Historical geology

Historical geology or paleogeology is a discipline that uses the principles and methods of geology to reconstruct the geological history of Earth. Historical geology examines the vastness of geologic time, measured in billions of years, and investigates changes in the Earth, gradual and sudden, over this deep time. It focuses on geological processes, such as plate tectonics, that have changed the Earth's surface and subsurface over time and the use of methods including stratigraphy, structural geology, paleontology, and sedimentology to tell the sequence of these events. It also focuses on the evolution of life during different time periods in the geologic time scale.
Historical development.
During the 17th century, Nicolas Steno was the first to observe and propose a number of basic principles of historical geology, including three key stratigraphic principles: the law of superposition, the principle of original horizontality, and the principle of lateral continuity.
18th-century geologist James Hutton contributed to an early understanding of the Earth's history. Hutton proposed the theory of uniformitarianism, which is now a basic principle in all branches of geology. Uniformitarianism describes an Earth formed by the same natural phenomena that are at work today, the product of slow and continuous geological changes. The theory can be summarized by the phrase "the present is the key to the past." Hutton also described the concept of deep time. The prevailing conceptualization of Earth history in 18th-century Europe, grounded in a literal interpretation of Christian scripture, was that of a young Earth shaped by catastrophic events. Hutton, however, depicted a very old Earth shaped by slow, continuous change. Charles Lyell further developed the theory of uniformitarianism in the 19th century. Modern geologists have generally acknowledged that Earth's geological history is a product of both sudden, cataclysmic events (such as meteorite impacts and volcanic eruptions) and gradual processes (such as weathering, erosion, and deposition).
The discovery of radioactive decay in the late 19th century and the development of radiometric dating techniques in the 20th century provided a means of deriving absolute ages of events in geological history.
Use and importance.
Geology is considered a historical science; accordingly, historical geology plays a prominent role in the field.
Historical geology covers much of the same subject matter as physical geology, the study of geological processes and the ways in which they shape the Earth's structure and composition. Historical geology extends physical geology into the past.
Economic geology, the search for and extraction of fuel and raw materials, is heavily dependent on an understanding of the geological history of an area. Environmental geology, which examines the impacts of natural hazards such as earthquakes and volcanism, must rely on a detailed knowledge of geological history.
Methods.
Stratigraphy.
Layers of rock, or strata, represent a geologic record of Earth's history. Stratigraphy is the study of strata: their order, position, and age.
Structural geology.
Structural geology is concerned with rocks' deformational histories.
Paleontology.
Fossils are organic traces of Earth's history. In a historical geology context, paleontological methods can be used to study fossils and their environments, including surrounding rocks, and place them within the geologic time scale.
Sedimentology.
Sedimentology is the study of the formation, transport, deposition, and diagenesis of sediments. Sedimentary rocks, including limestone, sandstone, and shale, serve as a record of Earth's history: they contain fossils and are transformed by geological processes, such as weathering, erosion, and deposition, through deep time.
Relative dating.
Historical geology makes use of relative dating in order to establish the sequence of geological events in relation to each another, without determining their specific numerical ages or ranges.
Absolute dating.
Absolute dating allows geologists to determine a more precise chronology of geological events, based on numerical ages or ranges. Absolute dating includes the use of radiometric dating methods, such as radiocarbon dating, potassium–argon dating, and uranium–lead dating. Luminescence dating, dendrochronology, and amino acid dating are other methods of absolute dating.
Plate tectonics.
The theory of plate tectonics explains how the movement of lithospheric plates has structured the Earth throughout its geological history.
Weathering, erosion, and deposition.
Weathering, erosion, and deposition are examples of gradual geological processes, taking place over large sections of the geologic time scale. In the rock cycle, rocks are continually broken down, transported, and deposited, cycling through three main rock types: sedimentary, metamorphic, and igneous.
Paleoclimatology.
Paleoclimatology is the study of past climates recorded in geological time.
External links.
Geology - Earth history | Encyclopedia Britannica
Historical Geology | OpenGeology.org
GEOL 102 Historical Geology | Lecture notes for course at the University of Maryland


Pomerado Conglomerate

The Pomerado Conglomerate Formation is a geologic formation in southwestern San Diego County, California.
It was named for exposures located along Pomerado Road, at the divide between Carroll Canyon and Poway Valley.
Geology.
The Pomerado Conglomerate is of the Late Eocene Epoch, and is a massive cobble conglomerate. It is lithologically identical to the local Stadium Conglomerate.
It overlies the sandstone Mission Valley Formation. It is the uppermost formation of the Poway Group, and has a maximum thickness of .
Fossils.
It preserves fossils dating back to the Late Eocene Epoch of the Paleogene period, during the Cenozoic Era.


David A. Hodell

David A. Hodell (born 1958) is a geologist and paleoclimatologist. He currently holds the position of Woodwardian Professor of Geology in the Department of Earth Sciences at the University of Cambridge, where he is also a fellow of Clare College. He is a dual citizen of the United Kingdom and the United States. Previously, he taught at the University of Florida from 1986–2008, earning the rank of full professor in geological sciences. Hodell was also the director of the Stable Isotope Laboratory from 1996–2008. Hodell earned his Ph.D. in 1986 in oceanography from the University of Rhode Island after earning his bachelor of arts in 1980 in geology from the University of Vermont.
Research by Hodell, Brenner, Curtis and Guilderson was instrumental in rethinking the Maya Collapse. Climate data derived from core samples retrieved from closed lake systems in the Mexico's Yucátan and Guatemala showed a period of extensive drought. In 1995, Hodell, Curtis and Brenner published a paleoclimate record from Lake Chichancanab on the Yucatán Peninsula that showed an intense, protracted drought occurred in the 9th century AD and coincided with the Classic Maya collapse. Hodell, Curtis and Brenner returned to Lake Chichancanab in May 2000 and collected new cores while being filmed for a BBC production on drought and Maya prehistory, as part of the BBC series "Ancient Apocalypse". These new cores showed that the devastating drought of the ninth century AD was only one in a series of drought episodes on the Yucatán Peninsula during the last 2,600 years. This research team points out that these dry events occur about every 208 years and coincide with episodes of greater solar intensity that have been shown previously to have a periodicity of 206 years. This suggests that the roughly bicentennial droughts that occur in the Maya lowlands are controlled partly by changes in solar intensity.
In 2007, Hodell was elected a fellow of the American Geophysical Union. Hodell's research areas include: lake sediment cores; speleothems; marine sediment cores; and geoarchaeology.
In October 2008, Hodell was appointed to the position of Woodwardian Professor of Geology at the University of Cambridge in the United Kingdom. He became a recipient of the Milutin Milankovic Medal in 2018.


Carterville Formation

The Carterville Formation is a geologic formation in Missouri. It preserves fossils dating back to the Carboniferous period.


Countries by tight oil reserves

Technically recoverable tight oil resources according to the EIA


List of geological faults of Wales

This is a list of the named geological faults affecting the rocks of Wales. See the main article on faults for a fuller treatment of fault types and nomenclature but in brief, the main types are normal faults, reverse faults, thrusts or thrust faults and strike-slip faults. Many faults may have acted as both normal faults at one time and as reverse or thrust faults at another and may or may not have also incorporated some degree of strike-slip movement too. Fault zones, fault belts and fault complexes typically describe assemblages of faults which have a common origin and history and whose alignments tend to be sub-parallel to one another.
There are also a number of 'disturbances', notably in South Wales. These linear features are a combination of faults and folds - the relative importance of faulting and folding varying along the length of each disturbance.
List of Disturbances.
The following named features comprise both faulting and folding;


Impact gardening

Impact gardening is the process by which impact events stir the outermost crusts of moons and other celestial objects with no atmospheres. In the particular case of the Moon, this is more often known as lunar gardening. Planetary bodies lacking an atmosphere will generally also lack any erosional processes, with the possible exception of volcanism, and as a result impact debris accumulates at the object's surface as a rough "soil," commonly referred to as regolith. Subsequent impacts, especially by micrometeorites, stir and mix this soil. It had long been estimated that the top centimeter of the lunar surface is overturned every 10 million years. However a 2016 analysis by the LRO satellite of impact ejecta coverage puts the figure closer to 80,000 years.


