Roof Shales Research Articles

The evolution process of fractures and their modification effects on the liquid–solid interface during liquid nitrogen cyclic freeze–thaw of coal and shale

Liquid nitrogen cyclic freezing-thawing fracturing (LNCFT) is an innovative method for the waterless fracturing of coal and rock, harnessing the effects of low temperature, phase change, and expansion. However, the mechanisms behind micro-fracture propagation, evolution, and surface modification during LNCFT remain elusive. This study concentrates on anthracite coal and roof shale in the Jiaozuo mining area. It conducts LNCFT experiments under various saturated water conditions and employs a stereoscopic fluorescence microscope and an optical contact angle measuring instrument for observations, analyzing the surface modification effects resulting from the propagation and evolution of fractures on solid surfaces. The study unveils the following findings: (1) LNCFT effectively creates a network of micro-fractures. The quantity and length of fractures significantly increase with the number of fracturing cycles, and the effect is more pronounced with higher water content, especially in coal compared to shale. Fracture evolution falls into three categories: extension, intersecting, and newly formed independent fractures, with the scale of extension and intersecting of the original fractures determining the modification effect. (2) The LNCFT process exhibits distinct stages and selectivity. The strength of early-stage modifications (before eight cycles) directly influences the overall modification effect. (3) Throughout the LNCFT process, the solid–liquid surface contact angle first increases and then decreases with the number of fracturing cycles. This pattern can be analyzed using the Wenzel model. Liquid nitrogen fracturing increases the surface roughness of coal and shale, leading to a transition from hydrophobicity to hydrophilicity on their surfaces. The research findings of this paper provide theoretical guidance for the modification of low-permeability reservoirs.

Cyclical water vapor sorption-induced structural alterations of mine roof shale

Understanding the nanoscale structural changes of shale in an unsaturated gas-water-shale system can shed light on the underlying mechanisms on water retention-induced shale deterioration. The simplified hypothesis here is that pore-scale shale structure can be passively altered by pore deformation/failure under cyclical water vapor treatments and can be described by a partially saturated effective stress law. Cyclical water vapor sorption tests were conducted on dried and water-saturated shale powders prepared by a hand-crushing (larger particle size) method and a cryogenic ball-milling (smaller particle size) method. Techniques including XRD, FESEM-EDS, and nanoindentation were used to provide evidence that the nano-porous shale is highly heterogeneous in nano-to micro-scale. The sorption curves of both samples with initial water-saturation treatments are higher than the raw samples, indicating enhanced sorption capacities in the treated samples. The degree of hysteresis among eight cycles (five cycles on raw sample and three cycles for treated sample) for both samples exhibit significant differences at low relative humidities, namely lower than ∼0.6. Very slight differences were observed among eight cycles when the relative humidity was higher than 0.6. An obvious decrease in the effective diffusion coefficients is observed in the treated samples compared to the raw samples, which is attributed to the physical alterations induced by the initial drying of water-saturated sample. In situ SANS data for shale at elevated relative humidity conditions suggest that the decrease in the scattering contrast between rock solid matrix and pores can be attributed to water capillary condensation. This occurs mainly in pores with radii smaller than ∼8.3 nm but larger than ∼1.25 nm and at a relative humidity of ∼59%. The capillary condensation continuously takes place in larger pores as the relative humidity increases to ∼87%. The results can ultimately provide the data for analyzing the interactions within an unsaturated air-water-shale system.

Seminal Insights Concerning the Variety of Sidertic Structures and Variable Genesis and of Sideritic Occurrences: An Unexplored Source of Palaeontological Information (Sydney Coalfield, Middle Pennsylvanian, Canada)

Abstract Reported are descriptions of twelve samples representing a variety of sideritic structures, including nodules mostly from roof shale of the Middle Pennsylvanian Sydney Coalfield, Canada. The co-occurrence of fossiliferous nodules and compression fossils in the shaley roof rocks at Point Aconi enhance greatly palaeontological information. Newly discovered in a coal seam, and part of the sample, is a 40 mm thick continuous sheet-like layer of siderite with abundant permineralized-like-compressed small to micron-sized structures in a rather evenly-sized sideritic matrix, probably indicating a genetic origin different from that of the nodules. Methods include some thin-section, and two X-Ray analysis. However, large systematic sampling is a prerequisite to explore that situation, which additionally could provide faunal information for Euromerican correlation.

