Size variation of Neogene Reticulofenestra coccoliths from Indian Ocean DSDP Cores

Abstract. Data is presented here on Reticulofenestra coccolith size distribution patterns from 122 Mid-Miocene to Pliocene samples from Deep Sea Drilling Project sites in the Western Indian Ocean and Red Sea. A clear pattern is revealed with a dramatic size reduction event occurring in the Late Miocene (nannofossil zone NN10). As a result of this event nannofloras from the interval above it are readily distinguishable by the absence of specimens longer than 5 microns; this interval is termed the “small Reticulofenestra interval”. Assemblages from above and below this interval contain large specimens but they can be reliably distinguished by different size distribution patterns within them. Analogous data from other studies is reviewed, possible causes of the pattern are discussed, and its biostratigraphic application described. The Neogene taxonomy of the genus Reticulofenestra is revised and four new combinations are proposed.