Hells Bells (cave formations)

Hells Bells are hollow bell- or cone-shaped structures of carbonate that can reach lengths of . They are found underwater in El Zapote cenote in Quintana Roo, Mexico, on the Yucatan Peninsula; similar formations exist in other caves. In a certain depth range, such structures cover the entire surface of the cave including submerged tree trunks and other Hells Bells, although they never touch each other.
The Hells Bells are speleothems that appear to have formed through incompletely understood complex interplays between water of the cave, microorganisms living in the cave, and the surface of the Hells Bells. The name refers both to their shape and their environment, and also to a song of the same name.
Name.
The name is a reference both to the shape of the structures and the lightless and toxic environment they are found in, and also to the song "Hells Bells" by AC/DC, and was proposed by cave divers. In Spanish they are called .
Appearance and site.
The Hells Bells are found underwater at depths of and have the forms of conical, hollow protrusions with shapes resembling bells, lampshades, tongues, trumpets, or trunks that hang off a surface and widen downward like a cone or bell. They cover the entire surface area of the cave, including larger specimens and tree trunks; nested forms are also common, but there is always some separation to adjacent surfaces away from the attachment point. Their surface is covered with irregularities such as granules, knobs, nubs, protrusions, pustules, and swellings and sometimes by flowstone produced by exposure to air; they are generally not smooth. Some of these structures are "bubble trails"; these are channels or clefts carved into limestone by carbon dioxide bubbles.
Hells Bells are usually elliptical or circular, with their lower surface strictly horizontal and usually with a lateral gap that gives them a horseshoe outline; this opening always faces the walls of the cave and in general the Bells tend to grow away from obstacles. The angle at which a Bell opens is usually the same over its entire length. They are large: their length can exceed and their width can reach , while their walls are up to thick. The Bells that formed on tree trunks are smaller and have shapes resembling balconies or consoles. In cross-cuts, the Bells are layered, with white to yellow to brown layers that are formed in part by blade-like calcite crystals that can reach length and in part by non-crystalline layers. Manganese oxide forms brown coats on some shallower speciments.
Hells Bells are in the El Zapote sinkhole (cenote), a water-filled bottle- or hourglass-shaped cavern. At the bottom of the cavern lies a debris mound; strong rain can sweep material into the sinkhole, including some submerged tree trunks that are up to long and leaves and other plant remains that cover the floor of the sinkhole. A shaft rises to the surface to the actual sinkhole and is about wide there, while the submerged cavern reaches a width of over ; there is no detectable flow of water in the deeper cavern. Sinkholes such as El Zapote are common in the wider region and form through the collapse of caves.
Their existence has been known to the local cave-diving community for a long time, and there is a visitor centre at El Zapote where a specimen taken from the cave floor is exhibited. The Hells Bells were researched by Wolfgang Stinnesbeck from the University of Heidelberg who was investigating caves for traces of human civilization and who authored the first academic work on them.
Location.
El Zapote and the Hells Bells are in southeastern Mexico, in the state of Quintana Roo west of Puerto Morelos and south of Cancun; the sinkhole lies from a road that connects Mexican Federal Highway 180 and Mexican Federal Highway 307. El Zapote is on the Yucatan Peninsula, which contains one of the largest karst-cave systems in the world, including 370 caves in Quintana Roo alone; the total length of all these caves probably exceeds and some individual systems are over long.
Formation processes.
Carbonate deposits (carbonate speleothems) in caves appear to usually form when evaporation or carbon dioxide escaping from water cause calcite to become saturated, which then precipitates and forms deposits. Underwater carbonate deposits are also known however and may form through biological and physical-chemical processes. The Hells Bells appear to belong to this underwater type, as there is little evidence of exposure to air on them, and water levels in the cave appear to have always exceeded the depths at which the Hells Bells developed.
Neighbouring sinkholes also contain Hells Bells-like structures, but they are smaller than these at El Zapote, while other cave systems on Yucatan and apparently elsewhere in the world have no such structures; the reason for their absence elsewhere is unknown although particular hydrological conditions are likely necessary for their formation. So-called "folia" carbonate deposits, to which the Hells Bells belong, are however widespread around the world.
The development of a Hells Bell appears to begin in the form of a hemispherical bud, which begins to grow conically downward and acquires the hollow cone shape once it has reached a length of and a width of , when calcite accumulation on the inner side stops. The growth of the Bells was unsteady, with slowdowns and stops alternating with rapid growth but within an overall stable environment where the transport of chemical substances through water is mainly due to diffusion, owing to the lack of water currents. Radiometric dating of some Hells Bells specimens indicates that they grew during the middle and late Holocene, beginning over 5,200 years ago, through to the present day; the cave was already flooded at that time.
The cave systems of Yucatan are partly flooded by salty groundwater derived from seawater and fresh groundwater from precipitation; the freshwater and saltwater are separated by a mixed layer (halocline). Sinkholes known as cenotes connect the cave systems to the atmosphere; often older cenotes contain turbid, stagnating water with oxygen-rich and oxygen-poor layers. That includes El Zapote, where the oxygen content drops in the halocline to anoxia, while the freshwater layer contains oxygen; the saltwater layer may or may not contain oxygen. In El Zapote, the Hells Bells have developed at the margin between the halocline and the freshwater layer above; they are not found elsewhere in the water column where calcite appears to dissolve. Their downward growth is constrained by the halocline. The region of the water column where they develop appears to coincide with the presence of a redox boundary that moves up and down in response to precipitation variations (such as hurricanes) and resulting changes in the water supply to El Zapote; the slow downward phase of movement may induce the growth of the Hells Bells. Identifying the chemical traits that correspond to Hells Bells formation is made difficult by the scarcity of hydrogeochemical data.
Biology and origin.
Both El Zapote and the Hells Bells structures contain a diverse ecosystem of microorganisms, including archea and bacteria and with chemolithotrophic, heterotrophic, and mixotrophic species. The microbes metabolize hydrogen, various nitrogen compounds, oxygen, and various sulfur compounds. The metabolism of these microorganisms may influence the growth of the Hells Bells by consuming carbon dioxide and thus facilitating the deposition of calcite by metabolizing nitrogen from alkaline to acidic to neutral compounds under the influence of sulfur and nitrogen redox processes, forming biofilms on the surface of the Bells and by producing organic polymers that can concentrate calcium.
The Hells Bells may have a biological origin; microbial activity may produce the lamination of the deposits, which resemble these of some freshwater stromatolites. It is difficult to conclusively link such calcite deposits to biological activity. Potentially, the oxidation of sulfur compounds in the oxygen-containing water layers acidifies them and thus stops the growth of the Bells, as would the consumption of dissolved calcite by neighbouring Bells; this might explain why they grow away from obstacles. However, the formation process of the Hells Bells is highly speculative and mostly non-biological mechanisms are also possible. The erosion of limestone by ascending carbon dioxide containing bubbles, and the precipitation of limestone from the resulting calcium-saturated water has been proposed as an alternative process. According to this theory, limestone precipitates at the edge of a bubble trapped under some obstacle, initiating the development of a Hells Bell. Fluctuations in the halocline would in turn chemically modify the limestone, producing a substrate for further limestone precipitation.
Because the growth of Hells Bells is so heavily constrained by the layering of the water, their depth and their growth history may be used to infer the position of the halocline, which in turn reflects former precipitation rates; this could be used to infer past climate. Additionally, the dark, submerged ecosystem of the Hells Bells may be used as an analogy to conditions on the early Earth when ionizing and UV radiation constrained the development of life.
The El Zapote cenote is also the place where the ground sloth genus "Xibalbaonyx" was first discovered; ground sloths during the Neogene were a diverse group of American megafauna that are poorly recorded in fossils from Central America. The remains of the animal specimen were found on the floor of the sinkhole.


Assemblage Zone


Dolomie de Fiennes

The Dolomie de Fiennes is a geologic formation in France. It preserves fossils dating back to the Devonian period.


Beattie Formation

The Beattie Formation, or Beattie Limestone, is a geologic formation in east-central Kansas, northeast-central Oklahoma, and southeastern Nebraska in the Midwestern United States. It preserves fossils dating to the Permian period.


Nipe Formation

The Nipe Formation is a geologic formation in Cuba. It preserves fossils dating back to the Paleogene period.


Caddo Creek Formation

The Caddo Creek Formation is a geologic formation in Texas. It preserves fossils dating back to the Carboniferous period.


Linwood Formation

The Linwood Formation is a geologic formation in Iowa. It preserves fossils dating back to the Devonian period.


Richard W. Hughes

Richard W. Hughes is an American gemologist and author, known as an authority on corundum, rubies and sapphires.
Career.
A.G. graduate of Bangkok's AIGS (1980), and a Fellow of the Gemmological Association of Great Britain (F.G.A.) (1982). He was the director of the Asian Institute of Gemological Sciences in Bangkok, Thailand during the 1980s, and also served at the American Gem Trade Association’s gemological laboratories in California and New York from 2005 to 2008. In 1997 he authored "Ruby & Sapphire", which is considered by many in the gem and jewelry industry to be the most authoritative treatise on the subject.
Hughes has authored or co-authored a number of books on gems as well as numerous articles on gemology over the past 34 years. In recognition of his contributions Hughes has received the American Gem Society's Richard T. Liddicoat Journalism Award in both 2004 and 2005. In 2010 Hughes received The Antonio Bonanno Award for Excellence in Gemology.
Hughes has worked both in lab gemology and also in the wholesale, retail and mining sides of the gem business. He currently resides in Thailand with his Thai wife and daughter, where he is engaged in continued gemological research. In 2012 together with the family, he has established a Gemological laboratory in Bangkok called Lotus Gemology.
In 2010, Richard was awarded the prestigious Antonio C. Bonanno Award for Excellence in Gemology by the Accredited Gemologists Association. This award recognizes Richard’s efforts in successfully advancing the profile of many gems and the countries that produce them through his travelogues, as well as more scientific writings and the generous sharing of this information through trade journals and his website. The award underscores the responsibility of the international gemological community to encourage and reward ongoing research, education and dissemination of information.


Tybo Shale

The Tybo Shale is a geologic formation in Nevada. It preserves fossils dating back to the Cambrian period.


