Main Seam Research Articles

Significance of organic matter in recording paleoenvironmental conditions of the Safa Formation coal sequence, Maghara Area, North Sinai, Egypt

Five coal and shale core samples of the Middle Jurassic Safa Formation were taken from a newly drilled water well at the depth interval from 191 to 208 m, and have been investigated in this study. Detailed organic and inorganic geochemical analyses of the Safa Formation reveal no significant differences between the upper seams and the main seam. The extracts of the coal samples have an unusual n-alkane distribution; the GC traces are dominated by unusual compounds eluting between n-C19 and n-C21. These compounds are thought to be diterpanes, which suggest significant conifer contributions to the coals. Higher amounts of hopanes and higher carbon preference index (CPI) values (n-C22 to n-C30) show significant bacterial contributions in samples characterized by high values of tissue preservation index (TPI). The C31 αβ (22S/22S+22R) hopane and C29 ααα (20S/20S+20R) sterane ratios show least variation through the shale–coal sequence. Shale and coal samples from the upper and main seams are characterized by high relative abundance of 17β (H)-hopanes, which could be derived from non-microbial organisms such as ferns. The petrographic and geochemical evidences suggest that the Maghara coal was formed in a “wet forest–swamp” environment situated in a marine-influenced lower delta plain.

Crocoite: an unusual mode of occurrence for lead in coal

What is believed to be a very unusual mode of occurrence for lead in coal has been identified as crocoite (PbCrO 4). As part of a larger study on trace elements and mineralogy in the Cretaceous Main Seam in New Zealand, crocoite was found in raw coal samples within the lower part of the coal seam. X-ray diffraction (XRD) and bulk chemical data from a SEM equipped with an energy dispersive X-ray analyser (EDXA) have confirmed the identity of this mineral. This is apparently the first time that crocoite has been reported in coal. Crocoite usually occurs only in the oxidised zone of lead mineral deposits. The occurrence of this mineral in the Main Seam coal implies that the deposit was exposed to an oxidising environment at some stage, most likely after coalification.

Die erste Wirbeltierfauna aus der miozänen Braunkohle der Niederrheinischen Bucht (Ville-Schichten, Tagebau Hambach)

This paper describes the first Miocene vertebrate fauna from the Ville Series of the Lower Rhine Embayment in western Germany. The fossil material was discovered in the vast Hambach open cast lignite mine ofRheinbraun. The numerous remains, mostly isolated teeth and disarticulated bones, were accumulated in a channel-fill within the main lignite seam. The fauna consists of chondrichthyans, teleosteans, amphibians, reptiles, and mammals which inhabited brackish-estuarine, lacustrine-fluviatile, and terrestrial environments. This is the first fauna to provide an insight into the diversity of vertebrates which lived in the forested peat swamps of the Rhenish Tertiary. Based on the rich association of more than 70 mammalian taxa, including about 30 rodent species, this late Orleanian fauna can be correlated with the upper part of the Mammalian Neogene biozone MN 5. Therefore the middle part of the main lignite seam (horizon 6C of the local lithostratigraphy) can be placed in the early middle Miocene. This means an age of 15.2-16.0 Ma (Langhian or Reinbekian of the stratigraphy of the NW German Tertiary). For some mammalian taxa (Lanthanotherium, Plesiosorex,Miopetaurista, Myoglis, Fahlbuschia, ‘Lartetomys’, Anchitheriomys, Dorcatherium), Hambach 6C is one of the richest European localities. In addition this assemblage contains some very rare mammals (‘Lartetomys’, Anchitheriomys, Orygotherium, Pliopithecus). The Hambach vertebrates are of great palaeobiogeographic importance as they represent the north westernmost outpost of terrestrial Miocene faunas in Europe. Die hier vorgestellte Vertebratenfauna aus den miozanen Ville-Schichten der Niederrheinischen Bucht gibt erstmals einen Einblick in den Artenreichtum der Tierwelt in den Braunkohle-Sumpfwaldern des rheinischen Tertiars. Die zahlreichen zusammengeschwemmten, disartikulierten Reste, vor allem Zahne und Knochen, stammen aus einer in das Rheinische Hauptfloz eingeschnittenen Flusrinne im Tagebau Hambach derRheinbraun AG. Die Fauna umfast Fische, Amphibien, Reptilien und Saugetiere aus brackisch-astuarinen, limnisch-fluviatilen und terrestrischen Habitaten. Die mit uber 70 Spezies, darunter ca. 30 Nagetierarten, sehr reiche Mammalierassoziation reprasentiert eine spatorleanische Fauna, die in den oberen Teil der Saugerzone MN 5 eingestuft wird. Damit kann fur den mittleren Abschnitt des Hauptflozes (Schicht 6C) erstmals ein biostratigraphisch begrundetes, fruhmittelmiozanes Bildungsalter von ca. 15.2-16.0 Ma (Langh bzw. Reinbek nach der NW-deutschen Tertiar-Gliederung) angegeben werden. Fur einige Mammalier (Lanthanotherium, Plesiosorex,Miopetaurista, Myoglis, Fahlbuschia, ‘Lartetomys’, Anchitheriomys, Dorcatherium) ist Hambach 6C eines der reichsten Vorkommen. Der Nachweis von sonst z.T. extrem seltenen Saugertaxa (‘Lartetomys’, Anchitheriomys, Orygotherium, Pliopithecus) ist auch palaobiogeographisch von Bedeutung, da es sich um die nordwestlichste Fundstelle im terrestrischen Miozan Europas handelt.

