Tim A. Moore

Peat/coal type and depositional environment: are they related?

Abstract Four bogs in New Zealand were investigated in order to understand the relationship between peat type and depositional environment. This relationship is important because peat type translates into coal type, and coal types can ultimately be used to infer how and under what conditions the original peat bog formed. In our study, no correlation was found between peat type and depositional environment in the four bogs examined. Moreover, no correlation was found between peat type and either tectonic setting or climate. Water table level and degree of fluctuation are the only parameters which seem to have a good causative relationship on peat type. The bogs, Whangamarino, Moanatuatua and Kopouatai in the North Island and Sponge Swamp in the South Island, all have different depositional settings ranging from coastal plain, to fluvial-meandering and fluvial-braided river floodplain. We found no diagnostic peat types that would allow those different environments to be distinguished from studies of the peat. Data from other tropical and temperate climate peat bogs also support our contention that no diagnostic peat types can distinguish particular depositional settings. However, the level and variability of water table does have a correlation, one that is also seen in bogs elsewhere. From our observations, we infer that the validity of using maceral ratios (directly related to coal type) to indicate depositional environment should be questioned. At best, coal type only represents to what degree the original plant components were degraded, but not how they were degraded. To infer other parameters such as depositional environment, tectonic setting or climate, other data (e.g. distribution of surrounding sediment types, palynology, etc.) must be collected and assessed.

Composition and grain size of an eocene coal bed in southeastern Kalimantan, Indonesia

Abstract A study of an Eocene coal in southeastern Kalimantan , Indonesia shows a relationship between megascopically determined coal types and microscopically determined kinds and sizes of organic components. Microscopic examination of small (3 × 3 × 3 cm), uncrushed, chemically eteched block samples revealed that the coal was composed of plant parts and tissues set in a matrix of both finegrained particulate and amorphous material. The material identified as plant parts consists of stems and roots with secondary growth, leaves, and one unknown plant structure. However, most components with cellular features cannot be identified as particular organs and are designated only as woody tissue and categorized by cell wall preservation, that is, well, moderately, or poorly preserved. The particulate matrix is composed of cell wall fragments, cell fillings, resins, spores, algae and unidentifiable fluorescing fragments. Fungal remains are also present within the matrix and are the only oxidized material represented within the coal. The amorphous matrix consists of unstructured (at × 400) humic gels and bitumen. Size measurement of the organic constituents shows that each particulate component possesses its own size distribution that approaches normality when transformed to a - log2 (O) scale. The size distribution of most of the plant parts is nearly symmetrical around a mean of 3–4 φ, whereas means of the particulate matrix components are in the 8–9 φ size range. Differences in proportions of the plant parts and matrix components determine the character of the megascopic coal types. Bright banded coal types contain the greatest proportion of well preserved plant parts; whereas the bright nonbanded and dull, steel-gray coal types contain fewer well preserved plant parts and consist mostly of plants parts with poor cell wall preservation. Hence, the megascopically recognizable coal types appear to reflect differences in particle size arising from the degree of preservation of the plant material. Concentration of decay-resistant resin and cell fillings in the non-banded and dull coal types is believed to be a result of the loss of intact plant material. An absence of larger (> 2 mm) plant material in the Eocene coal contrasts with the proportions indicated by data from a Miocene lignite and a Holocene peat, both from Kalimantan. In the latter two deposits logs and roots > 2 mm thick comprise as much as 10–15%. The paucity of large plant material in the Eocene coal is a function of the original peat-forming vegetation. The Eocene coal formed from palms and ferns which are easily degraded through microbial activity. In contrast, the lignite and peat deposits accumulated from woody angiosperms that are relatively more resistant to decay. However, all three deposits have similar size distributions among the smaller (