Anders Meibom

Anders Meibom (born 9 September 1969) is a Danish interdisciplinary scientist and former football player active in the field of bio-geochemistry. He is a professor at the École Polytechnique Fédérale de Lausanne (EPFL), where he heads the laboratory for biological geochemistry.
Career.
Meibom obtained a PhD in physics at the University of Southern Denmark in 1997. He then pursued a two-and-a-half-year postdoc at the Hawaii Institute for Geophysics and Planetology where he studied the mineralogy of primitive chondrotic meteorites. In 2000, he moved to Stanford University as a research associate in the Stanford-USGS ion microprobe laboratory, department of geological and environmental sciences. In 2005, he was appointed as an associate professor at the Museum National d’Histoire Naturelle in Paris, where he was promoted to full professor in 2007. From 2006 to 2011, he served as the director of the French National NanoSIMS analytical facility. In 2012, he was named full professor at the EPFL (École Polytechnique Fédérale de Lausanne) in the School of Architecture, Civil and Environmental Engineering (ENAC). He has also been full professor "ad personam" at the University of Lausanne since 2014. From 2015 to 2017, he was the director of the Institute of Environmental Engineering at EPFL.
In 2019, Meibom founded the Transnational Red Sea Center (TRSC), an initiative for scientific diplomacy supported by the Swiss Federal Department of Foreign Affairs and which aims to promote scientific collaboration in a politically unstable region endowed with fundamental ecological stakes.
Research.
Meibom currently leads the laboratory for biological geochemistry at EPFL. Research performed in his laboratory is interdisciplinary in nature, at the interface between isotope geochemistry and biology. Active themes in the laboratory include the use of NanoSIMS to visualize and characterize the diagenesis of biogenic substrates, as well as the study of metabolic processes in symbiotic organisms (notably corals) and how these processes may be influenced by environmental stress, in particular climate change.
Distinctions.
In 2008, Meibom was awarded with the Medal for Research Excellence by the European Mineralogical Union for his contributions in the field of cosmochemistry. From 2009 to 2012, he was appointed member of the Comité National Section 18 at the French National Centre for Scientific Research (CNRS), France. In 2009 and 2017, Meibom was awarded two advanced grants by the European Research Council for projects aiming to better understand biomineralization processes by marine organisms (Project BioCarb, 2009), as well as to better understand biocarbonate-based paleo-environmental records for the oceans (Project UltraPal, 2017).


Massenkalk Formation

The Massenkalk Formation is a geologic formation in Germany. It preserves fossils dating back to the Devonian period.


Coetas Formation

The Coetas Formation is a geologic formation in Texas. It preserves fossils dating back to the Neogene period.


Cumulate rock

Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture; cumulate texture is diagnostic of the conditions of formation of this group of igneous rocks. Cumulates can be deposited on top of other older cumulates of different composition and colour, typically giving the cumulate rock a layered or banded appearance.
Formation.
Cumulate rocks are the typical product of precipitation of solid crystals from a fractionating magma chamber. These accumulations typically occur on the floor of the magma chamber, although they are possible on the roofs if anorthite plagioclase is able to float free of a denser mafic melt.
Cumulates are typically found in ultramafic intrusions, in the base of large ultramafic lava tubes in komatiite and magnesium rich basalt flows and also in some granitic intrusions.
Terminology.
Cumulates are named according to their dominant mineralogy and the percentage of crystals to their groundmass (Hall, 1996).
Cumulate rocks are typically named according to the cumulate minerals in order of abundance, and then cumulate type (adcumulate, mesocumulate, orthocumulate), and then accessory or minor phases. For example:
Cumulate terminology is appropriate for use when describing cumulate rocks. In intrusions which have a uniform composition and minimal textural and mineralogical layering or visible crystal accumulations it is inappropriate to describe them according to this convention.
Geochemistry.
Cumulate rocks, because they are fractionates of a parental magma, should not be used to infer the composition of a magma from which they are formed. The chemistry of the cumulate itself can inform on the residual melt composition, but several factors need to be considered.
Chemistry.
The chemistry of a cumulate can inform upon the temperature, pressure and chemistry of the melt from which it was formed, but the number of minerals which co-precipitate need to be known, as does the chemistry or mineral species of the precipitated minerals. This is best illustrated by an example;
As an example, a magma of basalt composition that is precipitating cumulates of anorthite plagioclase plus enstatite pyroxene is changing composition by the removal of the elements which make up the precipitated minerals. In this example, the precipitation of anorthite (a calcium aluminium feldspar) removes calcium from the melt, which becomes more depleted in calcium. Enstatite being precipitated from the melt will remove magnesium, so the melt becomes depleted in these elements. This tends to enrich the concentration of other elements - typically sodium, potassium, titanium and iron.
The rock that is made of the accumulated minerals will not have the same composition as the magma. In the above example, the cumulate of anorthite + enstatite is rich in calcium and magnesium, and the melt is depleted in calcium and magnesium. The cumulate rock is a plagioclase-pyroxene cumulate (a gabbro) and the melt is now more felsic and aluminous in composition (trending towards andesite compositions).
In the above example, the plagioclase and pyroxene need not be pure end-member compositions (anorthite-enstatite), and thus the effect of depletion of elements can be complex. The minerals can be precipitated in any ratio within the cumulate; such cumulates can be 90% plagioclase:10% enstatite, through to 10% plagiclase:90% enstatite and remain a gabbro. This also alters the chemistry of the cumulate, and the depletions of the residual melt.
It can be seen that the effect on the composition of the residual melt left behind by the formation of the cumulate is dependent on the composition of the minerals which precipitate, the number of minerals which co-precipitate at the same time, and the ratio of the minerals which co-precipitate. In nature, cumulates usually form from 2 mineral species, although ranges from 1 to 4 mineral species are known. Cumulate rocks which are formed from one mineral alone are often named after the mineral, for example a 99% magnetite cumulate is known as a magnetitite.
A specific example is the Skaergaard intrusion in Greenland. At Skaergaard a 2500 m thick layered intrusion shows distinct chemical and mineralogic layering:
The Skaergaard is interpreted to have crystallised from a single confined magma chamber.
Residual melt chemistry.
One way to infer the composition of the magma that created the cumulate rocks is to measure groundmass chemistry, but that chemistry is problematic or impossible to sample. Otherwise, complex calculations of averaging cumulate layers must be utilised, which is a complex process. Alternatively, the magma composition can be estimated by assuming certain conditions of magma chemistry and testing them on phase diagrams using measured mineral chemistry. These methods work fairly well for cumulates formed in volcanic conditions (i.e.; komatiites). Investigating magma conditions of large layered ultramafic intrusions is more fraught with problems.
These methods have their drawbacks, primarily that they must all make certain assumptions which rarely hold true in nature. The foremost problem is that in large ultramafic intrusions, assimilation of wall rocks tends to alter the chemistry of the melt as time progresses, so measuring groundmass compositions may fall short. Mass balance calculations will show deviations from expected ranges, which may infer assimilation has occurred, but then further chemistry must be embarked upon to quantify these findings.
Secondly, large ultramafic intrusions are rarely sealed systems and may be subject to regular injections of fresh, primitive magma, or to loss of volume due to further upward migration of the magma (possibly to feed volcanic vents or dyke swarms). In such cases, calculating magma chemistries may resolve nothing more than the presence of these two processes having affected the intrusion.
Though crystallized at high temperature, cumulate can remelt when later intruded by a sill or dyke of magma.
Economic importance.
The economic importance of cumulate rocks is best represented by three classes of mineral deposits found in ultramafic to mafic layered intrusions.
Silicate mineral cumulates.
Silicate minerals are rarely sufficiently valuable to warrant extraction as ore. However, some anorthosite intrusions contain such pure anorthite concentrations that they are mined for feldspar, for use in refractories, glassmaking, semiconductors and other sundry uses (toothpaste, cosmetics, etc.).
Oxide mineral cumulates.
Oxide mineral cumulates form in layered intrusions when fractional crystallisation has progressed enough to allow the crystallisation of oxide minerals which are invariably a form of spinel. This can happen due to fractional enrichment of the melt in iron, titanium or chromium.
These conditions are created by the high-temperature fractionation of highly magnesian olivine or pyroxene, which causes a relative iron-enrichment in the residual melt. When the iron content of the melt is sufficiently high, magnetite or ilmenite crystallise and, due to their high density, form cumulate rocks. Chromite is generally formed during pyroxene fractionation at low pressures, where chromium is rejected from the pyroxene crystals.
These oxide layers form laterally continuous deposits of rocks containing in excess of 50% oxide minerals. When oxide minerals exceed 90% of the bulk of the interval the rock may be classified according to the oxide mineral, for example "magnetitite", "ilmenitite" or "chromitite". Strictly speaking, these would be magnetite orthocumulate, ilmenite orthocumulate and chromite orthocumulates.
Sulfide mineral segregations.
Sulfide mineral cumulates in layered intrusions are an important source of nickel, copper, platinum group elements and cobalt. Deposits of a mixed massive or mixed sulfide-silicate 'matrix' of pentlandite, chalcopyrite, pyrrhotite and/or pyrite are formed, occasionally with cobaltite and platinum-tellurium sulfides. These deposits are formed by melt immiscibility between sulfide and silicate melts in a sulfur-saturated magma.
They are not strictly a cumulate rock, as the sulfide is not precipitated as a solid mineral, but rather as immiscible sulfide liquid. However, they are formed by the same processes and accumulate due to their high specific gravity, and can form laterally extensive sulfide 'reefs'. The sulfide minerals generally form an interstitial matrix to a silicate cumulate.
Sulfide mineral segregations can only be formed when a magma attains sulfur saturation. In mafic and ultramafic rocks they form economic nickel, copper and platinum group (PGE) deposits because these elements are chalcophile and are strongly partitioned into the sulfide melt. In rare cases, felsic rocks become sulfur saturated and form sulfide segregations. In this case, the typical result is a disseminated form of sulfide mineral, usually a mixture of pyrrhotite, pyrite and chalcopyrite, forming copper mineralisation. It is very rare but not unknown to see cumulate sulfide rocks in granitic intrusions.