Relationship between reflectance and volatile-matter yield at the Maudlin (H) horizon of the offshore Northumberland and Durham coalfields

Seventy coal samples from the Maudlin (H) horizon (the main seam and two thin seams, one above and one below the main seam), from thirty boreholes on offshore easterly extensions to the contiguous Northumberland and Durham coalfields were analysed for vitrinite reflectance and volatile-matter yield of the whole coals. Geologically, the two extensions are parts of the “Northumberland Basin” and the “Alston Block”, lying on the Mid North Sea High, which are separated by important east–west trending structures, the Stublick and Ninety Fathom faults. Data for samples from the Maudlin seam in both Basin and Block, when plotted, show similar trends but lie in different parts of a general envelope formed by published data for the relationship between vitrinite reflectance and volatile-matter yield. Equivalent plots for the same properties for the two thin seams show similar separation and trends. In both cases, the separation between the two groups of measurements can be attributed to differing thermal gradients which were relatively low in the Basin and, together with thermal conductivities, high on the Block. Strong support for this explanation is given by the shift of plots for the relationship between reflectance and volatile-matter yield for coals in the Basin, which have been rapidly heated by igneous intrusion. These plots fall in the part of the reflectance/volatile-matter yield envelope occupied by the more rapidly heated coals of the Block. Stress is again laid on the inadvisability of placing too much reliance, for low-rank coals particularly, on the use of specific correlations between coal parameters for predictive purposes without taking due account of the range of geological circumstances existing within any particular coalfield region.

ASSESSING THE EFFECT OF MINE SUBSIDENCE ON DWARF SHRUB ERICOID HEATH COMM.UNITIES WITHIN A SITE OF NATIONAL IMPORTANCE

Planning consent was applied for in 1997 to extract coal from the Stanley Main seam beneath Skipwith Common, North Yorkshire in the United Kingdom. The 293ha Common is of national importance for its dwarf shrub ericoid heath communities, and has statutory protection under UK law as a Site of Special Scientific Interest (SSSI). Current planning guidance requires the effects of the mining proposals to be rigorously examined. The distribution of the heath vegetation is largely determined by the surface topography and sub-surface clay features, these determine relative site subsidence on drainage, and hence soil wetness and heath vegetation. Up to date topographical, soil and vegetation surveys were undertaken. This data was used in conjunction with the mining company`s subsidence predictions to model the effects of the mining of the previous and deeper Barnsley seam, as well as the proposed extraction of the Stanley Main seam. Overall, the model predicted there would be no adverse effect of subsidence from the mining of the Barnsley seam or cumulative effects following the extraction of the Stanley Main seam on the site features which determine relative wetness and heath distribution. The prediction for the Barnsley seam was tested using past and current vegetation andmore » soil wetness records. On a broad scale, there was no field evidence that the previous mining has resulted in a reduction in the extent of ericiod heath communities within the SSSI. On a local scale, there was some evidence for a very small effect at the one location where a potential effect was predicted. As the principal physical changes to the SSSI are induced by the previous mining of the Barnsley seam, no further effects were predicted for extracting the Stanley Main seam. The modelling approach has proved to be valuable, both technically and as a means of explaining the potential effects of mining on a nationally important nature conservation site to various interested parties, including the regulatory bodies.« less

