Joan Esterle

The geology, botany and chemistry of selected peat-forming environments from temperate and tropical latitudes

Abstract Peat has been studied in several geologic settings: (1) glaciated terrain in cold temperate Maine and Minnesota, U.S.A.; (2) an island in the Atlantic Ocean off the coast of Maine, where sea level is rising; (3) the warm temperate U.S. Atlantic and Gulf Coastal Plains, where sea level has changed often; and (4) the tropical coast of Sarawak, Malaysia, and the tropical delta of the Batang Hari River, Sumatra, Indonesia. Most of these deposits are domed (ombrotrophic or partly ombrotrophic) bogs in which peat accumulation continued above the surface of the surrounding soil. However, the bogs of the U.S. Atlantic and Gulf Coastal Plains are comparatively not as domed, and many have almost level surfaces. In some bogs, aquatic or semi-aquatic plant materials accumulated, replaced water in the depressions, and formed a surface on which marsh or swamp vegetation could subsequently live, die, and accumulate. In others, the plant materials accumulated initially on level silt or sand surfaces supporting marshes or swamps. As the peat dome formed, plants growing on it changed from luxuriant ones near the base of the dome, where nutrients were brought into the bog by surface and ground water, to stunted ones at the top of the dome, where the raised bogs are fed by nutrient-poor precipitation. The physical and chemical changes that take place in the sequence of environments from the pond stage of deposit development, through the grassy marsh stage, through the forested swamp stage, and finally through the heath dome stage can be measured in terms of acidity and ash, volatile matter, carbon, hydrogen, nitrogen, sulfur and oxygen contents, as well as in the kind and distribution of trace elements. The organic and inorganic contents of the deposits relate to geomorphology, and geomorphology relates to their settings. As models of coal formation, some domed peat deposits may help in solving problems of distribution and character of ancient coal beds. But clearly not all peat deposits are precursors of coal. Most Holocene peat deposits are subject to destruction by erosion, fire and decomposition through microbial and chemical oxidation before burial. The best environments for coal precursors have biomass accumulation, a continuously rising water table within the mass, and minimum influx of clay and silt until preservation by burial. The most suitable settings for future economic coal deposits are domed bogs that accumulate thick, widespread peat having low ash and low sulfur contents. The ombrotrophic peat deposits of tropical Sarawak and Sumatra are thick and extensive, contain low-ash and low-sulfur peat, and have high heating values. They are considered to be the best tropical coal analogs because of their extent and chances of preservation; the base of the peat is below adjacent river levels, and chemical and structural conditions are favorable for accumulation.

Spatial variability in modern tropical peat deposits from Sarawak, Malaysia and Sumatra, Indonesia: Analogues for coal

Petrographic and chemical variability in two tropical, low ash, domed peat deposits of similar age and physiographic setting, but different external morphology, were examined as modern analogues for coal. Both occur in microtidal alluvial to deltaic plain settings, support similar arborescent vegetation and have accumulated in the past 5,000 years. One deposit is an extremely convex, mature done, with a surface that rises 10 m above river level; the other is a low-gradient dome, rising only 3 m above river level but with a concave base up to 6 m below. Both deposits have been eroded by adjacent rivers, yet peat in the mature dome has accumulated remote from persistent flooding and exhibits distinctive internal stratigraphy. Decomposed sapric peat floors the deposits and is overlain by increasingly better preserved woody hemic and a cap of coarse fibrous peat derived from less arborescent vegetation. Consistent flooding in the low-gradient dome has maintained conditions for the accumulation of predominantly woody hemic peat, which interfingers with and is overlain by oxidised sapric peat and levee-derived clastic sediments. Peat types in both deposits exhibit distinctive polymodal textures and organo-chemical signatures that correspond to botanical input and degree of decay. Due to the abundance of pre-huminite/vitrinite macerals in all peat types from these deposits, megascopic and microscopic texture is a better discriminator for comparison to ancient coal types. It is suggested that the upward vertical sequence of decreasing woodiness and increasing lightness in colour observed in the mature dome might best be compared to sequences observed in Tertiary brown coals. This ‘typical’ sequence can be modified or overprinted due to flooding in the burial process.