Kouphichnium

Kouphichnium is an ichnogenus that has been attributed to limulids (horseshoe crabs). "Kouphichnium" fossils resemble the footprints of birds, sometimes in conjunction with a medial line, and were initially thought to be bird or pterosaur tracks. The footprints are now believed to be the imprints of specialized limulid appendages, called pushers, terminating in four plates, used to push against the sediment. The medial line is left by the animal's telson. This ichnogenus is registered in the Carboniferous to the Cretaceous, in marine marginal environments in Tennessee, the United States and in Poland, as well as non-marine environments of Argentina and England, among others. The genus contains five species, "K. arizonae", "K. cordifomnis", "K. lithographicum", "K. minusculum" and "K. walchi".


Hillsborough River Formation

The Hillsborough River Formation is a geologic formation in Prince Edward Island. It preserves fossils dating back to the Permian period.


Honeycut Formation

The Honeycut Formation is a geologic formation in Texas. It preserves fossils dating back to the Ordovician period.


Goasquellou Formation

The Goasquellou Formation is a geologic formation in France. It preserves fossils dating back to the Devonian period.


Ellisdale Fossil Site

The Ellisdale Fossil Site is located near Ellisdale in the valley of the Crosswicks Creek, in Monmouth County, New Jersey, United States. The site has produced the largest and most diverse fauna of Late Cretaceous terrestrial animals from eastern North America, including the type specimens of the teiid lizard "Prototeius stageri" and the batrachosauroidid salamander "Parrisia neocesariensis". The site occurs within the basal portion of the Marshalltown Formation, and dates from the Campanian Stage of the Late Cretaceous. The site is classified as a Konzentrat-Lagerstätten resulting from a prehistoric coastal storm.
History of the discovery.
The Ellisdale site was discovered in 1980 by two avocational paleontologists, Robert K. Denton Jr. and Robert C. O'Neill, who brought it to the attention of David C. Parris, the Director of the Bureau of Natural History at the New Jersey State Museum. Parris encouraged the two collectors to continue monitoring the site, and within a few years hundreds of disarticulated bones of dinosaurs, crocodilians, turtles and fish had been donated to the New Jersey State Museum, which is the repository for the collection. The significance of the Ellisdale Site was recognized by the National Geographic Society which sponsored research under Society grants in 1986 and 1987. To date over 20,000 specimens have been collected. The Ellisdale Site is currently owned by Monmouth County Park System and is under the management of the New Jersey State Museum. Fossil collecting by the general public is prohibited.
Geological setting.
The Ellisdale site occurs within the basal portion of the Marshalltown Formation, of the Late Cretaceous Matawan Group of New Jersey. The exposures of the Marshalltown Formation at Ellisdale have basal lenticular bedded estuarine clays underlain by crossbedded coastal sands of the Englishtown Formation. The estuarine clays are overlain by well-sorted, crossbedded sand and offshore glauconites, respectively. The entire sequence is interpreted as preserving the landward migration of a barrier beach/backbay/estuarine/deltaic complex during the Marshalltown transgression. Vertebrate fossils are concentrated with rip-up clasts near the base of the estuarine clay sequence in a lag deposit consisting of siderite pebbles, poorly graded sand, and lignite. The fossil layer is considered a single-event storm deposit based on sedimentology and stratigraphy. The upper (marine) member of the Marshalltown was formerly considered latest Campanian in age, due to the presence of the foraminifer "Globotruncana calcarata"; however the "G. calcarata" zone has since been redated as Middle Campanian in age (75-76 Ma). A recent study of fossil pollen from the estuarine strata enclosing the fossil layer has determined an Early to Mid-Campanian age for the stratum (76 - 80 Ma) and a fresh or brackish water tidal marsh environment of deposition.
Paleoecology and taphonomy.
Remains of animals from at least four paleoenvironments are represented at the Ellisdale Site: marine, lagoonal/backbay, estuarine/freshwater, and terrestrial. Mixed faunal assemblages of this type are typically associated with transgressive lag deposits, and result from the slow accumulation of transported skeletal remains in tidal channels, backbays, and lagoons. Wave action and storms relocated the bones of marine animals to shallow water, while river currents and flooding events transported and deposited the remains of freshwater and upland terrestrial animals such as crocodilians and dinosaurs.
Megafossils of at least three different types of plants have been found at the site: "Liriodendron", "Metasequoia", and "Picea". In addition, possible remains of Mangrove roots have been found encased in siderite concretions. Amber has been found at the site occurring in small droplets, generally less than 5 millimeters in size. Taphonomic analysis of the Ellisdale fauna has revealed two distinctly different types of preservation. Bones of both marine and upland terrestrial animals are typically broken, heavily worn, and missing the outermost layer of bone (periosteum). Some bones show evidence of boring by the marine shipworm "Teredo". In contrast, the bones of microvertebrates such as amphibians, lizards and mammals are much more complete, with delicate processes and the periosteum intact.
The small animal fauna of the site probably represents a "proximal" assemblage that lived at or near the final point of deposition, while the heavily worn bones represent a "distal" fauna. It is thought that the proximal fauna may have lived within a freshwater deltaic estuary that was affected by a coastal storm surge or a possible tsunami. The presence of numerous well-preserved amphibian fossils support the idea that the environment was freshwater, as amphibians are salt-intolerant. The disarticulated bones which accumulated in the lagoonal backbays by river transport, and in the shallow marine environment offshore, would have been mixed with the skeletal remains of the animals that lived within the delta as the storm surge swept over the estuary. Return flooding from the overfilled lagoons and estuarine channels after the storm's passage would have subsequently filled with debris, resulting in the mixed assemblage of animal and plant remains that are found at the site today.
Significance.
During Late Cretaceous times, the North American Continent was divided by an inland sea into two subcontinents: a western continent now known as "Laramidia", and an eastern continent named "Appalachia". Although a rich and diverse assemblage of taxa has been found from Laramidia, little is known of the contemporaneous terrestrial fauna of the Appalachian subcontinent. The Ellisdale Site has provided the first detailed look at the terrestrial fauna of Appalachia, including the rare fossil remains of frogs, salamanders, lizards and mammals.
It has been suggested that land animals may have migrated between Laramidia and Appalachia, and possibly even the European Archipelago, throughout the Late Cretaceous; however the presence of an endemic "Ellisdalean" land fauna does not support this hypothesis. The Ellisdale fauna together with geological data suggest that eastern North America was an isolated continent from the Turonian Stage of the Late Cretaceous onward, and thus may have become a refugium for relatively underived Early Cretaceous taxa that underwent vicariant speciation. If dispersal to the European archipelago did take place via a North Atlantic route, it could not have happened until near the close of the Cretaceous Period, based on paleogeographic and paleontologic studies.


List of rock types

The following is a list of rock types recognized by geologists. There is no agreed number of specific types of rocks. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type. Additionally, different classification systems exist for each major type of rock. There are three major types of rock: igneous rock, metamorphic rock, and sedimentary rock.
Specific varieties.
The following are terms for rocks that are not petrographically or genetically distinct but are defined according to various other criteria; most are specific classes of other rocks, or altered versions of existing rocks. Some archaic and vernacular terms for rocks are also included.


Panaca Formation

The Panaca Formation is a geologic formation in Nevada. It preserves fossils dating back to the Neogene period.


Elm Point Formation

The Elm Point Formation is a geologic formation in Manitoba. It preserves fossils dating back to the Devonian period.


Couches de Barroubio

The Couches de Barroubio is a geologic formation in France. It preserves fossils dating back to the Ordovician period.


Darwin Canyon Formation

The Darwin Canyon Formation is a geologic formation in California. It preserves fossils dating back to the Permian period.


Dominique Weis

Dominique Weis is a Canadian scientist. She is a Canada Research Chair in the Geochemistry of the Earth's Mantleat at the University of British Columbia.
Early life and education.
Weis obtained her B.Sc in Geology and Mineralogy (1979) and PhD (1982) from the Université Libre de Bruxelles (Belgium). She later completed a master's degree in Environmental Sciences (1983) and Habilitation Geochemistry (1992) at Université Libre de Bruxelles.
She later undertook Postdoctoral Research Fellowships at University of Paris VII (1984) and California Institute of Technology (1985–7). Weis was also a "Chercheur" "Qualifié" FNRS (1985–1993), "Maître de Recherches (1993–1998)" and "Directeur de Recherches (1998–2001)" at the University of Brussels, Belgium.
Career.
In 2002, Weis was appointed a Tier 1 Canada Research Chair at the University of British Columbia in Vancouver, Canada as she established the Pacific Centre for Isotopic and Geochemical Research (PCIGR). In this role, she published "High‐precision isotopic characterization of USGS reference materials by TIMS and MC‐ICP‐MS" in the journal Geochemistry, Geophysics, Geosystems.
By 2009, she was the recipient of the Killam Faculty Research Senior Fellows Award and renewed as a Canada Research Chair. The following year, the PCIGR was approved for funding from the Canada Foundation for Innovation and B.C. Knowledge Development Fund. This allowed the centre to update its geochemical analytical equipment. As a result of her research, Weis was elected a Geochemical Fellow by the Geochemical Society and the European Association of Geochemistry.
In 2016, Weis was elected to sit on the Geochemical Society Board and a Fellow of the Royal Society of Canada. In the following years, she was also renewed as a Canada Research Chair in the Geochemistry of the Earth’s Mantle and named President-elect of the Volcanology, Geochemistry, and Petrology Section of the American Geophysical Union.
Research interests.
Weis' innovative use of trace element and isotopic geochemistry spans a wide range of applications in the Earth and environmental sciences. Her research interests include the distribution of elements and isotopes in Earth systems with an emphasis on the use of abundances and isotopic ratios in earth (petrology/volcanology/geochronology) and environmental sciences. This includes defining the source and evolution of igneous and metamorphic rocks, the interactions between different reservoirs (mantle, crust and atmosphere) and the role of tectonic settings. Other interests include geochemical and isotopic studies of sedimentary rocks, global changes and reconstitution of past environments; distribution of pollutants in natural and anthropogenic systems; application of non-traditional heavy stable to environmental issues and analytical technique developments, techniques for high precision chemical and isotope analysis.