A logging correlation scheme for the Main coal seam of the North Bohemian brown coal basin, and the implications for the palaeogeographical development of the basin

Abstract A method for correlating the Main coal seam in the North Bohemian brown coal basin by interpreting borehole logs is described. The most important well log was the gamma-gamma density log, but in some boreholes it was also necessary to use the natural radioactivity and electric resistance logs or technological sampling of the core. All these methods, at various levels of sensitivity, reflect changes in the amount of organic matter in the borehole profile. Vertical changes of coal matter content characterize variations of sedimentation conditions. In close boreholes gamma-gamma density logs are easily correlatable so that changes of sedimentation can be correlated over great distances. The method has been used to correlate the main seam along the axis of the basin. The main result of this correlation is that coal-bearing sedimentation occurred uninterruptedly along the main axis of the basin, with the development of swamp and lake conditions. During the swamp conditions peat accumulated over the majority of the present basin area, whilst during the shallow lake conditions the region of clastic sedimentation was controlled by the distance from the inflowing sediment source. The coal-bearing sedimentation cycle started by a levelling of the palaeorelief by infilling the depressions, and was followed an extension of the sedimentation area. Compaction of the previously deposited layers affected the ensuing strata. No significant variations in stratal thickness were found along the length of the main borehole line nor in any of the auxiliary lines whole, indicating that tectonic controls in basin subsidence were unimportant. Thus changes of sedimentation conditions dominantly of climatic conditions caused water levels in the basin area to fluctuate. For many reasons it is concluded that the correlatable boundaries are isochronal. The correlation scheme represents the first really objective correlation of the main coal seam over the area of the whole North Bohemian basin.

Depositional controls on coal distribution and quality in the Eocene Brunner Coal Measures, Buller Coalfield, South Island, New Zealand

The Buller Coalfield on the West Coast of the South Island, New Zealand, contains the Eocene Brunner Coal Measures. The coal measures unconformably overlie Paleozoic-Cretaceous basement rocks and are conformably overlain by, and laterally interfinger with, the Eocene marine Kaiata Formation. This study examines the lithofacies frameworks of the coal measures in order to interpret their depositional environments. The lower part of the coal measures is dominated by conglomeratic lithofacies that rest on a basal erosional surface and thicken in paleovalleys incised into an undulating peneplain surface. These lithofacies are overlain by sandstone, mudstone and organic-rich lithofacies of the upper part of the coal measures. The main coal seam of the organic-rich lithofacies is thick (10–20 m), extensive, locally split, and locally absent. This seam and associated coal seams in the Buller Coalfield are of low- to high-volatile bituminous rank (vitrinite reflectance between 0.65% and 1.75%). The main seam contains a variable percentage of ash and sulphur. These values are related to the thickening and areal distribution of the seam, which in turn, were controlled by the nature of clastic deposition and peat-forming mire systems, marine transgression and local tidal incursion. The conglomeratic lithofacies represent deposits of trunk and tributary braided streams that rapidly aggraded incised paleovalleys during sea-level stillstands. The main seam represents a deposit of raised mires that initially developed as topogenous mires on abandoned margins of inactive braidbelts. Peat accumulated in mires as a response to a rise in the water table, probably initially due to gradual sea-level rise and climate, and the resulting raised topography served as protection from floods. The upper part of the coal measures consists of sandstone lithofacies of fluvial origin and bioturbated sandstone, mudstone and organic-rich lithofacies, which represent deposits of paralic (deltaic, barrier shoreface, tidal and mire) and marine environments. The fluvial sandstone lithofacies accumulated in channels during a sea-level stillstand. The channels were infilled by coeval braided and meandering streams prior to transgression. Continued transgression, ranging from tidal channel-estuarine incursions to widespread but uneven paleoshoreline encroachment, accompanied by moderate basin subsidence, is marked by a stacked, back-stepping geometry of bioturbated sandstone and marine mudstone lithofacies. Final retrogradation (sea-level highstand) is marked by backfilling of estuaries and by rapid landward deposition of the marine Kaiata Formation in the late Eocene.

