Thin Seams Research Articles

Study on Joint Residual Stress Induced by Laser Beam Welding of High Strength Automobile Thin Sheet

Despite the advantages of the high energy density, high welding velocity and low deformation, some detrimental residual stresses were still introduced during the laser beam welding (LBW) process. The aim of this work was to study the magnitude and distribution of the residual stress in the LBW seam of the high strength automobile thin sheet. With the feature of applicable to the measurement of the residual stresses in the narrow area, the indentation strain method (ISM) was employed. By appropriate design of the biaxial strain rosette with the small size, the ISM was successfully used to measure the residual stress in the thin sheet LBW seam. Also, the finite element method (FEM) was used to calculate the residual stress. The comparison of the measured residual stresses through the ISM was made with those of the cutting relaxation method (CRM) as well as the FEM results. The ISM results showed that the highest tensile residual stress located at the seam centerline and exceeded to the 60 percent of the yield strength of the base metal.

Shearer mining application to soft thin-seam with hard roof

Study status on shearer mining in thin seams in the world is introduced. Base on the geological conditions of instable and soft thin-seam with hard roof in Caoyao Coal Mine of Yima Coal Group, China, and combined with related parameters of strata behaviors at coal faces, the paper concludes that the strata control on the thin-seam coal face is comparatively easy in line with the criteria for classification on strata stability of gently-inclined coal faces in China. Hydraulic supports of two-prop shielding with rated effective resistance of 2400kN can be employed in thin seam coal faces. Basic requirements for coordination equipments of shearer are summed up while mining thin seams. According to successful experiences of extracting thin seams in similar geological conditions in China, the scheme of feasibility coordination equipments of shearer is optimized in thin seams with thickness of 0.8-1.4m and 1.1-1.9m, respectively. The conclusions will provide a reference value for Caoyao Coal Mine on carrying out mechanized mining of the mine, improving safety production capability, and prolonging the mine life.

Quartz Exposure Can Cause Pneumoconiosis in Coal Workers

To the Editor: We read with interest the recent article by McCunney, Morfeld, and Payne entitled What Component of Coal Causes Coal Workers' Pneumoconiosis (CWP)?1 The intent of the article was to identify the specific substance(s) in the underground coal mining environment that are directly responsible for causing CWP. In addressing this question, the authors use a substantial portion of their work to point out that exposure to silica does not likely contribute to CWP. The authors are not wrong in their assessment of the role of silica in the development of CWP when it occurs at low levels. Epidemiologic studies dating back to the early 1970s showed through modeling of quantitative exposure data that mixed coal mining dust was the primary factor relating to CWP development, whereas silica's role was much smaller.2–4 Anthracite workers in many parts of the world have long been known to suffer high rates of CWP, although anthracite usually contains very low levels of silica. We believe that by downplaying silica in their desire to seek a more precise explanation for the cause of CWP, the authors have potentially done coal miners a great disservice. There is an important distinction that the authors fail to highlight in their report—silica may not be a major factor in the development of the clinical condition known as CWP, but silica does cause another form of pneumoconiosis among coal workers—silicosis. Silica remains a major risk factor for coal miners. This was amply demonstrated by the rapid development of pneumoconiosis among Scottish coal miners who had been engaged in cutting through a fault composed of sandstone rock.5 Weight for weight, silica is considerably more toxic than coal dust, and failure to control silica dust using a standard intended for coal dust can easily lead to massive overexposure to silica. In this, the approach to enforcing a silica standard in underground coal mines in the United States has been criticized as inadequate.6–9 As easily accessible coal seams are being depleted, attention is being paid increasingly to thin seams or to seams with rock intrusions that might not have been considered economically feasible to mine in the past. Mining these seams often requires cutting the adjacent rock, the roof, the floor, and intrusions, leading to exposures rich in silica dust.10 It is, therefore, critically important that the role of silica not be discounted when evaluating pneumoconiosis risk among coal miners. As surface and underground thin seam mining becomes more prominent the likelihood of increased silica exposure among miners, and the development of pneumoconiosis associated with those exposures becomes increasingly important. Situations where there is a risk of silica exposure must be identified, and silica dust levels controlled to the regulated level or lower. Only in this way will the potential future tragedy of an epidemic of silicosis in coal miners be averted. A. Scott Laney, PhD Michael D. Attfield, PhD Surveillance Branch, Division of Respiratory Disease Studies National Institute for Occupational Safety and Health Centers for Disease Control and Prevention Morgantown, WVa

