Organic geochemistry

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Organic geochemistry is the study of the impacts and processes that organisms have had on the Earth. It is mainly concerned with the composition and mode of origin of organic matter in rocks and in bodies of water. [1] The study of organic geochemistry is traced to the work of Alfred E. Treibs, "the father of organic geochemistry." [2] Treibs first isolated metalloporphyrins from petroleum. This discovery established the biological origin of petroleum, which was previously poorly understood. [3] Metalloporphyrins in general are highly stable organic compounds, and the detailed structures of the extracted derivatives made clear that they originated from chlorophyll.

Contents

Applications

Energy

Petroleum

Carbon cycle diagram Carbon cycle-cute diagram.jpeg
Carbon cycle diagram

The relationship between the occurrence of organic compounds in sedimentary deposits and petroleum deposits has long been of interest. [4] Studies of ancient sediments and rock provide insights into the origins and sources of oil and petroleum, as well as the biochemical antecedents of life. Oil spills in particular have been of interest to geochemists in regards to the impact of petroleum and oil on the current geological environment. Following the Exxon Valdez Oil Spill, organic geochemistry knowledge on oil-spill chemistry bloomed with the analyses of samples from the spill. [5]

Geochemists study petroleum-inclusions in geological samples to compare present-day fluid-inclusions to dated samples. This analysis provides insight into the age of the petroleum samples and the surrounding rock. Spectrographic, optical, destructive, and nondestructive methods are used to analyze samples via mass spectrometry or Raman spectroscopy. The discovered differences in samples, such as oil-to-gas ratio or viscosity are typically attributed to the rock source of the sample. Other characteristics typically noted are pressure/volume/temperature properties, sample texture, and sample composition. Complications in analysis arise when the source rock is near or in a water source. [6]

Carbon-13 Placement in Isotope Chart where N is number of neutrons and Z is atomic number Carbon-13.svg
Carbon-13 Placement in Isotope Chart where N is number of neutrons and Z is atomic number

Petroleum is also studied via carbon isotope analysis. Carbon isotopes provide insight into the Earth's carbon cycle and geological processes. Geochemists are able to discern the composition of petroleum deposits by examining the ratio of carbon isotopes and comparing this ratio to known values for carbon based structures of which the petroleum could be composed. [7]

Coal

Vast knowledge about coal has been attained since the inception of its use as an energy source. However, modern geochemists are still studying how plant material changes into coal. They have determined coalification results from a selective degradation of plant materials, while other plant material is preserved. Coal macromolecules are usually made up of these degradation-resistant biopolymers contained in algae, spores, and wood. Geochemists have unraveled the mysteries behind coal formation by comparing properties of the biopolymers to properties found in existing coal macromolecules. The analytical methods of Carbon NMR and gas chromatography-mass spectrometry (GC-MS) combined with flash pyrolysis has greatly enhanced the ability of organic geochemists to analyse the minute structural units of coal. [8]

Example of isochron dating diagram and analysis Isochron.jpg
Example of isochron dating diagram and analysis

Further knowledge into the age of coal sediments has been attained via isochron dating of uranium in the coalified samples. Examination of the parent to daughter ratio of uranium isotopes has led to the dating of select samples to the Late Cretaceous Period. [9]

Environmental

Modern organic geochemistry includes studies of recent sediments to understand the carbon cycle, climate change, and ocean processes. In connection with petroleum studies, petroleum-focused geochemists also examine the impact of petroleum on the geological environment. [10] Geochemistry also examines other pollutants in geological systems, such as metabolites formed from the degradation of hydrocarbons. Organic geochemistry analytical techniques, such as GC-MS, allow chemists to determine the intricate effects of organic metabolites and human-derived waste products on the geological environment. [11] Of specific concern are the human-derived pollutants stemming from agricultural work. The use of animal manure, in combination with general municipal and sewage waste management, has changed many physical properties of the agricultural soil involved and the surrounding soils. [12]

Organic geochemistry is also relevant to aqueous environments. Pollutants, their metabolites, and how both enter bodies of water are of particular importance in the field. This organic matter can also be derived from geological processes in or near bodies of water, similarly influencing nearby lifeforms and protein production. Fluorescence spectroscopy has been introduced as a technique to examine organic matter in bodies of water, as dissolved organic matter is typically fluorescent. [13]

Winds disperse vast quantities of dust (red), sea salt (blue), sulphate (white) and black and organic carbon (green) around the world.