NON-MARINE BIVALVES FROM THE MOSPYNE FORMATION (UPPER BASHKIRIAN) OF THE DONETS BASIN: TAXONOMY, PALEOECOLOGY, AND STRATIGRAPHIC SIGNIFICANCE

Remains of non-marine bivalves are widespread in the Carboniferous of the Donets Basin (Eastern Ukraine). The studies of this group of fauna are important for stratigraphy, paleoecology and paleobiogeography. The remains of non-marine bivalves were found in sediments of the Mospyne Formation; Carbonicola obtusa (Hind) and Naiadites sp. were found in the roof shale of the g2 coal bed; Curvirimula trapeziforma (Dewar) and C. tesselata (Jones) were identified in the roof shale of the g12 coal bed, and Carbonicola rectilinearis Trueman et Weir and C. limax Wright were found in the siltstone below G12 limestone layer. The upper part of the lower half of the Mospyne Formation is attributed to the Carbonicola rectilinearis Member, which probably corresponds to the upper part of the lenisulcata Zone (Langsettian) of Western Europe. The lower limit of this member is in the floor of a thick sandstone bed 43 m below G12 limestone layer. The upper boundary of Carbonicola rectilinearis Member is situated at the g12 coal layer. The Carbonicola pseudorobusta Zone, previously identified by M.T. Sergeeva as member with fauna, is distinguished between the roof shale of the g12 coal bed and h61 coal bed. This zone corresponds to the communis Zone in Western Europe. Bivalves from the roof shale of the g12 coal layer and roof shale of the g2 coal layer lived in shallow-water eutrophic freshwater or brackish lakes in the coastal accumulation lowland. These basins were characterized by significantly reduced aquatic organism assemblage and hydrogen sulfide contamination of silts and, possibly, the bottom layer of the water column. Representatives of the genera Curvirimula and Naiadites were found in the sediments of these lakes. These genera apparently led a pseudoplanktonic lifestyle, attaching themselves to various bottom objects with byssus. The bivalves from the siltstones below the G12 limestone layer (Carbonicola) lived in a shallow-water, refreshed lagoon.

Geological and Geochemical Characteristics of the Terrestrial Lower Jurassic Shale in Tarim Basin and its Favorable Exploration Areas

Large amounts of conventional gas resources that originated from terrestrial Lower Jurassic shale were discovered in the Tarim Basin, indicating promising exploration prospects for shale gas resources, whereas limited understandings were obtained on the geological and geochemical characteristics of the Lower Jurassic shale. In this study, based on cores of exploration wells and field outcrops, total organic carbon (TOC) pyrolysis, microscopic composition, organic elements, vitrinite reflectance, x-ray diffraction, and methane isothermal adsorption experiments were carried out on Lower Jurassic shale in the Tarim Basin. The results show that the TOC content of shale is relatively high, but the TOC content of shale in different regions is quite different. Among them, the Kuqa Depression is the highest (more than 3%), the Southwest Tarim Basin is second (more than 1%), and the East Tarim Basin is the lowest. The main types of kerogen in shale are mainly type III and type II2. The thermal evolution maturity of shale in different regions is quite different; the highest Ro of shale in the Southwest Tarim Basin is more than 2.0% and that of shale in the Kuqa depression is higher than 1.5%, both of which have entered the stage of high-over-mature evolution, and the shale in the East Tarim Basin is only in the low maturity–mature stage. The overall content of brittle minerals such as quartz in shale is greater than 40%, which has good fracturing properties. The adsorbed gas content of shale is high, but there is a great difference (0.5–4 m3/t), which is related to the large difference in the abundance of organic matter, thermal maturity, and clay mineral content of shale. Therefore, the Lower Jurassic shale gas in the Tarim Basin has good prospects for exploration. Based on the superposition method of the main controlling geological factors, it is predicted that the favorable areas for shale gas exploration are mainly located in the Keshen and Yinan-Yeyun areas of the Kuqa Depression and the Caohu Sag-Mandong area of the East Tarim Basin. This research not only provides basic data for the evaluation of shale gas resources in our country, but also provides certain guidance for the exploration of Lower Jurassic shale gas in the Tarim Basin.

