Silicoflagellates have been recognized in land outcrops and deep-sea sediments, but they have not been accepted widely as biostratigraphic indicators. In order to evaluate their occurrences and to establish a workable biostratigraphic framework, approximately 100 deep-sea sediments were studied. These were from a broad geographic area and were of Cretaceous (Cenomanian) and the middle Eocene to Holocene ages. The samples chosen were dated by other planktonic microfossils, thus making cross correlation possible.

The complete absence of silicoflagellates in the few JOIDES samples examined from the Upper Cretaceous and the lack of samples from the Paleocene through the early Eocene interval prevent a complete zonation. Three zones are recognized from the middle Eocene to the top of the Oligocene. There was a sharp decrease in the silicoflagellate population in the Oligocene. In the Miocene evolutionary diversification of taxa permits greater biostratigraphic resolution; 7 zones have been recognized. A massive extinction of silicoflagellates occurred toward the end of the Miocene, with only a few species continuing into the Holocene. The brief recurrence of Mesocena cf. elliptica at the Jaramillo event within the Matuyama Reversed Epoch both in low and middle latitudes of the Pacific marks a bio tratigraphic datum within the Pleistocene. Determining the first appearance of many Holocene taxa will add further resolution within the Quaternary interval.

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