The geology, petrology and geochemistry of coal seams from the St. Rose and Chimney Corner coalfields, Cape Breton, Nova Scotia, Canada

Seams from the St. Rose and Chimmey Corner coalfields, Nova Scotia, Canada, were sampled and examined for petrographic and geochemical composition. Rank determinations indicate a rank of high volatile C-B bituminous. Seams show regular alternations of dull and bright microbanded lithotypes, with dull lithotypes predominant in the central portion of the main seam (No. 5 seam). Brighter lithotypes are dominated by vitrinite (>80%), with minor inertinite (avg. 12%) and minor liptinite. Duller lithotypes contain greater amounts of inertinite (up to 40%) and liptinite (primarily sporinite). Mineral matter consists of epigenetic pyrite, with lesser amounts of clay and quartz. Cabonates are common in the Chimney Corner seams. Elemental composition of the seams is similar to other Canadian coals and fall within world coal ranges, with the exception of high concentrations of Cl, Zn, Ni, Mo, Pb, Cu and As. Depositional environment of the seams as indicated by maceral composition, lithotypes and geology suggest a predominance of wet forest to reed moor conditions, in a fluvial-lacustrine setting. Periodic episodes of flooding and drying are indicated by lithotype, maceral and mineral variations.

The origin of the Tertiary lignite deposits in the Lower Rhine region, Germany

The Miocene lignite deposits of the Lower Rhine region amount to 55,000 million t. The Main seam is up to 100 m thick, the Upper seam is locally up to 40 m thick. The two seams occur in a complementary manner: the Main seam reaches its maximum thickness in areas where the Upper seam is replaced by clastics, and vice versa. The Main seam is found approximately in the centre of a subsiding basin, whereas the Upper seam is deposited near its margin. These observations suggested an investigation of subsidence, initial peat thickness, peat compaction and the factors governing the distribution of marine and continental sediments. Interpretation of the findings greatly depends on the length of time needed for the forming of the peat. Chronostratigraphic sections of the Lower Rhine Tertiary indicate that the peat of the Main seam may have been accumulated within a period of about 9 Ma and the Upper seam in 2 Ma. It can be argued from an initial peat thickness of up to 270 m that subsidence and peat growth rate averaged 0.03 mm/a or less. This seems to be reasonable as far as the distribution of contemporary clastics is concerned, but it would indicate an extremely low peat growth rate compared to observations from other regions. During the accumulation of the Main seam peat, two concurrent subsidence patterns can be recognized. One may have been initiated by the North Sea rift system. The other seems to be related to Variscan fold structures below the Tertiary. Above Variscan synclines, the surface subsided more than above anticlines, leading to an increased thickness of peat and clastics above synclines. Information from a great number of boreholes in the region, earthquake activity, and the recent tectonic stress field seem to indicate that the Variscan structures have been continuously deformed in the 35 Ma since the early Oligocene. Fluvial sedimentation shifted during the accumulation of the Main seam towards the rim of the subsiding basin. This phenomenon greatly improved the possibility of uninterrupted peat growth in the basin centre. The accumulation of the Main seam ceased when a new river system was established. Compaction of the Main seam peat and the beginning of pronounced block-tilting were important factors which lead to the peat of the Upper seam being deposited only near the southwestern margin of the former basin.

Mineral matter in low-rank coals and associated strata of the Mae Moh basin, northern Thailand

The mineral and other ash-forming constituents in lignites of the Mae Moh basin in northern Thailand have been identified and evaluated in relation to the minerals present in the associated interseam non-coal strata and the intra-seam non-coal bands. Treatment of the coal with water, ammonium acetate and hydrochloric acid shows that a considerable part of the ash-forming inorganic matter occurs in water-soluble, acid-soluble or ion-exchangeable form. Although the distribution of elements may be modified by the effects of pyrite oxidation, the mobile fraction of the fresh coal is dominated by water-soluble, ion-exchangeable and acid-soluble calcium, water-soluble and exchangeable magnesium, water-soluble sodium and sulphur, and acid-soluble iron and aluminium. Calcium is most abundant, especially in coals where a low proportion of silicate minerals (quartz, clay, etc.) is present; it combines readily with the different sulphur forms on combustion to produce an ash with a distinctively high CaO and SO 3 content. The main minerals in the coals are quartz, pyrite, and a clay fraction consisting of kaolinite, illite and an expandable, irregular mixed-layer mineral. The mixed-layer clay appears to be more abundant in the coal, and illite less so, than in the mudrocks of the associated non-coal strata. The non-coal partings within the main seams contain quartz, pyrite and a similar clay mineral assemblage, but they also contain an abundance of calcite and/or aragonite, and in some cases consist entirely of carbonate minerals. Shell fragments and possibly plant replacement structures are present in some of these materials. Gypsum, bloedite, hexahydrite and other sulphate minerals, and calcite, are deposited as fracture fillings and surface coatings on some exposed open-cut mine faces.

