Oil shale geology - AbsoluteAstronomy.com

Oil shale geology is a branch of geologic sciences

Geology

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

which studies the formation and composition of oil shale

Oil shale

Oil shale, an organic-rich fine-grained sedimentary rock, contains significant amounts of kerogen from which liquid hydrocarbons called shale oil can be produced...

s–fine-grained sedimentary rock

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

s containing significant amounts of kerogen

Kerogen

Kerogen is a mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks. It is insoluble in normal organic solvents because of the huge molecular weight of its component compounds. The soluble portion is known as bitumen. When heated to the right...

, and belonging to the group of sapropel

Sapropel

Sapropel is a term used in marine geology to describe dark-coloured sediments that are rich in organic matter...

fuel

Fuel

Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...

s. Oil shale formation takes place in a number of depositional settings and has considerable compositional variation. Oil shales can be classified by their composition (carbonate minerals such as calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

or detrital

Detrital

Detritus is a geological term used to describe particles of rock derived from pre-existing rock through processes of weathering and erosion. Detrital particles can consist of lithic fragments , or of monomineralic fragments...

minerals such as quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

and clays

Clay minerals

Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products and low...

) or by their depositional environment

Sedimentary depositional environment

In geology, sedimentary depositional environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock...

(large lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

s, shallow marine, and lagoon

Lagoon

A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...

/small lake settings). Much of the organic matter in oil shale is of algal

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

origin, but may also include remains of vascular land plants

Vascular plant

Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...

. Three major type of organic matter (maceral

Maceral

A maceral is a component of coal or oil shale. The term 'maceral' in reference to coal is analogous to the use of the term 'mineral' in reference to igneous or metamorphic rocks. Examples of macerals are inertinite, vitrinite and liptinite.- Inertinite :...

s) in oil shale are telalginite

Telalginite

Telalginite is a structured organic matter in sapropel, composed of large discretely occurring colonial or thick-walled unicellular algae such as Botryococcus, Tasmanites and Gloeocapsomorpha prisca. Telalginite is present in large algal bodies. It fluoresce brightly in shades of yellow under...

, lamalginite

Lamalginite

Lamalginite is a structured organic matter in sapropel, composed of thin-walled colonial or unicellular algae that occur as distinct laminae, cryptically interbedded with mineral matter. It displays few or no recognisable biologic structures. Lamalginite fluoresce brightly in shades of yellow...

, and bituminite. Some oil-shale deposits also contain metals which include vanadium

Vanadium

Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...

, zinc

Zinc

Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

, copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

, uranium

Uranium

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

.

Most oil shale deposits were formed during Middle Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

, Early and Middle Ordovician

Ordovician

The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...

, Late Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

, Late Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

, and Paleogene

Paleogene

The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...

times through burial by sedimentary loading on top of the algal swamp deposits, resulting in conversion of the organic matter to kerogen by diagenetic

Diagenesis

In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration and metamorphism. These changes happen at relatively low temperatures and pressures...

processes. The largest deposits are found in the remains of large lakes such as the deposits of the Green River Formation

Green River Formation

The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in winter. Each pair of layers is called a varve and...

of Wyoming and Utah, USA. Oil-shale deposits formed in the shallow seas of continental shelves generally are much thinner than large lake basin deposits.

Classification and varieties

There are varying classifications of oil shales depending on their mineral content, type of kerogen, age, depositional history, and organisms from which they are derived. The age of the oil shale deposits ranges from Cambrian

Cambrian

to Tertiary

Tertiary

The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...

age. Lithologies

Lithology

The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition. It may be either a detailed description of these characteristics or be a summary of...

range from shale

Shale

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

s to marl

Marl

Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...

and carbonate rock

Carbonate rock

Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite and dolostone, which is composed of the mineral dolomite .Calcite can be either dissolved by groundwater or precipitated by...

s, all of which form a mixture of tightly bound organic and inorganic materials.

Oil shales have been divided into three categories based on mineral composition – carbonate

Carbonate

In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....

