Arthur D. Cohen

Interpreting the characteristics of coal seams from chemical, physical and petrographic studies of peat deposits

Abstract The purpose of this paper is to illustrate some of the kinds of information about coals that are at present being generated from studies of peat deposits and also to point out some possible new areas of research that might be undertaken in the future. Some notable examples of new ideas about coal seam composition or formation that have been generated from studies of modern peat deposits include: (1) discovery of the probable progenitors of certain coal macerals and elucidation of the processes by which they may have formed; (2) evidence that some types of mineral matter may be dissolved out of peat deposits; (3) verification of the role of marine waters in emplacement of sulphur in peat; (4) discovery of the importance of ‘doming’ in peat deposit development; (5) discovery of a new way to form a split in a coal seam, i.e. development of a ‘fire splay’; (6) elucidation of the mechanisms responsible for producing stratification in coal seams; (7) recognition of the world-wide importance of ‘back-barrier’ coal-forming environments. These kinds of discoveries are important in themselves; however, they can also be shown to have many additional practical applications, especially if woven into models to predict the economic characteristics of coal seams.

The Changuinola peat deposit of northwestern Panama: a tropical, back-barrier, peat(coal)-forming environment

Abstract A large (> 82 km 2 ), thick (> 8 m), low-ash, low-sulfur peat deposit has formed on the northwestern coast of Panama. Its low ash and low sulfur contents can be attributed partly to: (1) doming; (2) the occurrence of a relatively continuous, marine-blocking, beach-barrier shoreline feature; and (3) leaching of the mineral matter. This deposit is roughly rectangular in shape and oriented with its longest axis parallel to the beach-barrier shoreline. It would produce an economic coal bed that is bright and finely banded in its thickest central region and more coarsely banded at its margins. Its northwestern margin would be characterized by interfingering of coal with sandstone and siltstone of the Changuinola River flood plain, whereas its southeastern boundary would be characterized by truncation of the upper part of the seam by marine to brackish shales, siltstones, and carbonates that were derived from Almirante Bay. Total sulfur was found to be very low (less than 0.2% dry wt.) except in a few places. In these rare cases, nearly all of the sulfur was pyritic and the total sulfur content was anomalously high (> 14%). Although the general tendency was for total sulfur to increase wherever the deposit was influenced by marine conditions, one case was found where sulfur was high at the base of an inland freshwater peat core, which suggests either a “hidden” marine influence or the need for some new mechanism to explain sulfur enrichment in such an anomalous case. Differences in inherent fixed carbon contents and calorific values due to changes in peat type and analytical uncertainties tended to mask seamwide trends in these parameters. However, fixed carbon contents and calorific values showed a slight tendency to increase with depth (especially if plotted for single peat types). Vitrinite reflectance within the hypothetical Changuinola coal bed would be expected to increase as follows: (1) toward the margins of the deposit; (2) toward the bottom and top of the bed; and (3) toward stream channels or tidal inlets.

Effects of chemical and physical differences in peats on their ability to extract hydrocarbons from water

Abstract This paper reports on the first phase of a project designed to determine the potential of peats in extracting hydrocarbons from groundwater. Peat samples with markedly different compositions were slurried under controlled conditions in either saturated solutions or emulsions of benzene, toluene, or m -xylene. All peats were characterized in order to determine the possible correlation between various parameters and extraction capacities. All peats were found to be capable of extracting substantial amounts of either free-phase or dissolved hydrocarbons from water. Free-phase extraction ranged from 30 to 50% of the starting wet volume of the peats. Solution extraction produced reductions in concentrations of between 53 and 97%, depending on the peat type. In solution, toluene was found to be more slowly adsorbed than either benzene or m -xylene. In general, the best hydrocarbon adsorption from solution can be achieved by using peats that are low in fiber and birefringent organics and high in ash and guaiacyl lignin pyrolysis products.

Organic chemical and petrographic changes induced by early-stage artificial coalification of peats

Abstract In order to investigate the changes that can occur during the earliest stages of coalification, a series of peat samples representing different depositional and vegetational settings were subjected to increasing temperatures and pressures in an open experimental system designed to simulate an approximate depth of burial of 1–1.5 km. Petrographic and chemical techniques (pyrolysis GC/FT-IR/FID and pyrolysis GC/MS) were utilized to analyze samples before and after coalification. Petrographic changes consisted not only of purely physical changes, such as compaction and creation of distinct microbands, but also, changes in color, obliteration of distinct cell walls in certain tissues, and the formation of new macerals. Chemical changes supported the destruction of the cellulosic components in the absence of microbial activity.

