Silicoflagellates are very sparse or absent in many of the Leg 207 samples studied (see Table T1). Of 27 samples from ODP Sites 1257A, 1257B, 1257C, and 1258A examined for silicoflagellates, 16 were found to be barren, despite the examination of multiple slides of three size fractions. No silicoflagellate specimens were found in the two samples examined from Hole 1257C. For Holes 1257A and 1257B, only two samples were found in each hole to contain silicoflagellates, and the total diversity was only eight species. The frequent barren intervals did not provide sufficient information to determine biostratigraphic zonations.
Silicoflagellates were more consistently abundant and diverse in the Hole 1258A samples that were examined (see Table T2). Silicoflagellates were found in all samples except for a barren interval from Samples 207-1258A-5R-CC through 8R-CC. In the two samples from above the barren interval, silicoflagellates were sparse, with only a few specimens per slide. Dictyocha spinosa, found in Sample 207-1258A-4R-CC, is usually restricted to a narrow stratigraphic interval (see Engel and McCartney, 2005; McCartney and Wise, 1990). Dictyocha spinosa is commonly associated with D. frenguelli or D. deflandei, but these associated taxa were not found in Sample 207-1258A-4R-CC, and no attempt is made to therefore assign this sample to an existing silicoflagellate zone.
Silicoflagellates were relatively abundant in Samples 207-1258A-15R-CC through 16R-CC. This interval is placed in the Naviculopsis foliacea Zone (Bukry, 1981), based on the co-occurrence of N. foliacea, N. eobiapiculata, and N. constricta and the absence of Dictyocha hexacantha. This interval also includes two taxa that have not previously been recorded from this early. Most noteworthy is the lower Eocene occurrence of Bachmannocena diodon in Samples 207-1258A-15R-CC through 16R-CC. Naviculopsis lata obliqua is also an early occurrence, although this is a rarely seen taxon.