Melville Formation

The Melville Formation is a geologic formation in Montana. It preserves fossils dating back to the Paleogene period.


Infracombe Slates Group

The Infracombe Slates Group is a geologic group in England. It preserves fossils dating back to the Devonian period.


Montgomery Limestone

The Montgomery Limestone is a geologic formation in California. It preserves fossils dating back to the Ordovician period.


Commission for the Geological Map of the World

The Commission for the Geological Map of the World (CGMW or CCGM) is an association and a standardization body in the field of geology and stratigraphy. Its main role is the production of small-scale maps of continents, oceans, regions of the Earth. It works in particular in collaboration with the International Commission on Stratigraphy to develop a geological time scale.
The CGMW is one of the oldest international organizations in earth sciences: It was created in 1881 during the second International Congress of Geology, of which it is in fact a commission. When the International Union of Geological Sciences was created, it joined to expand its cartographic work.
Its current president is Philippe Rossi. Its last general assembly was held in Cape Town, South Africa, from August 27 to September 4, 2016.


Niguel Formation

The Niguel Formation is a geologic formation in California. It preserves fossils dating back to the Neogene period.


Lenox Hills Formation

The Lenox Hills Formation is a geologic formation in Texas. It preserves fossils dating back to the Permian period.


Burlington Limestone

The Burlington Limestone is a geologic formation in Missouri, Iowa and the Midwest region. It preserves fossils dating back to the Mississippian subperiod.
Physical properties.
Burlington Limestone is unusually course-grained, crystalline, crinoidal limestone. Its texture is sufficiently distinctive and persistent to permit recognition of the formation commonly on this basis alone. The Burlington Limestone is made of almost entirely on the remains of various fossils, by far the most important of which are crinoids. Some portions of the Burlington, however, are not so evidently crinoidal, as for example, the so-called "white ledge" quarried in the northeastern part of Missouri.
Natural occurrence.
Burlington Limestone is present in nearly all major Mississippian outcrop regions in Missouri. It is known from Iowa to northwestern Arkansas and from western Illinois to western Kansas. It is present throughout Missouri, except in the Ozark uplift, where it has been removed by erosion. Differentiation of the Burlington with the overlaying, lithologically similar Keokuk Limestone is often difficult or impossible, so the sequence of Osagean limestones is sometimes identified as "Burlington-Keokuk Limestone".


Henryetta Coal Formation

The Henryetta Coal Formation is a geologic formation in Oklahoma. It preserves fossils dating back to the Carboniferous period.
As of a 1955 government report, the mapped area of the Henryetta mining district included about 168 square miles in Okmulgee County. Coal occurred in the Senora formation in two minable beds: the Morris bed and the overlying Henryetta bed. The Morris bed averaged about 16 inches in thickness, while the Henryetta coal bed averaged about 25 to 36 inches in thickness. The coal in both beds was of high volatile A and B bituminous ranks. Remaining coal reserves were estimated to be 275 million tons, 271 million tons of which was in the Henryetta bed.


Alapah Limestone

The Alapah Limestone is a geologic formation in Alaska. It preserves fossils dating back to the Carboniferous period.


Vik Formation

The Vik Formation is a geologic formation in Norway. It preserves fossils dating back to the Silurian period.


Moraga Formation

The Moraga Formation or Moraga Volcanics is a Pliocene epoch volcanic geologic formation in the Berkeley Hills of the East Bay region of the San Francisco Bay Area, California.
The basaltic lava flow formation is found within Alameda County and Contra Costa County. It can be seen in the Robert Sibley Volcanic Regional Preserve and Caldecott Tunnel area of the Berkeley Hills. It is named for an exposed occurrence in the Moraga Valley.
It overlies the Orinda Formation, and underlies the Siesta Formation of Great Valley Group.
It preserves freshwater fossils dating back to the Pliocene epoch of the Neogene period.


Matfield Shale

The Matfield Shale is a geologic formation in Kansas. It preserves fossils dating back to the Permian period.


Duolbasgaissa Formation

The Duolbasgaissa Formation is a geologic formation in Norway. It preserves fossils dating back to the Cambrian period.


Rocknest (Mars)

Rocknest is a sand patch on the surface of Aeolis Palus, between Peace Vallis and Aeolis Mons (Mount Sharp), in Gale crater on the planet Mars. The patch was encountered by the "Curiosity" rover on the way from Bradbury Landing to Glenelg Intrigue on September 28, 2012. The approximate site coordinates are: .
The sand patch is downhill from a cluster of dark rocks. NASA determined the patch to be the location for the first use of the scoop on the arm of the Mars "Curiosity" rover. The Rocknest patch is about by .
On October 7, 2012, a mysterious bright object (), discovered in the sand at Rocknest, drew scientific interest. Several close-up pictures (close-up 1) (close-up 2) were taken of the object and preliminary interpretations by scientists suggest the object to be "debris from the spacecraft". Nonetheless, further images in the nearby sand have detected other bright particles (image) (close-up 1). These newly discovered objects are presently thought to be native Martian material.
On October 17, 2012 at Rocknest, the first X-ray diffraction analysis of Martian soil was performed. The results from the rover's CheMin analyzer revealed the presence of several minerals, including feldspar, pyroxenes and olivine, and suggested that the Martian soil in the sample was similar to the weathered basaltic soils of Hawaiian volcanoes.
On September 26, 2013, NASA scientists reported the Mars "Curiosity" rover detected "abundant, easily accessible" water (1.5 to 3 weight percent) in soil samples at the Rocknest region of Aeolis Palus in Gale Crater. In addition, NASA reported the rover found two principal soil types: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic type, similar to other martian soils and martian dust, was associated with hydration of the amorphous phases of the soil. Also, perchlorates, the presence of which may make detection of life-related organic molecules difficult, were found at the "Curiosity" rover landing site (and earlier at the more polar site of the "Phoenix" lander) suggesting a "global distribution of these salts". NASA also reported that Jake M rock, a rock encountered by "Curiosity" on the way to Glenelg, was a mugearite and very similar to terrestrial mugearite rocks.


Kermeur Sandstone

The Kermeur Sandstone is a geologic formation in France. It preserves fossils dating back to the Ordovician period.


Nye Formation

The Nye Formation is a geologic formation in Oregon. It preserves fossils dating back to the Neogene period.


Transgressive systems tract


Hillhead Formation

The Hillhead Formation is a geologic formation in Scotland. It preserves fossils dating back to the Devonian period.


Ichnology


Parasequence

A parasequence is a fundamental concept of sequence stratigraphy. Parasequences are not directly related to sequences.
Definition.
A parasequence is defined as a genetically related succession of bedsets that is bounded by marine flooding surfaces (or their correlative surfaces) on top and at the bottom. The succession is supposed to be relatively conformable in the sense that breaks in deposition within the parasequence are much shorter than the time of deposition of the parasequence itself.
Most parasequences show a shallowing upward, which is sometimes also included into the definition.
Properties.
Since parasequences are relatively conformable, so Walther's law applies within a parasequence. This is not necessarily the case for transitions from one parasequence to another. They are also typically of the size of one up to tens of meters.


Pamela Lamplugh Robinson

Pamela Lamplugh Robinson (18 December 1919 – 24 October 1994) was a British paleontologist who worked extensively on the fauna of the Triassic and Early Jurassic of Gloucestershire and later worked in India on the Mesozoic and Gondwanan fauna. She helped establish the geology unit at the Indian Statistical Institute and directed research in vertebrate paleontology of India in the 1960s.
Biography.
Robinson was born in Manchester to James Arthur Robinson and Ann (née Lamplugh) in 1919. She went to a private school and later the Manchester Girls' High School. After the divorce of her parents in 1938 she went to the University of Hamburg for premedical studies but this was interrupted by the war. Returning to England, she worked at the British Woollen Industries Research Association in Leeds where she attended evening lectures in Paleontology at Leeds University by Dorothy Rayner, which captured her interest. She worked from 1942 to 1945 at the Royal Ordnance factory at Thorp Arch, West Yorkshire. She worked for about two years as a librarian at the Geological Society in London before enrolling for geology at the University College London in 1947. She was influenced at university by J. B. S. Haldane and Walter Georg Kühne. Graduating in 1951 with first-class honours, he continued post-graduate research and became an assistant lecturer in zoology in the department headed by Peter Medawar and later Avrion Mitchison. She received a Ph.D., the last of D. M. S. Watson's students, in 1957 for her studies on the gliding lizard "Kuehneosaurus" but she also studied the stratigraphy and fossils of the Mendip Hills in Gloucestershire. She published on the Late Triassic fauna of the Bristol Channel. She was invited through the influence of Haldane to the Indian Statistical Institute at Calcutta by Prasanta Chandra Mahalanobis and helped establish a geology department there. She mentored and influenced Indian researchers and created a program for the study of the paleontology of the Gondwana strata as well as the Maleri Formation in the Deccan region. A symposium on Gondwana Stratigraphy was held in 1967.
Robinson became Alexander Agassiz visiting professor at Harvard University in 1972 and was awarded the Wollaston award by the Geological Society for her work in India in 1973. She supervised three doctoral students including Beverly Halstead. From the 1960s she took an interest in the palaeoenvironment and palaeoclimate. In a landmark essay "Climates Ancient and Modern" published in 1964 she noted that the world's annual mean temperature had risen by 0.5 °C since the end of the nineteenth century and that winter mean temperatures had risen by 1 °C leading to rising tree-lines, shrinking inland lakes and an expansion of steppe and prairie land apart from a "spectacular" decline in glaciers and floating ice. She noted that Swiss glaciers had shrunk by a quarter of their area of 1877 by 1932.
She retired in 1982 and lived in London and spent time on gardening and studying Indian philosophy. She died at Newham General Hospital on 24 October 1994 after suffering from a stroke. She never married. "Malerisaurus robinsonae", "Pamelina", "Lamplughsaura" and "Pamelaria" are named in her honour.


