Sedimentary rock

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.

Sedimentary rocks are also important sources of natural resources including coal, fossil fuels, drinking water and ores.

The subdivision of these three broad categories is based on differences in clast shape (conglomerates and breccias), composition (sandstones), or grain size or texture (mudrocks).

Examples include: Chemical sedimentary rock forms when mineral constituents in solution become supersaturated and inorganically precipitate.

Diagenesis includes all the chemical, physical, and biological changes, exclusive of surface weathering, undergone by a sediment after its initial deposition.

[9] Early stages of diagenesis, described as eogenesis, take place at shallow depths (a few tens of meters) and is characterized by bioturbation and mineralogical changes in the sediments, with only slight compaction.

Sediments are typically saturated with groundwater or seawater when originally deposited, and as pore space is reduced, much of these connate fluids are expelled.

Pressure solution contributes to this process of cementation, as the mineral dissolved from strained contact points is redeposited in the unstrained pore spaces.

Iron(II) oxide (FeO) only forms under low oxygen (anoxic) circumstances and gives the rock a grey or greenish colour.

Iron(III) oxide (Fe2O3) in a richer oxygen environment is often found in the form of the mineral hematite and gives the rock a reddish to brownish colour.

The mineralogy of a clastic rock is determined by the material supplied by the source area, the manner of its transport to the place of deposition and the stability of that particular mineral.

[27] The amount of weathering depends mainly on the distance to the source area, the local climate and the time it took for the sediment to be transported to the point where it is deposited.

The chance of fossilisation is higher when the sedimentation rate is high (so that a carcass is quickly buried), in anoxic environments (where little bacterial activity occurs) or when the organism had a particularly hard skeleton.

[29][30] The most common minerals involved in permineralization are various forms of amorphous silica (chalcedony, flint, chert), carbonates (especially calcite), and pyrite.

Their formation can be the result of localized precipitation due to small differences in composition or porosity of the host rock, such as around fossils, inside burrows or around plant roots.

Density contrasts between different sedimentary layers, such as between sand and clay, can result in flame structures or load casts, formed by inverted diapirism.

When the bottom of the sea has a small inclination, for example, at the continental slopes, the sedimentary cover can become unstable, causing turbidity currents.

Turbidity currents are sudden disturbances of the normally quiet deep marine environment and can cause the near-instantaneous deposition of large amounts of sediment, such as sand and silt.

At a beach, dominantly denser sediment such as sand or gravel, often mingled with shell fragments, is deposited, while the silt and clay sized material is kept in mechanical suspension.

In the quiet water of swamps, lakes and lagoons, fine sediment is deposited, mingled with organic material from dead plants and animals.

The depositional environment of the Touchet Formation, located in the Northwestern United States, had intervening periods of aridity which resulted in a series of rhythmite layers.

This means that sedimentary facies can change either parallel or perpendicular to an imaginary layer of rock with a fixed age, a phenomenon described by Walther's Law.

Where the lithosphere moves upward (tectonic uplift), land eventually rises above sea level and the area becomes a source for new sediment as erosion removes material.

Due to divergent movement, the lithosphere is stretched and thinned, so that the hot asthenosphere rises and heats the overlying rift basin.

At the same time, tectonic uplift forms a mountain belt in the overriding plate, from which large amounts of material are eroded and transported to the basin.

[60][61] Climate change can influence the global sea level (and thus the amount of accommodation space in sedimentary basins) and sediment supply from a certain region.

There are usually some gaps in the sequence called unconformities which represent periods where no new sediments were laid down, or when earlier sedimentary layers were raised above sea level and eroded away.

All rock exposed at Earth's surface is subjected to physical or chemical weathering and broken down into finer grained sediment.

The purpose of sedimentary provenance studies is to reconstruct and interpret the history of sediment from the initial parent rocks at a source area to final detritus at a burial place.

