Geology topics

A.G. Borrego

Publications and source records attributed to A.G. Borrego.

4 recordsLinked to original sources

USGS2024

The petrology of dispersed organic matter in sedimentary rocks: Review and update

Organic petrology developed from coal petrology, and, in the 1960s, it began to be applied to the study of dispersed organic matter (DOM) in sedimentary rocks other than coal. Over the last few decades, the petrology of DOM has been used to characterize organic matter in sedimentary basins with an emphasis on fossil fuel resource exploration. Today, due to the global research shift on topics related to climate, organic petrology has expanded into new application areas, such as geothermal exploration, biological carbon storage (biochar), disposal, and management of radioactive waste. From the publication of the International Handbook of Coal Petrology (mid-20th century) to the present day, a large number of standards, books, and articles have been published as a result of the work of organic petrographers and petrologists around the world and efforts of the International Committee for Coal and Organic Petrology (ICCP) and The Society for Organic Petrology (TSOP) to promote the study of organic petrology. The current fundamentals and standards of organic petrology provide the international scientific community with well-informed guidance and recommendations to promote in-depth research. However, this information is currently widely scattered, leading to discrepancies in methodology and terminology. Therefore, this paper aims to present a comprehensive review of the main analytical standard test methods and techniques currently used in the petrology of DOM under reflected white light and UV and blue-light excitation, and to provide an efficient and well-defined reference guide. Furthermore, considering the important role of the ICCP in the development of organic petrology since the 1950s, a brief review of the ongoing activities of ICCP dealing with DOM is also presented.

International Journal of Coal Geology↗

USGS2017

Identification of alginite and bituminite in rocks other than coal. 2006, 2009, and 2011 round robin exercises of the ICCP Identification of Dispersed Organic Matter Working Group

The paper presents results of round robin exercises on photomicrograph-based identification of dispersed organic matter in source rocks that represent a range of marine and lacustrine deposits from worldwide localities and cover a range of thermal maturities. The round robin exercises were conducted by the Identification of Dispersed Organic Matter Working Group (IDOM WG) of the International Committee for Coal and Organic Petrology (ICCP). The round robin exercises aimed to (1) assess the applicability of the established ICCP definitions of bituminite, (2) identify deficiencies and improve the existing nomenclatures, and (3) provide a basis for the revision of the bituminite and alginite definitions in the ICCP Handbook (Taylor et al., 1998). Three round robin exercises performed in 2006, 2009 and 2011 involved 18 participants from research laboratories at universities and within government and industry. Participants were asked to identify macerals on the basis of existing definitions in 129 photomicrographs taken in incident white light and fluorescent mode and also in fluorescence light mode at prolonged (15 min) blue light irradiation. The results indicate that the definition of telalginite permits its positive and satisfactory agreement among the participants. In contrast, the descriptive characteristics of lamalginite referring to film-like appearance (filamentous) and lack of inner or outer structure are insufficient and inadequate to enable an unequivocal discrimination between it and telalginite. Furthermore, based on the amorphous nature of bituminite and lack of adherence to its established description and character (Taylor et al., 1998), the highest discrepancies were observed in its identification. Differentiation of bituminite from a fluorescent groundmass and in some cases from lamalginite proved to be particularly challenging. The findings of these round robin exercises are useful for improving the identification of sedimentary organic matter in source rocks and may be an important foundation for the modification of the ICCP definitions of alginite and bituminite.

International Journal of Coal Geology↗

USGS2015

Microscopical characterization of carbon materials derived from coal and petroleum and their interaction phenomena in making steel electrodes, anodes and cathode blocks for the Microscopy of Carbon Materials Working Group of the ICCP

This paper describes the evaluation of petrographic textures representing the structural organization of the organic matter derived from coal and petroleum and their interaction phenomena in the making of steel electrodes, anodes and cathode blocks. This work represents the results of the Microscopy of Carbon Materials Working Group in Commission III of the International Committee for Coal and Organic Petrology between the years 2009 and 2013. The round robin exercises were run on photomicrograph samples. For textural characterization of carbon materials the existing ASTM classification system for metallurgical coke was applied. These round robin exercises involved 15 active participants from 12 laboratories who were asked to assess the coal and petroleum based carbons and to identify the morphological differences, as optical texture (isotropic/anisotropic), optical type (punctiform, mosaic, fibre, ribbon, domain), and size. Four sets of digital black and white microphotographs comprising 151 photos containing 372 fields of different types of organic matter were examined. Based on the unique ability of carbon to form a wide range of textures, the results showed an increased number of carbon occurrences which have crucial role in the chosen industrial applications. The statistical method used to evaluate the results was based on the “raw agreement indices”. It gave a new and original view on the analysts' opinion by not only counting the correct answers, but also all of the knowledge and experience of the participants. Comparative analyses of the average values of the level of overall agreement performed by each analyst in the exercises during 2009–2013 showed a great homogeneity in the results, the mean value being 90.36%, with a minimum value of 83% and a maximum value of 95%.

International Journal of Coal Geology↗

USGS2006

Influence of particle and surface quality on the vitrinite reflectance of dispersed organic matter: Comparative exercise using data from the qualifying system for reflectance analysis working group of ICCP

The development of a qualifying system for reflectance analysis has been the scope of a working group within the International Committee for Coal and Organic Petrology (ICCP) since 1999, when J. Koch presented a system to qualify vitrinite particles according to their size, proximity to bright components and homogeneity of the surface. After some years of work aimed at improving the classification system using photomicrographs, it was decided to run a round robin exercise on microscopy samples. The classification system tested consists of three qualifiers ranging from excellent to low quality vitrinites with an additional option for unsuitable vitrinites. This paper reports on the results obtained by 22 analysts who were asked to measure random reflectance readings on vitrinite particles assigning to each reading a qualifier. Four samples containing different organic matter types and a variety of vitrinite occurrences have been analysed. Results indicated that the reflectance of particles classified as excellent, good or poor compared to the total average reflectance did not show trends to be systematically lower or higher for the four samples analysed. The differences in reflectance between the qualifiers for any given sample were lower than the scatter of vitrinite reflectance among participants. Overall, satisfactory results were obtained in determining the reflectance of vitrinite in the four samples analysed. This was so for samples having abundant and easy to identify vitrinites (higher plant-derived organic matter) as well as for samples with scarce and difficult to identify particles (samples with dominant marine-derived organic matter). The highest discrepancies were found for the organic-rich oil shales where the selection of the vitrinite population to measure proved to be particularly difficult. Special instructions should be provided for the analysis of this sort of samples. The certainty of identification of the vitrinite associated with the vitrinite reflectance values reported has been assessed through a reliability index which takes into account the number of readings and the coefficient of variation. The same statistical approach as that followed in the ICCP vitrinite reflectance accreditation program for single seam coals has been used for data evaluation. The results indicated low to medium dispersion for 17 out of 22 participants. This, combined with data from other sets of comparative analyses over a long period, is considered an encouraging result for the establishment of an accreditation program on vitrinite reflectance measurements in dispersed organic matter. ?? 2006 ICCP.

International Journal of Coal Geology↗