Petrography of Permian “Gondwana” coals from boreholes in northwestern Bangladesh, based on semiautomated reflectance scanning

Drilling through Quaternary alluvium and Tertiary cover at low-gravity anomalies in northwestern Bangladesh showed the presence of Permian sedimentary rocks in depressions that may be as much as a thousand meters deep in the crystalline basement. These Permian strata include low-sulfur, high-volatile bituminous coals in beds as thick as 15 m. The maceral group composition of these coals was determined by semiautomated reflectance scanning with a motorized microscope stage, rather than by point counting. This method was chosen to give objectively recorded raw analytical data and to provide a graphical picture of each sample. The coals are mostly “Gondwana” type (poorly layered “plum pudding” with abundant minerals and inertinite in a vitrinite groundmass) that would be classed as semi-dull (inerto-gelitite) coals. However, six samples have more than 70% vitrinite. None of the samples would be classed as sapropelic (liptinitic). The upper, middle, and lower main seams in borehole GDH-45 were sampled in 10 benches (0.1–3 m thick) each. Inertinite ranges from 7 to 100 vol% (mineral free basis) in individual benches, but composite seam averages are 41, 54 and 67%. Inertinite increases toward the top of two main seams so the bottom would yield the most valuable first mine slices. Some benches with extremely high inertinite content, such as the top 7 m of the lower thick seam, might be mined specially for blending with foreign low-inert coals to increase coke strength. The free swelling index reaches 7.5 in several vitrinite-rich benches, which can indicate good coking coal. Much of the vitrinite is fluorescent, which indicates secondary bituminization characteristic of vitrinite in good coking coals. Ash yields range from 8 to 52%, with composite seam averages of 15, 14 and 24%. Rare visible pyrite is in veinlets or small nodules; framboids and dispersed pyrite are absent. In borehole GDH-40 near Barapukuria (200–500 m depth), the mean random reflectance of vitrinite “A” ranges from 0.60 to 0.80% R o and vitrinite “B” ranges from 0.55 to 0.65%. In borehole GDH-45 near Khalaspir (287–442 m), the reflectance of vitrinite ranges from 0.79 to 0.94%. In individual cases, the vitrinite is difficult to define because of semivitrinite at higher reflectance (forming a separate peak on several reflectograms) and because of surface bitumen films or resinous (?) inclusions at lower reflectance. On the basis of vitrinite reflectance, the coals can be considered to have entered the “main phase of bitumen generation” of organic thermal maturation as understood in petroleum geochemistry.

The association of major, minor and trace inorganic elements with lignites. III. Trace elements in four lignites and general discussion of all data from this study

Fourteen trace elements (La, Cr, Sc, Y, Yb, Ga, Ni, V, Be, Zr, Ge, Pb, Sn, Ce) have been determined by emission spectroscopy in the ash from 7–17 levels within four early Tertiary lignite seams from Wyoming, Texas and Alabama, and two elements (Cu, Zn) in the acid-soluble and acid-insoluble fractions of the samples by inductively coupled plasma arc emission spectrometry. These elements were also determined in the roof and floor strata enclosing the seams. The concentrations of a number of elements ( e.g. Be, V, Cu, Y, Yb) were considerably higher in the coal ash than in the adjacent inorganic layers, and these elements are most probably associated with organic matter as coordination complexes. Several elements (Be, Y, Yb, Ga, Sc) were frequently found to be concentrated near the margins of the seam relative to the main body. One of the seams has a 6 cm “rider” separated from the top of the main seam by 9 cm of clayey sand. Analysis of fractions separated by specific gravity and solubility in acid showed this to be rich in trace elements, of which V, Be, Cu, Ni, Ge, Cr, Y, Yb, Ga and Sc appeared to be partly complexed with organic matter, and Sn and Pb were present only in minerals. The rider evidently acted as an efficient trap for unusually large amounts of many trace elements. Cluster analysis showed that the distributions of elements with depth in three of the seams represent three very distinctly separate populations of data; each seam constitutes a different geochemical problem. In a general discussion of the results of the whole series of three papers, a model describing the incorporation of inorganic components in peats is presented, based on the erosion of rocks by chelating organic acids and other agents, followed by transport in water and trapping of mineral grains and dissolved ions by the organic matter of peat. Inorganic materials in peat thus constitute the principal input of mineral matter into coals. The elements that tend to be enriched near the margins of lignite seams are mostly those that have complexed with organic matter. However, the data on this enrichment from our own and previously published work are quite variable, no doubt depending on the nature and efficiency of transport of the incoming cations.

