Pleistocene through lower Oligocene carbonate-rich sediments were recovered at Site 1264. All samples contain nannofossils with moderate to good preservation. Planktonic foraminifers with generally good preservation are abundant. Well-preserved benthic foraminifers are rare in all samples. Preservation for all fossil groups deteriorates in the lower part of the record. Several upper Miocene nannofossil and planktonic foraminifer markers are missing because of the temperate environmental conditions at this site. Oligocene benthic foraminifer assemblages show downslope transport and reworking. Benthic foraminifers indicate upper abyssal depths (2000–3000 m) during the late Oligocene through Pleistocene and possibly lower bathyal depths (~2000 m) during the early Oligocene.
Shipboard examination of calcareous nannofossils and planktonic foraminifers permitted preliminary zonal and stage assignments (Fig. F18; Tables T5, T6). Biochronological ages plotted against mcd delineate overall sedimentation rates (Fig. F19) (see "Age Model and Mass Accumulation Rates"). A nearly complete Neogene and upper Oligocene section is present and was deposited at variable sedimentation rates. An upper Miocene unconformity representing ~0.6 m.y. occurs between 76.8 and 77.2 mcd. The middle Miocene is condensed and is represented between 177.3 and 203.6 mcd. The records of Sites 1263 and 1264 can be correlated over the interval 28–30 Ma, jointly providing a "complete" coverage for the last 58 m.y.
Calcareous nannofossil assemblages taken from core catcher samples of all holes and additional discrete (toothpick) samples from critical intervals were examined. The nannofossil biostratigraphy suggests that the recovered section represents an almost complete record from the upper Pleistocene–Holocene (Zones CN15 and NN21b) through the upper part of the lower Oligocene (approximately at the Zone CP18/CP17 boundary). Depth and age estimates of key biostratigraphic markers are shown in Table T5. Table T7 shows a distribution chart of the core catcher samples. Nannofossils are present throughout the section and have generally good preservation. Lower Oligocene and middle Miocene discoasterids (from 110 mcd to the bottom of the section) are overgrown with secondary calcite.
The complete succession of Pleistocene nannofossil assemblages is present in Sections 208-1264A-1H-1 through 1H-5, 208-1264B-1H, and 208-1264C-1H, including the events based on the size change of Gephyrocapsa. Sample 208-1264C-1H-1, 0–2 cm, has an upper Pleistocene assemblage belonging to Zone CN15 (Subzone NN21b). The Pliocene/Pleistocene boundary is placed between 9.7 and 11.4 mcd (between Samples 208-1264A-1H-5, 70 cm, and 1H-6, 70 cm) between the lowest occurrence of medium Gephyrocapsa spp. and the highest occurrence of Discoaster brouweri.
Pliocene assemblages mainly consist of reticulofenestrids, sphenoliths, and discoasterids. Helicoliths and ceratholiths belonging to the genus Amaurolithus are common, whereas representatives of the genus Ceratholithus are very rare. The middle and upper Pliocene assemblages are dominated by small placoliths (2–4 µm), mainly small Reticulofenestra spp. and Pseudoemiliania lacunosa (Cores 208-1264A-2H, 3H, and 208-1264B-2H and 3H). The consistent presence of D. brouweri, Discoaster brouweri var. triradiatus, Discoaster pentaradiatus, Discoaster surculus, Discoaster tamalis, and Discoaster asymmetricus provided a detailed biostratigraphic subdivision of the middle–upper Pliocene (Subzones CN12d–CN12aA; Zones NN18–NN16).
An expanded lower Pliocene section is present between 29.4 and 77.0 mcd (Sections 208-1264A-3H-4 through 7H-6 and 208-1264B-4H-CC through 8H-CC), corresponding to Zone CN11 and Subzone CN10c (NN13–NN15). The discoasterid assemblage is characterized by Discoaster variabilis gr., D. pentaradiatus, Amaurolithus delicatus, and Amaurolithus primus and by common to abundant Scyphosphaera spp. The Miocene/Pliocene boundary marker Ceratolithus acutus is present in Sample 208-1264A-7H-6, 80 cm, and the uppermost Miocene ceratolith marker Nicklithus amplificus occurs in Sample 208-1264A-7H-7, 20 cm. This indicates the presence of an unconformity in Core 208-1264A-7H (within Section 6 or 7) at the Miocene–Pliocene transition, spanning a time interval of at least 0.63 m.y. and corresponding to Subzones CN10a and CN9bC.