Slope stability probability classification, Waikato Coal Measures, New Zealand

Abstract Ferm classified lithological units have been identified and described in the Waikato Coal Measures in open pits in the Waikato coal region. These lithological units have been classified geotechnically by mechanical tests and discontinuity measurements. Using these measurements slope stability probability classifications (SSPC) have been quantified based on an adaptation of Hacks [Slope Stability Probability Classification, ITC Delft Publication, Enschede, Netherlands, vol. 43, 1998, 273 pp.] SSPC system, which places less influence on rock quality designation and unconfined compressive strength than previous slope/rock mass rating systems. The Hack weathering susceptibility rating has been modified by using chemical index of alteration values determined from XRF major element analyses. Slaking is an important parameter in slope stability in the Waikato Coal Measures lithologies and hence, a non-subjective method of assessing slaking in relation to the chemical index of alteration has been introduced. Another major component of this adapted SSPC system is the inclusion of rock moisture content effects on slope stability. The main modifications of Hacks SSPC system are the introduction of rock intact strength derived from the modified Mohr–Coulomb failure criterion, which has been adapted for varying moisture content, weathering state and confining pressure. It is suggested that the subjectivity in assessing intact rock strength within broad bands in the initial SSPC system is a major weakness of the initial system. Initial results indicate a close relationship between rock mass strength values, calculated from rock mass friction angles and rock mass cohesion values derived from two established rock mass classification methods (modified Hoek–Brown failure criteria and MRMR) and the adapted SSPC system. The advantage of the modified SSPC system is that slope stability probabilities based on discontinuity-independent and discontinuity-dependent data and a maximum slope height are predicted. The modified SSPC system may be useful in predicting initial optimum pit slope designs in proposed greenfield mine sites. XRF major element and chemical index of alteration (CIA) results obtained for lithologies in the Waikato coal region may be a useful mine management tool to quantify stratigraphic thickness and palaeoweathering from wash drill cuttings. This paper explains the systematic approach of using the adapted SSPC system to classify slope stability in the Waikato open pit coal mines.

Palynofloral and organic characteristics of a Miocene bog-forest, Kalimantan, Indonesia

Palynological investigations of a 20-m-thick Miocene lignite from southeastern Kalimantan, Indonesia, reveal that there are distinct vertical variations in palynofloral characteristics. Three palynofloral zones likely represent large-scale successional changes that were a product of long-term ecological and depositional changes within the original mire. All three zones are represented by palynofloras of both bog-forest and mangrove affinity. The abundance and diversity of these bog-forest palynofloras, accompanied by extremely low sulphur contents (<0.4%), suggests predominantly freshwater, terrestrial deposition. It is probable that the mangrove pollen is allochthonous and was transported into the mire by winds. Increasing relative abundances of mangrove pollen within the total palynofloral assemblage suggests encroachment of the mangrove swamp toward the bog-forest. Pollen common and abundant within all assemblages includes that of species of the genera Calophyllum, Melanorrhea and Dactylocladus. Overall, the vegetation that formed this Miocene lignite is virtually identical to the present-day peat-forming vegetation of Indonesia. Despite the vertical variations in vegetation within this Miocene lignite as deduced from palynology, coal petrographic investigations reveal that there is little variation in the organic characteristics within this seam. Petrographic analyses show that maceral assemblages are similar for most parts of this seam. Analyses of the plant-parts and matrix illustrate that these characteristics are similar for much of the seam, and that the composition and grain-size of organic components are wholly comparable to results of similar analyses from a Holocene mire. This suggests that degradation processes during the Miocene were similar to processes occurring in present-day Indonesian mires. It further suggests that these degradation processes have homogenized the organic characteristics within the lignite, despite original vegetational differences.