-rich shale, siliceous

Silicon dioxide

The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

shale and cannel shale

Cannel coal

Cannel coal, also known as candle coal, is a type of coal, also classified as terrestrial type oil shale, with a large amount of hydrogen, which burns easily with a bright light and leaves little ash....

. Carbonate-rich shales derive their name from the large amount of carbonate minerals such as calcite

Calcite

and dolomite

Dolomite

Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....

. As many as twenty carbonate minerals have been found in oil shale, the majority of which are considered authigenic

Authigenic

An authigenic mineral or sedimentary rock deposit is one that was generated where it is found or observed. Authigenic sedimentary minerals form during sedimentation by precipitation or recrystallization instead of being transported from elsewhere by water or wind. Authigenic sediments are the main...

or diagentic

Diagenesis

. Carbonate-rich oil shales, particularly that of lacustrine

Lake

-sourced deposits, have usually the organic-rich layers sandwiched between carbonate-rich layers. These deposits are hard formations that are resistant to weathering and they are difficult to process using ex-situ methods. Siliceous oil shales are usually dark brown or black shales. They are not rich in carbonates but rather in siliceous minerals such as quartz

Quartz

, feldspar

Feldspar

Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....

, clay, chert

Chert

Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...

and opal

Opal

Opal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most...

. Siliceous shales are not as hard and weather-resistant as carbonate-rich shales, and may be better suited for extraction via ex-situ methods. Cannel shales are usually dark brown or black shales, which consist of organic matter that completely encloses other mineral grains. They are suitable for extraction via ex-situ methods.

Another classification according to the type of kerogen, is based on the hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, and oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

content of oil shales' original organic matter. This classification is known as the "van Krevelen diagram". The most used classification of oil shales was developed between 1987 and 1991 by Adrian C. Hutton of the University of Wollongong

University of Wollongong

The University of Wollongong is a public university located in the coastal city of Wollongong, New South Wales, Australia, approximately 80 kilometres south of Sydney...

, adapting petrographic

Petrography

Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. Petrographic descriptions start with the field notes at the...

terms from coal terminology. According to this classification, oil shales are designated as terrestrial, lacustrine

Lake

(lake-bottom-deposited), or marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

(ocean bottom-deposited), based on the environment where the initial biomass

Biomass

Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

was deposited. Hutton's classification scheme has proven useful in estimating the yield and composition of the extracted oil.

***Classification of oil shales by environment of deposition***
Terrestrial	Lacustrine	Marine
cannel coal	lamosite; torbanite	kukersite; tasmanite; marinite

Cannel coal

(also called candle coal) is a type of terrestrial shale, which is hydrogen-rich brown to black coal, sometimes with shaly texture, composed of resins, spores, wax

Wax

thumb|right|[[Cetyl palmitate]], a typical wax ester.Wax refers to a class of chemical compounds that are plastic near ambient temperatures. Characteristically, they melt above 45 °C to give a low viscosity liquid. Waxes are insoluble in water but soluble in organic, nonpolar solvents...

es, cutin

Cutin

Cutin is one of two waxy polymers that are the main components of the plant cuticle, which covers all aerial surfaces of plants. The other major cuticle polymer is cutan, which is much more readily preserved in the fossil record,...

aceous and corky materials derived from terrestrial

Terrestrial plant

A terrestrial plant is one that grows on land. Other types of plants are aquatic , epiphytic , lithophytes and aerial ....

vascular plants as well as varied amounts of vitrinite

Vitrinite

Vitrinite is one of the primary components of coals and most sedimentary kerogens. Vitrinite is a type of maceral, where "macerals" are organic components of coal analogous to the "minerals" of rocks. Vitrinite has a shiny appearance resembling glass . It is derived from the cell-wall material or...

and inertinite

Inertinite

Inertinite is oxidized organic material or fossilized charcoal. It is found as tiny flakes within sedimentary rocks. The presence of inertinite is significant in the geological record, as it signifies that wildfires occurred at the time that the host sediment was deposited. It is also an indication...