Relationship between petrographic and chemical properties and coal seam geometry, Hance seam, breathitt formation, southeastern Kentucky

The Upper Hance coal seam in southeastern Kentucy was used as a template to examine the spatial distribution of ash yield, sulfur content and petrographic constituents relative to the geometry of the deposit. Geometric characteristics include thinning and splitting of the two main benches, leaders and riders. Analytical data showed the thick, non-split portions of the coal body to be low in ash and sulfur as well as vitrinite content, whereas the thinned and split margins were higher in ash, sulfur and vitrinite content. These relationships suggest that thick non-split portions of the Upper Hance peat accumulated in areas isolated from detrital influx while thinner marginal peat was subject to intermittent flooding from adjacent channels. Marginal peat was derived from larger trees which flourished at the mires edge in the presence of adequate nutrients, whereas only stunted vegetation, subsisting in the nutrient-depleted center, contributed to interior peat accumulation. Ponds formed on the sparsely vegetated mature surface of the bogs interior. The petrographic and chemical character of the Hance coal body is analogous to ombrogenous (domed) peats which characteristically contain higher concentrations of inorganics at the periphery of the deposit.

A test for the analogy of tropical domed peat deposits to “dulling up” sequences in coal beds—Preliminary results

Abstract Megascopic and microscopic characteristics of a domed peat deposit in Sarawak, Malaysia were examined to test their analogy to “dulling up” sequences in low-ash coal beds. Preliminary petrographic results show high concentrations (> 95%) of vitrinite precursor material for all peat types, but that fibrous peats in the upper central portion of the deposit contain more preserved plant material than peats toward the base and margins which, although more decomposed, contain large fragments (5–150 cm) of wood. These results present contradictory evidence in support of a dulling up model and suggests that modern tropical peat domes are perhaps poor petrographic analogues for dulling up sequences. This deposit would produce an “all bright” coal seam with bright vitrain bands of variable thickness and amount, set in bright, high vitrinite matrix.

Peat-accumulating depositional systems of Sarawak, East Malaysia

Many coal deposits originate in deltaic, estuarine, and coastal plain settings and a knowledge of interrelationships between the tectonic and depositional elements active at the time of sediment deposition is necessary to formulate basin scale models. The prograding coastal depositional systems of Sarawak all contain domed peat-accumulating environments in which low-ash, low-sulfur peats are being deposited in areas of active clastic siliciclastic sedimentation. These depositional systems are as large as 11,400 km2 and individual peat deposits within systems are in excess of 20 m thick and 1000 km2 in area. The geographic positions and drainage basin areas of each depositional system are controlled by fault and fold systems. Although prograding into the same receiving basin, individual system geomorphology is variable and ranges from a wave-dominated microtidal delta, to a wave-dominated meso- to macro-tidal delta/coastal plain system, to a tide-dominated macrotidal estuarine embayment along a 450 km stretch of coastline. System variation is a function of sediment supply, shelf and embayment geometry, wave climate, and tidal range. These factors, which control depositional system geomorphology, also control the resulting long axis orientation of the thick, domed peat deposits. The surface vegetation and internal characteristics of most domed peat deposits, however, are similar. Internal characteristics consist of basal high-ash, high-sulfur, degraded peats overlain by low-ash, low-sulfur, well preserved peats in vertical profile. These systems demonstrate variable responses to late Pleistocene/Holocene sea-level rise and, in these instances, the variation is most attributable to local differences in siliciclastic sediment supply, which is a function of the drainage basin area.

Provenance and sediment dispersal in the Rajang River delta/coastal plain system, Sarawak, East Malaysia