The study of organic geochemistry also extends to the atmosphere. Particularly, geochemists in this field study the makeup of insoluble material in the lower atmosphere. They have defined certain consequences of organic aerosols including physiological toxicity, direct and indirect climate forcing, smog, rain acidification, and incorporation into the natural carbon cycle. [14]

Further reading

Related Research Articles

<span class="mw-page-title-main">Kerogen</span> Solid organic matter in sedimentary rocks

Kerogen is solid, insoluble organic matter in sedimentary rocks. It consists of a variety of organic materials, including dead plants, algae, and other microorganisms, that have been compressed and heated by geological processes. All the kerogen on earth is estimated to contain 1016 tons of carbon. This makes it the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold.

Isotope geochemistry is an aspect of geology based upon the study of natural variations in the relative abundances of isotopes of various elements. Variations in isotopic abundance are measured by isotope-ratio mass spectrometry, and can reveal information about the ages and origins of rock, air or water bodies, or processes of mixing between them.

Petroleum geochemistry is a branch of geochemistry which deals specifically with petroleum and its origin, generation, and accumulation, as well as its extraction, refinement, and use. Petroleum, also known as crude oil, is a solid, liquid, and/or gaesous mix of hydrocarbons. These hydrocarbons are from the burial and metamorphosis of organic matter from millions of years ago; the organic matter is from marine animals, plants, and algae. Petroleum is extracted from the Earth, refined, and used as an energy source.

Pristane is a natural saturated terpenoid alkane obtained primarily from shark liver oil, from which its name is derived. It is also found in the stomach oil of birds in the order Procellariiformes and in mineral oil and some foods. Pristane and phytane are used in the fields of geology and environmental science as biomarkers to characterize origins and evolution of petroleum hydrocarbons and coal.

<span class="mw-page-title-main">Paleolimnology</span> Scientific study of ancient lakes and streams

Paleolimnology is a scientific sub-discipline closely related to both limnology and paleoecology. Paleolimnological studies focus on reconstructing the past environments of inland waters using the geologic record, especially with regard to events such as climatic change, eutrophication, acidification, and internal ontogenic processes.

<span class="mw-page-title-main">Cholestane</span> Chemical compound

Cholestane is a saturated tetracyclic triterpene. This 27-carbon biomarker is produced by diagenesis of cholesterol and is one of the most abundant biomarkers in the rock record. Presence of cholestane, its derivatives and related chemical compounds in environmental samples is commonly interpreted as an indicator of animal life and/or traces of O2, as animals are known for exclusively producing cholesterol, and thus has been used to draw evolutionary relationships between ancient organisms of unknown phylogenetic origin and modern metazoan taxa. Cholesterol is made in low abundance by other organisms (e.g., rhodophytes, land plants), but because these other organisms produce a variety of sterols it cannot be used as a conclusive indicator of any one taxon. It is often found in analysis of organic compounds in petroleum.

Phytane is the isoprenoid alkane formed when phytol, a chemical substituent of chlorophyll, loses its hydroxyl group. When phytol loses one carbon atom, it yields pristane. Other sources of phytane and pristane have also been proposed than phytol.

<span class="mw-page-title-main">Tarball (oil)</span> Blob of petroleum from the ocean

A tarball is a blob of petroleum which has been weathered after floating in the ocean. Tarballs are an aquatic pollutant in most environments, although they can occur naturally and as such are not always associated with oil spills.

<span class="mw-page-title-main">Abietane</span> Chemical compound

Abietane is a diterpene that forms the structural basis for a variety of natural chemical compounds such as abietic acid, carnosic acid, and ferruginol which are collectively known as abietanes or abietane diterpenes.

