An Organic Sediment

In the chemical and geological senses, coal is an organic natural product or, more correctly, an organic rock formed from partially decomposed (and decomposing) plant debris (and, in some cases, animal debris) which had collected in regions where waterlogged swampy conditions prevailed (Terres, 1931 Lowry, 1945 Francis, 1961 Lowry, 1963 Murchison and Westoll, 1968 Elliott, 1981 Bend et al., 1991 Bend, 1992). These conditions prevented complete decay of the debris (to carbon dioxide and water) as it accumulated and was subsequently metamorphosed to eventually lead to the material now known as coal. 

A sedimentary rock is formed by sedimentation at the surface of the earth and within bodies of water—sedimentation being the collective name for processes that cause minerals and organic particles (detritus) to settle and accumulate or minerals to precipitate from solution. In general terms, the debris consisted of trees, rushes, lycopods (a class of plants often loosely grouped as the ferns and club mosses), and several thousand plant species that have been identified in coal beds from their remnants (Francis, 1961 Van Krevelen, 1961). However, it does appear that none of the species identified in many different coals originated in brackish-water locales. 

Similar types of botanical remains are found in all different types (ranks) of coal. But, as anticipated because of local and regional variations in the distribution of floral species (i.e., site specificity), the relative amounts can vary considerably from one site to another (Stutzer, 1940). In addition to variations in the types of flora, there is also the potential for regional variations in the physical maturation conditions (Table 3.1) these include differences such as variations in the oxygen content of the water as well as acidity/alkalinity and the presence (or absence) of microbial life forms. Variations of the plant forms (Table 3.2) due to climatic differences between the geological eras/ periods would also play a role in determining the chemical nature of the constituents of the prenatal coal (Bend et al., 1991 Bend, 1992 Speight, 2007). 

it is not surprising that coal differs markedly in composition from one locale to another. Indeed, pronounced differences in analytical properties (Chapter 8) of coal from one particular seam are not uncommon, due not only to the wide variety of plant debris that could have formed the precursor but also to the many different chemical reactions that can occur during the maturation process. Indeed, the development of maturation indices may enable scientists to determine the path (pathways) by which maturation occurred (Richardson and Holba, 1987 Ekwenchi et al., 1991). 

Once plant debris has accumulated under the correct but difficult-to-define conditions, the formation of peat gradually occurs. Peat is not actually classified as coal and is not usually included in the coal series, but it is, nevertheless, believed to be that material that is formed at the initial 

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Coal is die compressed and dehydrated fossilized remains of plants. These materials are classified by some as sediments, even though they are composed largely of organic compounds. Coal is discussed in detail as an organic sediment in Chapter 2. 

This is an important parameter particularly for naturally occurring mixed cultures of organisms in the natural environment temperature may result in important changes in the composition of the microbial flora as well as on the rates for different processes. An illustrative example of its importance includes the following. An anaerobic sediment sample was incubated with... 

The atmospheric height is selected as an arbitrary 1000 m reflecting that region of the troposphere which is most affected by local air emissions. A water surface area of 10% or 10,000 km2 is used, with a water depth of 20 m. The water volume is thus 2 x 10n m3. The soil is viewed as being well mixed to a depth of 10 cm and is considered to be 2% organic carbon. It has a volume of 9 x 109 m3. The bottom sediment has the same area as the water, a depth of 1 cm and an organic carbon content of 4%. It thus has a volume of 10s m3. 

Uptake is the process by which chemicals (either dissolved in water or sorbed onto sediment and/or suspended solids) are transferred into and onto an organism. For surfactants, this generally occurs in a series of steps a rapid initial step controlled by sorption, where the surface phenomenon is especially relevant then a diffusion step, when the chemical crosses biological barriers, and later steps when it is transported and distributed among the tissues and organs. 

For instance, 2-methylpropene reacted with acetic acid at 18°C in the presence of Al-bentonite to form the ester product (75). Ion-exchanged bentonites are also efficient catalysts for formation of ketals from aldehydes or ketones. Cyclohexanone reacted with methanol in the presence of Al-bentonite at room temperature to give 33% yield of dimethyl ketal after 30 min of reaction time. On addition of the same clay to the mixture of cyclohexanone and trimethyl orthoformate at room-temperature, the exothermic reaction caused the liquid to boil and resulted in an almost quantitative yield of the dimethyl ketal in 5 min. When Na- instead of Al-bentonite is used, the same reaction did not take place (75). Solomon and Hawthorne (37) suggest that elimination reactions may have been involved in the geochemical transformation of lipid and other organic sediments into petroleum deposits. 

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