Delineation of the distinctive nature of Tertiary coal beds

Abstract Floral character in mires has changed progressively through time. In the Carboniferous, pteridophytes, sphenophytes and lycophytes were dominant but by the Permian gymnosperms were an important component of mire flora. During the early Mesozoic gymnosperms remained the characteristic mire vegetation, together with pteridophytes, and conifers became dominant during the Jurassic. Cretaceous and Paleocene vegetation are similar, with taxodiaceous flora being important in mire vegetation. From the Eocene onwards, however, angiosperms were increasingly dominant in mire communities and in the Miocene herbaceous vegetation began to play a significant role. Together with these changes in floral character at least three aspects of coal character also appear to vary sequentially with time and are distinctive in the Tertiary: (1) proportions and thickness of vitrain banding, (2) coal bed thickness and (3) proportions of carbonised material. A compilation has been made of data from the coal literature comparing older coals with those of the Tertiary, in order to give a perspective in which to examine Tertiary coals. It was found that only Tertiary coals contain significant proportions of coal devoid of vitrain bands. In addition, Tertiary coals are the thickest recorded coal beds and generally contain low percentages of carbonised material (many less than 5%) as compared to older coals. It is interesting to note that Paleocene coal beds are similar to Cretaceous coals in that they tend to be thinner and contain higher proportions of carbonised material than do younger Tertiary coals. The absence of vitrain bands in some Tertiary coal beds is thought to result from the floras dominated by angiosperms, which are relatively easily degraded as compared to gymnosperms. The thickness of Tertiary coals may be related to an increase in biomass production from the Carboniferous through to the Tertiary, as plants made less investment in producing lignin, an energy-intensive process. In addition, with less lignin in plants, easier degradation of biomass may have facilitated nutrient recycling which, in turn, led to greater biomass production. Increased biomass production may have also ‘diluted’ the carbonised material present in some Tertiary peats, leading to lower proportions in the coal. Another possible cause of decreased carbonised components in Tertiary coal is that decreasing lignin content resulted in decreased charring during fires, as lignin is particularly prone to charring. A third possibility is that the carbonised component of peat may be concentrated during coalification so that Tertiary coals, generally of lower rank than Mesozoic or Paleozoic coals, contain a smaller fraction of carbonised plant material. It is not at present clear which of these mechanisms may have affected carbonised material in peat and coal but it is clear that lignin type and content has had an important role in determining peat and coal character since the Paleozoic.

Factors affecting the geochemistry of a thick, subbituminous coal bed in the Powder River Basin: volcanic, detrital, and peat-forming processes

Abstract The inorganic geochemistry and mineralogy of three cores from the Anderson-Dietz 1 coal bed, a 15.2-m-thick subbituminous coal bed in the Tongue River Member (Paleocene) of the Fort Union Formation, were examined (1) to determine if the cores could be correlated by geochemical composition alone over a total distance of 2 km and (2) to identify the major factors that influenced the geochemistry of the coal bed. Chemical data (46 elements on a coal-ash basis) for 81 coal samples and 4 carbonaceous rock samples, with most samples representing a 0.6-m-thick (2-ft) interval of core, were grouped into compositional clusters by means of cluster analysis. Seven major clusters were produced; two of these clusters can be used to correlate the coal bed throughout the study area. Data from scanning electron and optical microscope analyses indicate that several factors influenced the geochemistry of the Anderson-Dietz 1 coal bed. The majority of mineral grains in the coal bed are interpreted to be detrital (water borne); evidence includes the presence of rounded to subrounded quartz grains having two-phase, aqueous fluid inclusions characteristic of hydrothermal or low-to-moderate grade metamorphic quartz. These quartz grains are found throughout the coal bed but are most abundant in samples from the midpart of the bed, which was influenced by detrital input associated with the deposition of the clastic rocks that form the split between the Anderson and Dietz 1 coal beds 900 m to the east of the study area. In addition to the detrital minerals mentioned above, volcanic ash that was fluvially transported to the sites of peat deposition or possibly deposited as air-fall volcanic ash also affected the geochemistry of the coal bed. For example, crandallite(?), a mineral reported to form as an alteration product of volcanic ash, is found in seven samples from the coal bed. The presence of quartz grains containing silicate-melt inclusions in eight samples from the coal bed.provides further support for a volcanic ash component. Other factors that probably affected the geochemistry of the coal bed include (1) detrital input associated with the deposition of the roof rocks of the coal bed, (2) peat-forming processes and plant material, and (3) epigenetic ground-water flow.

