is a structural geologic feature where a larger basin is divided into a series of smaller basins with intervening intrabasinal highs. Some subbasins are referred to as "sags", [1] although that term has a broader definition than a subbasin does. [2]
Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also refer to the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology significantly overlaps all other earth sciences, including hydrology and the atmospheric sciences, and so is treated as one major aspect of integrated earth system science and planetary science.
A structural basin is a large-scale structural formation of rock strata formed by tectonic warping of previously flat-lying strata. Structural basins are geological depressions, and are the inverse of domes. Some elongated structural basins are also known as synclines. Structural basins may also be sedimentary basins, which are aggregations of sediment that filled up a depression or accumulated in an area; however, many structural basins were formed by tectonic events long after the sedimentary layers were deposited.
The term subbasin has common use in geologic literature, [3] [4] [5] [6] but has yet to be included in the API[ clarification needed ] Glossary of Geology. [7]
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 compound from which iron can be smelted commercially. This term is customarily restricted to hard coarsely banded, nonbanded, and noncherty 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.
In geology, the term 'sial' refers to the composition of the upper layer of the Earth's crust, namely rocks rich in silicates and aluminium minerals. It is sometimes equated with the continental crust because it is absent in the wide oceanic basins, but "sial" is a geochemical term rather than a plate tectonic term. As these elements are less dense than the majority of the earth's elements, they tend to be concentrated in the upper layer of the crust.
A syneclise is a large, relatively shallow depression formed in a continental platform setting, due to slow and steady subsidence. Covering a large area, the slow subsidence generally leads to thick, convergent sedimentary layers with low-angle dips.
An anteclise is a large uplifted structure in a continental platform setting, with low-angle, divergent dips, formed by slow and steady central uplift.
In geology and climatology, a pluvial is either a modern climate characterized by relatively high precipitation, or an interval of time of variable length – decades to thousands of years – during which a climate is characterized by either relatively high precipitation or humidity. Subdivisions of a pluvial, which are characterized by relatively high precipitation, are known as a subpluvials. Formally, pluvials were equated with glacial stages of the Quaternary. However, pluvials, as in equatorial regions, can also occur during interglacial stages. Lower latitudes have even experienced major pluvials in early to mid-Holocene times.
A pelite or metapelite is a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone. The term was earlier used by geologists to describe a clay-rich, fine-grained clastic sediment or sedimentary rock, i.e. mud or a mudstone, the metamorphosed version of which would technically have been a metapelite. It was equivalent to the now little-used Latin-derived term lutite. A semipelite is defined in part as having similar chemical composition but being of a crystalloblastic nature.
A moulin or glacier mill is a roughly circular, vertical to nearly vertical well-like shaft within a glacier or ice sheet which water enters from the surface. The term is derived from the French word for mill.
In sedimentology and geology, a nodule is small, irregularly rounded knot, mass, or lump of a mineral or mineral aggregate that typically has a contrasting composition, such as a pyrite nodule in coal, a chert nodule in limestone, or a phosphorite nodule in marine shale, from the enclosing sediment or sedimentary rock. Normally, a nodule has a warty or knobby surface and exists as a discrete mass within the host strata. In general, they lack any internal structure except for the preserved remnants of original bedding or fossils. Nodules are closely related to concretions and sometimes these terms are used interchangeably. Minerals that typically form nodules include calcite, chert, apatite (phosphorite), anhydrite, and pyrite.
Calcarenite is a type of limestone that is composed predominantly, more than 50 percent, of detrital (transported) sand-size, carbonate grains. The grains consist of sand-size grains of either corals, shells, ooids, intraclasts, pellets, fragments of older limestones and dolomites, other carbonate grains, or some combination of these. Calcarenite is the carbonate equivalent of a sandstone. The term calcarenite was originally proposed in 1903 by Grabau as a part of his calcilutite, calcarenite and calcirudite carbonate classification system based upon the size of the detrital grains composing a limestone. Calcarenites can accumulate in a wide variety of marine and nonmarine environments. They can consist of grains of carbonate that have accumulated either as coastal sand dunes (eolianites), beaches, offshore bars and shoals, turbidites, or other depositional settings.
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.
Psammite is a general term for sandstone. It is equivalent to the Latin-derived term arenite and is commonly used in various publications to describe a metamorphosed sedimentary rock with a dominantly sandstone protolith. In Europe, this term was formerly used for a fine-grained, fissile, clayey sandstone. Pettijohn gives the following descriptive terms based on grain size, avoiding the use of terms such as "clay" or "argillaceous", which carry an implication of chemical composition:
Lutite is old terminology, which is not widely used, by Earth scientists in field descriptions for fine-grained, sedimentary rocks, which are composed of silt-size sediment, clay-size sediment, or a mixture of both. When mixed with water lutites often disintegrate into mud. Because this is a field term, there is a lack of any precise definition for it based upon specific grain-size characteristics. Lutites include a variety of fine-grained sedimentary rocks, including calcisiltite, calcilutite, claystone, mudstone, shale, and siltstone. It is equivalent to the term mudstone and the Greek-derived term pelite. Lutite was first used in 1904 by Grabau, who derived it from the Latin word for mud. He also proposed a number of prefixes to be used with and attached to "lutite" in order to designated various types of lutites. None of these prefixes are used by Earth scientists nowadays.
