Geochemistry of Ammonium in Rocks

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Knowledge of the nitrogen cycle, which includes determination of reservoirs of nitrogen in the atmosphere, hydrosphere, and lithosphere, is hindered by limited data on nitrogen abundance in rocks. Recent investigations of coal-rich shale, illite/smectite clays, and hot spring deposits suggests that ammonium (NH4) bearing minerals may be much more abundant than previously recognized. This research will investigate the geochemistry of NH4 in coal-rich shale and glauconite-bearing strata. Specific goals include a better understanding of fluid/mineral reactions associated with coal-bearing, low grade metamorphic shales and with the environment of glauconite formation. To achieve these goals, it will be necessary to characterize the mineralogy and chemistry of these strata using various laboratory techniques (NH4 analysis, SEM, BSEM, TEM, XRD, XRF, and petrography) and to conduct hydrothermal experiments and geochemical calculations that measure equilibrium constants of NH4 fixation reactions. The results may show that NH4 - illite in coal-rich shale can be used as thermal indicator. Presence of NH4-illite should seriously affect measurements of the illite crystallinity index, long used to measure the thermal maturity of shales. Additional results may include possible explanations for low radiometric ages of glauconite and for differences in alkali contents between Fe-rich illite/smectite (glauconite) and Al- rich illite/smectite.