The sequence of radiolarian faunal events observed in Hole 1138A (Table T2) is, with one exception, that expected for the late Miocene to earliest Pliocene, with (in order from the base of the studied section to the top) the presence of the Actinomma golownini, Cycladophora spongothorax, Acrosphaera australis, Siphonosphaera vesuvius, Acrosphaera? labrata, and Amphymenium challengerae Zones. The regularity of the sequence is interrupted by the co-ocurrence of several events within a short interval, near the top of the studied interval between Samples 183-1138A-12R-2, 20 cm, and 183-1138A-13-2, 20 cm, corresponding to the boundary between lithologic Units I and II. Several Miocene species (Stichocorys peregrina, A. labrata, Eucyrtidium pseudoinflatum, and Lychnocanium grande) disappear in this interval, and several others typical of the Pliocene (Antarctissa cylindrica, Helotholus vema, Lampromitra coronata and Cycladophora pliocenica) appear for the first time (Table T1). The A. challengerae Zone is represented here by a single sample with rare A. challengerae in Sample 183-1138A-12R-3, 20 cm. The Tau Zone appears to be totally absent, and the marker for the next younger zone—H. vema—in fact, is present in the same sample as A. challengerae.
Between Samples 183-1138A-13R-4, 105 cm, and 183-1138A-14R-2, 20 cm, another set of events seems to occur within a fairly short depth interval, with the first appearance of Cenosphaera sp. Keany (1979), the first common appearance of S. peregrina, the disappearance of L. stigi and S. vesuvius, as well as the last traces of A. australis. The LAD of C. spongothorax also occurs in, or just below, this interval. Only the latter is is a formally defined stratigraphic marker, and this is present in the expected sequence within the standard zonation.
The marker events for the subzones within the C. spongothorax Zone—the LAD of A. golownini and the FAD of E. pseudoinflatum—could not be resolved at the sampling resolution of this study from the top of the C. spongothorax Zone itself. Nor was the occurrence of Dendrospyris megalocephalis—the marker for the upper A. golownini Subzone—observed.