Identification of rural vernacular building character and conservation strategy from the perspective of rural tourism -- a case study of Yayou Gou Village in Shandong Province, China

Rural vernacular building is a traditional dwelling house with the characteristics of the time and regions, which is now greatly impacted by urbanization and modernization. This research takes the rural vernacular building of Yayou Gou Village as the study case and uses document analysis, observation, and interview method to investigate the character and conservation strategies of rural building. The paper suggests that the building site characters are greatly influenced by topography and living conditions, followed by village traffic. The architectural forms represent the rural style of southern Shandong province with the unique roof shale covered. The layout of the building helps to maintain kinship and improve the local microclimate. Under the background of rural tourism development, effective protection methods for traditional buildings include function revitalization, museum transformation, homestay transformation, and local residents’ living are identified. Through the analysis of rural characteristics and conservation methods exploration, it is beneficial to further research on the character of rural architectural elements, promote the utilization and protection of rural building landscape, and provide enlightenment for rural development.

New records of Pennsylvanian plants, in situ and dispersed cuticles from the Kladno-Rakovník Basin, Radnice Member, Czech Republic

New collection from the spoil heap of the Lužná mine in Lužná near Rakovník contains about 23 species of lycopsids, sphenopsids, ferns, pteridosperms, progymnosperms and cordaitaleans. The exploited coal seam is called the Upper Radnice Coal seam and belonged to the Radnice Member, Kladno Formation of the upper Duckmantian Substage (lower Moscovian Stage). Plant remains were discovered in tuffaceous partings (so called Velká opuka) and roof shales (here called Mydláky). As roof shales are friable, only a few fossils were found, e. g., Lepidodendron aculeatum Sternberg and Calamites cf. cistii Brongniart that are considered here as autochthonous or parautochthonous. Tuffaceous partings (Velká opuka) yielded a diversified assemblage, including large fragments including for instance progymnosperms (Noeggerathia foliosa Sternberg) and pteridosperms (Spheno pteris pulcherrima Crépin), in some layers also including allochthonous small fragments of undeterminable plant debris and pinnule fragments of medullosalean pteridosperms e. g. Laveineopteris tenuifolia (Sternberg) Cleal, Shute et Zodrow and other species. Noeggerathia foliosa Sternberg is the dominant species in this locality. Cuticles obtained from coal can be classified into several groups. Most of the fragments belong probably to the sporangium wall of the subarborescent lycopsid Omphalophloios feistmantelii (Němejc) Bek et al. Other cuticles correspond to leaf cushions of arborescent lycopsids (Lepidodendron Sternberg and Lepidophloios Sternberg), and others lacking cell and stomatal structures are undeterminable. Pteridosperm or fern cuticles from rachises or midvein areas without stomata are difficult to classify. Also, bizarre multicellular bodies of uncertain affinity are present. Sphenopsid and cordaitalean cuticles were absent in the dispersed cuticular spectra.

Palaeobiogeographical implications of the earliest botryopterid ferns in Cathaysia

ABSTRACT The Wuda Tuff Flora from the Taiyuan Formation of Inner Mongolia is a palaeobotanical lagerstätte that is key to our current understanding of the composition and ecology of the earliest Permian Cathaysian floras. We investigate an anatomically preserved axis that represents an additional plant family recorded in this flora and considers its palaeobiogeographical implications. The specimen possesses an ω-shaped vascular strand and has features that conform to the botryopterid fern Botryopteris. Comparisons indicate greatest similarity with Botryopteris scottii from the Pennsylvanian of England but due to limited information we assign it to Botryopteris cf. scottii. The new finding represents the earliest stratigraphic occurrence of botryopterids in the Cathaysian floras. Alongside Botryopteris tridentata and Botryopteris cf. forensis in slightly younger Cisuralian strata from China, it demonstrates migration of closely related species from the Pennsylvanian wetlands of Euramerica into the Permian wetlands of Cathaysia. Together with unexpectedly early stratigraphic occurrences of the ‘Methuselah taxa’ Yuania, Gigantonoclea and Autunia in the roof shale flora of the coal seam overlying the Wuda Tuff Flora, B. cf. scottii adds to a growing body of evidence that records significant floral interchange and migration from different ecological settings in the Cathaysian and Euramerican floras by the earliest Permian.

