Bituminous coals on emergent surfaces in an Asbian, lower Carboniferous (Mississippian) limestone succession on the North Wales carbonate platform, UK, and implications for palaeoclimate

Emergent surfaces in the Mississippian (Asbian to Brigantian) carbonate platform succession of North Wales record periods of plant colonisation and peat formation that led ultimately to the local development of coals. Examination of bituminous coals on three emergent surfaces within Cefn Mawr Quarry reveals information on palaeoclimate that is not available from study of the limestones alone. Three coal seams in the Asbian Loggerheads Limestone Formation were identified and the lowest one studied in detail. Vitrinite reflectance data from alternating bands of vitrite and duroclarite microlithotypes, the distribution of pyrite within them, and the sharp contacts between them, suggest that there were abrupt changes in marine influence during the development of the peats that formed the coals. It is inferred that local palaeoclimate alternated between periods of high and low rainfall, the amount of rainfall influencing the extent to which seawater encroached into the peats, with higher rainfall suppressing the ingress of saline waters into groundwater. On the basis of modern peat growth rates, the timescale of the alternation indicated by each duroclarite-vitrite couplet is suggestive of an annual cycle, such as would arise in a monsoonal climate. The low proportion of ash in the three coals, the preservation of internal lamination, the low diversity of spore species in the lowest coal compared with the over- and underlying mudrock, and the presence of rhizoconcretions in palaeokarstic limestone beneath the lowest and highest coals, demonstrate that the peat swamps were isolated from the hinterland and autochthonous. This study demonstrates that a wider application of palynology and coal petrology is an important contribution to the study of marine carbonate successions of any age where terrestrial organic matter, formed during emergence, has been preserved.

Hydrocarbon systems of the Crimean-Caucasian segment of the Alpine folded system

The article is devoted to the generation and accumulation systems in the territory of the Crimean-Caucasian segment of the Alpine folded system. An area of prolonged and stable sagging in the Mesozoic and Cenozoic – the Azov-Kuban Trough, which is a typical foreland basin – is distinguished within this segment. According to the results of geological and geochemical studies and modelling, depocentres are identified in this area, consolisated in four generative and accumulative hydrocarbon systems: Triassic-Jurassic, Cretaceous, Eocene and Maikop. Chemical-bitumenological, pyrolytic and coal petrology analysis of rock samples were carried out to assess geochemical conditions of oil and gas content in Meso-Cenozoic sediments. The modelling results made it possible to study and model the elements and processes of hydrocarbon systems in the Meso-Cenozoic in the Western Crimean-Caucasian region. It has been established that the extended catagenetic zoning is typical for these areas, which is caused by high rates of sedimentation and sagging, and large thicknesses of oil-bearing sediments in the source of oil formation, accordingly. The degree of organic matter depletion characterized the residual potential of the oil and gas source strata, was investigated. It is important for predicting and assessing the possibility of hydrocarbon generation.

The evolution characteristics of organic sulfur structure in various Chinese high organic sulfur coals

Understanding the organic sulfur structure and its evolution characteristics is crucial to the desulfurization of coal, as they are the dominant factors determining the removal of organic sulfur from coal. To learn the organic sulfur structure characteristics, a series of high-organic-sulfur coals from China with different ranks were studied by coal petrology, structural chemistry, and organic geochemistry theory in this paper. Coal petrological analysis shows some of the high-organic-sulfur coals with high TPI values and low GI values indicating that they have experienced unusual conditions when the coal was forming. Through the FTIR analysis, the organic sulfur structural parameters shows the relative abundance of aliphatic sulfur (thiol, thioether and sulfone) in these coals decreased with the increasing coal rank and the relative abundance of aromatic sulfur in coal generally showed an increasing trend with increasing coalification, divided into three different evolutionary stages (0.37%–1.40%, 1.40%–1.99% and 1.99%–3.93% of Rm). Comprehensive analysis shows that EID and TPI had a significant correlation with the organic sulfur structural parameters, which means regardless of the coal rank the impact of the environment on the structure of organic sulfur is independent. These results give a new insight into organic sulfur characteristics in coal and its evolution characteristics with coal rank, which are potentially useful for the efficient remove the organic sulfur from coal.

Coal petrology analysis and implications in depositional environments from Upper Cretaceous to Miocene: a study case in the Eastern Cordillera of Colombia

Coal petrological characteristics along the Piedemonte Llanero and the reconstruction of the deposit environment were obtained from macerals and micro-lithotypes analysis since these data provide information about the processes and prevalent conditions during the peat formation. We analyzed seams from Cenomanian to Miocene geological units (Chipaque Formation, Palmichal Group, Arcillas del Limbo Formation, and San Fernando Formation). Coal range decreases gradually from high-volatile C bituminous (HVCB) in the Chipaque Formation to sub-bituminous C in the San Fernando Formation. The coals are enriched in macerals of vitrinite, whereas the liptinite and inertinite concentrations vary according to the stratigraphic position. The micro-lithotypes are bi-maceral and tri-macerals, being the highest concentrations of clarite and vitrinertoliptite. The results of the facies analysis show that the peat in which the coals developed is mainly of arboreal and herbaceous affinity (rich in lignin and cellulose). Peats are ombrotrophic (rainfed) to mesotrophic (transitional or mixed mires) with variations in the flooding surface and influxes of brackish water. Good tissue preservation is inferred from the wet conditions in forest swamps with few humification and gelation. According to the micro-lithotypes composition, the peat environment was deduced as estuarine system, evolving to lacustrine environment of the deltaic system, both restricted by changes in sea level, which are evidenced by oxic and anoxic periods in the analyzed sequence.