Petrographic composition of coal within the Benue Trough, Nigeria and a consideration of the paleodepositional setting (original) (raw)

The petrographic composition of coals hosted in the Benue Trough, Nigeria are presented and discussed in terms of paleodepositional setting that influenced the coal-bearing formations. The Benue Trough is a failed arm of the triple ‘RRr’ junction of an inland sedimentary basin that extends in a NE-SW direction from the Gulf of Guinea in the south, to the Chad Basin in the north. A total of twenty-nine (29) coal samples were obtained from 19 coal localities in the Upper (UBT), Middle (MBT), and Lower Benue Trough (LBT). The proximate data indicates the coal samples have a high volatile matter content, low ash yield, and high calorific value (24.82 MJ/Kg, on average). The sulphur values are generally low (average of 0.94 %). The coal samples are generally high in vitrinite, with an average of 59.3% by volume (mineral-matter free). Variation was noted in the inertinite content for the three sub-region samples. Liptinite macerals were not commonly observed in the studied samples and are...

The designation of strata into lithologic facies and characterization of stratigraphic intervals using defined facies are used to interpret depositional environments and to develop a sequence-stratigraphic framework for better understanding coal bed gas production and resource potential. Coal facies are characterized by coal types that depend on paleogeographic and tectonic framework of coal basins, paleoclimate, flora and fauna of coal forming swamps, coal constituent characteristics and especially depositional environments. The depositional environments are considered as the main topic of discussion because the environments can explain the origin of coal, its characteristics, its relation with surrounding sediments and its position in sedimentation sequence. But not only depositional environments are responsible ,but also timing of peat accumulation relative to the balance between sediment supply and eustasy and subsidence are responsible for coal formation.

Abundant coal resources that were previously neglected due to a crude oil boom need revitalisation and integration into the national electricity mix to address the energy demands of the Nigerian population. Selected coal samples from the Benue Trough sedimentary basin in Nigeria were examined by various techniques, including proximate and ultimate analyses, organic petrography, Fourier transform infrared ray spectroscopy, and thermogravimetric analysis. Based on vitrinite reflectance, the Lafia-Obi (OLB), Garin Maiganga (GMG), Imiegba (IMG), and Okaba (OKB) coals are classified as subbituminous, while the Lamja1 (LMJ1), Lamja2 (LMJ2) and Chikila (CHK) coals are high volatile B bituminous. The Enugu (ENG) coal is on the boundary between subbituminous and high volatile C bituminous. Organic petrographic results indicate vitrinite and fusinite contents steadily increase from the Lower Benue Trough coals to the Upper Benue Trough coals, while semifusinite and total mineral contents foll...

The South Sumatra basin is among the most important coal producing basins in Indonesia. Results of an organic petrography study on coals from Tanjung Enim, South Sumatra Basin are reported. The studied low rank coals have a mean random huminite reflectance between 0.35% and 0.46% and are dominated by huminite (34.6–94.6 vol.%). Less abundant are liptinite (4.0–61.4 vol.%) and inertinite (0.2–43.9 vol.%). Minerals are found only in small amounts (0–2 vol.%); mostly as iron sulfide.Based on maceral assemblages, the coals can be grouped into five classes: (1) humotelinite-rich group, (2) humodetrinite-rich group, (3) humocollinite-rich group, (4) inertinite-rich group and (5) humodetrinite–liptinite-rich group. Comparing the distribution of maceral assemblages to the maceral or pre-maceral assemblages in modern tropical domed peat in Indonesia reveals many similarities. The basal section of the studied coal seams is represented typically by the humodetrinite–liptinite-rich group. This section might be derived from sapric or fine hemic peat often occurring at the base of modern peats. The middle section of the seams is characterized by humotelinite-rich and humocollinite-rich groups. The precursors of these groups were hemic and fine hemic peats. The top section of the coal seams is typically represented by the humodetrinite-rich or inertinite-rich group. These groups are the counterparts of fibric peat at the top of the modern peats. The sequence of maceral assemblages thus represents the change of topogenous to ombrogenous peat and the development of a raised peat bog.A comparison between the result of detailed maceral assemblage analysis and the paleodepositional environment as established from coal maceral ratio calculation indicates that the use of coal maceral ratio diagrams developed for other coal deposits fails to deduce paleo-peat development for these young tropical coals. In particular, mineral distribution and composition should not be neglected in coal facies interpretations.

The Crowsnest coalfield is a separated structural coalfield at the East Kootenay basin within southeast British Columbia. Selected Jurassic-Cretaceous two coals seam S-10 and S-C of the Mist-Mountain formation were investigated from the points of coal petrography to construct a Paleo-limnological setting. Twenty-two channel coal samples were assembled and measured from S-10 and S-C coal seams. Vitrinite reflectance measuring of the S-10 coal concern to low-volatile bituminous (1.61, on average). While the vitrinite reflectanc measurements of S-C coal seam show an average value of 0.98 related to high-volatile bituminous. Petrographic analysis demonstrates that the S-10 coal seam appears to be rich in inertinite than the S-C coal seam that appears rich in vitrinite. Applying coal facies indices of Tissue Preservation Index, Gelification Index, Ground Water Index, Vegetation Index and coal facies diagrams for the studied coal seams aid to suggest a condition of the depositional Paleo-environments. The results promote Paleo-depositional sites of telmatic to limno-telmatic setting of rheotropic systems swamp. The obtained results show a trend of increase in both herbaceous flora and anoxic waterlogged limo-telmatic setting toward the younger coal seam S-C than the older S-10 coal seam.