. Lacustrine shales consist of Lamosite

Lamosite

Lamosite is an olive-gray brown or dark gray to brownish black lacustrine-type oil shale, in which the chief organic constituent is lamalginite derived from lacustrine planktonic algae. In minor scale it also consists of vitrinite, inertinite, telalginite, and bitumen.Lamosite deposits are the most...

and Torbanite

Torbanite

Torbanite, also known as boghead coal, is a variety of fine-grained black oil shale. It usually occurs as lenticular masses, often associated with deposits of Permian coals. Torbanite is classified as lacustrine type oil shale....

. Lamosite is a pale-brown and grayish-brown to dark-gray to black oil shale whose chief organic constituent is lamalginite derived from lacustrine planktonic

Plankton

Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

algae. Torbanite, named after Torbane Hill in Scotland, is a black oil shale whose organic matter is telalginite derived from lipid-rich Botryococcus and related algal forms. Marine shales consist of three varieties, namely Kukersite

Kukersite

Kukersite is a marine type oil shale of Ordovician age, found in the Baltic Oil Shale Basin in Estonia and North-West Russia. It was named after Kukruse settlement in Estonia in 1917 by Russian paleontologist Mikhail Zalessky....

, Tasmanite

Tasmanite

Tasmanite is a rock type almost entirely consisting of the prasinophyte alga Tasmanites. It is commonly associated with high-latitude, nutrient-rich, marginal marine settings find in Tasmania. It is classified as marine type oil shale. It is found in many oil-prone source rocks and, when present,...

, and Marinite

Marinite

Marinite is a gray to dark-gray or black oil shale of marine origin in which the chief organic components are lamalginite and bituminite derived from marine phytoplankton, with varied admixtures of bitumen, telalginite and vitrinite. Marinite deposits are the most abundant oil-shale deposits...

. Kukersite, named after Kukruse in Estonia, is a light-brown marine oil shale whose principal organic component is telalginite derived from the green alga, Gloeocapsomorpha prisca. Tasmanite, named after Tasmania

Tasmania

Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...

, is a brown to black oil shale whose organic matter consists of telalginite derived chiefly from unicellular tasmanitid algae of marine origin. Marinite is a gray to dark-gray to black oil shale of marine origin in which the chief organic components are lamalginite and bituminite derived from marine phytoplankton

Phytoplankton

Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...

with varied admixtures of bitumen, telalginite, and vitrinite.

Composition

As a sapropel fuel, oil shale differs from humus fuels in its lower content of organic matter. The organic matter has an atomic ratio of hydrogen to carbon of about 1.5 – approximately the same as that of crude oil and four to five times higher than coal

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

s. The organic matter in oil shales forms a complex macromolecular structure which is insoluble in common organic solvents. It is mixed with varied amounts of mineral matter. For commercial grades of oil shale, the ratio of organic matter to mineral matter is about 0.75:5 to 1.5:5.

The organic portion of oil shale consists largely of prebitumen bituminous groundmass, such as remains of algae, spore

Spore

In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...

s, pollen

Pollen

Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

, plant cuticle

Plant cuticle

Plant cuticles are a protective waxy covering produced only by the epidermal cells of leaves, young shoots and all other aerial plant organs without periderm...

s and corky fragments of herbaceous

Herbaceous

A herbaceous plant is a plant that has leaves and stems that die down at the end of the growing season to the soil level. They have no persistent woody stem above ground...

and woody plants, and cellular debris from other lacustrine, marine, and land plants. While terrestrial oil shales contain resins, spores, waxy cuticles, and corky tissues of roots and stems of vascular terrestrial plants, lacustrine oil shales include lipid

Lipid

Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

-rich organic matter derived from algae. Marine oil shales are composed of marine algae, acritarch

Acritarch

Acritarchs are small organic fossils, present from approximately to the present. Their diversity reflects major ecological events such as the appearance of predation and the Cambrian explosion.-Definition:In general, any small, non-acid soluble Acritarchs are small organic fossils, present from...

s, and marine dinoflagellate

Dinoflagellate

The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...

s. Organic matter in oil shale also contains organic sulfur

Sulfur

Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

(about 1.8 % on average) and a lower proportion of nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

.

