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Organic Petrology


Article Thumbnail Image The 66th meeting of the International Committee for Coal and Organic Petrology (ICCP) will take place in Kolkata, India from 20-27 September, 2014. Meeting venue will be Science City, Kolkata. The meeting is organised and hosted by Dr. Ashok K. Singh, Principal Scientist and Head of the group...
Sunday, February 23, 2014  Type: Conference

Article Thumbnail Image The 31st Annual Meeting of the Society for Organic Petrology (TSOP) will be held in Sydney, Australia from September 27 to October 3, 2014. This represents the 10th anniversary of the successful and highly acclaimed Sydney meeting held in 2004, and again provides an opportunity to showcase...
Sunday, February 23, 2014  Type: Conference

Article Thumbnail Image So as to better understand how the gas generation potential of coal changes with increasing rank, same-seam samples of bituminous coal from the Illinois Basin that were naturally matured to varying degrees by the intrusion of an igneous dike were subjected to hydrous pyrolysis (HP) conditions of 360...
Monday, January 13, 2014  Type: Outside Publication

Article Thumbnail Image We used Rock-Eval pyrolysis and vitrinite reflectance to examine the petroleum source potential of rock samples from the Sheep Creek 1 well in the Susitna basin of south-central Alaska. The results show that Miocene nonmarine coal, carbonaceous shale, and mudstone are potential sources of...
Thursday, January 09, 2014  Type: Publication

Article Thumbnail Image The Wind River Basin is a large Laramide (Late Cretaceous through Eocene) structural and sedimentary basin that encompasses about 7,400 square miles in central Wyoming. The basin is bounded by the Washakie Range and Owl Creek and southern Bighorn Mountains on the north, the Casper arch on...
Monday, February 04, 2013  Type: Publication

Article Thumbnail Image The Bighorn Basin is a large Laramide (Late Cretaceous through Eocene) structural and sedimentary basin that encompasses about 10,400 square miles in north-central Wyoming and south-central Montana. The purpose of this report is to present new vitrinite reflectance data collected from Cretaceous...
Wednesday, December 19, 2012  Type: Publication

Article Thumbnail Image The Organic Petrology Laboratory (OPL) of the U.S. Geological Survey (USGS) Eastern Energy Resources Science Center in Reston, Virginia, contains several thousand processed coal sample materials that were loosely organized in laboratory drawers for the past several decades...
Thursday, September 27, 2012  Type: Publication

Article Thumbnail Image The Energy Resources Program's new Photomicrograph Atlas provides 1) Education – A basic tutorial in the nomenclature of organic materials as they occur in sedimentary rocks such as coal and shale 2) Classification – Information on the taxonomies used by various groups and organizations 3)...
Wednesday, August 29, 2012  Type: Site News

Article Thumbnail Image Electron beam microanalysis of coal samples in U.S. Geological Survey (USGS) labs confirms that As is the most abundant minor constituent in Fe disulfides in coal and that Se, Ni, and other minor constituents are present less commonly and at lower concentrations than those for As.
Tuesday, May 01, 2012  Type: Outside Publication

Article Thumbnail Image Geochemistry is a constantly expanding science. More and more, scientists are employing geochemical tools to help answer questions about the Earth and earth system processes. Scientists may assume that the responsibility of examining and assessing the quality of the geochemical data they generate is...
Tuesday, September 13, 2011  Type: Publication
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Photomicrograph of coal from the Trinity Group in Bradley County, Arkansas.
Photo: Photomicrograph of coal from
the Trinity Group in Bradley County,
Arkansas. The image contains a
mix of huminite, liptinite and
inertinite macerals.

Organic petrology is the comprehensive investigation of organic materials occurring in sedimentary rocks; in particular, coal and petroleum source rocks. Organic petrology also includes study of the utilization products of coal and petroleum source rocks, for instance, coke, fly ash, and liquefaction residue. Studies of the origin, occurrence, structure, and history of sedimentary organic matter typically are pursued through techniques of optical microscopy. Complementary geochemical methods of investigation include pyrolysis, gas and liquid chromatography, solvent extraction, and mass spectroscopy.

Organic petrology research is used to understand and predict the behavior of coal in utilization and/or thermal maturity of petroleum source rocks, and to understand and predict hydrocarbon generation. Other important themes of organic petrology research include the impact of coal composition on coalbed gas generation and storage. Research in the USGS Organic Petrology Laboratory at the National Center in Reston includes all of these themes.