Maximizing Energy at Coalface for Coalbed-Methane Fracturing

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 114974, "Maximizing Energy at Coalface for Coalbed-Methane- Fracturing Operations," by Abbas Mahdi, SPE, Schlumberger; Mike Yu, SPE, EnCana; Doug Pipchuk, SPE, Craig Wasson, SPE, Jim Nguy, SPE, and Nathan Kathol, Schlumberger, originally prepared for the 2008 CIPC/ SPE Gas Technology Symposium Joint Conference, Calgary, 16–19 June. The paper has not been peer reviewed. Nitrogen coiled-tubing (CT) fracturing is the predominant method for completing and stimulating dry-coalbed-methane (CBM) formations, such as the Horseshoe Canyon in the west-ern Canadian sedimentary basin. Currently, energy that can be delivered to the coalface of these dry-CBM wells has been limited by the frictional pressure loss through CT. The full-length paper discusses the development of a technique that releases a large-volume pressure pulse downhole during the fracturing process to create an order-of-magnitude change in available energy at the fracture face. Introduction The Horseshoe Canyon dry-coal formations have been exploited commercially since late 2000. The Horseshoe Canyon CBM play is a unique CBM play, in that it consists of a dry underpressured coal, which does not require dewatering before production. The coal consists of multiple thin seams, ranging from 10 to 30 seams per well, that are treated individually. Coal-seam thick-ness ranges from 0.1 to 2.5 m. The production rates from these CBM wells dictate that an efficient drilling and completion model be adopted to be economic. The wells are drilled with CT drilling rigs, cased, and cemented. Wireline perforating crews perforate the zones of interest in a rigless operation. The individual coal seams then are stimulated by injection of dry nitrogen at high rates through a CT reel equipped with a fracturing isolation tool. The dry coal has not responded well to any other form of stimulation. To optimize the completion process, high-rate nitrogen-pumping units were developed to reduce the footprint and cost and to increase efficiency of the operation to the point where one and a half to two wells can be stimulated per day. Since the introduction of that change, various optimization initiatives have been attempted. The optimization of nitrogen-pumping rates and pumped volumes has been the focus of these attempts. High rates have been limited by the inside diameter of the CT string. Several CT sizes have been used for this application. Economics and logistics have limited the CT size for CT fracturing to 2 7/8 in. for deeper wells and 3 1/4 in. for shallow wells. The migration to bigger pipe did pro-vide some reduction in frictional pressure loss, but effective pressure at the coalface still was not transported from the surface efficiently.

Sire and growth-path effects on sheep meat production. 3. Fascicular structure of lamb loin muscle (m. longissimus lumborum) and the impact on eating quality

The effects of sire genetics and growth path on the fascicular structure (FS) of lamb loin muscle (m. longissimus lumborum; LL) and the consequences for eating quality were studied in progeny (n = 299) of 20 Poll Dorset sires and Merino ewes. Sires were selected on the basis of their Australian sheep breeding values (ASBV) for post-weaning growth (PWWT), loin eye muscle depth (PEMD) and subcutaneous fat (PFAT). Growth of lambs was varied by time of weaning (early or late) and by feeding level within weaning group, where lambs were either fully fed throughout or were feed restricted for 55 days then re-alimented to achieve liveweight of ~45 kg at slaughter. The FS variables were determined in differentially stained histological sections of LL by using automated image segmentation and circle geometry methodology and were defined as percentage connective tissue, perimysial seam thickness and fascicular width. Sire ASBV was not a significant covariate to measures of FS, despite ASBV-related effects on growth, carcass leanness and fatness. Independent of weaning time, faster growth was induced by re-alimentation of feed-restricted lambs, resulting in LL with less connective tissue as a percentage of cross-sectional area and larger fascicles than for fully fed peers. The direction of the perimysial seam thickness response varied with treatment and time of weaning. Rapid growth of re-alimented early weaned restricted lambs resulted in thinner seams than for fully fed peers, whereas the opposite response was observed in the late-weaned lamb contrast. This suggests that the weight and age of the lamb at the time of nutritional compromise and re-alimentation are important factors in determining the thickness of perimysial connective-tissue seams. Whilst the evidence confirms differential accretion of the myofibrillar and connective tissues and despite reports of positive effects on tenderness brought about by such changes, variation in structural measures was not associated with variation in either objective measures (compression) or sensory scores for tenderness of the loin muscle. The data from the present study support the tenet that rapid growth before slaughter, combined with appropriate sire genetics, will not compromise the physical characteristics and sensory qualities of the meat.