Geomicrobiology

Geomicrobiology is the scientific field at the intersection of geology and microbiology. It concerns the role of microbes on geological and geochemical processes and effects of minerals and metals to microbial growth, activity and survival. Such interactions occur in the geosphere (rocks, minerals, soils, and sediments), the atmosphere and the hydrosphere. Geomicrobiology studies microorganisms that are driving the Earth's biogeochemical cycles, mediating mineral precipitation and dissolution, and sorbing and concentrating metals. The applications include for example bioremediation, mining, climate change mitigation and public drinking water supplies.
Rocks and minerals.
Microbe-aquifer interactions.
Microorganisms are known to impact aquifers by modifying their rates of dissolution. In the karstic Edwards Aquifer, microbes colonizing the aquifer surfaces enhance the dissolution rates of the host rock.
In the oceanic crustal aquifer, the largest aquifer on Earth, microbial communities can impact ocean productivity, sea water chemistry as well as geochemical cycling throughout the geosphere. The mineral make-up of the rocks affects the composition and abundance of these subseafloor microbial communities present. Through bioremediation some microbes can aid in decontaminating freshwater resources in aquifers contaminated by waste products.
Microbially precipitated minerals.
Some bacteria use metal ions as their energy source. They convert (or chemically reduce) the dissolved metal ions from one electrical state to another. This reduction releases energy for the bacteria's use, and, as a side product, serves to concentrate the metals into what ultimately become ore deposits. Biohydrometallurgy or "in situ" mining is where low-grade ores may be attacked by well-studied microbial processes under controlled conditions to extract metals. Certain iron, copper, uranium and even gold ores are thought to have formed as the result of microbe action.
Subsurface environments, like aquifers, are attractive locations when selecting repositories for nuclear waste, carbon dioxide (See carbon sequestration), or as artificial reservoirs for natural gas. Understanding microbial activity within the aquifer is important since it may interact with and effect the stability of the materials within the underground repository. Microbe-mineral interactions contribute to biofouling and microbially induced corrosion. Microbially induced corrosion of materials, such as carbon steel, have serious implications in the safe storage of radioactive waste within repositories and storage containers.
Environmental remediation.
Microbes are being studied and used to degrade organic and even nuclear waste pollution (see Deinococcus radiodurans) and assist in environmental cleanup. An application of geomicrobiology is bioleaching, the use of microbes to extract metals from mine waste.
Soil and sediment: microbial remediation.
Microbial remediation is used in soils to remove contaminants and pollutants. Microbes play a key role in many biogeochemistry cycles and can effect a variety of soil properties, such as biotransformation of mineral and metal speciation, toxicity, mobility, mineral precipitation, and mineral dissolution. Microbes play a role in the immobilization and detoxification of a variety of elements, such as metals, radionuclides, sulfur and phosphorus, in the soil. Thirteen metals are considered priority pollutants (Sb, As, Be, Cd, Cr, Cu, Pb, Ni, Se, Ag, Tl, Zn, Hg). Soils and sediment act as sinks for metals which originate from both natural sources through rocks and minerals as well as anthropogenic sources through agriculture, industry, mining, waste disposal, among others.
Many heavy metals, such as chromium (Cr), at low concentrations are essential micronutrients in the soil, however they can be toxic at higher concentrations. Heavy metals are added into soils through many anthropogenic sources such industry and/or fertilizers. Heavy metal interaction with microbes can increase or decrease the toxicity. Levels of chromium toxicity, mobility and bioavailability depend on oxidation states of chromium. Two of the most common chromium species are Cr(III) and Cr(VI). Cr(VI) is highly mobile, bioavailable and more toxic to flora and fauna, while Cr(III) is less toxic, more immobile and readily precipitates in soils with pH >6. Utilizing microbes to facilitate the transformation of Cr(VI) to Cr(III) is an environmentally friendly, low cost bioremediation technique to help mitigate toxicity in the environment.
Acid mine drainage.
Another application of geomicrobiology is bioleaching, the use of microbes to extract metals from mine waste. For example, sulfate-reducing bacteria (SRB) produce H2S which precipitates metals as a metal sulfide. This process removed heavy metals from mine waste which is one of the major environmental issues associated with acid mine drainage (along with a low pH).
Bioremediation techniques are also used on contaminated surface water and ground water often associated with acid mine drainage. Studies have shown that the production of bicarbonate by microbes such as sulfate-reducing bacteria adds alkalinity to neutralize the acidity of the mine drainage waters. Hydrogen ions are consumed while bicarbonate is produced which leads to an increase in pH (decrease in acidity).
Microbial degradation of hydrocarbons.
Microbes can affect the quality of oil and gas deposits through their metabolic processes. Microbes can influence the development of hydrocarbons by being present at the time of deposition of the source sediments or by dispersing through the rock column to colonize reservoir or source lithologies after the generation of hydrocarbons.
Early Earth history and astrobiology.
A common field of study within geomicrobiology is origin of life on earth or other planets. Various rock-water interactions, such as serpentinization and water radiolysis, are possible sources of metabolic energy to support chemolithoautotrophic microbial communities on Early Earth and on other planetary bodies such as Mars, Europa and Enceladus.
Interactions between microbes and sediment record some of the earliest evidence of life on earth. Information on the life during Archean Earth is recorded in bacterial fossils and stromatolites preserved in precipitated lithologies such as chert or carbonates. Additional evidence of early life on land around 3.5 billion years ago can be found in the Dresser formation of Australia in a hot spring facies, indicating that some of Earth's earliest life on land occurred in hot springs. Microbially induced sedimentary structures (MISS) are found throughout the geologic record up to 3.2 billion years old. They are formed by the interaction of microbial mats and physical sediment dynamics, and record paleoenvironmental data as well as providing evidence of early life. The different paleoenvironments of early life on Earth also serves as model when searching for potential fossil life on Mars.
Extremophiles.
Another area of investigation in geomicrobiology is the study of extremophile organisms, the microorganisms that thrive in environments normally considered hostile to life. Such environments may include extremely hot (hot springs or mid-ocean ridge black smoker) environments, extremely saline environments, or even space environments such as Martian soil or comets.
Observations and research in hyper-saline lagoon environments in Brazil and Australia as well as slightly saline, inland lake environments in NW China have shown that anaerobic sulfate-reducing bacteria may be directly involved in the formation of dolomite. This suggests the alteration and replacement of limestone sediments by dolomitization in ancient rocks was possibly aided by ancestors to these anaerobic bacteria.
In July 2019, a scientific study of Kidd Mine in Canada discovered sulfur-breathing organisms which live 7900 feet below the surface, and which breathe sulfur in order to survive. these organisms are also remarkable due to eating rocks such as pyrite as their regular food source.


Flowerpot Formation

The Flowerpot Formation is a geologic formation in Oklahoma. It preserves fossils dating back to the Permian period.