A tidal origin for coarsening-upward sequences above two Wilcox lignites in East Texas

Conventional palaeogeographic reconstructions show a large river system occupying the East Texas Embayment during the deposition of the Wilcox Group. Coarsening-upward sequences above Wilcox lignites in East Texas have been interpreted as floodplain splays. However, the bedding types, sedimentary structures and shallow scour surfaces in a coarsening-upward sequence above the main seam at the Martin Lake Mine in Panola County indicate deposition in water stirred by tidal and wave activity. The bedding types include sand streaks in mud and lenticular, wavy and flaser bedding. The sedimentary structures include abundant wave-ripple lamination and large-scale crossbeds with thin, closely-spaced mud drapes. These crossbeds suggest traction currents of short duration alternating with periods of slack water. Pollen from broadleaf hardwood trees is the most common element of the palynoflora from the coarsening-upward sequence at the mine. The upper reaches of riverine estuaries along the SE coast of the United States provide a modern analogue for the environment of deposition of the Wilcox sediments at the Martin Lake Mine. Here tidal currents extend inland to places where freshwater aquatic plants and forests border the estuaries. The same bedding types and sedimentary structures that occur in the sediments at the Martin Lake Mine occur in a coarsening-upward sequence above a lignite at the Big Brown Mine in Freestone County. Recognition of the tidal origin of the coarsening-upward sequences suggests an embayed coast or a shoreline within the East Texas Embayment during the deposition of the strata above the lignites.

Petrographic Investigation of River Gem Coal, Whitley County, Eastern Kentucky Coal Field: ABSTRACT

The River Gem coal of the Breathitt Formation (Middle Pennsylvanian) was studied at three sites in a surface mine in the Holly Hill quadrangle, Whitley County, Kentucky. The River Gem coal is correlative with the Lily and Manchester coals in neighboring Knox, Laurel, and Clay Counties, Kentucky, and the Clintwood coal in Pike County, Kentucky. At the northern site, a 14-cm rider is separated from the 92.5-cm seam by 22 cm of shale. At the two southern sites, the rider is missing. At the latter sites, the 10 cm thick top bench of the seam is separated from the lower 63 cm of the seam by a 14-cm bony lithotype not found at the northern site. The lower 63 cm of the seam in the south and the main seam in the north are characterized by moderate ash and sulfur percentages (4.4-6.8% ash, 1.4-2.3% total sulfur, 0.6-1.1% pyritic sulfur, 74-81% vitrinite, 23-32% Fe/sub 2/O/sub 3/, and 2.3-4.5% CaO). In contrast, the upper bench in the south and the rider have 18.7-27.0% ash, 8.8-11.4% total sulfur, 5.1-6.4% pyritic sulfur, 92.3-93.6% vitrinite, 45.7-57.8% Fe/sub 2/O/sub 3/ and 0.13-0.20% CaO. The bone has over 26% ash, 5.5% total sulfur, 3.2% pyritic sulfur, andmore » 93.1% vitrinite. The overall similarity of the seam and rider characteristics between the north and south suggests that the southern bone is the lateral equivalent of the northern shale. The sulfide in the upper bench or rider and in the bone consists of fine (generally less than 10 ..mu..m), euhedral and framboidal pyrite with common massive pyrite. Massive pyrite appears as an overgrowth of fine pyrite in some places. Massive forms of marcasite, less abundant than pyrite, exhibit some evidence of developing later than the massive pyrite. A variety of < 2-..mu..m pyrite occurs as abundant, but isolated, unidimensional to tabular grains within corpocollinite, some of which is transitional to resinite.« less