Rudite is a general name used for a sedimentary rocks that are composed of rounded or angular detrital grains, i.e. granules, pebbles, cobbles, and boulders, which are coarser than sand in size. Rudites include sedimentary rocks composed of both siliciclastic, i.e. conglomerate and breccia, and carbonate grains, i.e. calcirudite and rudstone. This term is equivalent to the Greek-derived term, psephite. Rudite was initially proposed by Grabau as "rudyte." It is derived from the Latin word, "rudus," for "crushed stone," "rubbish," "debris," and "rubble."
Psephite is either a sediment or sedimentary rock composed of fragments that are coarser than sand and which are enclosed in a matrix that varies in kind and amount. It is equivalent to a rudite. Shingle, gravel, breccia, and especially conglomerate, would all be considered psephites. It is equivalent to the Latin-derived term rudite. Psephite is more commonly used for a metamorphosed rudite.
Malpaís is a term used in the Southwestern United States, Spain, Mexico, and other Spanish-speaking regions for a rough and barren landscape that consists of relict and largely uneroded lava fields exhibiting recognizable lava flows, volcanic cones, and other volcanic landforms. This type of volcanic landscape is extremely rough and difficult to traverse. It is characteristic of an arid environment because in more humid climates, lava fields are quickly destroyed by weathering and erosion.
Peloids are allochems that are composed of micrite, irrespective of size, shape, or origin. The two primary types of peloids are pellets and intraclasts. Another type of peloid is pseudo-oolith.
Calcisiltite is a type of limestone that is composed predominantly, more than 50 percent, of detrital (transported) silt-size carbonate grains. These grains consist either of the silt-size particles of ooids, fragments of fossil shells, fragments of older limestones and dolomites, intraclasts, pellets, other carbonate grains, or some combination of these. Calcisiltite is the carbonate equivalent of a siltstone. Calcisiltites can accumulate in a wide variety of coastal, lacustrine, and marine environments. It is typically the product of abrasion and bioerosion.
Calcirudite is a type of limestone that is composed predominantly, more than 50 percent, of carbonate grains that are larger in size than sand. The grains can consist of either fragments of fossils, fragments of older limestones and dolomites, other carbonate grains, or some combination of these. The term calcirudite was originally proposed in 1903 by Grabau as a part of his calcilutite, calcarenite and calcirudite classification system based upon the size of the detrital grains composing a limestone. Depending on roundness of the grains, calcirudite is the carbonate equivalent of either a breccia, in the case of predominantly angular grains, or conglomerate, in the case of predominantly rounded grains. Calcirudites can accumulate in a wide variety of coastal, lacustrine, and marine environments.
Calcilutite is a type of limestone that is composed of predominantly, more than 50 percent, of either clay-size or both silt-size and clay-size detrital (transported) carbonate grains. These grains consist either of fossil fragments, ooids, intraclasts, pellets, other grains, or some combination of them. The term calcilutite was originally proposed in 1903 by Grabau as a part of his calcilutite, calcarenite and calcirudite classification system based upon the size of the detrital grains composing a limestone. In the original classification of limestone according to the dominant grain-size, calcisiltites were not named and are classified as calcilutite. In this classification, which the majority of geologists follow, a calcilutite consists of both silt- and clay-size, less than 0.062 mm in diameter, grains. It is the carbonate equivalent of a mudstone. Calcilutites can accumulate in a wide variety of marine and lacustrine environments.
The Earth scientists, who study rivers and streams, define a pothole as a smooth, bowl-shaped or cylindrical hollow, generally deeper than wide, found carved into the rocky bed of a watercourse. Other names used for riverine potholes are pot, (stream) kettle, giant's kettle, evorsion, hollow, rock mill, churn hole, eddy mill, and kolk. Although somewhat related to a pothole in origin, a plunge pool is the deep depression in a stream bed at the base of a waterfall; it is created by the erosional forces of turbulence generated by water falling on rocks at a waterfall's base where the water impacts. Potholes are also sometimes referred to as swirlholes. This word was created to avoid confusion with an English term for a vertical or steeply inclined karstic shaft in limestone. However, given widespread usage of this term for a type of fluvial sculpted bedrock landform, pothole is preferred in usage to swirlhole.
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