LATE EOCENE CRYSTAL‐BEARING SPHERULES: TWO LAYERS OR ONE?

Abstract

Late Eocene crystal‐bearing spherules have been found in deep sea cores from the Caribbean Sea, Gulf of Mexico, equatorial Pacific Ocean, and eastern equatorial Indian Ocean. Keller et al. (1987) have suggested that the spherules from the western equatorial Pacific (Site 292, core 38) and eastern Indian Ocean (Site 216) are older (Globigerapsis semiinvoluta Zone) than those from the central equatorial Pacific, Gulf of Mexico, and Caribbean Sea (Globorotalia cerroazulensis Zone). The strongest argument in favor of two layers is the biostratigraphic data; however, published biostratigraphic interpretations are at odds with Keller et al.'s (1987) conclusions. Furthermore, paleomagnetic data for Site 292 seems to contradict Keller et al.'s conclusion that the spherules found in core 36 occur in sediments of the same stratigraphic age as those found in the central equatorial Pacific, Gulf of Mexico, and Caribbean Sea sites. Although the spherules from Sites 216 and 292 (core 38) do have higher average CaO, and lower average Al2O3 and FeO contents than the late Eocene spherules from the other sites, there is a great deal of overlap in composition. It is our opinion that the similarities in composition and petrography between the late Eocene crystal‐bearing spherules are greater than the differences. Additionally, there seems to be a systematic change in composition and in amount of iridium excess from east to west when all the sites containing the crystal‐bearing spherules are considered. We believe, therefore, that it is likely that the late Eocene crystal‐bearing spherules all belong to a single event.