Three major types of organic matter (maceral

Maceral

s) in oil shale are telalginite, lamalginite, and bituminite. Telalginite is defined as structured organic matter composed of large colonial or thick-walled unicellular algae such as Botryococcus and Tasmanites. Lamalginite includes thin-walled colonial or unicellular algae that occur as distinct laminae, but display few or no recognizable biologic structures. Under the microscope, telalginite and lamalginite are easily recognized by their bright shades of yellow under ultraviolet/blue fluorescent light. Bituminite is largely amorphous, lacks recognizable biologic structures, and displays relatively low fluorescence

Fluorescence

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...

under the microscope. Other organic constituents include vitrinite

Vitrinite

and inertinite

Inertinite

, which are macerals derived from the humic matter of land plants. These macerals are usually found in relatively small amounts in most oil shales.

Mineral matter in oil shale contains fine-grained silicate

Silicate

A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...

and carbonate minerals

Carbonate minerals

Carbonate minerals are those minerals containing the carbonate ion: CO32-.-Anhydrous carbonates:*Calcite group: Trigonal**Calcite CaCO3**Gaspeite CO3**Magnesite MgCO3**Otavite CdCO3**Rhodochrosite MnCO3**Siderite FeCO3**Smithsonite ZnCO3...

such as calcite

Calcite

, dolomite

Dolomite

Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....

, siderite

Siderite

Siderite is a mineral composed of iron carbonate FeCO3. It takes its name from the Greek word σίδηρος sideros, “iron”. It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus...

, quartz

Quartz

, rutile

Rutile

Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...

, orthoclase

Orthoclase

Orthoclase is an important tectosilicate mineral which forms igneous rock. The name is from the Greek for "straight fracture," because its two cleavage planes are at right angles to each other. Alternate names are alkali feldspar and potassium feldspar...

, albite

Albite

Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence...

, anorthite

Anorthite

Anorthite is the calcium endmember of plagioclase feldspar. Plagioclase is an abundant mineral in the Earth's crust. The formula of pure anorthite is CaAl2Si2O8.-Mineralogy :...

, muscovite

Muscovite

Muscovite is a phyllosilicate mineral of aluminium and potassium with formula KAl22, or 236. It has a highly-perfect basal cleavage yielding remarkably-thin laminæ which are often highly elastic...

, amphipole

Amphipole

Amphipoles, in antiquity, were archons, or chief magistrates, of the city of Syracuse. They were first established by Timoleon, after his expulsion of Dionysius the Elder, tyrant of Syracuse. They governed Syracuse for a space of three hundred years; and Diodorus Siculus assures us, they subsisted...

, marcasite

Marcasite

The mineral marcasite, sometimes called white iron pyrite, is iron sulfide with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both structures do have in common that they contain the disulfide...

, limonite

Limonite

Limonite is an ore consisting in a mixture of hydrated iron oxide-hydroxide of varying composition. The generic formula is frequently written as FeO·nH2O, although this is not entirely accurate as limonite often contains a varying amount of oxide compared to hydroxide.Together with hematite, it has...

, gypsum

Gypsum

Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...

, nahcolite

Nahcolite

Nahcolite is a soft, colourless or white carbonate mineral with the composition of sodium bicarbonate also called thermokalite. It crystallizes in the monoclinic system....

, dawsonite

Dawsonite

Dawsonite is a mineral composed of sodium aluminium carbonate hydroxide, chemical formula NaAlCO32. It crystallizes in the orthorhombic crystal system. It is not mined for ore. It was discovered in 1874 during the construction of the Redpath Museum in a feldspathic dike on the campus of McGill...

and alum

Alum

Alum is both a specific chemical compound and a class of chemical compounds. The specific compound is the hydrated potassium aluminium sulfate with the formula KAl2.12H2O. The wider class of compounds known as alums have the related empirical formula, AB2.12H2O.-Chemical properties:Alums are...

. Some oil-shale deposits also contain metals such as vanadium

Vanadium

, zinc

Zinc

, copper

Copper

, uranium

Uranium

among others.

