Geothermal Subject

I find it interesting that in the strata studied by Schopf and Long, the sills lay above the coal seams. This means that the temperature gradient owing to the sill was of opposite sign to the geothermal gradient, and therefore in sequences of samples like those in the table on pp. 166-7, it is the coals that were initially of lowest rank that were more intensely subjected to thermal alteration. This situation may account for the observed variations in H/C-O/C relations with depth below the sill (which are complex) however, since the samples were not taken from vertical boreholes, some lateral variations in the strata no doubt also affect the relations. 

The latter reaction can form long chain phosphates, where n is theoretically infinite. Being formed by heat treatments, these phosphates are excellent candidates for high-temperature ceramics and glasses. Because the subject of this volume is low-temperature ceramics, we will not discuss the condensed phosphates in detail, except in one case in Chapter 15, where cements for geothermal wells are discussed with sodium metaphosphate. However, bear in mind that CBPCs can be precursors to high temperature phosphates and glasses. For this reason, as we have seen in the literamre survey presented in Chapter 3, early interest in CBPCs was the formation of refractory shapes at room temperature, which were then fired to produce the final refractory components. 

The effect of the volcanic eruptions during the 19th and 20th centuries on the tanperature of the atmosphoe was evaluated in a series of papers by Self et al. (1981), Newell (1981), Robok (1981), and Walker (1981), all of whom published their contribulions in volume 11 of the Journal of Volcanology and Geothermal Research. The occurrence of tephra layers in the East Antarctic ice sheet is the subject of reports by Keys et al. (1977), Koeberl et al. (1987), Palais and Sigurdsson (1989), and Faure et al. (1994, with assistance from Mary Davis and Keith Henderson). 

Rank. Coal rank reflects the degree of metamorphism (or coalification) to which the original mass of plant debris (peat) has been subjected during its burial history. This depends in turn on the maximum temperature to which it has been exposed and the time it has been held at that temperature. For most coals, rank also reflects the depth of burial and the geothermal gradient prevailing at the time of coaliflcation in the basin concerned. 

In areas where the rocks have been subjected to complex folding and faulting or have been intruded by igneous rocks, the geothermal maturity of the oil shale should be evaluated for proper determination of the economic potential of the deposit. 

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