[BPT06-P08] Size variation of a calcareous nannofossil genus Coccolithus Schwartz during the Miocene
Keywords:Calcareous nannofossil, Size variation
A similar trend of the size variation of Coccolithus specimens was observed in the Caribbean and Pacific cores. It is characterized by increasing of larger specimens upward and sudden replacing with smaller specimens at certain boundaries. Large specimens disappeared about 10.3 Ma and 9 Ma. Coccolithus specimens over 12 µm in diameters are only recognized below 10.3 Ma and their morphologic features are clearly different from smaller specimens. They must be involved in Coccolithus miopelagicus Bukry and the age of their disappearance is considered to about 10.7 Ma. On the other hand, there are no morphologic differences between other larger and smaller common specimens. Abundant occurrences of smaller Coccolithus specimens during 9-8 Ma mostly correspond to the interval of smaller Reticulofenestra specimens (e.g., Young, 1990). Thus, downsizing of coccolith specimens may be possibly common phenomenon in Miocene calcareous nannoplankton.
McIntyre, A. and Bé, A. W. H., 1967, Deep - Sea Res., 14, 561–597.
Nishida, S., 1982, Bull. Nara Univ. Educ., 31, 63–77 (in Japanese with English abstruct).
Okada, H. and Bukry, D., 1980, Marine Micropaleontology, 5, 321–325.
Parente, A. et al., 2004, Micropaleontology, 50, 107–120.
Young, J. R., 1990, Micropaleontology, 9(1), 875–912.