***General composition of oil shales***
Inorganic matrix	Bitumens	Kerogens
quartz Quartz Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,... ; feldspar Feldspar Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust.... s; clay Clay Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals... s (mainly illite Illite Illite is a non-expanding, clay-sized, micaceous mineral. Illite is a phyllosilicate or layered alumino-silicate. Its structure is constituted by the repetition of tetrahedron – octahedron – tetrahedron layers. The interlayer space is mainly occupied by poorly hydrated potassium cations... and chlorite Chlorite The chlorite ion is ClO2−. A chlorite is a compound that contains this group,with chlorine in oxidation state +3. Chlorites are also known as salts of chlorous acid.-Oxidation states:... ; carbonates (calcite Calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:... and dolomite Dolomite Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone.... ); pyrite Pyrite The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold... and others	soluble in CS₂ Carbon disulfide Carbon disulfide is a colorless volatile liquid with the formula CS2. The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non-polar solvent...	insoluble in CS₂; containing uranium Uranium Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons... , iron Iron Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust... , vanadium Vanadium Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature... , nickel Nickel Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile... , molybdenum Molybdenum Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores... , etc.

Formation

Most oil shale formations took place during mid-Cambrian

Cambrian

, early and middle Ordovician

Ordovician

, late Devonian

Devonian

, late Jurassic

Jurassic

and Paleogene

Paleogene

The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...

periods. These were formed by the deposition of organic matter in a variety of depositional environments

Sedimentary depositional environment

including freshwater to highly saline lakes

Salt lake

A salt lake or saline lake is a landlocked body of water which has a concentration of salts and other dissolved minerals significantly higher than most lakes . In some cases, salt lakes have a higher concentration of salt than sea water, but such lakes would also be termed hypersaline lakes...

, epicontinental marine basins

Epeiric Sea

An epeiric sea is a shallow sea that extends over part of a continent.Epeiric seas are usually associated with the marine transgressions of the geologic past, which have variously been due to either global eustatic sea level changes, local tectonic deformation, or both, and are occasionally...

and subtidal shelves and were restricted to estuarine areas

Estuary

An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

such as oxbow lake

Oxbow lake

An oxbow lake is a U-shaped body of water formed when a wide meander from the main stem of a river is cut off to create a lake. This landform is called an oxbow lake for the distinctive curved shape, named after part of a yoke for oxen. In Australia, an oxbow lake is called a billabong, derived...

s, peat bogs, limnic and coastal swamp

Swamp

A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...

s, and muskeg

Muskeg

Muskeg is an acidic soil type common in Arctic and boreal areas, although it is found in other northern climates as well. Muskeg is approximately synonymous with bogland but muskeg is the standard term in Western Canada and Alaska, while 'bog' is common elsewhere. The term is of Cree origin, maskek...

s. When plants die in such an anaerobic aquatic environment, low oxygen levels prevent their complete bacterial decay.

For undecayed organic matter to be preserved and to form oil shale, the environment must remain uniform for prolonged periods of time in order to build up sufficiently thick sequences of algal matter. Eventually, the algal swamp or other restricted environment is disrupted and oil shale accumulation ceases. Burial by sedimentary loading on top of the algal swamp deposits converts the organic matter to kerogen by the following normal diagenetic processes:

Compaction due to sediment loading on the coal, leading to compression of the organic matter.
With ongoing heat and compaction, removal of moisture in the peat
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...

and from the intracellular
Intracellular
Not to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...

structure of fossilized plants, and removal of molecular water.
Methanogenesis
Methanogenesis
Methanogenesis or biomethanation is the formation of methane by microbes known as methanogens. Organisms capable of producing methane have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with...

—similar to treating wood in a pressure cooker— results in methane being produced, removing hydrogen, some carbon, and some further oxygen.
Dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...

, which removes hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...

groups from the cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....

and other plant molecules, resulting in the production of hydrogen-reduced
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

coals or oil shales.