PRESERVATION OF NEUROPTERIS OVATA IN ROOF SHALE AND IN FLUVIAL CREVASSE-SPLAY FACIES (LATE PENNSYLVANIAN, SYDNEY COALFIELD, CANADA). PART I: AN INFRARED-BASED CHEMOMETRIC MODEL

ABSTRACTAnalytical questions relating to the influence of sedimentation on the preservation states of Carboniferous plant fossils are seldom addressed in the literature. Here we address specifically the influence facies differences have on preservation states and suggest how they can be analyzed. The case study involves the seed fern Neuropteris ovata (Hoffmann) that occurs as opaque pinnules in the roof shale and as transparent pinnules in an associated crevasse-splay of the basal Cantabrian in age, Point Aconi Coal Seam, Sydney Coalfield, Canada. The color differences imply different molecular pathways for organic matter transformation over geological time, which resulted in production of compression fossils in the roof shale and fossilized-cuticle in the crevasse-splay, respectively. Fourier transform infrared spectroscopy methods are used to quantify functional groups, and the derived data are chemometrically evaluated. Results indicate that the compressions are, as anticipated, characterized in the crevasse-splay facies by a predominantly aromatic composition. The fossilized-cuticles, however, are mainly characterized by oxygen-containing aliphatics, confirming the influence of facies changes on preservation states of the species studied. Implications for preservation, taxonomy, and paleoecology are emphasized.

Omphalophloios wagneri sp. nov., a new sub-arborescent lycopsid from the middle Moscovian (Middle Pennsylvansian) of the Illinois Basin, USA

Described is a new species of sub-arborescent lycopsid, Omphalophloios wagneri sp. nov. from roof shale of the middle Moscovian (Bolsovian/Atokan) (Middle Pennsylvanian) Lower Block Coal in the Illinois Basin, Indiana, USA. Available material represents mostly fragments of 16 to >60 mm wide fertile axes that bear densely spaced sporangia, which are flattened due to compaction into disc-like shape, 2.5–3.1 mm in diameter. The outer sporangial cell wall layer displays a gradual transition from isometric cells in the central parts of adaxial and abaxial sporangial valves, to a narrow belt of elongated cells in the equatorial area, interpreted as a dehiscence zone. Micro- and megasporangia alternate in irregular patches, a single sporangium being attached adaxially to an extended sporophyll base. Cyperites-like sporophyll distal laminae are ~25 mm long at fertile shoot apices but become progressively longer (>110 mm) down the shoots. Based on size distribution of stems, fertile shoots are estimated to bifurcate at least five times, which suggests that O. wagneri formed a relatively dense crown. The entire habit of the plant is difficult to assess from existing material; however, the tree was probably small and interpreted as colonizing low lying to slightly raised peat swamps. Omphalophloios wagneri differs from all other adpression-based species of the genus in having the smallest sporangia and several orders of fertile-axis bifurcations. In situ megaspores of the Zonalesporites brassertii type also are different from all other Omphalophloios megaspores.

Nanopore characterization of mine roof shales by SANS, nitrogen adsorption, and mercury intrusion: Impact on water adsorption/retention behavior

