Robert Raymond

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.

Cation-ratio dating of rock varnish: Why does it work?

Cation-ratio dating of rock varnish is an empirical surface-exposure dating method based on decreases in the cation ratio (Ca+K):Ti over time. Although these changes were attributed to the preferential leaching of Ca and K from varnish, the existence of such leaching has not been demonstrated. In varnish collected from the Cima volcanic field, California, distributions of the minor elements used in cation-ratio (CR) dating reflect varnish stratigraphy as defined by the major elements Mn, Fe, and Si. In general, K is associated with Si, Ca with Mn, and Ti with Fe. Because of these associations, variations in CRs both within samples and between samples typically reflect variations in major element composition associated with varnish stratigraphy. No systematic changes with depth or age are present in the ratios K:Si or Ca:Mn as would be expected if K and Ca have been preferentially leached from varnish. Available data suggest that, instead of a leaching process, thickness-dependent changes in the amount of substrate being incorporated into varnish analyses contribute to the empirical trend of decreasing CR with increasing surface age, although further research is required to verify this hypothesis.

Relationship between peat geochemistry and depositional environments, Cranberry Island, Maine

Abstract The Heath, Great Cranberry Island, Maine, offers a unique locality for studying lateral and vertical relationships between radically different peat types within 1 km 2 . The majority of The Heath is a Sphagnum moss-dominated raised bog. Surrounding the raised bog is a swamp/marsh complex containing grass, sedge, Sphagnum moss, alder, tamarack, and skunk cabbage. Swamp/ marsh-deposited peat occurs both around the margins of The Heath and under Sphagnum -dominated peat, which was deposited within the raised bog. A third peat type, dominated by herbaceous aquatics, is present underlying the swamp/marsh-dominated peat but is not present as a dominant botanical community of The Heath. The three peat types have major differences in petrographic characteristics, ash contents, and associated minerals. Sulfur contents range from a low of 0.19 wt.% (dry) within the raised bog to a high of 4.44 wt% (dry) near the west end of The Heath, where swamp/marsh peat occurring directly behind a storm beach berm has been influenced by marine waters. The presence of major geochemical variations within a 1-km 2 peat deposit suggests the need for in-depth characterization of potential peat resources prior to use.

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

Abstract A large (approximately 82 km2), low-ash, low-sulfur peat deposit has formed on the northwestern coast of Panama (Fig. 1). Its low ash and sulfur contents can be attributed partly to (1) doming, (2) the occurrence of a marine-blocking, beach-barrier shoreline feature, and (3) leaching of the mineral matter. The coal seam formed by this deposit would be roughly rectangular in shape and oriented with its longest axis parallel to the beach-barrier shoreline. It would be 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 sandstones and siltstones of the Changuinola River flood plain; whereas, its southeastern boundary would be characterized by truncation of the upper part of the seam and replacement with marine to brackish bay rocks. 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 light (approximately 14%). Although the general tendency was for total sulfur to increase wherever the deposit was influenced by marine conditions, one case was found where the sulfur was high a the base of an inland freshwater core, suggesting the need for a new mechanism to explain sulfur enrichment in such a case. Differences in inherent fixed carbon and Btu contents due to changes in peat type tended to mask seam-wide trends in these parameters. However, fixed carbon and Btu showed a slight tendency to increase with depth (especially if plotted for single peat types). Vitrinite reflectance within the hypothetical Changuinola coal seam can be predicted to increase toward the margins of the deposit, toward the bottom and top of the seam, and toward stream channels or tidal inlets. A detailed description of this deposit and discussion of its relevance to coal genesis can be found in Cohen et al. (1989).

Electron Probe Microanalyzer in Coal Research

Publisher Summary This chapter discusses electron probe microanalyzer in coal research. The capability of nondestructive quantitative analysis on micrometer-size points of a sample is a characteristic unique to electron beam instruments. The heterogeneous and fine-grained nature of coal constituents, therefore, makes the electron probe microanalysis (EPM) uniquely adaptable to many aspects of coal characterization. At the same time, as with other types of instruments, it has limitations that restrict it to specific problems. The EPM offers potential solutions to many problems concerning organic and inorganic chemistry of coal, especially if used in conjunction with other techniques such as X-ray diffraction, Mossbauer spectroscopy, scanning and transmission electron microscopy, and optical microscopy. Use of the EPM in coal research is in its infancy and is certain to increase significantly in the near future.

Relationship Between Reflectivity and Organic Sulfur Content of Macerals with Respect to Total Organic Sulfur Content and Rank of Coals: ABSTRACT

The potential exists for predicting organic sulfur (So) contents of specific macerals within a coal based on total So content of the coal, rank of the coal, and maximum reflectivity in oil (Ro) of the macerals in question. In the past, determination of So content of specific macerals necessitated either a microanalysis technique, such as electron probe microanalysis (EPM), or analysis of maceral separates. Ten coal samples ranging in rank from low volatile to lignite and total So content from 0.47 to 4.51 wt. % were studied. Within each of the 10 coals, approximately 100 macerals ranging from the lowest reflecting exinites to the highest reflecting inertinites were analyzed for So content (using EPM techniq es) and Ro (using petrographic techniques). For each coal, log of maceral So content was plotted versus log of maceral Ro, and a linear regression of the data points was performed. On a three-dimensional plot, slopes of the 10 linear regressions were plotted versus the respective coal ranks versus the respective coal total So contents. Results indicate that relationships between So content and Ro of macerals within a coal are dependent on both the rank and total So content of the coal. As total So content of a coal equals So content of the vitrinite in that coal, the results suggest that predictive relationships exist between maceral So content, maceral Ro, coal total o content, and coal rank that may allow determination of maceral So contents without the need for microanalysis. End_of_Article - Last_Page 946------------

Evidence for Pervasive Bioerosion of Silica Substrates in a Freshwater Peat Environment: ABSTRACT

Siliceous particles (30 to 100 µm) collected from freshwater peat deposits in the Okefenokee swamp show extensive effects of bioerosion. When viewed with the SEM these effects include: (1) depressions (similar to those produced by diatoms); (2) perforations (holes 2 µm in diameter); and (3) borings (holes > 2 µm in diameter). These features are most likely to be of biological origin because of their smooth surfaces and the consistency of the geometry of the cavities. The delicate nature of the eroded grains dictates that the biological agents responsible must have lived in the peat-forming environment. For example, monaxon sponge spicules have lost as much as half their original mass through hundreds of tubular microborings, rendering them far too fragil for transport. Heretofore, microborings have been observed to commonly occur on carbonate substrates, and in only two cases has bioerosion been reported in siliceous sediments in a marine environment. Our observations show that freshwater organisms are also capable of boring/dissolving silica, and that this form of degradation may play a major role in silicon mobility within peat-forming environments. End_of_Article - Last_Page 543------------