<span class="mw-page-title-main">Dinosterol</span> Chemical compound

Dinosterol (4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol) is a 4α-methyl sterol that is produced by several genera of dinoflagellates and is rarely found in other classes of protists. The steroidal alkane, dinosterane, is the 'molecular fossil' of dinosterol, meaning that dinosterane has the same carbon skeleton as dinosterol, but lacks dinosterol's hydroxyl group and olefin functionality. As such, dinosterane is often used as a biomarker to identify the presence of dinoflagelletes in sediments.

<span class="mw-page-title-main">John M. Hayes (scientist)</span> American oceanographer (1940–2017)

John Michael Hayes was an American oceanographer. He worked at Indiana University Bloomington, and Woods Hole Oceanographic Institution in Woods Hole, Massachusetts.

Crocetane, or 2,6,11,15-tetramethylhexadecane, is an isoprenoid hydrocarbon compound. Unlike its isomer phytane, crocetane has a tail-to-tail linked isoprenoid skeleton. Crocetane has been detected in modern sediments and geological records as a biomarker, often associated with anaerobic methane oxidation.

Bituminite is an autochthonous maceral that is a part of the liptinite group in lignite, that occurs in petroleum source rocks originating from organic matter such as algae which has undergone alteration or degradation from natural processes such as burial. It occurs as fine-grained groundmass, laminae or elongated structures that appear as veinlets within horizontal sections of lignite and bituminous coals, and also occurs in sedimentary rocks. Its occurrence in sedimentary rocks is typically found surrounding alginite, and parallel along bedding planes. Bituminite is not considered to be bitumen because its properties are different from most bitumens. It is described to have no definite shape or form when present in bedding and can be identified using different kinds of visible and fluorescent lights. There are three types of bituminite: type I, type II and type III, of which type I is the most common. The presence of bituminite in oil shales, other oil source rocks and some coals plays an important factor when determining potential petroleum-source rocks.

<span class="mw-page-title-main">24-Norcholestane</span> Chemical compound

24-Norcholestane, a steroid derivative, is used as a biomarker to constrain the source age of sediments and petroleum through the ratio between 24-norcholestane and 27-norcholestane, especially when used with other age diagnostic biomarkers, like oleanane. While the origins of this compound are still unknown, it is thought that they are derived from diatoms due to their identification in diatom rich sediments and environments. In addition, it was found that 24-norcholestane levels increased in correlation with diatom evolution. Another possible source of 24-norcholestane is from dinoflagellates, albeit to a much lower extent.

Ruth E. Blake is an American geochemist and environmental scientist. She is a professor at Yale University in earth & planetary sciences, environmental studies, and chemical & environmental engineering. Blake's work focuses on marine biogeochemical processes, paleoclimate, astrobiology, and stable isotope geochemistry.

<span class="mw-page-title-main">Lycopane</span> Chemical compound

Lycopane (C40H82; 2,6,10,14,19,23,27,31-octamethyldotriacontane), a 40 carbon alkane isoprenoid, is a widely present biomarker that is often found in anoxic settings. It has been identified in anoxically deposited lacustrine sediments (such as the Messel formation and the Condor oil shale deposit). It has been found in sulfidic and anoxic hypersaline environments (such as the Sdom Formation). It has been widely identified in modern marine sediments, including the Peru upwelling zone, the Black Sea, and the Cariaco Trench. It has been found only rarely in crude oils.

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Biphytane (or bisphytane) is a C40 isoprenoid produced from glycerol dialkyl glycerol tetraether (GDGT) degradation. As a common lipid membrane component, biphytane is widely used as a biomarker for archaea. In particular, given its association with sites of active anaerobic oxidation of methane (AOM), it is considered a biomarker of methanotrophic archaea. It has been found in both marine and terrestrial environments.