Concentration of PGE in the Earth's Crust with Special Reference to the Bushveld Complex

Concentration of PGE in the Earth's Crust with Special Reference to the Bushveld Complex

Logistic regression model for prediction of roof fall risks in bord and pillar workings in coal mines: An approach

The roof fall hazards are the major problems in underground coal mines, which are generally unpredictable due to the associated uncertainties arising out of the complexity of geological conditions and variability in mining parameters. During the six year period, 1996–2001, 253 Indian coal miners lost their lives and 401 are seriously injured in 490 different roof fall accidents. In India, 32.7% of the total fatal injuries in coal sectors are due to roof fall in bord and pillar method of workings. This paper attempts to predict the severities of roof fall accidents based on some major contributing parameters using the binary logistic regression model. In total, 128 roof fall accidents for the last few years from five underground coal mines in India having bord and pillar method of working are analyzed for this study. The results revealed that wider gallery width is more prone to major and serious accidents than narrower gallery width. Thin seams are more amenable to major accidents in comparison to thick seams. Unsupported or partially supported roofs have higher risk for contributing major as well as serious accidents. Deep workings are more prone to major accidents as compared to shallow depth workings.

Void detection at an anthracite mine using an in-seam seismic method

An in-seam seismic (ISS)-based void detection technique was developed at Penn State University. Among various features, the most important one is its capability of acquiring high quality and broadband signals ranging from 50 to 5000 Hz. This feature is essential for acquiring and analyzing signals for a thin seam condition. The technique was tested at an underground anthracite mine. It successfully detected a mined out void at a distance of 46 m (150 ft) from the coal face. The seam height at the test site was 1.4 m (4.5 ft) on average. The transmission surveys generated well developed Love seam waves. This made it possible to reliably assess the dispersion characteristics of Love waves for this particular site. The Airy-phase had a typical frequency range of 400–600 Hz with a fairly stable velocity of 975 m/s (3200 ft/s). An elliptical method was used for void mapping in order to accommodate highly irregular sensor and source locations. The mapping error was within ± 4.6 m (15 ft) based on the test results.

Palynological evidence for late Westphalian–early Stephanian vegetation change in the Dobrudzha Coalfield, NE Bulgaria

The Dobrudzha Coalfield in northeast Bulgaria has coal-bearing deposits ranging from latest Namurian to early Stephanian age (late Bashkirian to Moscovian age). Palynology of the coals in the upper Makedonka, Krupen and Gurkovo formations has been used to identify major changes in the vegetation during late Westphalian and early Stephanian times. The palynomorphs were grouped in two different ways (according to general morphotype and according to parent plant group) and stratigraphical trends in the two sets of groups used to identify vegetation change through the succession. Detrended Correspondence Analysis was also used to identify ecological relationships between the palynofloras. In the upper Makedonka and Krupen formations, lycophyte spores mostly comprise 15–25 % of the palynofloras in the thicker seams, but in the thinner coals they can represent up to 55 %. Of the other plant groups, ferns are the most abundant, representing 31–69 % in the thicker seams, 12–41 % in the thinner seams. This suggests that the arborescent lycophytes were mainly restricted to pioneer vegetation in these upland areas, and were replaced by ferns as the peat substrates became better developed, suggesting better-drained conditions. The thinner seams also have a noticeable component of sphenophyll spores, indicating significant areas of open conditions allowing colonization by these scrambling plants. In the Gurkovo Formation coals, lycophytes form an even smaller part of the palynological spectra, usually less than 10 % and in only one sample just over 25 %; fern spores make up 43–57 % of the palynofloras. This is in contrast to the palynofloras reported from contemporaneous clastic deposits in South Wales, most of which consist mostly of 34–60 % lycophyte spores and 14–34 % fern spores. Even more marked is the difference from the contemporaneous coals formed in lowland settings in the USA, which have mostly > 50 % lycophyte spores. This evidence suggests that the timing of the decline in abundance of arborescent lycophytes varied according to elevation above sea-level. In lowland coastal settings, the lycophytes remained dominant until middle–late Cantabrian times, but in more inland areas they were progressively replaced mainly by arborescent ferns during late Westphalian times.

