Abstract
ABSTRACT Using luminescence petrography equipment previously described in the literature, and modifications of this equipment reported here, one can usually distinguish secondary from primary quartz in sandstones. It is thus possible to distinguish solution and overgrowth phenomena even when usual petrographic criteria fail. By luminescence, examples of concavo-convex boundaries, long boundaries, and sutured contacts, all criteria of pressure solution, are revealed to result from optically continuous quartz overgrowths. The luminescence not only prevents ambiguity regarding mechanisms active in the sandstones, but reveals the detrital fabric so that size, shape, and degree of rounding of the detrital grains may be clearly seen. Features relating to prior cycles of sedimentation are also freque tly seen. Fractures and crushing events, long since healed by growth of secondary quartz, are also distinguishable by the luminescence technique; in some immature sandstones such events seem to be very common. Often, the crystal regions revealed by crossed nicols are related to, but are by no means identical with, the fractured fragments, giving evidence of recrystallization with mobility of grain boundaries. Crenulated boundaries also form in the fracturing-healing-recrystallization process resulting in polycrystalline grains showing metamorphic quartzite texture. It is suggested that many of the polycrystalline quartz grains found in sandstones originate in this way either in place or in precursor source rocks. All these features are well documented with photomicrographs.
Published Version
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