Because the focus of Leg 200 was on basement drilling, we did not have a paleontologist on board. Bob Goll, from ODP-TAMU (Texas A&M University), examined sediment samples for radiolarians and wrote a first draft of the following report. In addition, John Firth, also from ODP-TAMU, examined several samples for calcareous nannofossils, but the samples were found to be barren.
A total of six samples were investigated for radiolarians: 200-1223A-1H-1, 72-74 cm; 1H-3, 125-127 cm; 1H-CC, 19-21 cm; 1H-CC, 29-31 cm; 6X-4, 17-19 cm; and 6X-CC, 15-17 cm. Of these, only three samples (200-1223A-1H-1, 72-74 cm; 1H-CC, 29-31 cm; and 6X-4, 17-19 cm) contain radiolarians. Sample 200-1223A-1H-1, 72-74 cm, contains common opal-CT replacement pseudomorphs of radiolarians that cannot be identified taxonomically, and the sample cannot be dated on the basis of these occurrences.
Mixed preservation states characterize the remaining two samples, where moderately preserved specimens are present in association with opal-CT forms. Specimens in the original opal-A silica phase are rare but sufficient to provide a general age. The Eocene species, Eusyringium fistuligerum, was observed in Sample 200-1223A-1H-CC, 29-31 cm. This sample is from the dark-brown clay (lithologic Unit 3) that overlies the bulk of those deposits thought to be related to the Nuuanu Landslide.
The presence of numerous specimens of Phormocystis striata exquisita and one specimen of Phormocystis striata striata in Sample 200-1223A-6X-4, 17-19 cm, is regarded as reliable evidence to support the assignment of this fauna to the Buryella clinata Zone as indicated by Sanfilippo et al. (1985). This sample comes from lithologic Unit 13, which is near the base of the cored interval.
Both samples have radiolarians that indicate an early Eocene age. Without consideration for reworking, this age is in conflict with the age constraint from the geochemistry of the tuffs which indicates that the vitric tuffs have an age no older than ~3 Ma (i.e., no older than the volcanics from which the Site 1223 deposits were derived, which the geochemistry indicates is from one of the Hawaiian Islands). Similarly, the magnetostratigraphy indicates that the sediments above the dark-brown clay of lithologic Unit 3 were deposited during Chrons C2n to C1n, with all underlying sediments, including those samples with identifiable radiolarians, falling within a dominantly reversed polarity zone interpreted to be Chron 2r (1.950-2.581 Ma).
Reworking of radiolarians would, however, be expected in landslide-related deposits, though less so in the dark-brown clay of Unit 3 if it is a pelagic clay. The depositional environment for the clay is not known at this time, and the unit is thin enough that bioturbation could have resulted in reworking of sediments from below and above, with both being either turbidites or landslide units where reworked radiolarians could occur. Reworking may also be suggested by the lack of radiolarians in the second sample analyzed from lithologic Unit 3 (Sample 200-1223A-1H-CC, 19-21 cm), which is only 10 cm above that which contains early Eocene radiolarians. Sporadic occurrences of these microfossils and the mixed, generally poor, preservation states support the interpretation of reworking. We consider that reworking is likely and that the early Eocene age is not representative of the age of the units.
3This section was written by Bob Goll, Ocean Drilling Program, Texas A&M University, 1000 Discovery Drive, College Station TX 78745-9547. goll@odpemail.tamu.edu