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Montoya Group
The Montoya Group is a group of geologic formations in westernmost Texas and southern New Mexico. It preserves fossils dating back to the late Ordovician period.Richardson 2008Pope 2004 Description The group consists mostly of dolomitePray 1953 but with some limestone and a basal sandstone. The total thickness is about .Pope 2004, p.46 The group overlies the El Paso Formation and is overlain by the Fusselman Formation or Percha Formation,Pope 2004, p.52 with both contacts difficult to define in some exposure areas.Paige 1916 Biostratigraphy of the group is consistent with deposition in the Cincinnatian.Kottlowski 1963, pp.17-22 The group is divided into the Cable Canyon Sandstone, Upham Dolomite, Aleman Formation, and Cutter FormationKelley and Silver 1952 These are treated as members in most of southern New Mexico, where the Montoya is relatively thin and remains at formation rank.Pope 2004, p.47 The Cable Canyon Sandstone is present in the northern exposures of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Group (stratigraphy)
In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into supergroups. Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying the stratigraphy of large regions. Geologists exploring a new area have sometimes defined groups when they believe the strata within the groups can be divided into formations during subsequent investigations of the area. It is possible for only some of the strata making up a group to be divided into formations. An example of a group is the Glen Canyon Group, which includes (in ascending order) the Wingate Sandstone, the Moenave Formation, the Kayenta Formation, and the Navajo Sandstone. Each of the formations can be distinguished from its neighbor by its lithology, but all were deposited in the same vast ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Biostratigraphy
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock Stratum, strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of Biology'', 8th ed., Oxford University Press, 2019. The primary objective of biostratigraphy is ''correlation'', demonstrating that a particular Horizon (geology), horizon in one geological section represents the same period of time as another horizon at a different section. Fossils within these strata are useful because sediments of the same age can look completely different, due to local variations in the Sedimentary depositional environment, sedimentary environment. For example, one section might have been made up of clays and marls, while another has more chalky limestones. However, if the fossil species recorded are similar, the two sediments are likely to have been laid down around the same time. Ideally these fossils are used to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbonate Mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, W. H. Freeman, 2nd ed, 529 pp. The term ''mudstone'' is also used to describe carbonate rocks ( limestone or dolomite) that are composed predominantly of carbonate mud. However, in most contexts, the term refers to siliciclastic mudstone, composed mostly of silicate minerals. The NASA Curiosity rover has found deposits of mudstone on Mars that contain organic substances such as propane, benzene and toluene. Definition There is not a single definition of mudstone that has gained general acceptance,Boggs 2006, p.143 though there is wide agreement that mudstones are fine-grained sedimentary rocks, composed mostly of silicate grains with a grain size less than . Individual grains this size are too small to be disti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bioturbation
Bioturbation is defined as the reworking of soils and sediments by animals or plants. It includes burrowing, ingestion, and defecation of sediment grains. Bioturbating activities have a profound effect on the environment and are thought to be a primary driver of biodiversity. The formal study of bioturbation began in the 1800s by Charles Darwin experimenting in his garden. The disruption of aquatic sediments and terrestrial soils through bioturbating activities provides significant ecosystem services. These include the alteration of nutrients in aquatic sediment and overlying water, shelter to other species in the form of burrows in terrestrial and water ecosystems, and soil production on land.Shaler, N. S., 1891, The origin and nature of soils, in Powell, J. W., ed., USGS 12th Annual report 1890-1891: Washington, D.C., Government Printing Office, p. 213-45. Bioturbators are deemed ecosystem engineers because they alter resource availability to other species through the physical ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wackestone
Under the Dunham classification (Dunham, 1962Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. In: W.E. Ham (Ed.), Classification of Carbonate Rocks. American Association of Petroleum Geologists Memoir. American Association of Petroleum Geologists, Tulsa, Oklahoma, pp. 108–121.) system of limestones, a wackestone is defined as a mud-supported carbonate rock that contains greater than 10% grains. Most recently, this definition has been clarified as ''a carbonate-dominated rock in which the carbonate mud (2 mm)''. The identification of wackestone A study of the adoption and use of carbonate classification systems by Lokier and Al Junaibi (2016) highlighted that the most common problem encountered when describing a wackestone is to incorrectly estimate the volume of 'grains' in the sample – in consequence, misidentifying wackestone as mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diagenetic
Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a role as sediments become buried much deeper in the Earth's crust. In the early stages, the transformation of poorly consolidated sediments into sedimentary rock (lithification) is simply accompanied by a reduction in porosity and water expulsion (clay sediments), while their main mineralogical assemblages remain unaltered. As the rock is carried deeper by further deposition above, its organic content is progressively transformed into kerogens and bitumens. The process of diagenesis excludes surface alteration (weathering) and deep metamorphism. There is no sharp boundary between diagenesis and metamorphism, but the latter occurs at higher temperatures and pressures. Hydrothermal solutions, meteoric groundwater, rock porosity, permeability, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calcisiltite
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.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. Flügel, E. (2010) ''Microfacies of Carbonate Rocks'', 2nd ed. Springer-Verlag Berlin, Germany. 976 pp. Calcisiltites can accumulate in a wide variety of coastal, lacustrine, and marine environments. It is typically the product of abrasion and bioerosion.Scholle, P.A., D.G. Bebout, and C.H. Moore (1983) ''Carbonate Depositional Environments.'' Memoir no. 33. Tulsa, Oklahoma, American Association of Petroleum Ge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sponge Spicule
Spicules are structural elements found in most sponges. The meshing of many spicules serves as the sponge's skeleton and thus it provides structural support and potentially defense against predators. Sponge spicules are made of calcium carbonate or silica. Large spicules visible to the naked eye are referred to as megascleres, while smaller, microscopic ones are termed microscleres. The composition, size, and shape of spicules are major characters in sponge systematics and taxonomy. Overview Sponges are a species-rich clade of the earliest-diverging (most basal) animals. They are distributed globally, with diverse ecologies and functions, and a record spanning at least the entire Phanerozoic. Most sponges produce skeletons formed by spicules, structural elements that develop in a wide variety of sizes and three dimensional shapes. Among the four sub-clades of Porifera, three (Demospongiae, Hexactinellida, and Homoscleromorpha) produce skeletons of amorphous silica and on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chert
Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a precipitation (chemistry), chemical precipitate or a diagenesis, diagenetic replacement, as in petrified wood. Chert is typically composed of the petrified remains of siliceous ooze, the biogenic sediment that covers large areas of the deep ocean floor, and which contains the silicon skeletal remains of diatoms, Dictyochales, silicoflagellates, and radiolarians. Precambrian cherts are notable for the presence of fossil cyanobacteria. In addition to Micropaleontology, microfossils, chert occasionally contains macrofossils. However, some chert is devoid of any fossils. Chert varies greatly in color (from white to black), but most often manifests as gray, brown, grayish brown and light green to rusty redW.L. Roberts, T.J. Campbell, G.R. Rapp Jr. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hardground
Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer, 1992). A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limestone sequences and distinguished from later-lithified sediments by evidence of exposure to normal marine waters. This evidence can consist of encrusting marine organisms (especially bryozoans, oysters, barnacles, cornulitids, hederelloids, microconchids and crinoids), borings of organisms produced through bioerosion, early marine calcite cements, or extensive surfaces mineralized by iron oxides or calcium phosphates (Palmer, 1982; Bodenbender et al., 1989; Vinn and Wilson, 2010; Vinn and Toom, 2015). Modern hardgrounds are usually detected by sounding in shallow water or through remote sensing techniques like side-scan sonar. Carbonate hardgrounds often host a unique fauna and flora adapted to the hard surface. Organisms usually cement ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calcarenite
Calcarenite is a type of limestone that is composed predominantly, more than 50 percent, of detrital (transported) sand-size (0.0625 to 2 mm in diameter), 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 GrabauGrabau, A.W. (1903) ''Paleozoic coral reefs.'' Geological Society of America Bulletin. vol. 14, pp. 337-352.Grabau, A.W. (1904) ''On the classification of sedimentary rocks.'' American Geologist. vol. 33, pp. 228-247. as a part of his calcilutite, calcarenite and calcirudite carbonate classification system based upon the size of the detrital grains composing a limestone.Flügel, E. (2010) ''Microfacies of Carbonate Rocks'', 2nd ed. Springer-Verlag Berlin, Germany. 976 pp. Neuendorf, K.K.E., J.P. Mehl, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grainstone
Under the Dunham classification (Dunham, 1962) system of limestones, a grainstone is defined as a grain-supported carbonate rock that contains less than 1% mud-grade material. This definition has recently been clarified as ''a carbonate-dominated rock that does not contain any carbonate mud and where less than 10% of the components are larger than 2 mm.'' The spaces between grains may be empty (pores) or filled by cement. The identification of grainstone The presence of any primary carbonate mud precludes a classification of grainstone. A study of the use of carbonate classification systems by Lokier and Al Junaibi (2016) highlighted that the most common source of confusion in the classification of grainstone was to misidentify fine-grained internal micrite, generated by in-situ processes, as clay–silt grade sediment - thus resulting in the misidentification of grainstone as packstone Under the Dunham classification (Dunham, 1962Dunham, R.J. (1962) Classification of carbonate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