Moisture-induced reduction in the strength of shales is one of the primary mechanisms of roof degradation affecting the stability and safety of underground coal mines. The underlying mechanisms of nanoscale matrix-water interactions remains unclear. Thus, an improved understanding of the nanopore structure, and dependent water adsorption and retention behavior of shale is key in defining strength degradation due to seasonal variations in humidity and temperature in underground coal mines. We use small-angle neutron scattering (SANS), low-pressure N2 adsorption (LPNA), and high-pressure mercury intrusion porosimetry (MIP) to characterize the nanopore structure of a fireclay (7F) and four coal mine roof shales (6R, 5A, 6F, H6) from the Illinois basin. The results show that overall distributions of pore volume obtained from SANS, LPNA and MIP techniques agree well between methods and over a wide range of pore size from ~1 nm to ~100 nm. Mercury porosities for the five ordered (7F, 6R, 5A, 6F, H6) samples (7.3%, 7.8%, 8.3%, 12.3%, 4.6%) are higher than the respective N2 porosities (5.0%, 6.3%, 3.8%, 8.2%, 2.5%), as attributed to the dilation of mesopores and compression of the grain skeleton induced by high pressure intrusion of mercury. The SANS porosities for samples 7F, 6R, 5A, 6F (4.0%, 6.2%, 4.1%, 8.8%) are in good agreement with their N2 porosities. Among all tested samples, H6 shale exhibits a relatively high SANS porosity (8.0%) but the lowest N2 (2.5%) and mercury porosities (4.6%). This is attributed to the interlayer micro-pore spaces within montmorillonite, which is detected by SANS but not by the two fluid penetration methods due to the inaccessibility of N2 molecules and mercury. Based on LPNA, larger micropores (1.5–2 nm) and mesopores (2–50 nm) predominantly contribute to the total porosity (~77.8%–87.6%) for the five tested samples.The water adsorption isotherms are measured by dynamic vapor sorption (DVS) and water retention curves are calculated based on the characterized pore size distribution (PSD) by LPNA and MIP techniques. Pore structures of the five studied samples evidently exert a strong influence on their water adsorption and retention behaviors. Water adsorption capacity correlates positively with total porosity/specific surface area (SSA), with a large proportion of micro/meso-pores resulting in the strong water retention capacity with matric suction reaching ~100–150 MPa for liquid saturation < 3%. Among the studied fireclay/shales, samples with higher retention capacity tend to adsorb more water. Thus, nanopore structure and its impact on water adsorption and retention behavior exert the key controls on shale-water interaction and its implication on strength reduction of roof shales in underground coal mines.

Vegetational zonation in a swamp forest, Middle Pennsylvanian, Illinois Basin, U.S.A., indicates niche differentiation in a wetland plant community

A rich fossil flora occurs in the roof shale of the Middle Pennsylvanian (Moscovian) age, Springfield Coal flanking the Galatia channel, a river deposit approximately 1km in width and 150km long, partially contemporaneous with the Springfield peat swamp. Siltstone and sandstone, >30m thick, were deposited in the channel during the final estuarine phase. The river formed under seasonal subhumid climate during early deglaciation as marine waters retreated from the land surface. It existed continuously through glacial maximum, under increasingly humid climate, as a low-sediment or black-water river with peat along its flanks. During early deglaciation, under subhumid climate and sea-level rise, the river became a sediment-laden estuary, drowning the peat swamp and burying vegetation in place under extensive mudflats. This buried flora was studied in three underground mines in southern Illinois, permitting vegetation to be characterized spatially. Three transects, comprising 100 sites, a total linear distance of ~12km, reveal distinct zonation perpendicular to the channel margin. An innermost belt, 0.5 to 2.5km wide, consists almost exclusively of the pteridosperm Neuropteris flexuosa. North of a river bend, three belts succeed the N. flexuosa zone: mixed pteridosperms and marattialean tree ferns; mixed arborescent lycopsids and marattialians; lycopsids with rare marattialians. South and inside the same bend, N. flexuosa is succeeded by mixed lycopsids, particularly Sigillaria, and marattialean ferns. Within the transects, marattialian ferns have wider distribution than other groups, suggesting broader environmental tolerances. Neuropteris flexuosa channel-margin mono-dominance may reflect high sedimentation rates, elevated nutrient conditions, or floating-seed dispersal. Lycopsid dominance in interior areas conforms with tolerance of deep, standing water. The spatial scale examined affects our perception of community assembly. Overall, distinct vegetational zonation suggests niche-assembly; however, within vegetational bands, there is considerable small-scale spatial variation suggesting stochastic properties.

