RECRYSTALLIZATION IN LIVING PORCELANEOUS-FORAMINIFERA (ARCHAIAS-ANGULATIS) - TEXTURAL CHANGES WITHOUT MINERALOGIC ALTERATION

Mineralogic stabilization of porcelaneous foraminifera has been cited as an example of diagenesis in which chemical change occurs without an y textural alteration. In contrast, our study of living specimens of a common species of this group, Archaias angulatis, indicates a sequenc e in which textural alteration of the magnesium calcite skeleton occur s without loss of magnesium from the test, In samples of A, angulatis from Florida Bag, Florida, skeletal rods (1-2 mu m long and 0.1 mu m w ide) are extensively recrystallized to dense minimicrite (0.05-0.1 mu m anhedral equant crystals), Both rods and minimicrite contain 9-11.5 mole % MgCO3. Micritization increases with age of the skeletons and oc curs more rapidly in septal and basal walls than in lateral walls and pillars, Recrystallization could be due to change in the partial press ure of CO2 resulting from changing distributional patterns of respirat ion and photosynthesis of algal symbionts. Recrystallization within li ving foraminifera has important implications for studies of fossil dia genesis and biomineralization.