<span class="mw-page-title-main">Martin Schoell</span> German geochemist

Martin Schoell is a German geochemist. His research focuses on using stable isotopes to characterize the geochemistry of petroleum. Schoell is known for his work regarding CO2, sedimentary rocks, methane, natural gas, carbon isotopes, and acetate fermentation and how these factors enable identification of the origins of greenhouse gasses. Schoell was the founder, CEO and president of Gas Consult International, Inc., a private natural gas consulting firm, from 2001 to 2015. Schoell was awarded the Alfred Treibs Award by the Geochemical Society in 2008.

References

  1. ↑ Hobson, G. D. (1966-01-01). "The organic geochemistry of petroleum". Earth-Science Reviews. 2: 257–276. Bibcode:1966ESRv....2..257H. doi:10.1016/0012-8252(66)90031-6. ISSN   0012-8252.
  2. ↑ Kvenvolden, Keith A. (2006). "Organic geochemistry – A retrospective of its first 70 years". Organic Geochemistry. 37: 1–11. doi:10.1016/j.orggeochem.2005.09.001
  3. ↑ Treibs, A.E. (1936). "Chlorophyll- und Häminderivate in organischen Mineralstoffen". Angewandte Chemie. 49: 682–686. doi:10.1002/ange.19360493803
  4. ↑ Trask, P.D. "Origin and Environment of Source Sediments" The Gulf Publishing Co., 1932, Houston, TX
  5. ↑ A.E. Bence, K.A. Kvenvolden, M.C. Kennicutt, Organic geochemistry applied to environmental assessments of Prince William Sound, Alaska, after the Exxon Valdez oil spill—a review, Organic Geochemistry, Volume 24, Issue 1,1996, 7-42, https://doi.org/10.1016/0146-6380(96)00010-1.
  6. ↑ Herbert Volk, Simon C. George, Using Petroleum Inclusions to Trace Petroleum Systems – A Review, Organic Geochemistry, 2019 https://doi.org/10.1016/j.orggeochem.2019.01.012.
  7. ↑ Stahl W.J. (1979) Carbon Isotopes in Petroleum Geochemistry. In: Jäger E., Hunziker J.C. (eds) Lectures in Isotope Geology. Springer, Berlin, Heidelberg
  8. ↑ Patrick G Hatcher, David J Clifford,The organic geochemistry of coal: from plant materials to coal, Organic Geochemistry, Volume 27, Issues 5–6, 1997,251-274,https://doi.org/10.1016/S0146-6380(97)00051-X.
  9. ↑ Breger, I.A. (1974). The role of organic matter in the accumulation of uranium: the organic geochemistry of the coal-uranium association. International Atomic Energy Agency (IAEA): IAEA.
  10. ↑ A.E. Bence, K.A. Kvenvolden, M.C. Kennicutt, Organic geochemistry applied to environmental assessments of Prince William Sound, Alaska, after the Exxon Valdez oil spill—a review, Organic Geochemistry, Volume 24, Issue 1,1996, 7-42, https://doi.org/10.1016/0146-6380(96)00010-1.
  11. ↑ Hans H. Richnow, Richard Seifert, Jens Hefter, Matthias Kästner, Bernd Mahro, Walter Michaelis, Metabolites of xenobiotica and mineral oil constituents linked to macromolecular organic matter in polluted environments, Organic Geochemistry, Volume 22, Issues 3–5,1994, 671-IN10, https://doi.org/10.1016/0146-6380(94)90132-5.
  12. ↑ Khaleel, R., K. R. Reddy, and M. R. Overcash. 1981. Changes in Soil Physical Properties Due to Organic Waste Applications: A Review1. J. Environ. Qual. 10:133-141. doi:10.2134/jeq1981.00472425001000020002x
  13. ↑ Hudson, N. , Baker, A. and Reynolds, D. (2007), Fluorescence analysis of dissolved organic matter in natural, waste and polluted waters—a review. River Res. Applic., 23: 631-649. doi:10.1002/rra.1005
  14. ↑ Jacobson, M. C., H.‐C. Hansson, K. J. Noone, and R. J. Charlson (2000), Organic atmospheric aerosols: Review and state of the science, Rev. Geophys., 38(2), 267–294, doi:10.1029/1998RG000045.
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