Miocene nannofossil assemblages are rich and diverse, and most of the Miocene zonal boundaries can be recognized (Fig. F18). The upper Miocene is characterized by the presence of common A. primus and A. delicatus (Cores 208-1264A-8H through 10H), by the absence interval ("paracme") of Reticulofenestra pseudoumbilicus (Cores 208-1264A-10H and 11H), and by the presence of abundant Minylitha convallis and Calcidiscus spp. (Cores 208-1264A-11H through 13H). The upper and middle Miocene Discoaster assemblages are rich in species and compose a large part of the total nannofossil assemblage at Site 1264. Nevertheless, the upper Miocene Discoaster marker species Discoaster quinqueramus and Discoaster berggrenii are missing in the area. Therefore, the upper Miocene zonal boundaries CN10a/CN9 (NN12/NN11) and CN9/CN8 (NP11/NP10), marked by the last occurrence of D. quinqueramus and the first occurrence of D. berggrenii, respectively, were not recognized. Other discoasterid markers are present with atypical morphotypes (e.g., Discoaster hamatus).
The range of common Discoaster kugleri (11.6–11.88 Ma; Backman and Raffi, 1997) provides a distinct middle Miocene biostratigraphic marker that is consistently isochronous between low and middle latitudes (Hilgen et al., 2000). The lowest common occurrence and highest common occurrence of this species could not be determined in detail because the events occur within the break between Cores 208-1264A-16H and 17H. In the middle Miocene (~180 to ~202 mcd), the Zone CN4/CN3 (NN5/NN4) boundary was not defined because the marker Helicosphaera ampliaperta is absent. In the lower Miocene, Triquetrorhabdulus carinatus is very rare or absent; Discoaster druggii is missing; and the zonal boundaries NN3/NN2 and CN1c/CN1a+b (NN2/NN1) could therefore not be recognized.
The presence of Sphenolithus disbelemnos in Core 208-1264A-24H and the range of Sphenolithus delphix in Core 25H indicate that the O/M boundary is between Section 208-1264A-24H-CC and Sample 25H-1, 10 cm, and Sections 208-1264B-25H-3 and 25H-CC at ~258 mcd.
The lower section of Site 1264 is placed in the upper Oligocene and the upper part of the lower Oligocene (Cores 208-1264A-25H through 30H and Sections 208-1264B-25H-CC through 28H-CC). Key elements in the observed low-diversity assemblages are the Oligocene markers Sphenolithus ciperoensis and Sphenolithus distentus. These small sphenoliths define the bases of Zones NP24 and NP25 (Subzones CP19a and CP19b). A nannofossil assemblage with abundant Braarudosphaera bigelowii occurs in distinct layers in Sections 208-1264A-29H-3 and 29H-4 (299.7 and 300.8 mcd). The "Braarudosphaera layers" are a typical feature of the lower upper Oligocene in the South Atlantic Ocean (Roth, 1974). The assemblages mainly consist of B. bigelowii, with the secondary components Dictyococcites bisectus, Sphenolithus predistentus, S. distentus, Sphenolithus moriformis, Zygrhablithus bijugatus, and Cyclicargolithus abisectus. The high relative abundance of B. bigelowii has been related to low salinity (Takayama, 1972) or eutrophication (Cuhna and Shimabakuro, 1996).
Planktonic foraminifers were examined in all core catcher samples from Holes 1264A, 1264B, and 1264C and in additional samples around critical intervals in Holes 1264A and 1264B (Tables T6, T8). Generally, planktonic foraminifers are abundant and well preserved. Reworking of planktonic foraminiferal specimens is rare, except for specimens in Sections 208-1264A-1H-CC and 30H-CC.
Sample 208-1264C-1H-1, 0–2 cm (mudline), contains a mixture of well-preserved subtropical and temperate Pleistocene species. The fauna is dominated by Globorotalia crassaformis, Globorotalia truncatulinoides, Globorotalia tumida, Globoconella inflata, Globigerinoides ruber, Globigerinoides sacculifer, Globigerinella siphonifera, Hirsutella scitula, Menardella menardii, and Orbulina universa.
The uppermost occurrence (top) of Globorotalia tosaensis (base of Subzone PT1b; 0.65 Ma) is between Samples 208-1264C-1H-1, 0–1 cm (0.1 mcd), and 1H-2, 0–1 cm (1.5 mcd). The Pliocene/Pleistocene boundary is between Sections 208-1264B-1H-CC and 208-1264A-1H-CC (7.3–12.3 mcd). We used the uppermost occurrence of Globigerinoides extremus to approximate the boundary because Globigerinoides fistulosus is absent.
