Preferential selection of titanium-bearing minerals in agglutinated Foraminifera: Ilmenite (FeTiO 3) in Textularia hauerii d’Orbigny from the Bazaruto Archipelago, Mozambique

Abstract

The biserial agglutinated foraminifer Textularia hauerii d’Orbigny frequently occurs at shallow depths in reefal habitats off Bazaruto Island, Mozambique. X-ray diffraction, scanning electron- and light microscopy analyses show the enhanced concentration of the titanium-bearing mineral ilmenite (FeTiO 3) in the agglutinated tests of this species. The mineral constitutes an insignificant component in the surrounding sediment (< 1%), but accounts for more than 26% of the foraminiferal test content. The accumulation of ilmenite in T. hauerii and its absence in co-occurring agglutinated Foraminifera suggest the preferential selection for ilmenite. The tendency for ilmenite particles to be arranged along sutures and on the apertural face (1) provides further evidence that certain Foraminifera can specifically select grains, and (2) implies that there exists a selective mechanism to control the timing and placement during test and chamber construction. The preferential uptake represents the first record of ilmenite selection in Foraminifera. Potential driving forces controlling the selective agglutination of Ti minerals, the preferential adsorption to Ti surfaces, and interactions between cellular compounds of the foraminiferal reticulopods and the mineral surfaces are explored.