Roof Shale Flora of Coal Seam 6 from the Asselian (Lower Permian) Taiyuan Formation of the Wuda Coalfield, Inner Mongolia and Its Ecostratigraphic Significance

Roof shale floras help understand the transition of vegetational landscapes from a peat–forming environment to a clastic one, but are seldom investigated in the Cathaysian province (typical present day China and East Asia). Here the roof shale flora of Coal Seam 6 from the lower Permian Taiyuan Formation of the Wuda Coalfield, Inner Mongolia, is systematically described and its ecostratigraphic and phytogeographic implications are discussed. The flora is composed of seven plant groups, including Lepidodendrales, Medullosales, Gigantopteridales, Peltaspermales, Noeggerathiales, Cordaitales and Cycadales. Many of these taxa are also documented in Euramerica, and the floral composition indicates a more intimate relationship between Cathaysia and Euramerica during the Cisuralian than previously thought. However, there are few genera and species in common with those of the underlying peat–forming flora. Moreover, the flora is hardly comparable with the commonly known flora of the Taiyuan Formation. Such assemblage differences are very likely due to changes of taphonomic and environmental phases, rather than evolutionary floral succession. For a full and more precise understanding of the floral composition, succession and the floristic discrepancy in different depositional environments, an ecostratigraphic investigation on the Late Palaeozoic of Cathaysia is advocated.

A reappraisal of Pecopteris miltonii (Artis) Brongniart, a mid-Westphalian (Early–Mid Pennsylvanian) fern

Pecopteris miltonii , a middle Westphalian fern originally described from Yorkshire, England, is redescribed and figured here from roof shales of the Barnsley Seam, the level from which it was first recorded. This material is regarded as complementary to the holotype, a fertile specimen showing limited morphological variation and almost lacking venation. Pinna shape of the holotype, including terminals, and the shape and dimensions of pinnules, match that of the material in hand. An analysis of the literature shows that only a limited number of specimens recorded with the miltonii epithet may be regarded as properly assigned. This includes a magnificent specimen figured from Lower Silesia by Stur. Although the species is apparently rare, it is fairly widespread, from North America to central Europe (Bohemia, Lower Silesia). The taxonomic position of Pecopteris miltonii is discussed with reference to the genera Lobatopteris and Crenulopteris , and its synonymy with Pecopteris aspidioides is proposed. A full analysis of Pecopteris miltonii and its synonymy serves to delimit this classical species, which has been often misidentified.

Paleoenvironmental analysis of the Glenalum Tunnel coal and roof rock, southern West Virginia—Implications for sulfur origin and trends

Unexpected variations in sulfur were encountered during mining of the Glenalum Tunnel coal in Wyoming County, West Virginia, in the Central Appalachian Basin. A geological analysis was initiated to determine the cause of the sulfur variations and provide a predictive tool for anticipating high-sulfur anomalies during future mining operations.The coal seam is comprised of six benches including bright to dull clarain, bone coal, and carbonaceous shale. The lower three benches are consistently less than 1% in raw and 1.5sp.gr. sulfur, with average values for each bench less than 0.73%. The average raw and 1.5sp.gr. sulfur for each of the upper benches is greater than 1.23%, and ranges from 0.27 to 6.07%. The majority of the sulfur occurs as finely disseminated pyrite. Thirteen cores drilled in 2012 indicate that the coal is overlain by laterally and vertically variable lacustrine, deltaic and estuarine facies. This interval averages 6.7m thick and is overlain by the Oceana Shale, a widespread marine unit.A sinuous, branching belt of high-sulfur coal approximately 305–610m wide and 3.22km long extends across the southern portion of the property. This belt correlates with cores where the lacustrine shale of the immediate roof is thin or absent and where the stratigraphic interval between the coal and the base of the Oceana Shale is comprised mostly of sandstone. Raw sulfur generally exceeds 1% and is more variable where the lacustrine roof shale is less than 52cm thick and where roof sandstone occupies 78–100% of the interval. The 1.5sp.gr. sulfur generally exceeds 1% where the lacustrine roof shale is less than 33.5cm and where the roof sandstone occupies 80–100% of the interval. High-sulfur areas are attributable to 1) the local influence of brackish to marine waters from tidal or deltaic distributaries which eroded down to the peat, and/or 2) thinning or removal of impermeable, lacustrine roof shale by channel erosion and hydraulic connection of the Oceana Shale marine pore fluids to the peat via permeable channel-fill sands.