Garnet-biotite geothermometry

Garnet-Biotite Geothermometry is a method used to evaluate the peak temperature at which metamorphic rocks have formed. Geothermometry makes up one component of geothermobarometry , which also includes the evaluation of pressure (geobarometry). There are many geothermometers, but garnet-biotite is particularly useful because of the frequent occurrence of biotite and garnet together in medium grade metamorphic rocks. The garnet biotite thermometer correlates temperature with the partitioning of Fe and Mg in coinciding garnet and biotite. The garnet-biotite thermometer has been "calibrated" many times since the 70's by both experimental and empirical methods, however Ferry and Spear's 1978 experimental calibration study is reported thoroughly and commonly cited. Given a rock containing both garnet and biotite, an equilibrium constant (KD) can be found simply by using microprobe analysis. Then, by comparing the found KD value to the calculated garnet-biotite geothermometer, the peak temperature of rock formation can be determined.
Experimental Petrology.
Determining the temperature and/or pressure of formation of metamorphic rocks began as a mostly qualitative science. Pelitic index minerals were used to estimate the metamorphic grade of rocks, and the relative conditions of metamorphism across an area.
Experimental petrology has allowed researchers to move beyond the qualitative approach and employ quantitative methods. Experimental petrology consists of modeling natural geological systems at different temperatures and pressure in a lab setting. One quantitative method derived from experimentation is geothermobarometry. Geothermobarometry allows for the calculation of equilibrium temperatures and pressures from measured distributions of elements between coexisting phases. Geothermobarometry encompasses both geothermometry (concerning temperature) and geobarometry (concerning pressure).
Calibrating the Garnet-Biotite Exchange Geothermometer.
Ferry and Spear's calculation of the garnet-biotite geothermometer (1978), involved running experimental reactions between biotite and garnet at a constant pressure (0.207 GPa) and varying temperatures between 500°C and 800°C. The focus of the reactions was on the Fe-Mg exchange:
 Fe3Al2Si3O12 + KMg3AlSi3O10(OH)2 = Mg3Al2Si3O12 + KFe3AlSi3O10(OH)2
Ferry and Spear (1978) used a garnet solid solution of almandine and pyrope (All90Prp10) with an iron mole fraction of XFe = 0.9 for all reactions. Varying biotite compositions (from XFe = 0.5 to XFe = 1.0) were selected based on the known bracket of the equilibrium distribution for Mg and Fe that corresponded with the garnet composition. To compensate for the slow nature of garnet equilibration in metamorphic settings, a ratio of 98:2 garnet to biotite was used. Using an excess of garnet forced the biotite do the majority of the work to reach the equilibrium value (KD), expediting the reaction process. Experiments were ran for 13 to 56 days to ensure enough time to reach equilibrium.
The resulting data from the experiments (final biotite composition and Fe / Mg concentration) were used to calculate an equilibrium constant (KD) at each reaction temperature. Specific data and figures can be found in Winter (2010) and Ferry and Spear (1978). The relationship between the inverse of temperature (1/K) and the natural log of KD plots as a straight line. Additionally, a linear regression of the data fits the same trend line, indicating a valid geothermometer.
 Experimental Calculation of Equilibrium Constant: KD = Linear Regression of data: lnKD = -2109 / T + 0.782
Isopleths plotted on a P-T diagram of various KD values are nearly vertical. This indicates that the garnet-biotite reaction is much more susceptible to temperature, and relatively insensitive to pressure (another line of evidence for a good geothermometer)
In summary, Ferry and Spear (1978) created a graph that plots KD values versus temperature for the garnet-biotite exchange reaction. KD values of garnet and biotite in rock samples can be easily determined using microprobe analysis. So, given a rock containing garnet and biotite, the temperature of formation can be determined by finding the KD value, and comparing it to the calculated trend line.
Limitations.
Pressure: The Ferry and Spear (1978) calibration was performed at a constant pressure of 0.207 GPa, making varying pressure a limitation for an accurate calculation. However, Spear argues that the garnet-biotite geothermometer is relatively insensitive to pressure changes, and can apply to rocks at any mid-crustal level. This pressure insensitivity is demonstrated by plotting KD isopleths for the garnet-biotite exchange reaction against pressure (y-axis) and temperature (x-axis). The isopleths plot nears vertical, indicating the relative insignificance of pressure.
Non-ideal Minerals: Ferry and Spear (1978) used idealized biotite and garnet compositions. As nothing is perfect in nature, Ca can be found in garnet, and Al and Ti can be found in biotite. Consequently, while this geothermometer is useful for rocks found in the greenschist or amphibolite metamorphic facies, it is not as useful for rocks in other facies with higher Ca-garnets and mixed biotites. Several calibrations have been completed that take into account the non-ideal nature of minerals (see below).
Applications.
Geothermometry plays a role in determining the tectonic history of rocks and geologic regions all over the world.
Other Calibration Studies.
The garnet-biotite geothermometer has been calibrated in numerous studies since the 70's.


Wilberns Formation

The Wilberns Formation is a geologic formation in Texas. It preserves fossils dating back to the Cambrian period.


Kaub Formation

The Kaub Formation is a geologic formation in Germany. It preserves fossils dating back to the Devonian period.


Bonanza King Formation

The Bonanza King Formation is a geologic formation in Nevada. It preserves fossils dating back to the Cambrian period.


Dyserth Quarry Limestone

The Dyserth Quarry Limestone is a geologic formation in Wales. It preserves fossils dating back to the Carboniferous period.


Evolutionary gap


Forest Hills Formation

The Forest Hills Formation is a geologic formation in New Brunswick. It preserves fossils dating back to the Cambrian period.


Fort Thompson Formation

The Fort Thompson Formation is a geologic formation in Florida. It preserves fossils dating back to the late Pleistocene. It was influenced by sea level changes.


Jules Fejer

Jules Fejer (; 22 January 1914 – 21 December 2002) was a Hungarian physicist. Fejer was born in Budapest, Austria-Hungary. In the late 1950s he wrote a fundamental paper on incoherent backscatter, explaining why the width of the backscattered echo was determined primarily by the ion thermal velocity rather than by the electron thermal velocity. He was one of a group of ionospheric physicists brought together by Henry G. Booker to start what became the Electrical and Computer Engineering department at the University of California, San Diego. He was elected a Fellow of the American Geophysical Union in 1990 and continued work with graduate students until 1995.


Dove Spring Formation

The Dove Spring Formation is a geologic formation in California. It preserves fossils dating back to the Neogene period.


Eskridge Shale

The Eskridge Shale or Eskridge Formation is a geologic formation in Kansas, Oklahoma, and Nebraska dating to the early Permian period.


T. Mark Harrison

T. Mark Harrison is an isotope geochemist based in California. He is Distinguished Professor of Geochemistry in the Department of Earth, Planetary and Space Sciences, University of California – Los Angeles.
Education.
A native of Vancouver, Canada, Harrison received his B.Sc. (Hons.) from the University of British Columbia, in 1977. His Ph.D. research from 1978 to 1980 developing 40Ar/39Ar thermochronology was conducted under the supervision of Prof. Ian McDougall at the Australian National University.
Academic life.
Following a postdoctoral fellowship at the Carnegie Institution of Washington, Harrison spent 8 years on the faculty of the Department of Geological Sciences at the State University of New York at Albany rising from Assistant to Full Professor. In 1989, he moved to UCLA where he served as Chair of the Department of Earth and Space Sciences from 1997 to 2000 becoming a Distinguished Professor in 2003. He took leave from UCLA to take up an appointment as University Professor and Director of the Research School of Earth Sciences at the Australian National University from 2001 to 2006. He returned to UCLA in 2006 to take up Directorship of the Institute of Geophysics and Planetary Physics until 2011.
Awards.
Harrison received the Presidential Young Investigator Award of the National Science Foundation in 1985, the Outstanding Young Alumnus Award of the University of British Columbia in 1988, the Norman L. Bowen Award of the American Geophysical Union in 1995, the Outstanding Contributions in Geoscience Research award from the Department of Energy in 1996, and the Arthur L. Day Medal of the Geological Society of America in 2009. He is a Fellow of the American Geophysical Union (1996), the Geochemical Society (2007), the European Association of Geochemistry (2007), and Geological Society of Australia (2007). He is member of both the Australian Academy of Science and the U.S. National Academy of Science and an Einstein Professor of the Chinese Academy of Sciences.
Research interests.
Harrison has published over 260 papers and books on a range of topics including the evolution of the Tibet-Himalaya orogenic system, geochemical kinetics, the origin and transport of magmas, geochronology, interpretive models for heat and mass flow, evolution of petroleum reservoirs and geothermal systems, and investigations of the very early Earth, including documenting the earliest evidence of oceans, continents, plate tectonics, and life. He is the co-author of the monograph "Geochronology and Thermochronology" "by the" "40Ar/39Ar Method" (1999) and author of "Hadean Earth" (2020). His publications have attracted over 50,000 citations and correspond to an H-index value of 113.


Thomas H. Jordan

Thomas H. Jordan (born October 8, 1948) is an American seismologist, and former director (2002-2017) of the Southern California Earthquake Center at The University of Southern California. He was formerly the head of the Earth, Atmospheric and Planetary Sciences Department at the Massachusetts Institute of Technology and is a member of the National Academy of Sciences.
Research.
Jordan has made significant contributions to plate tectonics concerning the structure of continents, the depth of lithospheric slab penetration, and the nature of mantle convection, for example determining the exact nature and processes involved in plate subduction. Jordan has also pioneered many seismic imaging techniques which he developed for his doctoral dissertation and are now used widely to understand the interior of the earth. Jordan has served on international committees concerning seismic hazard.
Publications.
He has published over 190 articles in scientific journals. He has also published two textbooks, "Understanding Earth" and "The Essential Earth".


El Reno Group

The El Reno Group is a geologic group in Oklahoma. It preserves fossils dating back to the Permian period.


Vaser

The Vaser () is a right tributary of the river Vișeu in Romania. Its length is and its basin size is . It flows into the Vișeu in Vișeu de Sus.
Tributaries.
The following rivers are tributaries to the river Vaser:


Laval Formation

The Laval Formation is a geologic formation in Quebec. It preserves fossils dating back to the Ordovician period.


Chatwell Flags

The Chatwell Flags is a geologic formation in England. It preserves fossils dating back to the Ordovician period.


Molasse Coquilliere

The Molasse Coquilliere is a geologic formation in France. It preserves fossils dating back to the Neogene period, which started 23.03 million years ago and ended 2.58 million years ago.


Keasey Formation

The Keasey Formation is a geologic formation in northwestern Oregon. It preserves fossils dating back to the Paleogene period.