The slip surface in the D Zone of the Barton Clay

The most dominant of the preferred bedding plane surfaces of shearing in the Eocene Barton Clay coastal cliffs of the Hampshire Basin is that near the base of the D Zone. This is utilized as the basal surface of compound landslides virtually throughout its 2.3 km outcrop from near the cliff top to beach level, an elevation change of nearly 30 m. The shear zone is located along a thin seam of dark chocolate brown clay, which has been investigated by X-ray powder diffraction mineralogical analysis, X-ray fluorescence chemical analysis, scanning electron microscope study of the microfabric and ring shear tests. The dark seam is slightly more clay rich and has a slightly lower value of residual shear strength than the ambient D Zone clay. The reason for its preference during landsliding is discussed. The available evidence suggests that although some previous shear displacement by flexural slip during folding may have occurred, the main displacement results from the lateral rebound response to coastal recession, involving a reorientation of any previous clay particle alignment. Lateral rebound initiates progressive failure, which leads to the compound landsliding of the in situ clay slopes.

Petrographical, Palynological, and Sedimentological Aspects Regarding the Genesis of Palaeogene Lignites Near Alexandroupolis, Thrace, Greece

Several minor lignite deposits of Palaeogene (Eocene to Oligocene) age occur in the vicinity of Alexandroupolis, Thrace, northern Greece. A few rather thin seams were mined in the past by small private operations for local use. Coal samples have been collected from old mine dumps and outcrops around abandoned mine posts to be studied by means of maceral analysis at high magnification. The groundwater and vegetation index are calculated from the maceral composition and used to draw conclusions concerning the environment of deposition. In addition, block samples of coal cut perpendicular to bedding were studied at intermediate magnification and under fluorescence thus revealing some interesting bedding features as well as well-preserved plant organisms. The coals are characteristically finely laminated and highly gelified. Palynological preparations have thus far yielded only poorly preserved palynomorph assemblages rather low in diversity and dominated by fern spores. This fern dominance is rather unusual; however, it is compatible with the occurrence of fertile fern fronds observed in petrographic coal sections. Accompanying clastic sediments exhibit cyclic fining-upward sequences at a scale averaging about 1 m in vertical extent. Grain sizes range from small gravel to clay and silt. In some cases, siltstones in the roof of coal seams include abundant plant fragments showing parallel venation. The evidence presented from various sources suggests a rather unstable fluvial environment and a generally high water table on the flood plain for the formation of these lignites.

Centrifuge Modeling of Rigid Square Footings on Weak Jointed Rock

Abstract Four series of centrifuge tests were performed using a model rock made from a mixture of sand, bentonite, cement, and water. Tests were conducted to determine the effect of horizontal and vertical discontinuities in the bedrock on the load settlement response of a rigid, shallow footing. A prototype footing, measuring 1 m × 1 m, was simulated in the study. Horizontal and vertical joints, in-filled with compressible material, were simulated by incorporating thin seams of styrofoam. Results from this study are compared to the commonly used methods used to predict the ultimate bearing capacity of footings on jointed rock mass. It is concluded that the existing methods to predict the bearing capacity are conservative for the range of design parameters studied in this research.