Organic petrology, geochemistry, gas content and gas composition of Middle Pennsylvanian age coal beds in the Eastern Interior (Illinois) Basin: Implications for CBM development and carbon sequestration

Fifty four samples of coal and organic-rich roof shale strata were collected as part of a coal bed methane exploration program. Following canister desorption to document gas contents, the samples were analyzed by geochemical and petrographic methods. Coal samples were found to have moderate ash yields (avg. 13.5%, dry basis), and high total sulfur contents (avg. 4.3%, dry basis). The average gas content was 1.91m3/ton. Petrographically, the coals were dominated by vitrinite macerals (avg. 81.6%, mmf), especially telovitrinite. By comparison, liptinite (avg. 7.1%, mmf) and inertinite macerals (avg. 11.3%, mmf), were minor in occurrence. Coal samples ranged from high volatile C to high volatile A bituminous in rank (avg. Ro maximum, 0.76%).Shale samples had higher ash yields (avg. 76.1, dry basis), though total sulfur contents were comparable to the coal samples (avg. 4.2%, dry basis). Gas contents were lower than the corresponding coal samples (avg. 0.65m3/ton). Petrographically, the shale samples contained decreased amounts of vitrinite (avg. 25.6%, mmf), and higher amounts of liptinite (avg. 45.4%, mmf) and inertinite (avg. 29.0%, mmf) macerals, relative to the coal samples.Gas obtained from coal and shale beds in the Illinois Basin was relatively pure (high CH4 content). Limited data also indicated that Illinois Basin coals have the ability to adsorb fairly significant amounts of CO2. This suggests that CO2 injection to enhance methane production (ECBM), and/or to sequester CO2 may have some potential. Mineralization in the coals could negatively impact CBM production, but it was found that the majority of the mineralization was present in the roof strata.

Geotechnical Properties and Chemical Composition of Black Roof Shale as an Industrial Raw Material

Cretaceous pyritic roof shale from Onyeama mine in Enugu colliery was studied for the geotechnical and compositional characteristics relevant to its use in civil engineering construction and other industries. Properties investigated included moisture absorption, particle size distribution, plasticity, linear shrinkage, compaction, California bearing ratio (CBR), permeability, consolidation, the pH the sulphate content and chemical composition. The shale had a high fines content of 85%, a liquid limit of 55 %, a good standard Proctor compaction strength of 1690 kg/m3, preconsolidation pressure of 36 kN/m2, pH of 6.1 and sulphate content of 0.37%. The shale-water extract indicated a possibility of sulphate attack on concrete in contact with weathered pyritic shale. Permeability impairment of between 1x10-7cm/s to1x10-8 cm/s was observed on the compacted shale exposed to water and atmosphere. This was attributed to the formation of jarosite and ferric oxide which are the oxidation products of shale weathering. The relatively high silica content of 56% and the low combined potash and sodium content of 1.74% pointed to the potential of the oxidized black shale as a foundation for road bed, as a raw material for brick and a wide range of structural ceramics, and as filler for paints and plastics. The objectionable pyrite in the clay shale can be removed prior to use by treatment with sulphur-and iron-oxidizing bacterium-Thiobacillus ferroxidans or by aging the shale stockpile.

Organic petrology of Carbondale Formation coal beds and marine roof shales in Western Kentucky, Eastern Interior (Illinois) Basin, USA