Geochemistry and petrography of the Taupiri and Kupakupa coal seams, Waikato coal measures (Eocene), New Zealand

Abstract Geochemical and conventional petrographic techniques have been used to characterise variation within and between the Eocene Taupiri and Kupakupa coal seams in New Zealand. Both seams have a macroscopically bright lustre, but the Taupiri is dominated by non-banded coal in contrast to portions of the Kupakupa which contain large (1–3 cm thick) vitrain bands. Microscopically these bands contribute the bulk of the humotelinite (preserved tissue) found in both coals. The Kupakupa seam contains higher proportions (approx. 20%) of humotelinite than the Taupiri (approx. 10%) which contains higher concentrations of liptinite and sclerotinite. Both seams show a general decrease in humotelinite upwards in the seam, although inorganic partings can modify that general trend, especially in the Kupakupa. In all three splits of the Taupiri, eugelinite decreases upwards whilst detrogelinite proportions increase. These petrographic attributes suggest that the Taupiri palaeo-peat was subjected to higher levels of degradation than the Kupakupa. Coal geochemistry, when interpreted in the context of seam geometry and stratigraphic relationships, reveals a complex chemical history. Major element analyses supplemented by mineralogical analyses confirm previous work indicating a strong organic association for Ca, Mg, Na, Fe and B. These elements are more abundant in seams which are overlain by other coal seams, indicating depletion by circulation of groundwater of surface origin. For example, Na values in a split Taupiri seam at Maori Farm #3 Opencast vary across major sediment partings, being highest in the lowermost coal interval. Si/Al ratios vary widely, and commonly fall below the composition of kaolinite, indicating breakdown of silicates and transport of silica and alumina in solution at the time of peat accumulation. Ti and P in whole coal fluctuate substantially, and their present distribution also indicates mobility in solution. There appears to be little association between elemental and maceral variation. However, there is a clear association in the Kupakupa coal seam at the Weavers Opencast between P, presence of organic partings and the degree of vitrain banding. The highest concentrations of P are within and just below inorganic partings; similarly, the highest abundance of vitrain bands occur just above and/or below partings. Although probably not causally related, the increase in P and vitrain band abundance may be related to the same process; that is, flooding of the Kupakupa palaeo-mire with sediment-laden waters. A quicker burial from sediment loading and less aerobic degradation may have preserved the plant root material (vitrain bands). The P may have resulted either from the flood waters themselves or as residual P in buried plant material. In either case, immobilisation in insoluble form by reaction with Al species is probable.

Maceral and palynomorph facies from two tertiary peat-forming environments in the Powder River Basin, U.S.A.

Abstract The differences between the depositional settings of the Smith and Anderson subbituminous coal beds (Paleocene, central Powder River Basin, U.S.A.) are interpreted on the basis of their petrographic composition and palynologic assemblages. The Smith coal bed is relatively thin ( m ) and has a high degree of thickness variation (0–5 m) over short distances ( km ) , the result of deposition in an anastomosed fluvial environment where numerous lakes and small channels limited the extent of peat deposits. Although plants related to the living genus Glyptostrobus dominated the swamp, peat-forming plant communities contained mixes of ancestral species of Platanus and Ulmus as well as vegetation of lower stature such as Spagnum. Some intervals within the coal bed contain anomalously high concentrations of cell walls (humotelinite) and cell fillings (corpohuminite), some of which came from locally abundant, decay-resistant Pinaceae (or pinaceous) vegetation. Raised areas of the peat swamp characterized by Sphagnum were also favorable for the accumulation of carbonized plant components (inertinites). Because the peat of the Anderson coal bed formed on top of thick (> 50 m ) sandstone bodies of an abandoned meander-belt complex, the coal bed is generally thicker (> 7 m ) and more widespread (> 15 km ) in extent than the Smith coal bed. The sands provided a relatively stable, poorly compactable platform that was favorable to the growth of large, arborescent vegetation, such as the dominant ancestral Glyptostrobus, as well as ancestral Nyssa, Carya, and Betulaceae in a well-drained but moist swamp environment. The stability of the peat-forming environment resulted in a raised peat deposit of relatively uniform paleoflora and peat composition. In the thicker areas of the Anderson coal bed, the upward increase in carbonized plant components indicates a progressively drier or better-drained swamp environment. Intervals within the coal bed that overlie or are lateral to crevasse-splay deposits contain a high concentration of pollen attributable to Pterocarya and an absence of carbonized plant remains, an indication that ancestral Pterocarya preferred a water-saturated environment close to the edge of the swamp where detrial influx occurred.