Though similar in their formation process, oil shales differ from coals in several distinct ways. The precursors of the organic matter in oil shale and coal differ in a sense that oil shale is of algal origin, but may also include remains of vascular land plants that more commonly compose much of the organic matter in coal. The origin of some of the organic matter in oil shale is obscure because of the lack of recognizable biologic structures that would help identify the precursor organisms. Such materials may be of bacterial origin or the product of bacterial degradation of algae or other organic matter.

Lower temperature and pressure during the diagenesis process

Diagenesis

compared to other modes of hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

generation result in a lower maturation

Maturation

Maturation could refer to any of the following:* Fetal development* Developmental biology* Emotional development* Or physical maturation of any biological life form - see individual articles for maturation of different life forms....

level of oil shale. Continuous burial and further heating and pressure could result in the production of oil and gas from the oil shale source rock

Source rock

In petroleum geology, source rock refers to rocks from which hydrocarbons have been generated or are capable of being generated. They form one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been deposited in a variety of environments including...

. The largest deposits are found in the remains of large lakes such as the deposits of the Green River Formation

Green River Formation

of Wyoming and Utah, USA. Large lake oil shale basins are typically found in areas of block faulting or crustal warping due to mountain building

Orogeny

Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...

. Deposits such as the Green River may be as much as 2000 feet (609.6 m) and yield up to 40 gallons of oil for each ton (166 l/t) of shale.

Oil-shale deposits formed in the shallow seas of continental shelves generally are much thinner than large lake basin deposits. These are typically a few meters thick and are spread over very large areas, extending up to thousands of square kilometers. Of the three lithologic types of oil shales, siliceous oil shales are most commonly found in such environment. These oil shales are not as organically rich as lake-deposited oil shales, and generally do not contain more than 30 gallons per ton of oil shale. Oil shales deposited in lagoonal or small lake environments are rarely extensive and are often associated with coal-bearing rocks. These oil shales can have high yields– as much as 40 gallons per ton (166 l/t) of oil shale. However, due to their small areal extent, they are considered unlikely candidates for commercial exploitation.

