In sedimentology, imbrication is a primary depositional fabric consisting of a preferred orientation of clasts such that they overlap one another in a consistent fashion, rather like a run of toppled dominoes. Imbrication is observed in conglomerates and some volcaniclastic deposits. [1] [2]
The type of imbrication is generally related to paleoflow direction. [4] Wadell [5] found the long axis aligned with paleocurrent, and dipping basinward in glacial sediments, whereas deltaic gravels may be oppositely inclined. [6]
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at the Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.
Till or glacial till is unsorted glacial sediment.
Wadi, alternatively wād, North African Arabic Oued, is the Arabic term traditionally referring to a valley. In some instances, it may refer to a dry (ephemeral) riverbed that contains water only when heavy rain occurs.
Pyroclastic rocks are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroclasts. Pyroclastic rocks are a type of volcaniclastic deposit, which are deposits made predominantly of volcanic particles. 'Phreatic' pyroclastic deposits are a variety of pyroclastic rock that forms from volcanic steam explosions and they are entirely made of accidental clasts. 'Phreatomagmatic' pyroclastic deposits are formed from explosive interaction of magma with groundwater.
Conglomerate is a clastic sedimentary rock that is composed of a substantial fraction of rounded to subangular gravel-size clasts. A conglomerate typically contain a matrix of finer grained sediments, such as sand, silt, or clay, which fills the interstices between the clasts. The clasts and matrix are typically cemented by calcium carbonate, iron oxide, silica, or hardened clay.
A way up structure, way up criterion, or geopetal indicator is a characteristic relationship observed in a sedimentary or volcanic rock, or sequence of rocks, that makes it possible to determine whether they are the right way up or have been overturned by subsequent deformation. This technique is particularly important in areas affected by thrusting and where there is a lack of other indications of the relative ages of beds within the sequence, such as in the Precambrian where fossils are rare.
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, and in sediment deposits.
In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The original depositional layering is tilted, such tilting not being the result of post-depositional deformation. Cross-beds or "sets" are the groups of inclined layers, which are known as cross-strata.
In geology, ripple marks are sedimentary structures and indicate agitation by water or wind.
Beds are the layers of sedimentary rocks that are distinctly different from overlying and underlying subsequent beds of different sedimentary rocks. Layers of beds are called strata. They are formed from sedimentary rocks being deposited on the Earth's solid surface over long periods of time. The strata are layered in the same order that they were deposited, permitting discrimination as to which beds are younger and which ones are older. The structure of a bed is determined by its bedding plane, the surface that separates two layers. Beds can be differentiated in various ways, such as by particle size or rock or mineral type. The term is generally applied to sedimentary strata, but may also be used for volcanic flows or ash layers.
Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition.
In geology, a rock's fabric describes the spatial and geometric configuration of all the elements that make it up. In sedimentary rocks, the fabric developed depends on the depositional environment and can provide information on current directions at the time of deposition. In structural geology, fabrics may provide information on both the orientation and magnitude of the strains that have affected a particular piece of deformed rock.
A matrix-supported rock is a sedimentary rock of which a defined majority is the fine-grained matrix as opposed to the clasts or allochems. For a conglomerate, a rock is considered matrix-supported when clasts constitute less than 15% of its volume. Matrix support is considered to be characteristic of debris flow deposits, in which clasts are supported within a fabric of mud as they move downstream. Wackestones and mudstones under the Dunham classification of limestones are also considered to be matrix-supported due to the predominance of micrite.
A paleocurrent or paleocurrent indicator is a geological feature that helps one determine the direction of flowing water in the geologic past. This is an invaluable tool in the reconstruction of ancient depositional environments.
Parting lineation is a subtle sedimentary structure in which sand grains are aligned in parallel lines or grooves on the surface of a body of sand. The orientation of the lineation is used as a paleocurrent indicator, although the precise flow direction is often indeterminable. They are also the primary indicator of the lower part of the upper flow regime bedform.
A dish structure is a type of sedimentary structure formed by liquefaction and fluidization of water-charged soft sediment either during or immediately following deposition. Dish structures are most commonly found in turbidites and other types of clastic deposits that result from subaqueous sediment gravity flows.
A cobble is a clast of rock defined on the Udden–Wentworth scale as having a particle size of 64–256 millimeters (2.5–10.1 in), larger than a pebble and smaller than a boulder. Other scales define a cobble's size differently. A rock made predominantly of cobbles is termed a conglomerate. Cobblestone is a building material based on cobbles.
Herringbone cross-stratification is a type of sedimentary structure formed in tidal areas, such as tidal flats, where the current periodically flows in the opposite direction.
The Lowe sequence describes a set of sedimentary structures in turbidite sandstone beds that are deposited by high-density turbidity currents. It is intended to complement, not replace, the better known Bouma sequence, which applies primarily to turbidites deposited by low-density turbidity currents.
The Solund Basin is a sedimentary basin containing at least 6 km of mainly coarse conglomerates of Devonian age. It is the southernmost of a group of basins of similar age found along the southwest coast of Norway between Sognefjord and Nordfjord, developed in the hanging-wall of the Nordfjord-Sogn Detachment. It was formed as a result of extensional tectonics during the post-orogenic collapse of crust thickened during the Caledonian orogeny, towards the end of the Silurian period. It is named for the municipality of Solund in Vestland.