Preliminary sedimentologic investigations were conducted in the Rajang River delta/coastal plain system in Sarawak, East Malaysia, to determine the processes and timing of siliciclastic transport and sedimentation in tropical, peat-dominated systems. Methods involved depth profiling and collection and analysis of bottom and suspended sediment load samples from channels and offshore areas, and coring and trenching of subaerial channel, shoreline, and backswamp features. The Rajang delta occurs in an embayment formed by the folded Mesozoic and Cenozoic sediments of the Central Borneo Massif. It covers an area of 11,000 km2 and is physiographically separated into an alluvial valley floodplain, an abandoned tidally flushed delta plain, and an actively accreting rectilinear delta/coastal plain. From 50 to 80% of the surface area is covered by peat 1 to 20 m thick. During the dry season of July/August, 1992, river channels varying from 2 to 45 m deep with discharge rates from < 100 to approximately 3550 m3/s were carrying suspended sediment loads ranging from 0 to 2281 mg/l. At present, approximately 8.2 x 10(10) kg/yr of fine-grained sediment is supplied to the system and areal accretion rates are over 1.0 km2/yr. The structural configuration of the uplands/receiving basin and subsequent drainage patterns and tidal influence results in a contradictory distribution of mature, fine-grained sediments in the channels of the active delta/coastal plain, and immature. coarse-grained angular sands and gravels in the channels of the abandoned delta lobe. The contemporaneity of the peat and clastic accumulation is evidenced by the margins of the thick, domed, low ash peat deposits interfingering with and being overlain by root-penetrated siliciclastic sediments. Much of the fine-grained sediment, however, bypasses the delta plain due to in-channel density gradients. Delta/coastal plain accretion occurs by distributary mouth bar buildup, sand bar welding, and ridge and runnel accretion. All subaerially exposed surfaces are quickly vegetated. The aberrant depth and configuration of some channels suggest that drainage is, in part, controlled by contemporaneous faulting.

An investigation of the chemical variability of woody peat by FT-IR spectroscopy

Woody peats from Indonesia and Malaysia were examined by FT-IR spectroscopy to observe the variation in degree of humification between peat types and among botanical components and matrix material within a peat type. Results of the FT-IR analysis showed significant changes occurring in the 1600 and 1000 cm−1 regions which are interpreted to represent lignin and lignocellulose, respectively. These components were considered to describe variations in degree of humification. Between peat types the intensity of the lignocellulose region decreased accordingly between fibric, hemic, and sapric samples. Within a sample, variations in the relative amount of lignocellulose in the three different size fractions of a sample were observed that could generally, but not always, be related to peat type. In all peat types the coarse material still contained some lignocellulosic component, whereas the finer fractions contained variably less to no lignocellulose. The lignin-dominated composition of the finer matrix material suggests that these peats are derived mainly from trees and woody vines with little input from herbaceous, less decay-resistant (cellulose-dominant) plant material.

An energy-based model for swing hammer mills

An energy-based swing hammer mill model has been developed for coke oven feed preparation. it comprises a mechanistic power model to determine the dynamic internal recirculation and a perfect mixing mill model with a dual-classification function to mimic the operations of crusher and screen. The model parameters were calibrated using a pilot-scale swing hammer mill at various operating conditions. The effects of the underscreen configurations and the feed sizes on hammer mill operations were demonstrated through the fitted model parameters. Relationships between the model parameters and the machine configurations were established. The model was validated using the independent experimental data of single lithotype coal tests with the same BJD pilot-scale hammer mill and full operation audit data of an industrial hammer mill. The outcome of the energy-based swing hammer mill model is the capability to simulate the impact of changing blends of coal or mill configurations and operating conditions on product size distribution. Alternatively, the model can be used to select the machine settings required to achieve a desired product

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.

Stratigraphic and depositional framework of the Walloon Subgroup, eastern Surat Basin, Queensland

The Middle Jurassic Walloon Subgroup is a prolific coal seam gas (CSG) resource in the Surat Basin, Queensland. Sedimentary framework models constrain stochastic reservoir models of the geological heterogeneity, but there is limited basin analysis information in the public domain. Here we present a regionally consistent stratigraphic framework model for the Walloon CSG play in the eastern Surat Basin. Lithostratigraphic correlation of open-file industry and government wireline logs supports the interpretation of six subunits in the eastern Surat Basin (oldest–youngest: Durabilla Formation; Taroom Coal Measures; Tangalooma Sandstone; and Juandah Coal Measures, informally divided into three members named the lower Juandah Coal Measures, Juandah sandstone and upper Juandah Coal Measures). Important findings are that subunits within the Walloon Subgroup do not correlate along the entire CSG play area; in many places, the overlying Springbok Sandstone (Upper Jurassic) has incised to the lower Juandah Coal Measures level, removing the upper coal seam groups. The Walloon Subgroup thins to the south through a combination of depositional thinning and truncation. Lithofacies analysis and isopach maps support deposition in a southerly prograding fluvial system or clastic wedge. This stratigraphic and depositional interpretation informs models for hydrogeological studies of the Walloon Subgroup and underpins a regional assessment of controls on microbial methane distribution.