Clays recovered from Unit I at Site 1149 contain an abundant assemblage of siliceous plankton—mainly diatoms, silicoflagellates, and radiolarians. The abundance of siliceous plankton decreases in Core 185-1149A-12H, and Cores 185-1149A-13H to 185-1149B-3R are completely barren. The clays from Cores 185-1149A-1H to 185-1149B-3R contain ichthyolith assemblages, which increase in abundance downhole, probably as a response to downward decreasing sedimentation rates (see "Sedimentation Rates").
Carbonates recovered in Cores 185-1149B-16R to 29R yielded well to poorly preserved calcareous nannofossil assemblages. The assemblages have a high average diversity, which points to a fairly good preservation. Preliminary age assignments based on the study of core-catcher samples and additional paleontology analysis log (PAL) samples permit identification of the Hauterivian Lithraphidites bollii Zone from Core 185-1149B-16R down to 21R. Downhole assemblages are dominated by Watznaueria barnesae, Cruciellipsis cuvillieri, and Tubodiscus sp.; the first downhole occurrence of Tubodiscus verenae is in Core 185-1149B-24R and indicates the uppermost Valanginian-lowermost Hauterivian. Rucinolithus wisei, a species restricted to the Berriasian-Valanginian according to Thierstein (1971), occurs from Core 185-1149B-25R downhole. The persistence of T. verenae downhole to Core 185-1149B-29R confirms a late Valanginian age for the contact of sediment/basement consistent with magnetic Anomaly M11. This age assignment will be refined onshore, radiolarian assemblages will be studied, and an integrated biostratigraphy will be established.
Numerous microfossil groups are present in the cored interval. The clays and ashes in lithologic Unit I (Cores 185-1149A-1H to 11H) contain abundant assemblages of siliceous plankton, in particular, diatoms, silicoflagellates, and radiolarians. The preliminary study of silicoflagellate and diatom assemblages points to a Pliocene age for Sample 185-1149A-9H-CC, whereas 12H-CC is assigned a late Miocene age, according to Barron (1985). These age assignments are in agreement with paleomagnetic shipboard stratigraphic data (see "Magnetostratigraphy"). The abundance of the siliceous fossil groups decreases dramatically in Core 185-1149A-12H, as does the frequency of ash layers (see "Unit I"). Clays in Cores 185-1149A-13H to 185-1149B-3R are barren of siliceous plankton. Ichthyoliths are present in lithologic Units I and II, and their abundance increases downhole from Cores 185-1149A-13H to 185-1149B-3R. Cores 185-1149B-2R to 15R contain mainly porcelanite and chert pebbles, with a very low average recovery. Nevertheless, radiolarian assemblages were observed on cut surfaces of the cores under the microscope. Their relative abundance, in contrast to other fossil groups, will allow a shore-based biostratigraphic study for the otherwise unfossiliferous Unit III. The interval comprising lithologic Units I, II, and III, from Cores 185-1149A-1H to 185-1149B-15R, is barren with respect to calcareous microfossils. Unit IV, from Cores 185-1149B-16R to 29R, consists of radiolarian cherts and interbedded radiolarian nannofossil chalks/marls that contain fairly to well-preserved calcareous nannofossils, benthic foraminifers, and radiolarians.
The upper part of the stratigraphic section (lithologic Units I through III) is barren of calcareous nannofossils, with the exception of a thin, reworked layer in Core 185-1149A-3H (Sample 185-1149A-3H-1, 83 cm), that contains Sphenolithus moriformis, Sphenolithus dissimilis, Reticulofenestra ssp., Cyclicargolithus floridanus, and Reticulofenestra daviesii; this assemblage suggests an Oligocene to early Miocene age for the reworked sediment. Scattered occurrences of calcareous nannofossils of Cenozoic age (Cy. floridanus, Discoaster ssp., Tribrachiatus orthostylus, and Reticulofenestra ssp.) are recorded in several samples obtained from the porcelanite recovered in Unit III; however, it is not yet understood if this represents a downhole contamination or the very poorly preserved original assemblage. Shore-based preparation of these samples, performed with maximum care to avoid contamination, will help clarify this problem.
Carbonates recovered in Cores 185-1149B-16R to 29R yielded well to poorly preserved calcareous nannofossil assemblages. The best preserved assemblages are in the least lithified lithologies, such as the nannofossil ooze recovered in small pockets in irregularly bedded cherts or in soft chalks. Low average breakage of delicate structures, such as spines and cross bars, points to a moderate compaction rate. High porosity of the sediment is responsible for relatively high dissolution that in some cases has completely obliterated the delicate central-area structures of some taxa (e.g., Cretarhabdus and Cruciellipsis), hindering the determination to the species level. Occasional recrystallization processes occur, causing overgrowth of central area structures. Assemblages from soft lithologies have a high average diversity, which confirms the fairly good preservation of calcareous nannofossils in these sediments. Preliminary data are based on the study of some 30 samples, including the core-catcher samples and several additional samples from the softer lithologies. Assemblages are dominated by the continuous and abundant occurrence of Watznaueria barnesae; other fairly common and long-ranging species are Watznaueria britannica, Cyclagelosphaera margerelii, Diazomatolithus lehmanii, Assipetra infracretacea, Zeugrhabdotus embergeri, Helenea chiastia, Manivitella pemmatoidea, Lithraphidites carniolensis, Cruciellipsis cuvillieri, and Tubodiscus jurapelagicus. The marker species Lithraphidites bollii occurs from Core 185-1149B-16R to 21R, thus allowing a preliminary age assignment to the Hauterivian L. bollii Zone of Thierstein (1971, 1973) and corresponding to magnetic Anomalies M4 to M9/10 (Bralower, 1987; Channell et al., 1995) for the upper part of lithologic Unit IV. Downhole assemblages are dominated by W. barnesae, W. britannica, C. cuvillieri, Assipetra terebrodentarius, and Tubodiscus ssp. The last downhole occurrence of A. terebrodentarius is recorded in Core 185-1149B-20R. The first downhole occurrence of Tubodiscus verenae in Core 185-1149B-24R indicates the top of the magnetic Anomaly M11 (Bralower, 1987) and the uppermost Valanginian-lowermost Hauterivian (Channell et al., 1995) (see also Fig. F5 in the "Explanatory Notes" chapter). Rucinolithus wisei, a species whose known range is Berriasian to upper Valanginian according to Thierstein (1971), is present from Core 185-1149B-25R downhole. The continuous occurrence of T. verenae downhole to Core 185-1149B-29R suggests a late Valanginian age for the sediment/basement contact. This age assignment will be refined onshore, and radiolarian assemblages will be studied and integrated with the nannofossil biostratigraphy.
A spot-cored interval in Hole 1149C (Cores 185-1149C-3R to 6R) contains assemblages that are assigned to the L. bollii Zone of Thierstein (1971, 1973). The sediment/basement contact, recovered in Core 185-1149C-9R in this hole, is preliminarily assigned to the late Valanginian according to the presence of R. wisei and T. verenae in the calcareous nannofossil assemblage recorded in Sample 185-1149C-8R-1, 76-77 cm. The same assemblage characterizes the carbonate sediment above the sediment/basalt contact in Hole 1149D, where this surface is much shallower (307 mbsf).
We noticed that several typical Tethyan species (Nannoconus ssp.) were not found in this material, although they were recovered in the western Pacific in slightly younger stratigraphic intervals (Aptian-Albian at Site 878; Erba et al., 1995). Some biostratigraphic markers commonly used in this stratigraphic interval have a scattered occurrence at this site (e.g., Calcicalathina oblongata) and cannot therefore be used for biostratigraphic purposes.