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The Soutpansberg Coalfield is a Karoo-aged intracratonic rift basin in South Africa's Limpopo Province. This study aims to assess samples from the No. 6 coal seam in the Makhado and Voorburg south area of the Soutpansberg Coalfield to determine the peat-depositional conditions, organic matter provenance, and their relation to paleoclimate and tectonic setting based on coal-petrography, mineralogical and SEM-EDX analyses. The coals are classified as medium-rank bituminous coal, with high ash yield (avg. 36.08 wt%; db). Ash yields display increasing trends from the middle upper (MU) to bottom lower (BL) part of the seam, while fixed carbon content values decrease. The maceral composition indicates that most samples are rich in vitrinite (-62%), with some inertinite (-10%) and very low liptinite (~1.4%). However, BL and BU in one core from the Makhado valley area are marked by very high inertinite (avg. 64%) and low vitrinite (avg. 7.3%). The patchy occurrence of inertinite macerals indicates high oxidation conditions or forest fires in peatmire at certain times. The coal facies diagrams indicate that precursor peat of the No. 6 seam started accumulating under mesotrophic hydrological conditions with a limited oxygen supply and low degree of degradation. Megathermal terrestrial plants might be the major component of the vegetation and the peatmire was formed under mildly oxic-to-anoxic wet-forest conditions. The mineralogical composition indicates that inorganic matter in coal is mostly composed of quartz, kaolinite, siderite, muscovite, dolomite, calcite, and pyrite. The Al2O3/TiO2 ratio shows that clay minerals are derived from felsic igneous rocks of granite or granodiorite composition. The Al-Fe-Mn ternary plot suggests some influence of hydrothermal activity in the post mire as the sample has an A1/(A1 + Fe + Mn) value of < 0.4 and (Fe + Mn)/Ti value > 15. The presence of massive porphyritic-type pyrite in the coal also indicates they may be formed by hydrothermal mineralization instead of sedimentation, strongly indicating the occurrence of hydrothermal activity. The SEM-EDX analyses denoted that As, Ni, Pb. and Co are associated with pyrite. Enriching these elements in coal might be terrigenous during sedimentation/peatification, and/or hydrothermal fluids during igneous intrusion emplacement. The chemical index of weathering (CIW) and chemical index of alteration (CIA) range from 92.04 to 97.66 (avg. 95.40) and 98.25 to 99.67 (avg. 99.26), respectively. The geochemical indices like CIA, CIW, A-CN-K ternary diagram, and SiCL vs log (K2O/Na2O) plot show that the paleoclimate conditions were warm and the coal component suffered strong chemical weathering, under passive continental margin depositional environment supporting luxurious vegetation and organic matter preservation. The inferred tectonic setting is consistent with tectonic events seen in East and Central Africa during the Carboniferous to the Permian period. [ABSTRACT FROM AUTHOR]