***Properties of some oil shales deposits***.
Country	Location	Type	Age	Organic carbon (%)	Oil yield (%)	Oil conversion ratio (%)
Australia Australia Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...	Glen Davis Glen Davis, New South Wales Glen Davis is a village in the Central Tablelands of New South Wales, Australia. The village is located in the local government area of the City of Lithgow. It is located 250 km north-west of Sydney and approximately 80 kilometres north of Lithgow... , New South Wales New South Wales New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...	torbanite	Permian Permian The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...	40	31	66
	Tasmania Tasmania Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...	tasmanite	Permian	81	75	78
Brazil Brazil Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...	Irati Irati Irati is a town in State of Paraná, Brazil with an estimated population 54,805 in 2006 based on the 2000 censusIrati sprang up in the 1890s as a railroad town along the São Paulo–Rio Grande do Sul railroad line...	marinite	Permian		7.4
	Paraíba Valley Paraíba Valley The Paraíba Valley is located in the eastern part of the state of São Paulo along the rodovia Presidente Dutra , between Rio De Janeiro and São Paulo....	lacustrine shales	Permian	13-16.5	6.8-11.5	45-59
Canada Canada Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...	Nova Scotia Nova Scotia Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...	torbanite; lamosite	Permian	8-26	3.6-19	40-60
China China Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...	Fushun Fushun Fushun is a city in Liaoning, China, about 45 km east from Shenyang, with a population about 2,138 090 inhabitants at the 2010 census and an area of 11,271 km2, including 713 km2 of the city proper. Fushun is situated on the Hun He . It was formerly called Fouchouen in French...	cannel coal; lacustrine shales	Eocene Eocene The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...	7.9	3	33
Estonia Estonia Estonia , officially the Republic of Estonia , is a state in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia , and to the east by Lake Peipsi and the Russian Federation . Across the Baltic Sea lies...	Estonia Deposit	kukersite	Ordovician Ordovician The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...	77	22	66
France France The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...	Autun Autun Autun is a commune in the Saône-et-Loire department in Burgundy in eastern France. It was founded during the early Roman Empire as Augustodunum. Autun marks the easternmost extent of the Umayyad campaign in Europe.-Early history:... , St. Hilarie	torbanite	Permian	8-22	5-10	45-55
	Creveney Haute-Saône Haute-Saône is a French department of the Franche-Comté région, named after the Saône River.- History :The department was created in the early years of the French Revolution through the application of a law dated 22 December 1789, from part of the former province of Franche-Comté... , Severac		Toarcian Toarcian The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 183.0 Ma and 175.6 Ma...	5-10	4-5	60
South Africa South Africa The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...	Ermelo Ermelo, Mpumalanga Ermelo is the educational, industrial and commercial centre of the 7,750 km² Gert Sibande District Municipality in Mpumalanga province, Republic of South Africa. Mixed farming and anthracite, coal and torbanite mining take place here...	torbanite	Permian	44-52	18-35	34-60
Spain Spain Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...	Puertollano Puertollano Puertollano is an industrial city in province of Ciudad Real, Castile-La Mancha, Spain. It is situated on the AVE High Speed Train line linking Madrid and Seville . The city has a population of 51,842 .- Legend of the lie :...	lacustrine shale	Permian	26	18	57
Sweden Sweden Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....	Kvarntorp Kumla Municipality Kumla Municipality is a municipality in Örebro County in central Sweden. Its seat is located in the city of Kumla.The present municipality was formed during the latest nation-wide local government reform in Sweden, with the amalgamations taking place in 1966 and 1971.With 207 km² it is the...	marinite	Lower Paleozoic Paleozoic The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...	19	6	26
United Kingdom United Kingdom The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...	Scotland Scotland Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...	torbanite	Carboniferous Carboniferous The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...	12	8	56
United States United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...	Alaska Alaska Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...		Jurassic Jurassic The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...	25-55	0.4-0.5	28-57
	Green River Formation Green River Formation The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in winter. Each pair of layers is called a varve and... in Colorado Colorado Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains... , Wyoming Wyoming Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High... and Utah Utah Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...	lamosite	Eocene	11-16	9-13	70
	Mississippi Mississippi Mississippi is a U.S. state located in the Southern United States. Jackson is the state capital and largest city. The name of the state derives from the Mississippi River, which flows along its western boundary, whose name comes from the Ojibwe word misi-ziibi...	marinite	Devonian Devonian The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

Formations in the United States

The United States has two significant oil-shale deposits which are suited for commercial development due to their size, grade and location. The Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

Green River Formation

covers parts of Colorado

Colorado

Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...

, Wyoming

Wyoming

Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

and Utah

Utah

Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...

; the second significant deposit is Devonian

Devonian

oil shales in the eastern United States. In both places, there are sub-basins varying in volume and quality of the reserves. Oil shale in the Green River Formation is found in five sedimentary basins namely, Green River, Uinta, Piceance Creek, Sand Wash and Washakie. The first three have undergone some significant exploration and attempts to commercialize the oil shale reserves since the 1960s. The Green River Formation includes deposits from two large lakes which covered an area of over 65000 square kilometres (25,096.6 sq mi) during early to middle Eocene

Eocene

period. These lakes were separated by the Uinta

Uinta Mountains

The Uinta Mountains are a high chain of mountains in northeastern Utah and extreme northwestern Colorado in the United States. A subrange of the Rocky Mountains, they are unusual for being the highest range in the contiguous United States running east to west, and lie approximately east of Salt...

uplift and the Axial Basin anticline

Anticline

In structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...

. For significant periods during their 10 Ma life, the lakes became closed systems allowing many changes in size, salinity and sediment deposition. Oil shale is a result of abundant blue-green algae that thrived in the lakes.

The oil shale that underlies almost 750000 square kilometres (289,576.6 sq mi) in the eastern United States was formed in a marine depositional environment very different from the Green River Basins. These deposits have also undergone commercialization attempts; they are also resources for natural gas

Natural gas

Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

and have been mined for low-grade oil shale. These oil shales were formed during the Late Devonian

Devonian

and Early Mississippian periods. During this time, much of the eastern United States was covered by a large shallow sea. The oil shale is thought to have been the result of slow deposition of plankton

Plankton

ic algae. under anoxic conditions. In parts of the basin close to the shoreline, the organic mixture that helped form the oil shale contains organic-rich sediment from the rising Appalachian mountains

Appalachian Mountains

The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...