Middle Triassic marginal marine sequence of siltstones (reddish layers at the cliff base) and limestones (brown rocks above), Virgin Formation , southwestern Utah , U.S.
Uluru (Ayers Rock) is a large sandstone formation in Northern Territory , Australia .
Claystone deposited in Glacial Lake Missoula , Montana , United States . Note the very fine and flat bedding, common for deposits coming from lake beds further away from the source of sediment.
Sedimentary rock with sandstone in Malta , southern Europe
Lower Antelope Canyon was carved out of the surrounding sandstone by both mechanical weathering and chemical weathering. Wind, sand, and water from flash flooding are the primary weathering agents.
Outcrop of Ordovician oil shale ( kukersite ), northern Estonia
Fossils of Nerinea marine gastropods of Late Cretaceous ( Cenomanian ) age, in limestone in Lebanon
Cross-bedding and scour in a fine sandstone ; the Logan Formation ( Mississippian ) of Jackson County, Ohio
Pressure solution at work in a clastic rock . While material dissolves at places where grains are in contact, that material may recrystallize from the solution and act as cement in open pore spaces. As a result, there is a net flow of material from areas under high stress to those under low stress, producing a sedimentary rock that is harder and more compact. Loose sand can become sandstone in this way.
A piece of a banded iron formation , a type of rock that consists of alternating layers with iron(III) oxide (red) and iron(II) oxide (grey). BIFs were mostly formed during the Precambrian , when the atmosphere was not yet rich in oxygen. Moodies Group , Barberton Greenstone Belt , South Africa
Diagram showing well-sorted (left) and poorly sorted (right) grains
Diagram showing the rounding and sphericity of grains
Global collage of sand samples. There is one square centimeter of sand on every sample photo. Sand samples row by row from left to right: 1. Glass sand from Kauai, Hawaii 2. Dune sand from the Gobi Desert 3. Quartz sand with green glauconite from Estonia 4. Volcanic sand with reddish weathered basalt from Maui, Hawaii 5. Biogenic coral sand from Molokai, Hawaii 6. Coral pink sand dunes from Utah 7. Volcanic glass sand from California 8. Garnet sand from Emerald Creek, Idaho 9. Olivine sand from Papakolea, Hawaii. [1]
Fossil-rich layers in a sedimentary rock, Año Nuevo State Reserve , California
Burrows in a turbidite , made by crustaceans , San Vincente Formation (early Eocene ) of the Ainsa Basin , southern foreland of the Pyrenees
Cross-bedding in a fluviatile sandstone, Middle Old Red Sandstone ( Devonian ) on Bressay , Shetland Islands
Flute casts , a type of sole marking on the base of a vertical layer of Triassic sandstone in Spain
Ripple marks formed by a current in a sandstone that was later tilted ( Haßberge , Bavaria )
Halite crystal mold in dolomite, Paadla Formation ( Silurian ), Saaremaa , Estonia
Chert concretions in chalk , Middle Lefkara Formation (upper Paleocene to middle Eocene ), Cyprus
Common types of depositional environments
The swirls of tan, green, blue, and white are sediment in the shallow waters of the Gulf of Mexico off the Yucatan Peninsula . The blue-green cloud in this image roughly matches the extent of the shallow continental shelf west of the peninsula. This is a perfect example of a shallow marine depositional environment .
Shifting sedimentary facies in the case of transgression (above) and regression of the sea (below)
Plate tectonics diagram showing convergence of an oceanic plate and a continental plate. Note the back-arc basin , forearc basin , and oceanic basin .
Cyclic alternation of competent and less competent beds in the Blue Lias at Lyme Regis , southern England
The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah that makes up much of the famous prominent rock formations in protected areas such as Capitol Reef National Park and Canyonlands National Park . From top to bottom: Rounded tan domes of the Navajo Sandstone , layered red Kayenta Formation , cliff-forming, vertically jointed, red Wingate Sandstone , slope-forming, purplish Chinle Formation , layered, lighter-red Moenkopi Formation , and white, layered Cutler Formation sandstone. Picture from Glen Canyon National Recreation Area , Utah.
Distribution of detritus