Differentiation of volcanic ash-fall and water-borne detrital layers in the Eocene Senakin coal bed, Tanjung Formation, Indonesia

Abstract The Sangsang deposit of the Eocene Senakin coal bed, Tanjung Formation, southeastern Kalimantan, Indonesia, contains 11 layers, which are thin ( 70%). These layers are characterized by their pelitic macroscopic texture. Examination of eight of the layers by scanning-electron microscopy, energy-dispersive X-ray, and X-ray diffraction analyses show that they are composed primarily of fairly well-crystallized kaolinite, much of which is vermicular. Accessory minerals include abundant Ti oxide, rare-earth element-rich Ca and A1 phosphates, quartz that luminescences in the blue color range, and euhedral to subhedral pyroxene, hornblende, zircon, and sanidine. Although this mineral suite is suggestive of volcanic ash-fall material, only the four pelitic layers in the middle of the bed are thought to be solely derived from volcanic ash-falls on the basis of diagnostic minerals, replaced glass shards, and lithostratigraphic relationships observed in core and outcrop. The three uppermost pelitic layers contain octahedral chromites, some quartz grains that luminesce in teh orange color range, and some quartz grains that contain two-phase fluid inclusions. These layers are interpreted to be derived from a combination of volcanic ash-fall material and hydrologic transport of volcaniclastic sediment. In contrast, the lowermost pelitic layer, which contains large, rounded FeMg-rich chromites, is thought to have been dominantly deposited by water. The source of the volcanic ash-fall material may have been middle Tertiary volcanism related to plate tectonic activity between Kalimantan and Sulawesi. The volcanic ash was deposited in sufficient amounts to be preserved as layers within the coal only in the northern portions of the Senakin region: the southern coal beds in the region do not contain pelitic layers.

Petrography and palynology of the Blue Gem coal bed (Middle Pennsylvanian), southeastern Kentucky, USA

Petrographic and palynological trends in the Blue Gem coal bed (Middle Pennsylvanian Westphalian B, Breathitt Formation), a thin, low-sulfur, low-ash coal in southeastern Kentucky, were studied in order to establish a depositional model for the seam. Within the study area, the coal bed averages 67 cm and has two distinct zones. The lower and middle parts of the seam (the lower 45–55 cm) are enriched in well-preserved vitrinite and are dominated by arborescent lycopods, sphenopsids, and tree ferns. Fusinite-rich layers, dominated by arborescent lycopods, but also containing herbaceous lycopods and sphenopsids, occur within the lower and middle parts of the seam. The upper part of the seam (the upper 15–25 cm) is recognizable in the field and is distinct in that it contains a greater amount of degraded macerals, and is characterized by high palynomorph diversity, primarily by miospores that are associated with sphenopsids, herbaceous lycopods and arborescent lycopods. These data, in conjunction with geochemical data available for the seam, suggest that initially the peat swamp was fairly diverse and well-nourished (the base of the seam being characterized by a relatively diverse miospore assemblage and a slightly higher ash content). Following this initial planar stage, the Blue Gem peat swamp was probably planar to slightly domed during accumulation of most of the lower and middle parts of the seam, as suggested by the very low ash and sulfur contents, the high telovitrinite content, and the preponderance of arborescent lycopod spores. In its final stages, the peat swamp was domed and is characterized by a more diverse flora and greater levels of degradation of the peat constituents. Sulfur content of this seam is generally low (<1%) but can increase locally to 3–4%. Factors influencing sulfur content include the thickness and nature of the overburden (shale versus sandstone) and petrographic composition.