Because the focus of Leg 200 was on basement drilling, we did not have a paleontologist on board. John Firth, from ODP-TAMU (Texas A&M University), analyzed the calcareous nannofossils in the sediment cores postcruise and wrote a first draft of the following report. A graphical summary of smear slides analyzed for fossils from the sediments cored at Site 1224 is shown in Figure F55.
Smear slides were made from Cores 200-1224A-2X and 4X, 200-1224C-1H, and 200-1224E-2R for initial analysis of calcareous nannofossils. The highest and lowest occurrences of nannofossils were compared with those reported in Bralower and Mutterlose (1995) and with the zonation of Okada and Bukry (1980) and correlated to the geologic timescale of Berggren et al. (1995).
Sample 200-1224A-2X-CC was barren of nannofossils. Sample 200-1224A-4X-1, 78 cm, contains rare, poorly preserved nannofossils, including Chiasmolithus grandis, Coccolithus pelagicus, and Campylosphaera dela. The highest occurrence (HO) of C. grandis marks the top of Subzone CP14b of Okada and Bukry (1980), and the HO of C. dela falls within Subzone CP14b (according to Bralower and Mutterlose, 1995). Sample 200-1224A-4X-CC contains rare, poorly to moderately preserved nannofossils, including Reticulofenestra umbilicus, Discoaster barbadiensis, C. pelagicus, Coccolithus formosus, C. grandis, and Sphenolithus spiniger. The lowest occurrence (LO) of R. umbilicus marks the base of Subzone CP14a, and the HO of C. grandis marks the top of Subzone CP14b. Thus, Core 200-1224A-4X can be constrained to Zone CP14 (~37-43 Ma), of late middle Eocene age. Zone CP14 corresponds in time to polarity Chrons C17N to C20N.
Sample 200-1224C-1H-1, 40 cm, contains very rare, poorly to well preserved nannofossils including Reticulofenestra bisecta, Reticulofenestra dictyoda, and C. dela. The ranges of R. bisecta and C. dela overlap within Subzone CP14b (~37-40 Ma); thus, this sample is constrained to that subzone. Sample 200-1224C-1H-4, 27 cm, had very rare, very poorly preserved and unidentifiable nannofossils. Samples 200-1224C-1H-5, 52 cm, and 1H-CC, 5 cm, are barren of nannofossils.
Sample 200-1224E-2R-1, 45 cm, contains abundant, diverse, moderately preserved nannofossils, including C. grandis, Chiasmolithus solitus, Chiasmolithus gigas, C. pelagicus, C. dela, Sphenolithus furcatolithoides, and Braarudosphaera sp. Sample 200-1224E-2R-CC, 11 cm, contains abundant, moderately to well-preserved nannofossils, including C. grandis, C. gigas, Chiasmolithus nitidus, C. dela, and C. pelagicus. The presence of C. gigas in both samples from Core 200-1224E-2R constrains this core to be within Subzone CP13b (~44-46 Ma) of Okada and Bukry (1980), of middle Eocene age. Subzone CP13b corresponds in time to Chrons C20R and C21.
Sediments from the core catcher of Core 200-1224-2R are within 2 m of the sediment/basement contact. Marine magnetic anomalies over the basement at Site 1224 indicate the age of basement is near the Chron C20R/C21N contact. Thus, the paleontological age of the oldest sediments is consistent with the basement age. Surprisingly, nearly the entire sedimentary section appears to be middle Eocene in age.
3This section was written by John Firth, Ocean Drilling Program, Texas A&M University, 1000 Discovery Drive, College Station TX 78745-9547, USA. firth@odpemail.tamu.edu