Abstract

Ovate pellets of kaolinite from .05 to 15 millimeters in length occur in conglomerates interbedded with pyroclastic materials and waterlaid sediments in the Eocene Calapooya formation at Hobart Butte, Oregon. Although Miocene hydrothermal solutions invaded these rocks, altered welded tuffs to clay, and deposited kaolin minerals together with realgar, stibnite, pyrite, quartz, and other minerals, a hydrothermal or a volcanic origin for the pellets is considered unlikely. The sizes and shapes of the pellets, the presence of pellets and lithic fragments within pellets, the lack of radial and concentric structures, the presence of charcoal, lignitic material, and diatoms in the matrix suggest fluvial deposition of clay flakes, broken from thin clay layers that had dried on Eocene flood plains. The arrangement of the long axes of the pellets parallel to the bedding and the molding of pellets against quartz, lithic fragments, and pellets support the interpretation of a sedimentary origin for the pellets and the clays containing them.

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