Subsurface Characterization at Ground Failure Sites in Adapazari, Turkey

Ground failure in Adapazari, Turkey during the 1999 Kocaeli earthquake was severe. Hundreds of structures settled, slid, tilted, and collapsed due in part to liquefaction and ground softening. Ground failure was more severe adjacent to and under buildings. The soils that led to severe building damage were generally low plasticity silts. In this paper, the results of a comprehensive investigation of the soils of Adapazari, which included cone penetration test (CPT) profiles followed by borings with standard penetration tests (SPTs) and soil index tests, are presented. The effects of subsurface conditions on the occurrence of ground failure and its resulting effect on building performance are explored through representative case histories. CPT- and SPT-based liquefaction triggering procedures adequately identified soils that liquefied if the clay-size criterion of the Chinese criteria was disregarded. The CPT was able to identify thin seams of loose liquefiable silt, and the SPT (with retrieved samples) allowed for reliable evaluation of the liquefaction susceptibility of fine-grained soils. A well-documented database of in situ and index testing is now available for incorporating in future CPT- and SPT-based liquefaction triggering correlations.

A contribution to the study of kotoite: data on three Romanian occurrences

Samples of kotoite from three boron-bearing magnesian skarns in Romania (Baija Bihor, Pietroasa and Cacova Ierii) were investigated in order to add new data on this rare mineral species and to assess the influence of the chemical variation on the main physical and crystallographic constants of the mineral. In all three occurrences, the mineral is present in the outer skarn zones developed at the contact of igneous bodies of Upper Cretaceous-Paleocene age with dolomite sequences. The grains of kotoite are typically rounded and coated by thin seams of brucite. The compositional limits are given by 0.006 to 0.018 apfu Fe and 0.001 to 0.018 apfu Mn at Baita Bihor, 0.016 to 0.017apfu Fe and 0.003 to 0.004 apfu Mn at Pietroasa and 0.046 to 0.063 apfu Fe and 0.004 to 0.007 apfu Mn at Cacova Ierii. All the analyzed samples are Ca-poor. The increasing (Fe,Mn)-for-Mg substitution in kotoite causes an increase of the density, mean index of refraction, a cell parameter and cell volume; on the contrary, the c cell parameter decreases with increasing weighed ionic radius of the six-fold coordinated cations, then decreases with advancing (Fe,Mn)-for-Mg substitution. It is reasonable to assume that in all three occurrences kotoite crystallized in the temperature range of 400-575 °C, at pressures of up to 3 kbar. Subsequent alteration in szaibelyite+brucite or, more frequently, in brucite+sassolite, was influenced by the pH of the late hydrothermal solutions.

Analysis of shearing of a rock ridge

A rock ridge carrying a major roadway through a quarry in the greater Chicago, IL area sheared along sub-vertical regional joints causing significant distress of the roadway as a result of apparently limited adjacent quarry excavation of a glory hole. The large-scale movement rendered the road unusable. This paper presents a detailed analysis of factors contributing to this response. Post-event field observations of ridge movement revealed that lateral displacements were concentrated along a horizontal thin shaley seam below the bottom of the quarry. These observations show that the sheared ridge slid along the shaley seam and moved as a single block. Three-dimensional numerical analyses of the ridge and the quarry construction activities show that as the quarry was deepened, a buildup of large horizontal stresses occurred in the rock base above the shaley seam. The excavation of the glory hole through this rock base lead to arching and an increase in longitudinal stresses and a reduction in lateral confining stresses along the ridge. The analyses show how the unique combination of large horizontal stresses, the horizontal shaley seam, and stress redistribution due to glory hole construction lead to large shear displacements along the persistent sub-vertical regional joints.

