Asiwaju, Lanre and Mustapha, Khairul Azlan and Abdullah, Wan Hasiah and Ayinla, Habeeb Ayoola and Abd Aziz, Azharuddin (2023) Organic matter input, paleovegetation and paleoclimate of Upper Cretaceous lignite from Maiganga coalfield, Upper Benue Trough, Nigeria: Insights from biomarkers and stable isotopes. Journal of African Earth Sciences, 205. ISSN 1464-343X, DOI https://doi.org/10.1016/j.jafrearsci.2023.105010.
Full text not available from this repository.Abstract
Upper Cretaceous Gombe Formation coals from Maiganga coalfield, Upper Benue Trough, Nigeria were investigated to evaluate the thermal maturity, organic matter input, paleovegetation, paleoclimate, and depositional environment using bulk and molecular geochemical techniques. Vitrinite reflectance (<0.40 %Ro) and biomarker maturity indicators (C-31 homohopane 22S/(22S + 22R) < 0.3; 16(H) beta/( beta+alpha) phyllocladane <0.5; MPI-1 < 0.5; MPR <2.65) generally signify low thermal maturity. Source-related aliphatic and aromatic hydrocarbon ratios indicate that the coals are derived mainly from terrestrial organic matter but with considerable input from marine algal organic matter. The higher abundance of diterpenoids over triterpenoids and sesquiterpenoids suggests a prevailing contribution of gymnosperms to the Maiganga paleoflora. This is corroborated by the relatively heavier carbon isotopic composition (delta C-13 = 25.9% to 25.0%) and low angiosperm/gymnosperm ratios. A new proxy, the polycyclic aromatic hydrocarbon ratio (PAHr) which is calculated from PAHr = (phenanthrene + pyrene + fluoranthene + perylene)/(phenanthrene + pyrene + fluoranthene + perylene + retene + cadalene), was proposed to evaluate the abundance and origin of combustion-derived polycyclic aromatic hydrocarbons (PAHs). The mostly high (>0.9) PAHr values for the coals are characteristic of a pyrogenic/ combustion origin. Combustion-derived PAHs are abundant in the coals and their ratios indicate a mixed petrogenic/ pyrogenic to dominantly pyrogenic origin. However, the high proportion of unburnt organic matter and low abundance of 7-ring PAHs such as coronene indicates limited, high-temperature wildfires. The coronene index values suggest burning temperature in the 700-1000. C range, which is consistent with the estimated high pO(2) of similar to 26.5% in the Maastrichtian. n-Alkane proxies (P-wax, P-aq, n-C-23/n-C-29, n-C-27/n-C-31, etc.) and hydrogen isotope ratios ( 117% to 112%) are suggestive of humid paleoclimate with frequent dry periods and lower paleopeat water levels. Moderately high pristane/phytane ratios (2.0-4.8) indicate deposition under sub-oxic to oxic freshwater settings. Additionally, low total sulphur content (0.29-0.90) and dibenzothiophene/phenanthrene ratios (0.05-0.17) imply peat accumulation in lacustrine-swamp to fluvial/deltaic depositional environments with minor post-depositional marine influence.
| Item Type: | Article |
|---|---|
| Funders: | Nigerian Government through the Petroleum Technology Development Fund (PTDF), Malaysia-Thailand Joint Authority (MTJA) Cess Fund [Grant No: IF064-2019] |
| Uncontrolled Keywords: | Maiganga coal; Polycyclic aromatic hydrocarbons; Stable isotopes; Source input; Paleovegetation; Paleoclimate |
| Subjects: | Q Science > QE Geology |
| Divisions: | Faculty of Science > Department of Geology |
| Depositing User: | Ms. Juhaida Abd Rahim |
| Date Deposited: | 10 Nov 2025 03:16 |
| Last Modified: | 10 Nov 2025 03:16 |
| URI: | http://eprints.um.edu.my/id/eprint/49711 |
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