Many of the tropical/subtropical age-diagnostic taxa used to subdivide the upper Pliocene are missing because of the temperate environmental conditions. Boreal species (e.g., Globoconella crassaformis, Globoconella conomiozea, and Globoconella conoidea) dominate the assemblage. Although menardellids are extremely rare, the boundary between PL5 and PL6 could be defined by the highest occurrence of Menardella miocenica (Kennett and Srinivasan, 1983). We did not define Subzone PL1b because the highest occurrence of Hirsutella cibaoensis (base of Subzone PL1b) is, according to Lourens et al. (in press), younger than the highest occurrence of Globigerina nepenthes (Zone PL2). Our data confirm that the highest occurrence of H. cibaoensis (47.3 mcd) is above the highest occurrence of Globoturborotalita nepenthes (52.7 mcd). All other zonal boundaries could be recognized (Fig. F18). Dentoglobigerina altispira and Sphaeroidinellopsis seminulina both have their highest occurrence in Sections 208-1264A-2H-CC and 208-1264B-3H-CC, which makes it impossible to resolve Zone PL4 (160 k.y.).
The middle/upper Pliocene boundary is between Sections 208-1264B-2H-CC and 208-1264A-2H-CC (20.8 mcd), and the lower/middle Pliocene boundary is between Sections 208-1264A-2H-CC (23.4 mcd) and 3H-CC (26.7 mcd).
G. conoidea, G. conomiozea, Globigerina apertura, and Globoturborotalita nepenthes are typical and frequent species in the upper Miocene. The absence of Neogloboquadrina acostaensis prevented a division of Zones M13 and M12. The boundary between the middle and upper Miocene is between Sections 208-1264B-17-CC (178.0 mcd) and 208-1264A-17H-CC (182.5 mcd).
Middle Miocene assemblages are dominated by Globoquadrina dehiscens, Globorotalia archeomenardii, and the Praeorbulina–Orbulina lineage. The tropical/subtropical zonation between ~13.45 and 8.91 Ma is not applicable because most members of the Fohsella lineage are missing, which is typical for this latitude (Pujol, 1983; Boersma, 1984). Fohsella peripheroacuta and Fohsella peripheroronda are the only representatives of this lineage. Menardella praemenardii and Menardella archeomenardii are the only representatives of the menardellids. The absence of menardellids and fohsellids before ~11.6 Ma (below 180.3 mcd) might indicate either more subtropical conditions or a wider ecological tolerance of the founders of the lineages. Consequently, we used the transitional austral zonation (see "Planktonic Foraminifers" in "Biostratigraphy" in the "Explanatory Notes" chapter) for the middle and upper Miocene (Fig. F18). Below this level, sedimentation rates drop significantly, especially in a condensed interval between 196 and 204 mcd (corresponding to 14.7–17.5 Ma). The completeness of the sequence of foraminiferal events in this interval (especially the Praeorbulina–Orbulina lineage) points to a reduced sedimentation rate and not an unconformity. The lower/middle Miocene boundary is between Samples 208-1264B-20H-2, 78–80 cm, and 208-1264A-19H-6, 32–34 cm (202.0–202.5 mcd).
Lower Miocene assemblages contain G. dehiscens, Globigerina venezuelana, Globigerina angustiumbilicata, Globigerina praebulloides, Catapsydrax dissimilis, Paragloborotalia pseudokugleri, and Paragloborotalia kugleri. Globigerinatella insueta s.s. is missing, which prevents the definition of the base of Zone M3. The O/M boundary is between Section 208-1264A-24H-CC and Sample 25H-1, 32–34 cm (257.7 and 258.9 mcd).
The lowermost Miocene to uppermost Oligocene sediments are potentially condensed, with 2.9 m of sediment corresponding to the time interval from 22.9 to 24.3 Ma. The tentative age model must be refined to ascertain this observation. Upper Oligocene assemblages are dominated by G. venezuelana, G. praebulloides, Globigerina euapertura, G. angustiumbilicata, Paragloborotalia opima, and C. dissimilis. The upper/lower Oligocene boundary is between Sections 208-1264B-27H-CC and 28H-CC (284.0–294.4 mcd). Section 208-1264A-30H-CC contains some reworked Eocene to Paleocene specimens.
All core catcher samples from Hole 1264A were semiquantitatively investigated for benthic foraminifers. In addition, samples from the upper core in Holes 1264B and 1264C (0.1–7.3 mcd) and samples in the lower Miocene of Hole 1264B were studied (Table T9).
In all samples, benthic foraminifers are rare compared to planktonic foraminifers. Preservation is good in most samples, with the exception of Sections 208-1264A-24H-CC through 30H-CC (below 257 mcd to the bottom of the section). These contain specimens of variable preservation, with some reworked from upper Paleocene through Eocene and some indicative of downslope transport. Benthic foraminiferal assemblages indicate deposition at upper abyssal depths (2000–3000 m). Sections 208-1264A-28H-CC through 30H-CC (below 295 mcd) were probably deposited close to the upper abyssal/lower bathyal boundary (~2000 m), but paleodepth assignment is difficult because of reworking of specimens indicative of middle to lower bathyal depths.