LATE-STAGE CRYSTALLIZATION HISTORY OF THE JURASSIC NORTH MOUNTAIN BASALT, NOVA SCOTIA, CANADA. I. TEXTURAL AND CHEMICAL EVIDENCE FOR PERVASIVE DEVELOPMENT OF SILICATE-LIQUID IMMISCIBILITY

The Jurassic (201 Ma) quartz-normative continental tholeiitic basalts of the North Mountain Basalt (NMB) Formation of southern Nova Scotia, Canada, record evidence of pervasive silicate-liquid immiscibility. The basalts, up to 400 m thick, typically with phenocrysts of plagioclase (An50–70) and clinopyroxene (Wo40 En40Fs20), are subdivided into lower, middle, and upper units on the basis of the nature of the flows and petrographic features. Petrographic observations combined with image analysis indicate that the middle and upper units are characterized by an abundance of mesostasis material (i.e., quenched residual melt) that contains skeletal clinopyroxene, acicular plagioclase, skeletal Fe–Ti oxides, Fe–Ti–P-rich globules, and andesitic to rhyolitic glass. Raster analysis of the mesostasis tracks an in situ fractionation that culminated in formation of an interstitial felsic glass (i.e., 74 wt.% SiO2) that contains skeletal apatite and Fe-rich clinopyroxene. The composition of the skeletal clinopyroxene, ca. Wo20En15Fs65, acicular plagioclase (An35–55, ≤2.5 wt.% FeO), Fe–Ti–P-rich globules, and intergranular glass of the mesostasis are consistent with formation from an interstitial melt that evolved in a disequilibrium environment promoted by rapid cooling of the lavas. The mineralogical and chemical features are consistent with the process of silicate-liquid immiscibility within the residual liquids of basaltic systems, in this case late-stage intergranular melts. The presence within the NMB of (1) Fe-rich clinopyroxene-bearing mafic pegmatite, (2) thin (i.e., 1–2 cm) seams of rhyolite associated with the mafic pegmatites, and (3) locally abundant segregation pipes of mixed mafic–felsic composition, is considered to reflect mobilization of the Fe- and silica-rich immiscible melts.

Petrology of two diamondiferous eclogite xenoliths from the Lahtojoki kimberlite pipe, eastern Finland

Diamondiferous Group A eclogites constitute a minor portion of the mantle-derived xenoliths in the eastern Finland kimberlites. They have been derived from the depth interval 150–230 km where they are inferred to occur as thin layers or small pods within coarse-grained garnet peridotites. The chemical and isotopic composition of minerals suggest that they represent (Proterozoic?) mantle-derived melts or cumulates rather than subducted oceanic lithosphere. During magma ascent and emplacement of the kimberlites, the eclogite xenoliths were mechanically and chemically rounded judging from the types of surface markings. In addition, those octahedral crystal faces of diamonds that were partially exposed from the rounded eclogite xenolith became covered by trigons and overlain by microlamination due to their reaction with the kimberlite magma. The diamonds bear evidence of pervasive plastic deformation which is not, however, evident in the eclogite host. This suggests that annealing at ambient lithospheric temperatures has effectively recrystallised the silicates while the diamond has retained its lattice imperfections and thus still has the potential to yield information about ancient mantle deformation. One of our samples is estimated to contain approximately 90,000 ct/ton diamond implying that some diamonds occur within very high-grade pods or thin seams in the lithospheric mantle. To our knowledge, this is one of the most diamondiferous samples described.

Retrieved Human Allografts

We studied seventy-three massive preserved human allografts, retrieved from two to 156 months after implantation, to provide insight into the mechanisms of their repair. The specimens were studied with radiographic and histological techniques that permitted time-related quantitative analysis of the reparative mechanisms of union, cortical repair, soft-tissue attachment, fracture, and characteristics of the allograft-cement interface and the articular cartilage. Union at cortical-cortical junctions occurred slowly (approximately twelve months) by host-derived external callus that bridged the junction and filled the gap between abutting cortices. The bone in the gap did not undergo stress-oriented remodeling even after many years, and, when the union was intentionally disrupted, failure occurred at the cement line that marked the allograft-host junction. Repair of the necrotic graft matrix was both external and internal. External repair consisted of the apposition of a thin seam of host bone on the outer surface of the graft, coating about 40% of the surface at one year and 80% at two years. Internal repair was confined to the ends and the periphery of the cortices and penetrated so slowly that only 15% to 20% of the graft was repaired by five years, after which deeper repair seldom occurred. Graft fractures in specimens retrieved soon after fracture showed only necrotic bone adjacent to the fracture site, whereas those retrieved after fracture-healing showed a marked increase in internal repair of the bone about the fracture site. When bone cement had been used to fix a prosthesis, there was no evidence of bone resorption or loosening of the device. The osteoarticular specimens showed no survival of chondrocytes in the articular cartilage. However, the architecture of the acellular cartilage was well preserved after two to three years and occasionally after as many as five years. Late degenerative changes in the articular cartilage coincided with subchondral revascularization and fragmentation, and the articulating surfaces became covered by a pannus of fibrovascular reparative tissue. Degenerative changes in articular cartilage occurred earlier and were more advanced in specimens retrieved from patients with an unstable joint than in those retrieved from patients with a stable joint. Repair of massive human allografts is an indolent process that follows a fairly predictable course during the first few years and is influenced by other biological activities, such as fracture repair, supplementary autografting, and tumor recurrence.

