Abstract

Mineralogic stabilization of porcelaneous foraminifera has been cited as an example of diagenesis in which chemical change occurs without any textural alteration. In contrast, our study of living specimens of a common species of this group, Archaias angulatis, indicates a sequence in which textural alteration of the magnesium calcite skeleton occurs without loss of magnesium from the test. In samples of A. angulatis from Florida Bay, Florida, skeletal rods (1-2 micrometers long and 0.1 micrometers wide) are extensively recrystallized to dense minimicrite (0.05- 0.1 micrometers anhedral equant crystals). Both rods and minimicrite contain 9-11.5 mole % MgCO 3 . Micritization increases with age of the skeletons and occurs more rapidly in septal and basal walls than in lateral walls and pillars. Recrystallization could be due to change in the partial pressure of CO 2 resulting from changing distributional patterns of respiration and photosynthesis of algal symbionts. Recrystallization within living foraminifera has important implications for studies of fossil diagenesis and biomineralization.

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