The response of inertinite-rich Witbank coals (South Africa) to rapid heating was evaluated using petrography, selected Nuclear Magnetic Resonance (NMR) and X-Ray Diffraction (XRD) structural parameters. A total of thirteen (13) coal samples were collected from the No. 2 Seam; a set of six (6) samples from the western and the eastern sides of a ~ 0.4 m thick dolerite dyke emplaced into the coal seam at 0.25 m intervals. An unaltered coal (Un-C; the 13th sample), collected away from the dyke but within the same seam at the mine, was included for comparison. All 13 coal samples were dominated by inertinite. Semifusinite was most abundant in the samples from the western side of the dyke, whereas the proportion of inertodetrinite was highest in samples from the eastern side. Due to very low vitrinite contents, mean random total reflectance (%RoTmr) was used to compare the maturity of the inertinite-rich coals. A decrease in volatile matter was correlated with an increase in mean random total reflectance (%RoTmr; measured on semifusinite, inertodetrinite, and vitrinite), the latter used as a potential maturity indicator for the thermally altered inertinite-rich coals. Mean random total reflectance rose from a background value of 1.52%RoTmr (for Un-C) to 2.83%RoTmr for the coal sample at the western coal-dyke contact (0.0 m). The corresponding reflectance values for the thermally altered coals from the eastern side were less consistent, decreasing closest to the dyke (1.93%RoTmr for the sample at 0.0 m); this trend is also reflected in the NMR and XRD parameters. Eight (8) samples were selected for the NMR analysis, representative of the maceral composition and maturities of the coals investigated. For Un-C, the fraction of aromatic carbons (fa) was 0.88 (average number of carbons per aromatic cluster (C) = 17), and the interplanar spacing (d002) was 3.48 Å (with a crystallite height of 22.09 Å). For the thermally altered coals from the western side, fa decreased from 0.96 at the coal-dyke contact (C = 26 for sample at 0.0 m) to 0.92 for the sample at 1.25 m from the dyke (C = 20). For samples from the eastern side, fa increased from 0.91 (C = 19 for the sample at 0.25 m) to 0.93 (C = 23 for sample at 0.5 m), before decreasing to 0.89 further from the dyke (C = 18 for sample at 1.25 m). In general, the d002 values for the thermally altered coal samples were larger than for graphite. Similarly, only marginal increases in crystallite heights were observed. Although the dyke induced coal maturation and the resultant increase in fa , the overall lack of graphitic order in the thermally altered coals was ascribed to the limited thermal energy provided by the relatively thin dyke; increased heat input would be required to effect significant structural changes in the inertinite-rich coals. Differences between the two sets of thermally altered coal samples were attributed to the emplacement dynamics of the igneous intrusion, which require further investigation. [ABSTRACT FROM AUTHOR]

• Nine articles are reviewed for the VSI of the 38th Annual Conference of The Society for Organic Petrology [ABSTRACT FROM AUTHOR]

• Petrology, δ13C and gypsum of coal corroborate alternating dry and wet periods. • The fine-scale variability in the δ13C signature was controlled by plant type. • δ13C values positively correlated with angiosperm/gymnosperm and % gypsum. • A high δ13C spike caps each of the four longer-term cycles of peat deposition. • The atmosphere had a significant influence on the peat formation in the basin. Coal contains detailed long-term records of contemporaneous environment, climate, and subsequent diagenetic processes. Stable isotopes of carbon, petrological, palynological, and mineralogical analyses were carried out on a 28 m thick low-rank Miocene coal seam from the Mile Basin, Yunnan Province, China for the purpose of deciphering the palaeoclimate and sedimentary conditions during peat deposition. The coal is characterized by both pale and dark lithotypes. Palynological analyses show that both lithotypes are dominated by angiosperms, which is interpreted to indicate a moderately warm climate. The absence of Fagus and Taxodiaceae pollen suggests that there may have been dry periods during peat accumulation; in general, both Fagus and Taxodiaceae require a constant wet environment in order to proliferate. Organic petrography, δ13C, and gypsum concentrations corroborate that there were alternating drier and wetter periods within the palaeomire during peat accumulation. The fine-scale variability in the δ13C signature appears to be controlled by plant type. Angiosperm/gymnosperm ratios and Vegetation Index are directly correlated with δ13C isotopic values. Plant type, however, seems to be proximally controlled by water level. Angiosperms were more dominant during times of lower water table or less moist conditions, interpreted to correspond to less negative values of δ13C. The correlation of greater concentrations of gypsum with less negative δ13C values also supports drier conditions. However, in addition to the fine-scale variability, four larger scale cycles are defined based on less negative δ13C values. A less negative δ13C isotopic signature demarcates the top of each of these cycles, which represent spikes of lower water table and/or drier conditions. In addition, a general correlation of the δ13C variations in the studied coal seam with atmospheric CO 2 suggests that the atmosphere also had a significant influence on peat formation in the Mile Basin. Although the Mile Basin palaeomire accumulated over a long time, an integrated approach to its analysis has demonstrated considerable variation in palaeoclimate. Changes in wetness/dryness had a direct effect on the ecological composition of the palaeomire. These floral changes would not have only been restricted to the palaeomire but most likely had a regional influence. Thus, detailed analysis of coals can yield useful, insightful and practical knowledge on past regional palaeoenvironmental conditions, which can then be placed within a global context. [ABSTRACT FROM AUTHOR]