Anthropogenically-triggered iron pan formation in some Irish soils over various time spans

Podzolisation, with iron transport and deposition as coloured Bs or Bh horizons, is the fate of acid or decalcified, free-draining mineral soils in Ireland's cool temperate, humid climate. A second generation of iron accumulation, mainly in the form of thin seams (pans, placic horizons) has been studied at several locations in Ireland. These seams generally occur within a former cultivated horizon and within 20–25 cm of the current surface. The time span over which the iron pans developed ranges from a few decades to four or five centuries and invariably involved a change in land-use. The trigger for the new accumulation is a change in Eh/pH relations and/or acid/base conditions. Examples include (1) sudden and massive loading of a parkland pasture with peat debris in the 1950s, (2) acid litter from a single spruce crop (ca. 50 years) in a reclaimed podzol topsoil, (3) slow accumulation of peat debris over a number of decades in a peat fuel storage area, started about 100 years ago, (4) invasion of land abandoned ca. 1850 by heather and other acidophilic species and (5) run down of soil fertility and structure by grazing without amendments (pedogenic age, four to five centuries). The morphological and chemical characteristics of these soils show that where free iron is present in a horizon, any land-use change that establishes a pH or Eh/pH gradient is likely to initiate diffusion gradients and the local accumulation of iron oxides, irrespective of topographic position. This study investigates the effect of organic matter on iron accumulation and on the development of the second-generation eluvial/illuvial horizon sequence as affected by anthropogenic activities.

The anomalous behaviour of properties of seams at the Plessey (M) horizon of the Northumberland and Durham coalfields

The Plessey (M) coal in the Northumberland and Durham coalfields has never had the economic significance of many other coal seams in the region because of its variable thickness and its sporadic occurrence as several thin seams. Where mined, the seam has been long known to display aberrant coking properties compared with coals above and below in the succession. Samples of Plessey coals were analysed from nine offshore boreholes, three opencast prospecting boreholes and three collieries. Vitrinite-reflectance measurements consistently suggest that the seams have an anomalously lower degree of coalification than would be expected from their position in the geological succession. Higher volatile-matter yields from “whole-coal” samples of the Plessey seam, compared with the volatile-matter contents of coals immediately above and below in the succession, confirm this view. The suppressed vitrinite reflectances of the Plessey coals cannot be attributed to particular geothermal conditions and overlying seam lithologies, as other reduced reflectances of certain seams in the Durham coalfield have been in the past. Neither is the suppression caused by the now familiar close association that sometimes occurs between vitrinites and liptinitic macerals. The suppression and the raised volatile-matter yields are more likely to be caused by the original conditions under which the Plessey coals were deposited. The behaviour of the Plessey seam parallels that of the Katharina seam of the Ruhr coalfield, which, at the time of its deposition, was marine-influenced. Although no direct evidence exists that the Plessey seam was similarily affected, the close association of leaves of the Plessey seam in several boreholes with the Harvey Marine Band suggests that marine, near-marine or calcium-rich conditions, possibly aided by a high liptinite content in the marine band, are the most likely explanation for the production of the perhydrous coals. Bitumen exudates would have been generated early during the coalification process, so causing the aberrant properties and unexpectedly strong coking behaviour of the Plessey coals.