A Depositional Model of the Antelope Coal Field, Powder River Basin, Wyoming

ABSTRACT The Anderson and Canyon coal seams are the main seams at the Antelope coal field in the south-central Powder River Basin. Each seam splits into multiple and thinner coal seams to the southwest in the study area. The strata underlying the Canyon coal seam suggest that the area of the Antelope coal field was a poorly drained swamp that developed into a well-drained swamp with minor small channels. The area further changed to a poorly drained swamp which initiated peat accumulation in the Canyon coal swamp. The lithologies, sedimentary structures, and isopach maps of the Canyon seam partings indicate that crevasse splaying, lacustrine conditions, and small crevasse-channel development produced the observed splits in the Canyon coal seam. Distal overbank deposits occur at the top of the C nyon seam and at the base of the Anderson seam; well-drained swamp deposits and crevasse splay, lake, lacustrine delta, and small channel-fill deposits occur between the coal seams. The Anderson coal seam represents another development of a poorly drained swamp where peat accumulation was significant. The rocks overlying the Anderson seam represent a combination of the environments mentioned above, with deposits from lakes and well-drained swamp environments dominating. The coal-beating sediments were deposited in paludal and tributary subsystems along the northern margin of the Wright delta. Deposition of the Canyon and Anderson coal seams and associated parting lithologies may have occurred when a river system or parts of that system underwent anastomosis. The coal swamp in which the Anderson seam was deposited was destroyed when the anastomosed character of the river system ended or the anastomosed river system shifted westward. This may reflect a relative change in the rate of subsidence within the basin.

METHANE DRAINAGE POTENTIAL OF THE NORTHERN BOWEN BASIN

Large volumes of methane plus some other gases are generated during the coalification process. Under suitable conditions some of this gas is adsorbed within the microporosity of coals. The rate at which the gas can desorb is a function of the permeability, degree of fracturing or cleating, moisture content, geochemistry of the coals, and the pressure differential. Flow rates from coals are generally low but can be dramatically improved by artificial stimulation and techniques such as lateral drilling.Methane drainage or coal de-methanisation has been carried out for many years, primarily for safety reasons. The resource value of methane in coal seams is now being recognised and considerable research is being undertaken both overseas and in Australia.In the Northern Bowen Basin, several million tonnes of coal are mined each year. The main seams of the Permian Collinsville, Moranbah, German Creek, and Rangal Coal Measures are generally thick and laterally extensive. The area north of Blackwater probably contains more than 100 billion tonnes of coal from which several hundred billion m3 (several Bcf) methane could conceivably be recovered in those areas where the coals are too deep for commercial exploitation.The coals of the Northern Bowen Basin are considered to have better physical parameters for the commercial development of methane drainage projects than those of the central and southern Bowen Basin where methane drainage projects were undertaken several years ago. It is estimated that more than 85 million m3 (3 Bcf) of recoverable gas per square km could be present in some areas. This gas can probably be produced for less than $1.50/GJ (1 Mcft, a figure which compares favourably with many conventional natural gas sources.The Northern Bowen Basin is well-situated with respect to potential gas markets at Townsville and Gladstone. The gas could also be used as a chemical feedstock for products such as ammonia, fertilisers, explosives or synfuels, with the plants located close to the producing wells, thus significantly reducing gas transport costs.

Imaging of VSP Data

Migration of VSP data can be effectively accomplished using a focused-lag sum imaging technique, similar to the Kirchoff 'diffraction stack' method. The imaging procedure is sufficiently flexible to handle the irregular source-receiver geometry associated with walkaway-source and deviated hole VSP. Signal dispersion is readily accommodated by admitting both group and phase velocity parameters. The migration can be performed on transmission data (downgoing wave) to yield a velocity map or on reflection data (upgoing wave) to produce a reflector map. The accuracy of both reflector mapping and velocity mapping depends on the nature and form of the signal. Pulse compression and multiple suppression are desirable pre-processing operations. The technique has been tested on synthetic VSP data and successfully applied to shallow VSP data collected in the Sydney Basin coalfields. For the real data, average velocities of the coal measure sequence and blurred images of the main seams were obtained. An equivalent section migration technique, based on leastsquares theory, is formulated in the Appendix.

The microconstituents of Godavari coals, South India

The present paper deals in detail with the coal typology, rank and correlation of some Indian coal seams. Petrological evaluation of several known coal seams reveals that there are two main seams, the King (lower) seam and Queen (upper) seam, with distinctly different characteristics. All the other seams, locally known by different names elsewhere in the field, are correlatable with either the King or Queen seams. The coals are of inferior quality because of the predominance of mixed coals types associated with dispersed mineral matter. However, some seams show characteristics which are amenable to quality improvement with suitable preparation methods. The coals appear to have been formed rapidly in a fluctuating environment (aerobic to anaerobic) under relatively cold to gradually warming conditions.