Some observations regarding the potential effects of doming of tropical peat deposits on the composition of coal beds

Abstract Several important concepts relative to the origin of coal beds can be gleaned from studies of modern domed and planar peat deposits in tropical-subtropical settings. These are: (1) laterally, some portions of a single continuous peat deposit may be domed and some portions may be planar; (2) domed deposits are most often found to have begun as planar deposits; (3) domed-formed peat facies may be overridden by planar-formed peat facies, due to such factors as sea level rise and/or increased rate of local and basinal subsidence; (4) domed peat facies tend to have less mineral matter and contain fewer inorganic splits than planar facies; (5) sulfur intrusion from marine waters can be retarded by doming, allowing low-sulfur peats to form relatively near to the coastline; (6) marine transgression can cause high-sulfur, marine-influenced, planar, peat facies to override freshwater domed or planar facies, resulting in enrichment of the upper parts of these underlying facies in sulfur and ash; (7) dome-formed peat facies tend to be thicker and more uniform in composition than planar-formed facies, with dome-formed peat facies having the potential to produce the more uniform bright coal types (clarains and vitrains) and planar-formed peat facies often producing duller coal types and/or alternating, durainic (inertinite-rich) and vitrainic (wood-derived) bands; (8) actively developing peat domes in wet settings often exhibit no appreciable increase in inertinitic material toward their tops; although the tops of either domed or planar peat deposits can be enriched in inertinitic material if the water table is lowered by either local or regional changes in hydrology or climate.

Stratigraphic and micropetrographic occurrences of pyrite in sediments at the confluence of carbonate and peat-forming depositional systems, southern Florida, U.S.A.

Abstract This study was undertaken to investigate peat/carbonate relationships in a modern coal-forming setting, with initial research on pyrite and sulfur contents relative to stratigraphic and petrographic conditions. Over 40 closely spaced cores were taken from transects from Florida Bay inland through mangrove swamps and freshwater Everglades. Core stratigraphy confirms on overall transgressive sequence, but new evidence supports a small regression within the overall transgression. On average, both total S and pyrite are lowest at inland sites, highest near the coastline, and intermediate in Florida Bay sediments. Total S is higher in marine than freshwater peats, but freshwater peats overlain by marine peats are enriched in S. In cores that start with peat at the top, pyrite is generally absent or very low in the top 20 cm. Higher percentages of pyrite occur in carbonate rather than peat facies. Pyrite exists in three forms, framboidal aggregates, minute crystals, and large solitary crystals. Most of the pyrite occurs as minute crystals ( μ m) and framboidal aggregates. The occurrence of large crystals (> 2 μ m) is less common and generally restricted to the cavities of larger cells or cavities within other organics (e.g. formminifera, pollen grains, fungal sclerotia). A general relationship seem to exist in certain cases between the occurrence of spherical organic cell fillings and the occurrence of the framboidal form of pyrite.

Combining organic petrography and palynology to assess anthropogenic impacts on peatlands: Part 1. An example from the northern Everglades of Florida

Abstract Wetland peat deposits can be excellent archives of past changes in the depositional and ecological conditions under which they formed. Part of the story of these changes can be obtained from analysis of the palynomorphs preserved in these deposits; however, a more meaningful reconstruction can be achieved by combining organic petrography with palynology. An example of this approach is presented from a study of three sites in the northern Everglades of Florida. The primary purpose of this study was to test these combined methods for their utility in distinguishing between long-term, natural successions and recent, anthropogenically-derived disruptions of the ecosystem (such as diversions of drainage and introductions of contaminants from human sources). The combined palyno-petrographic method (supported by 137 Cs and 210 Pb dating) was able to establish with some certainty the first appearance of contaminant-driven plant types (such as cattails and duckweeds) into the region, with the organic petrography being more accurate in determining the actual presence of invading plants at a particular site and the palynologic analysis providing a broader picture of regional changes in the ecosystem (such as the direction of the plant invasion). The distribution of petrographic pyrite in these freshwater peats provided an additional new piece of evidence for contamination from the agricultural lands and also supported other evidence relative to the direction of contaminant infusion into the region. Additionally, the occurrence of significant quantities of pyrite at all three sites suggests that, in fact, none of these sites can be said to be totally unaffected by anthropogenic contamination. Longer hydroperiods were generally indicated by both methods for all sites before the early 1900s, confirming persistently wetter conditions in the Everglades prior to manmade changes in drainage. More specific paleohydrologic conditions could also be elucidated by this combined method, with all three sites displaying significant differences in hydrologic histories. Additionally, one of the sites is hypothesized to have been, until recently, in the center of a surface–water flow pathway, as indicated by the continuous presence at this site of deeper water aquatics (such as water lilies) and the smaller number of zones containing algal-derived carbonates and/or other petrographic indicators of oxidation or bioturbation.

Petrographic changes induced by artificial coalification of peat: comparison of two planar facies (Rhizophora and Cladium) from the Everglades-mangrove complex of Florida and a domed facies (Cyrilla) from the Okefenokee Swamp of Georgia