Ultra-high-pressure metamorphism

Ultra-high-pressure metamorphism refers to metamorphic processes at pressures high enough to stabilize coesite, the high-pressure polymorph of SiO2. It is important because the processes that form and exhume ultra-high-pressure (UHP) metamorphic rocks may strongly affect plate tectonics, the composition and evolution of Earth's crust. The discovery of UHP metamorphic rocks in 1984 revolutionized our understanding of plate tectonics. Prior to 1984 there was little suspicion that continental rocks could reach such high pressures.
The formation of many UHP terrains has been attributed to the subduction of microcontinents or continental margins and the exhumation of all UHP terrains has been ascribed principally to buoyancy caused by the low density of continental crust—even at UHP—relative to Earth's mantle. While the subduction proceeds at low thermal gradients of less than 10°C/km, the exhumation proceeds at elevated thermal gradients of 10-30°C/km.
Definition.
Metamorphism of rocks at pressures ≥27kbar (2.7GPa) to stabilize coesite, the high-pressure polymorph of SiO2, recognized by either the presence of a diagnostic mineral (e.g., coesite or diamond), mineral assemblage (e.g., magnesite + aragonite), or mineral compositions.
Identification.
Petrological indicators of UHP metamorphism are usually preserved in eclogite. The presence of metamorphic coesite, diamond, or majoritic garnet are diagnostic; other potential mineralogical indicators of UHP metamorphism, such as alpha-PbO2 structured TiO2, are not widely accepted. Mineral assemblages, rather than single minerals, can also be used to identify UHP rocks; these assemblages include magnesite + aragonite. Because minerals change composition in response to changes in pressure and temperature, mineral compositions can be used to calculate pressure and temperature; for UHP eclogite the best geobarometers involve garnet + clinopyroxene + K-white mica and garnet + clinopyroxene + kyanite + coesite/quartz. Most UHP rocks were metamorphosed at peak conditions of 800 °C and 3 GPa. At least two UHP localities record higher temperatures: the Bohemian and Kokchetav Massifs reached 1000–1200 °C at pressures of at least 4 GPa.
Most felsic UHP rocks have undergone extensive retrograde metamorphism and preserve little or no UHP record. Commonly, only a few eclogite enclaves or UHP minerals reveal that the entire terrain was subducted to mantle depths. Many granulite terrains and even batholithic rocks may have undergone UHP metamorphism that was subsequently obliterated
Global distribution.
Geologists have identified UHP terrains at more than twenty localities around the globe in most well-studied Phanerozoic continental orogenic belts; most occur in Eurasia.
Coesite is relatively widespread, diamond less so, and majoritic garnet is known from only rare localities. The oldest UHP terrain is 620 Ma and is exposed in Mali; the youngest is 8 Ma and exposed in the D'Entrecasteaux Islands of Papua New Guinea.
A modest number of continental orogens have undergone multiple UHP episodes.
UHP terrains vary greatly in size, from the >30,000 km2 giant UHP terrains in Norway and China, to small kilometer-scale bodies. The giant UHP terrains have a metamorphic history spanning tens of millions of years, whereas the small UHP terrains have a metamorphic history spanning millions of years. All are dominated by quartzofeldspathic gneiss with a few percent mafic rock (eclogite) or ultramafic rock (garnet-bearing peridotite). Some include sedimentary or rift-volcanic sequences that have been interpreted as passive margins prior to metamorphism.
Implications and importance.
UHP rocks record pressures greater than those that prevail within Earth's crust. Earth's crust is a maximum of 70–80 km thickness, and pressures at the base are <2.7 GPa for typical crustal densities. UHP rocks therefore come from depths within Earth's mantle. UHP rocks of a wide variety of compositions have been identified as both regional metamorphic terrains and xenoliths.
UHP ultramafic xenoliths of mantle affinity provide information (e.g., mineralogy or deformation mechanisms) about processes active deep in Earth. UHP xenoliths of crustal affinity provide information about processes active deep in Earth, but also information about what kinds of crustal rocks reach great depth in Earth and how profound those depths are.
Regional metamorphic UHP terrains exposed on Earth's surface provide considerable information that is not available from xenoliths. Integrated study by structural geologists, petrologists, and geochronologists has provided considerable data on how the rocks deformed, the pressures and temperatures of metamorphism, and how the deformation and metamorphism varied as a function of space and time. It has been postulated that small UHP terrains that underwent short periods of metamorphism formed early during continent subduction, whereas giant UHP terrains that underwent long periods of metamorphism formed late during continent collision.
Formation of UHP rocks.
Eclogite-facies HP to UHP metamorphic rocks are produced by subduction of crustal rocks to the lower crust to mantle depths for extreme metamorphism at the low thermal gradients of less than 10°C/km. All of these rocks occur at convergent plate margins, and UHP rocks only occur in collisional orogens. There is general agreement that most well-exposed and well-studied UHP terrains were produced by the burial of crustal rocks to mantle depths of >80 km during subduction. Continental margin subduction is well documented in a number of collisional orogens, such as the Dabie orogen where South China Block passive-margin sedimentary and volcanic sequences are preserved, in the Arabian continental margin beneath the Samail ophiolite (in the Al Hajar Mountains, Oman), and in the Australian margin presently subducting beneath the Banda Arc. Sediment subduction occurs beneath volcanoplutonic arcs around the world and is recognized in the compositions of arc lavas. Continental subduction may be underway beneath the Pamir. Subduction erosion also occurs beneath volcanoplutonic arcs around the world, carrying continental rocks to mantle depths at least locally.
Exhumation of UHP rocks.
The specific processes by which UHP terrains were exhumed to Earth's surface appear to have been different in different locations.
If continental lithosphere is subducted because of its attachment to downgoing oceanic lithosphere, the downward slab pull force may exceed the strength of the slab at some time and location, and necking of the slab initiates. The positive buoyancy of the continental slab—in opposition principally to ridge push—can then drive exhumation of the subducting crust at a rate and mode determined by plate geometry and the rheology of the crustal materials. The Norwegian Western Gneiss Region is the archetype for this exhumation mode, which has been termed 'eduction' or subduction inversion.
If a plate undergoing subduction inversion begins to rotate in response to changing boundary conditions or body forces, the rotation may exhume UHP rocks toward crustal levels. This could occur if, for example, the plate is small enough that continental subduction markedly changes the orientation and magnitude of slab pull or if the plate is being consumed by more than one subduction zone pulling in different directions. Such a model has also been proposed for the UHP terrain in eastern Papua New Guinea, where rotation of the Woodlark microplate is causing a rift in the Woodlark Basin).
If a subducting plate consists of a weak buoyant layer atop a stronger negatively buoyant layer, the former will detach at the depth where the buoyancy force exceeds slab pull, and extrude upward as a semi-coherent sheet. This type of delamination and stacking was proposed to explain exhumation of UHP rocks in the Dora Maira massif in Piedmont, Italy, in the Dabie orogen, and in the Himalaya. In addition it was demonstrated with analogue experiments. This mechanism is different from flow in a subduction channel in that the exhuming sheet is strong and remains undeformed. A variant of this mechanism, in which the exhuming material undergoes folding, but not wholescale disruption, was suggested for the Dabie orogen,where exhumation-related stretching lineations and gradients in metamorphic pressure indicate rotation of the exhuming block;
The buoyancy of a microcontinent locally slows the rollback of and steepens the dip of subducting mafic lithosphere. If the mafic lithosphere on either side of the microcontinent continues to roll back, a buoyant portion of the microcontinent may detach, allowing the retarded portion of the mafic slab to roll quickly back, making room for the UHP continental crust to exhume and driving back-arc extension. This model was developed to explain repeated cycles of subduction and exhumation documented in the Aegean and Calabria–Apennine orogens. UHP exhumation by slab rollback has not yet been extensively explored numerically, but it has been reproduced in numerical experiments of Apennine-style collisions.
If continental material is subducted within a confined channel, the material tends to undergo circulation driven by tractions along the base of the channel and the relative buoyancy of rocks inside the channel; the flow can be complex, generating nappe-like or chaotically mixed bodies. The material within the channel can be exhumed if:
Buoyancy alone is unlikely to drive exhumation of UHP rocks to Earth's surface, except in oceanic subduction zones. Arrest and spreading of UHP rocks at the Moho (if the overlying plate is continental) is likely unless other forces are available to force the UHP rocks upward. Some UHP terrains might be coalesced material derived from subduction erosion. This model was suggested to explain the North Qaidam UHP terrain in western China. Even subducted sediment may rise as diapirs from the subducting plate and accumulate to form UHP terrains.
Studies of numerical geodynamics suggest that both subducted sediment and crystalline rocks may rise through the mantle wedge diapirically to form UHP terranes. Diapiric rise of a much larger subducted continental body has been invoked to explain the exhumation of the Papua New Guinea UHP terrain. This mechanism was alo used to explain the exhumation of UHP rocks in Greenland. However, the mantle wedge above continental subduction zones is cold like cratons, which do not allow for diapirically ascending of the crustal materials. Foundering of the gravitationally unstable portions of continental lithosphere locally carries quartzofeldspathic rocks into the mantle and may be ongoing beneath the Pamir.


Saugh Hill Grits

The Saugh Hill Grits is a geologic formation in Scotland. It preserves fossils dating back to the Silurian period.


Appanoose Formation

The Appanoose Formation is a geologic formation in Missouri. It preserves fossils dating back to the Carboniferous period.


Oberhonsel Formation

The Oberhonsel Formation is a geologic formation in Germany. It preserves fossils dating back to the Devonian period.