Samples 208-1264C-1H-1, 0–2 cm, and 1H-CC (0–3 mcd) contain assemblages with common Globocassidulina subglobosa, Cibicidoides wuellerstorfi, Cibicidoides mundulus, Oridorsalis umbonatus, and Pyrgo spp., with varying relative abundances of the Uvigerina peregrina group, Pullenia spp., and minor Osangularia culter, Bulimina rostrata, Bolivinita pseudothalmanni, and Gyroidinoides spp. These samples do not contain pleurostomellid and siphonodosariid species and were probably deposited after the "Stilostomella extinction" at 0.65 Ma (Hayward, 2002). At present, similar assemblages occur along Walvis Ridge between ~2000 and 3300 m (Schmiedl et al., 1997), with common G. subglobosa indicative of locations on the slopes of ridges. At these depths, bottom waters are derived from northern sources (North Atlantic Deep Water), as indicated by the common presence of C. wuellerstorfi.
Assemblages between 7 and 172 mcd (Sections 208-1264B-1H-CC through 208-1264A-16H-CC) are very similar to those in the upper samples but contain pleurostomellid and siphonodosariid species in addition to those listed (Table T9). The upper Miocene incertae sedis "Bulava indica" (probably a pteropod) occurs in Section 208-1264A-16H-CC (172 mcd).
C. wuellerstorfi has its lowest occurrence between Sections 208-1264A-16H-CC and 17H-CC (172 and 183 mcd; 11.0–11.9 Ma). This first appearance of C. wuellerstorfi at Site 1264 is considerably later than its first appearance in the Atlantic Ocean at ~13.7 Ma (e.g., Thomas, 1986; age recalculated to the Leg 208 timescale). Therefore the first appearance of common C. wuellerstorfi at Site 1264 probably indicates that northern source deep water reached this location at that time.
The benthic foraminiferal assemblages show a gradual turnover in species composition between Sections 208-1264A-17H-CC and 19H-CC (183–204 mcd) at a time of global deep-sea benthic foraminiferal assemblage change (upper lower through middle Miocene; e.g., Boltovskoy and Boltvoskoy, 1989). Above this transition, typical middle Miocene and younger species such as Laticarinina pauperata, the U. peregrina group, B. rostrata, miliolid species (mainly Pyrgo spp.), and Melonis spp. are present, whereas below the transition, species typical of deposits older than middle Miocene occur (e.g., Buliminella grata, Nonion havanense, Vulvulina spinosa, and Bolivinoides huneri) and the abundance of siphonodosariid taxa is high (van Morkhoven et al., 1986; Thomas, 1986).
Between 258 and 282 mcd, evidence for reworking is convincing in some samples because they contain broken and worn specimens of Nuttallides truempyi, which has its uppermost appearance in the Eocene. In other samples there are no specimens older than Oligocene, but reworking is indicated by the presence of very large broken, bored, and abraded specimens of long-lived, thick-shelled specimens (e.g., O. umbonatus, various nodosarids, and Siphonodosaria pomuligera).
Between 210 and 212 mcd (Samples 208-1264B-21H-1, 78–80 cm, and 21H-2, 78–80 cm), benthic foraminiferal assemblages contain high relative abundances (>75%) of small smooth-walled bolivinid species. These occurrences reflect an unusual event in benthic foraminiferal faunas in the eastern Atlantic and western Indian Oceans, which is called the high abundance of bolivinids (HAB) event (Smart and Murray, 1994; Smart and Ramsay, 1995). The HAB event is coeval with the range of the calcareous nannofossil Sphenolithus belemnos (18.92–17.89 Ma in the Leg 208 timescale) at North Atlantic Site 608 (Thomas, 1987). The cause of this benthic event is not understood because in the present oceans, such high relative abundances of bolivinids occur within oxygen minimum zones in regions of upwelling and high productivity and the sedimentary record shows no indication of low-oxygen conditions during the HAB event.
Sections 208-1264A-28H-CC through 30H-CC (below 295 mcd) contain typical upper abyssal to lower bathyal upper Eocene through Oligocene assemblages with Bulimina semicostata, Bulimina elongata, C. mundulus, O. umbonatus, Gyroidinoides spp., N. havanense, common Siphonodosaria spp., as well as unilocular, laevidentalinid, and pleurostomellid taxa and rare V. spinulosa. These samples contain specimens indicating downslope transport and reworking as described above for Sections 208-1264A-24H-CC through 27H-CC. As a result of this reworking, the paleodepth assignment to the boundary between upper abyssal and lower bathyal is not certain.