Paul Hackley
Project Chief


Coal Petrology
Coal Petrology

Coal Petrology

The individual organic components of coal are termed “macerals,” similar to “minerals” in rock. Macerals are divided into three broad groups: vitrinite, inertinite, and liptinite. Vitrinites are the coalified remains of humic plant substances, primarily lignin and cellulose. In most cases, inertinites consist of the same original plant material as vitrinite but have been altered by charring or oxidation prior to coalification... [+]

In most cases, inertinites consist of the same original plant material as vitrinite but have been altered by charring or oxidation prior to coalification. Inertinites can also include fungal bodies. Liptinites are the remains of hydrogen-rich plant materials such as cutins, resins, fats, waxes, andsporopollenin (the outer cell walls of spores and pollen). The maceral content of coal is determined with a reflected light microscope (light is reflected from the sample towards the analyst) at magnifications of about 500x, using tungsten filament and gas arc light sources. Photomicrographs of USGS coal samples are contained in the organic petrology photomicrograph atlas.

Stanton, R.W., Warwick, P.D., and Swanson, S.M., 2005, Tar yields from low-temperature carbonization of coal facies from the Powder River Basin, Wyoming, USA: International Journal of Coal Geology, v. 63, p. 13-26.

Hackley, P.C., Warwick, P.D., and Gonzáles, E., 2005, Petrology, mineralogy, and geochemistry of mined coals, western Venezuela: International Journal of Coal Geology, v. 63, p. 68-97.

Maturation Studies
Maturation Studies

Maturation Studies

Measurement of the reflectance of the maceral vitrinite is a commonly performed analysis that is used to establish the rank of coals or the thermal maturity of petroleum source rocks. A well-established correlation exists between vitrinite reflectance and rank due to increases in the refractive and adsorption indices of vitrinite with increasing aromatization. Coal or source rocks samples are prepared in polished briquettes... [+]

which are then compared to the reflectance of calibrated glass standards on a reflected light microscope. The USGS is currently involved in maturation studies of coals and rock in support of coalbed methane exploration in Louisiana, Arkansas, and Texas.

Hackley, P.C., Guevara, E. H., Hentz, T.F., and Hook, R.W., 2009, Thermal maturity and organic composition of Pennsylvanian coals and carbonaceous shales, north-central Texas: implications for coalbed gas potential: International Journal of Coal Geology, v. 77, p. 294-309, doi:10.1016/j.coal.2008.05.006.

Coalbed Methane Organic Petrology
Coalbed Methane
Organic Petrology

Coalbed Methane Organic Petrology

The maceral composition of coals may impact the ability of coal to generate and/or store natural gases, primarily methane. The USGS is actively pursuing studies to elucidate the role of maceral content on gas generation and storage, primarily in the Gulf Coast region of the United States. Coal samples from coalbed methane test wells are desorbed to measure actual stored gas content, microscopically analyzed for organic... [+]

content, and subjected to adsorption isotherm analyses to measure the coal’s ability to store gas. These comparative studies allow predictions of the role of maceral content on gas storage and may help in understanding gas generation. For more information pertaining to coalbed methane, please visit the "Oil and Gas" section of this website.

Hackley, P.C., Warwick, P.D., and Breland, F.C., Jr., 2007, Organic petrology and coalbed gas content, Wilcox Group, northern Louisiana: International Journal of Coal Geology, v. 71, p. 54-71, doi:10.1016/j.coal.2006.05.009.

Warwick, P.D., Breland, F.C., Jr., and Hackley, P.C., 2008, Biogenic origin of coalbed gas in the northern Gulf of Mexico Coastal Plain, USA: International Journal of Coal Geology, v. 76, p. 119-137, doi:10.1016/j.coal.2008.05.009.

Paleoenvironmental Studies
Paleoenvironmental Studies

Paleoenvironmental Studies

The types and amounts of organic material preserved in coal beds are indicators of the environmental processes that operated in the original peat mires. In conjunction with other types of analytical and geologic data, the organic content of coals can be used to infer moisture stress (frequency and degree of fluctuations in the water table), depositional environment (acidity, mechanical stress), types and relative amounts of original plant... [+]

vegetation, tectonic environment (subsidence), and climateThe USGS Organic Petrology Laboratory is involved in a number of national and international projects which characterize paleoenvironments through organic petrology.

Hackley, P.C., and Martínez, M., 2007, Organic petrology of Paleocene Marcelina Formation coals, Paso Diablo mine, western Venezuela: Tectonic controls on coal type: International Journal of Coal Geology, v. 71, p. 505-526, doi:10.1016/j.coal.2006.05.002.

Hackley, P.C., SanFilipo, J.R., Azizi, G.P., Davis, P.A., and Starratt, S.W., 2010, Organic petrology of subbituminous carbonaceous shale samples from Chalâw, Kabul Province, Afghanistan: speculations on paleoenvironment and energy resource potential: International Journal of Coal Geology, v. 81, p. 269-280, doi:10.1016/j.coal.2009.12.007.

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Page Last Modified: Wednesday, February 12, 2014



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