Lower Karroo pollen and spore assemblages from the coal measures and underlying sediments of the Siankondobo coalfield, Mid‐Zambezi valley, Zambia

Abstract A palynological investigation of three boreholes in the Lower Karroo of the Kazinze area of the Siankondobo coalfield (GS 31, 35 and 36), has indicated pollen and spore assemblages in the coal measures and underlying arenaceous beds. The arenaceous sediments occuring at the bottom of the Karroo succession, are part of the Siankondobo Sandstone Formation. They are relatively unfossiliferous, although rare thin mudstone intercalations found in one of the boreholes (GS 36), contain assemblages dominated by monosaccate forms (Cannanoropollis obscurus and Plicatipollenites indicus). The Gwernbe Coal Formation, (Ecca series), which rests unconformably on the Siankondobo Sandstone Formation contains at its base a dominantly arenaceous member (Maamba Sandstone), and in one of the boreholes (GS 31) carbonaceous shale intercalations contain mainly trilete spores e.g. Punctatisporites gretensis, Acanthotriletes filiformis and Apiculatisporis levis. Overlying the Maamba Sandstone is a coal seam (Main Seam), which in turn is overlain by carbonaceous mudstones with thin coal seams. The Main Seam and the carbonaceous mudstones, are generally dominated by trilete and striate and non‐striate disaccate forms e.g. Punctatisporites gretensis, Acanthotriletes filiformis, A. tereteangulatus, Apiculatisporis levis, Leioiriletes directus, Protohaploxypinus limpidus, P. goraiensis, Vesicaspora ovala and V. potoniei; one notable exception to this is the upper part of GS 31 where Incertae sedis forms are the most common. The information obtained from the three wells suggests that three concurrent range zones can be recognized and a tentative zonation has been proposed. The Siankondobo coalfield assemblages show many similarities to those recorded from the lower and upper part of the Luwumbu Coal Formation some 1,000 kilometers to the north‐east, in the north Luangwa Valley of Zambia. Common to both areas is the high proportion of monosaccates in the beds underlying the carbonaceous sediments, followed by a general dominance of triletes and disaccates (striate and non‐striate) throughout most of the carbonaceous sediments, although dominance of triletes does occur in some instances in the lowermost carbonaceous beds.

The skull and skeleton ofEogyrinus attheyiWatson (Amphibia: Labyrinthodontia)

As a preliminary to the redescription of the anatomy ofEogyrinus attheyiWatson, an account is given of the problems of nomenclature of British members of the anthracosaur family Eogyrinidae to which it belongs. There is no evidence to show that the four named genera of British eogyrinids differ from one another in any significant feature not explicable by allometric growth. Reconstruction of a series of allometric curves based on known skull specimens allows estimation of the dimensions of incomplete specimens. The skulls then fall into four size groups which correspond, with some stratigraphical backing, to the four named genera. The lectotype skull ofEogyrinus, from the Low Main Seam, Newsham, Northumberland, has been cleaned using an ‘ Airbrasive’ unit and is used as the basis of a new description of the skull. Additional information is provided by other Newsham specimens and two skulls from the Middle Coal Measures of Lanarkshire. The skull is completely known and is typical of anthracosaurs. The skull roof is closely similar to that of the eogyrinidPalaeoherpeton('Palaeogyrinus’)but no anterior tectal bone is present above the naris inEogyrinus. The nature of the dermal ornament is fully described. The palate is typically anthracosaur, with toothless vomers, a ‘ tusk-pair ’ on each palatine and ectopterygoid, and additional small ectopterygoid teeth. The pterygoids descend below the level of the jaw line posteriorly as inPalaeoherpeton. The braincase is reconstructed from an isolated Newsham specimen, originally attributed by Watson, from the lectotype and from one of the Scottish skulls. The isolated specimen shows the course of the semicircular canals as well as the fenestra ovalis. Most of the cranial nerve foramina are present. A complete reconstruction of the lower jaws is possible both as single rami and in articulation. Description of the jaw articulation allows a reconstruction of the relative movements of the rami in opening and closure. The only associated material of the appendicular skeleton is the lectotype left femur, but an interclavicle from Newsham is certainly eogyrinid and probably pertains toEogyrinus. Isolated ventral scales are described and their pattern of articulation reconstructed. The material described in this paper is combined with that used in an earlier account of the axial skeleton to give a reconstruction of the whole skeleton ofEogyrinusin articulation, together with a restoration of the appearance of the living animal.