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Alteration of organic macerals by uranium irradiation in lower Paleozoic marine shales.
- Source :
-
International Journal of Coal Geology . Apr2021, Vol. 239, pN.PAG-N.PAG. 1p. - Publication Year :
- 2021
-
Abstract
- Measuring the degree of organic matter (OM) alteration caused by uranium (U) irradiation is important in the effective evaluation of the hydrocarbon potential and thermal maturity of U-rich source rocks. This study investigates OM alteration in the Baltoscandian U-rich, lower Paleozoic Alum shale obtained from three research wells in the thermally immature parts of eastern Sweden and western Estonia. The results show a marked increase in the proportion of refractory, non-generative organic carbon (NGOC) in the U-rich shale. Fluorescence spectrometry of unicellular alginites and lamalginites show a reduction of up to 95.6% in fluorescence relative intensity (RI) with increase in U content from 29 to 401 ppm. Fluorescence spectra of the liptinites exhibit a marked "red shift" as expressed by increase in red(R)/green(G) quotients. This change in fluorescence properties of the liptinites is associated with up to 77.6% decrease in hydrogen index (HI) and hence loss of hydrocarbon generation potential. Furthermore, organic molecules show significant loss of aromatic moieties as well as aliphatic constituents resulting in a more condensed macromolecular structure. The measured random reflectance of solid bitumen (BR o) appears to be significantly elevated in micro scale proximity to the U-containing minerals. The heterogeneous distribution of U-containing minerals and the contact with solid bitumen attributes to the wider range of BR o values and lead to the overall increase in mean BR o in samples with high U contents. In contrast, R o values of zooclast macerals (GR o , e.g., graptolite, chitinozoans and vitrinite-like fragments) appear to be less influenced by U irradiation and hence are a more reliable maturity indicator in U- rich lower Paleozoic shales. • Uranium (U) irradiation is responsible for alteration of organic matter, manifested by red shift in fluorescence spectra of liptinites (Red/Green quotient) and increase in solid bitumen (thucholite) reflectance (BR o). • U irradiation attribute to hydrogen index (HI) decrease, relative non-generative organic carbon (NGOC) increase and parent macromolecule condensation. • Zooclast fragments (GR o , Graptolite, Chitinzoan and vitrinite-like particles) are more reliable maturity indicators in U-rich rocks. [ABSTRACT FROM AUTHOR]
- Subjects :
- *PALEOZOIC Era
*MACERAL
*URANIUM
*SHALE
*HARD rock minerals
*URANIUM mining
Subjects
Details
- Language :
- English
- ISSN :
- 01665162
- Volume :
- 239
- Database :
- Academic Search Index
- Journal :
- International Journal of Coal Geology
- Publication Type :
- Academic Journal
- Accession number :
- 149687231
- Full Text :
- https://doi.org/10.1016/j.coal.2021.103713