Abstract Petrographic changes during coalification of three peat samples were investigated by artificial coalification experiments using a semi-open reactor system. Compressions of from 83 to 88% produced dark brown to black, shiny, flattened pellets exhibiting microscopic banding. Overall amounts of compression inversely correlated with the framework to matrix ratios ( F M ); although, certain tissue fragments remained relatively uncompressed due to the presence of tanniniferous cell fillings and also, hypothetically, to the presence of colorless plant secretions or gelified wall materials that were present in the cells but only recognizable after a change in color during coalification. The most distinct microscopic banding (longest and widest bands) developed in samples of the dome-formed peat facies, which had the highest framework to matrix ratios of any type and the greatest contents of surface litter composing the framework (i.e. highest S N ratio). The planar, root-dominated, Rhizophora facies showed the greatest change in microbanding character during coalification; in that, the numerous lens-like bands produced by the compressed roots were very distinct at the 60°/2100 psi (121.4 kg/cm 2 ) stage but nearly disappeared at the 175°/5000 psi (289.1 kg/cm 2 )) stage. This is explained as a result of differences in rates of coalification of the different telinitic precursors in the roots (multilinear vitrinization) and could explain why roots are significant components of many modern peats (and ancient coal ball concretions) but are difficult to recognize in bituminous coals. Similarly, separation of cuticles from leaves in modern peat-forming environments, due to irreversible shriveling and subsequent enhanced microbiological decay, partially explains why leaf remains are also difficult to recognize in most coals, even those with abundant cutinites. Microcracks developed in all pellets, with dominant orientations of cracks being either perpendicular to induced banding or horizontal to it. Minute, vertical microcracks (interpreted as ‘dewatering’ features) were observed primarily in gelinitic bands, especially in the most fire-prone, Cladium coal facies; but, these rarely extended into juxtaposed microlithotypes as did most of the larger vertical cracks. Horizontal cracks tended to form at microband boundaries. Almost all humotelinitic and humocollinitic precursors showed some changes in color during artificial coalification, with humotelinites exhibiting less or slower changes than humocolinites or humodetrinites (finer-grained matrix material). Additionally, nearly all dark brown, degraded tissues in the peats became dark orange or red during coalification; but, many of these tissue masses were observed to contain significant amounts of minute inertinite derived from microorganisms (‘pseudomicrinite’) that only became prominent after coalification and subsequent change in color of surrounding macerals. Fusinite precursors were only found in the fire-prone Cladium facies; and, although, the coalified, doming-generated, Cyrilla facies exhibited evidence of significant drying events (i.e. occasional bands or parts of bands containing significant pseudomicrinites, macrinites and sclerotinites), it was dominated by huminitic (vitrinitic) components. Liptinites were most common in the coalified, dome-formed, Cyrilla facies and displayed a slight qualitative increase in red/green fluorescence during coalification and some possible flow of components into nearby cracks. Changes in mean random reflectance of huminitic macerals, although still requiring more data and only measured to the 60°C/2100 psi (121.4 kg/cm 2 ) level, indicated increasing directions of change during artificial coalification, with humocollinitic macerals progressing from an average of about 0.21% to 0.32% and humotelinitic macerals (which consistently had lower inherent reflectances in the peats) progressing from 0.15 to 0.25%. The above petrographic results, along with previously reported chemical results, all suggest that the methods that we have used in these experiments have produced changes that might reasonably be expected to occur during natural coalification (despite the fact that we have speeded up the process). Although more work needs to be done to verify and refine these results and to establish a correlation between these artificial ‘coalification steps’ and true coalification, the new observations and conclusions from these studies might still be helpful in constructing models to predict or interpret coal seam characteristics and to establish the timing and release-potential of gaseous or liquid hydrocarbons from coals.

Effects of fires on the chemical and petrographic composition of peat in the Snuggedy Swamp, South Carolina

Abstract Charcoal-rich zones in a peat core from the Snuggedy Swamp in South Carolina were investigated to determine the chemical and physical changes associated with fires. Petrographic analyses of microtome thin sections revealed that three charcoal zones were present in the core and that the fires causing such zones were severe enough to penetrate into the subsurface and burn some of the peat. Despite these severe fires, only minor changes in the botanical composition occurred throughout the history of the study site, suggesting that these fires were not extensive enough to retard recolonization of the site from nearby unburned areas. pyrolysis gas chromatography/Fourier transform infrared/flame ionization detection and pyrolysis gas chromatography/mass spectrometry studies reveal distinct organic chemical changes in the peat that can be related to the fires. Decreases in aliphatic and cellulose compounds mirrored increases in charcoal abundance; while aromatic, lignin-related compounds increased as charcoal increased.

Effects of irradiating peats on their ability to extract BTEX and cadmium from contaminated water

Abstract This paper reports on research designed to investigate the effects of increasing amounts of gamma radiation on the abilities of peats with different chemical, physical, and microbiological properties to extract gasoline‐derived contaminants (BTEXs) and cadmium from water. Unaltered and irradiated peats were slurried under controlled conditions in aqueous solutions of gasoline and of cadmium. All peat types were also examined by various analytical methods for physical, chemical, or microbiological changes that might have occurred due to the radiation. Radiation was found to increase BTEX sorption capacity by 10–65%, depending on the peat type. A maximum BTEX sorption capacity was reached somewhere between 4.5 and 6.5 megarads of radiation. The more fibric peats tended to reach their BTEX sorption maximum more quickly than the more sapric peats. In contrast to the hydrocarbons, cadmium sorption capacity tended to be decreased by radiation, for the more fibric peats (by as much as 80%); while, the ...