Abstract Ten samples of Carbondale Formation (late Middle Pennsylvanian, Westphalian D) roof shale strata from the Western Kentucky Coal Field (Eastern Interior Basin, USA) were analyzed petrographically to gain a better understanding of the organic composition of the shales. The samples were collected in conjunction with a coal bed methane exploration program, so a direct comparison of the organic composition of the shales, and the coal beds that directly underlie them, could be made. Petrographically, total vitrinite contents in the shales average 20.8% (mineral matter free basis, mmf), which is significantly lower than the average vitrinite content of Carbondale Formation coal beds (avg. 81.8%, mmf; n = 32). In contrast, total liptinite contents average 49.7% (mmf) in the shales, which is significantly higher than the average liptinite content of Carbondale coals (avg. 7.0%, mmf). Amorphinite and bituminite were found to be the most abundant liptinite macerals in the shales, but were not recorded from the coal samples. Likewise, total inertinite contents were much higher in the shales (avg. 29.6%, mmf), than in the coals (avg. 11.0%, mmf). A type of macrinite identified as “granular macrinite” was the dominant inertinite maceral in the shales, but was absent in the coal samples. Although the average desorbed gas contents of Carbondale Formation coals and shales are low and currently uneconomical (avg. 0.9 ml/g [28.8 scf/ton] for the shales, 2.4 ml/g [76.9 scf/ton] for the coals, as received basis), they nonetheless represent a potential future gas resource.

Pennsylvanian (mid/late Bolsovian–Asturian) permineralised plant assemblages of the Pennant Sandstone Formation of southern Britain: Systematics and palaeoecology

We describe moderately diverse but extremely widespread calcified plant assemblages from the Pennsylvanian (mid/late Bolsovian–Asturian) Pennant Sandstone Formation (Warwickshire Group) of southern Britain, based on museum collections and new field discoveries. Fossils are documented from 21 sites where they comprise allochthonous accumulations within channel-lag conglomerate and coarse-grained sandstone facies of large, braided river channels draining the Variscan Orogen. Assemblages are dominated by cordaitaleans (87% of total, Amyelon, Mesoxylon, Dadoxylon), with a few tree-ferns (7%, Psaronius), and rare pteridosperms (1%, Myeloxylon), sphenopsids (2.5%, Arthropitys) and lycopsids (2.5%, ‘Lepidodendron’). These fossils clearly derived from a different plant community to those found in the coal seams (mixed fern/lycopsid-dominated based on palynofloras) and roof shales (pteridosperm-dominated based on megafloral adpressions), which occur between the fluvial sandstone deposits. Two competing hypotheses to explain these compositional differences are that (1) permineralised plants grew in extra-basinal settings adjacent to areas of Coal Forest or (2) permineralised plants grew on lowland interfluves during times of drier climate when Coal Forests had temporarily retreated. Data are currently insufficient to test between these hypotheses although the calcified preservational mode suggests burial under seasonally dry conditions.

A conifer-dominated palynological assemblage from Pennsylvanian (late Moscovian) alluvial drylands in Atlantic Canada: implications for the vegetation of tropical lowlands during glacial phases

Abstract: New research suggests that Pennsylvanian Coal Forests were commonly replaced by conifer-dominated vegetation during seasonally dry glacial phases. Here we describe palynological assemblages from stacked sequences of the Middle Pennsylvanian (late Moscovian) Sydney Mines Formation of Nova Scotia, Canada, which lends some support to this hypothesis. One critical sample from a widespread redbed succession below the Harbour Coal is dominated by conifer pollen (55%), together with abundant representatives of cordaitaleans, other coniferopsids, and rare pteridosperms, ferns and lepidodendrids. It differs markedly from 13 other samples obtained from coals, their roof shale–limestone and associated channel bodies, which are dominated by lepidodendrids, marattialean tree-ferns, cordaitaleans and/or calamiteans. The latter beds represent coastal wetlands, and are attributed to late transgressive and highstand systems tracts, whereas the conifer-bearing sample represents a dryland alluvial plain and may be attributed to lowstand or earliest transgressive systems tracts. Three additional samples from grey shale below a sequence boundary (late highstand) and between a redbed succession and major coal seam (early to mid-transgressive deposits) contain transitional palynofloras with a high proportion of herbaceous gleicheniaceous and sphenopteroid ferns, herbaceous lycopsids, and sphenophylls interspersed with cordaitaleans and/or lepidodendrids. The dominance of conifer pollen within the dryland components of well-defined sequences, which have been linked to relative sea-level change promoted by Gondwanan glaciation, supports the view that Pennsylvanian tropical biomes responded to the beat of glacial–interglacial cycles.