Formations in Brazil

Brazil has nine significant locations of oil shale deposits. The size, location and quality of oil shale deposits in the Paraiba Valley and the Irati Formation

Irati Formation

Irati Formation is the name of a geological formation of Brazil.It has previously been dated as Upper Permian using palynomorphs but is now dated as Lower Permian using zircon ages obtained from bentonite layers...

have attracted the most attention. These two contain an estimated 1.4 billion barrels of in-situ shale oil

Shale oil

Shale oil, known also as kerogen oil or oil-shale oil, is an unconventional oil produced from oil shale by pyrolysis, hydrogenation, or thermal dissolution. These processes convert the organic matter within the rock into synthetic oil and gas...

with total resources as much as more than three billion barrels. While the "Irati formation" deposit is the smaller of the two, containing an estimated 600 million barrels in-situ compared to 840 million in the Paraiba valley formation, the former is more economically viable.

The "Irati formation" consists of two oil shale beds separated by 12 metres (39.4 ft) of limestone and shale. The upper layer is thicker (9 metres (29.5 ft)) but the thinner lower bed (4 metres (13.1 ft)) is of greater value; the weight percent of shale oil yield is around 12 % for the lower layer as compared to 7 % for the upper one. The oil shale yield varies laterally, and may be as little as 7 % for the lower layer and 4 % for the upper layer. The formation is a very fine grained and laminated deposit ranging in color from dark gray to brown to black. While 60-70 % of the shale consists of clay minerals, the balance is made up of organic matter.

No consensus has been reached on the exact depositional nature of the Irati oil shale. One theory suggests that the organic material in the Irati oil shale originated from algae deposited in a lacustrine environment with salinity varying from that of freshwater

Freshwater

Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...

to brackish water

Brackish water

Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...

. Other theory suggests that the organic sediment may have been deposited in a shallow, partially restricted marine environment. Hutton's classification describes it as a marine source oil shale.

Formation in Estonia

The kukersite oil shale of Ordovician

Ordovician

age in Estonia

Estonia

Estonia , officially the Republic of Estonia , is a state in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia , and to the east by Lake Peipsi and the Russian Federation . Across the Baltic Sea lies...

is part of the Baltic oil shale basin and was deposited in shallow marine basins. The deposit is one of the world’s highest-grade deposits with more than 40 % organic content and 66 % conversion ratio into shale oil and gas. The oil shale is located in a single calcareous layer 2.5-3 meters in thickness and is buried at depths from 7 to 100 m. The total area of the basin is about 3,000 km². Oil yield from Kukersite is 30 to 47 %. Most of the organic matter is derived from the fossil green alga, Gloeocapsomorpha prisca, which has affinities to the modern cyanobacterium, Entophysalis major, an extant species that forms algal mat

Algal mat

An algal mat is a layer of usually filamentous algae on marine or fresh water soft bottoms. It may be considered one of many types of microbial mats. Algae and cyanobacteria are ubiquitous, often forming within the water column and settling to the bottom. In shallow environments, they are often...

s in inter-tidal to very shallow subtidal waters. Matrix

Matrix (geology)

The matrix or groundmass of rock is the finer grained mass of material in which larger grains, crystals or clasts are embedded.The matrix of an igneous rock consists of finer grained, often microscopic, crystals in which larger crystals are embedded. This porphyritic texture is indicative of...

minerals include low-magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

calcite, dolomite, and siliciclastic minerals

Siliciclastic

Siliciclastic rocks are clastic noncarbonate sedimentary rocks that are almost exclusively silica-bearing, either as forms of quartz or other silicate minerals. All siliciclastic rocks are formed by inorganic processes, or deposited through some mechanical process, such as stream deposits that are...

. It is not enriched in heavy metals.

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