Drilling at Site 1128 revealed the presence of two major biostratigraphic units, which were dated by nannofossils and planktonic foraminifers as upper Miocene-Pleistocene (0-55 mbsf) and lower Eocene-lower Oligocene (70-427 mbsf). The Neogene and Paleogene successions are separated by a series of spectacular debrites (55-70 mbsf) containing mixed Oligocene and Miocene nannofossils and planktonic foraminifers. Planktonic foraminifer data indicate a hiatus above a slump at the lower/upper Pliocene boundary and a major unconformity of ~20 m.y. at the Miocene/Oligocene boundary at ~70 mbsf. Nannofossil data further indicate possible hiatuses in the Neogene: two within the Pliocene (missing Zones NN17 and NN16 at ~24 mbsf and missing Zone NN13 at ~34 mbsf) and one within the Miocene (missing Zone NN10 at ~49 mbsf). Both nannofossil and planktonic foraminifer data show that the Miocene/Oligocene unconformity beneath the debrite spans a gap of at least 18 m.y. as the whole upper Oligocene is missing. The unconformity may represent an even larger hiatus as the age of the sediment above the debrite is <11.4 Ma. Seismic Horizons 1C_1 and 1C_2 detected on seismic profiles may correspond to a suspected hiatus in the upper lower Pliocene and to the major unconformity at the Miocene/Oligocene boundary, respectively. Changes in benthic foraminiferal assemblages are also noted at these levels.
Preservation of calcareous nannofossils and planktonic foraminifers is generally good down to ~45 mbsf, although it deteriorates downhole because of partial dissolution. Below 70 mbsf, nannofossils and planktonic foraminifers show increasing signs of dissolution and disappear at some levels, suggesting deposition near the lysocline and the CCD. Benthic foraminifers are generally abundant and relatively well preserved down to 55 mbsf, although they become rare below 70 mbsf and some intervals are barren in the lower part of Hole 1128D.
Five main benthic foraminiferal assemblages are distinguished. A diversified Pleistocene-upper Miocene calcareous assemblage indicates abyssal paleodepths above the CCD and relatively well oxygenated conditions. Displaced heterogeneous assemblages are also found within the same interval in turbidites. Below this interval, a series of displaced exotic assemblages occur within the debrites. An impoverished lower Oligocene-lower upper Eocene calcareous assemblage is indicative of lower bathyal to abyssal paleodepths near the lysocline. Fine-grained turbidites within this latter interval contain redeposited assemblages from the shelf. An impoverished lower upper-upper middle Eocene calcareous assemblage also indicates lower bathyal to abyssal paleodepths near the lysocline. Finally, an impoverished upper middle-upper lower Eocene agglutinated assemblage indicates deposition below the CCD.
Sedimentation rates are relatively low for the Pleistocene and Pliocene interval in comparison with rates recorded at shallower sites for coeval sediments. A marked increase in sedimentation rates is registered in the Paleogene succession, reaching ~50-60 m/m.y. in the lower Oligocene and ~40-45 m/m.y. in the Eocene.
An upper Pleistocene-lower/middle Eocene succession of calcareous nannofossil assemblages is recorded from Site 1128, where core recovery was good for most of the Pleistocene-Oligocene but much poorer for the Eocene. The Pliocene-Miocene seems to be punctuated by four hiatuses. The most significant of these is associated with a mixed assemblage in a thin ~3-m-thick unit—all the middle Miocene and a greater part of the lower Miocene are at least partly missing. In contrast, assemblages from the cores below indicate an expanded lower Oligocene. Another substantial disconformity marks the Neogene/Paleogene boundary—at least the entire upper Oligocene section seems to be missing. A poor Eocene record of nannofossils resulted from the combination of the generally poor core recovery and the occurrence of numerous barren levels (Fig. F11).
Evidence of severe nannofossil dissolution abounds in the lower Oligocene and Eocene section, suggesting deposition near the CCD. Barren intervals in much of the middle Eocene (Fig. F11) suggest deposition well below the CCD. The quality of nannofossil preservation in the lower Oligocene section fluctuates but remains generally poor, indicating fluctuation of the CCD.
Sample 182-1128B-1H-CC (5.63 mbsf) contains a well-preserved assemblage of calcareous nannofossils indicative of upper Zone NN19 of Pleistocene age, but with a minor reworked component. In situ species include Coccolithus pelagicus, Gephyrocapsa caribbeanica, Gephyrocapsa oceanica, small Gephyrocapsa spp. (including G. aperta), Helicosphaera carteri, Helicosphaera hyalina, Pseudoemiliania lacunosa (both circular and oval forms), Reticulofenestra asanoi, and Rhabdosphaera clavigera; the reworked Neogene Discoaster variabilis is also present. Assemblages readily assignable to Zone NN19 are also recorded from Samples 182-1128B-2H-CC and 3H-3, 18-22 cm (15.5-16.88 mbsf). These contain evidence of minor reworking not only from the Neogene but also from the upper Paleogene and Upper Cretaceous (e.g., Dictyococcites bisectus, D. variabilis, and Gartnerago obliquum).
The occurrence of R. asanoi in the upper part of Zone NN19 at this site is confirmed in assemblages from Samples 182-1128B-1H-CC (4.95 mbsf) and 182-1128A-1H-CC (9.28 mbsf). Both Calcidiscus macintyrei and Helicosphaera sellii make their simultaneous appearance downhole in Sample 182-1128C-2H-CC (16.74 mbsf), suggesting lower Zone NN19 at this level.
Zone NN18 (late Pliocene age) is indicated by the presence of rare Discoaster brouweri, in association with the dominant taxa Reticulofenestra minuta and Reticulofenestra minutula, and the common occurrence of C. pelagicus, P. lacunosa, and C. macintyrei in Sample 182-1128B-3H-CC (23.19 mbsf).
Two intra-Pliocene disconformities are proposed on the basis of the apparent absence of Zones NN17 and NN16 (mostly late Pliocene age) and Zone NN13 (early Pliocene age) from the calcareous nannofossil succession. Nannofossil assemblages recovered indicate Zone NN15 from Sample 182-1128C-3H-CC (26.61 mbsf); the combined Zones NN14-NN15 from Sample 182-1128B-4H-4, 56-63 cm (29.78 mbsf), and 4H-CC (33.99 mbsf); and Zone NN12 from Sample 182-1128C-3H-CC (35.75 mbsf) (Fig. F11). The Zone NN15 assemblage contains common Discoaster surculus; few Discoaster asymmetricus, Discoaster pentaradiatus, and P. lacunosa; and rare Discoaster tamalis and Reticulofenestra pseudoumbilicus. Evidence of reworking in Zone NN15, particularly from Paleogene sediments, is indicated by the presence of common Cyclicargolithus floridanus, D. bisectus, and Sphenolithus moriformis. The assignment to the combined Zones NN14-NN15 is based on the presence of few to common D. tamalis and R. pseudoumbilicus, and the association of few Amaurolithus ninae and common D. asymmetricus in Sample 182-1128B-4H-4, 56-63 cm, together with abundant (acme of) D. asymmetricus in Sample 182-1128B-4H-CC.
The Zone NN12 assemblage of early Pliocene age, recorded from Sample 182-1128C-3H-CC, contains A. ninae, Calcidiscus leptoporus, C. macintyrei, C. pelagicus, Ceratolithus acutus, D. pentaradiatus, D. surculus, D. variabilis, H. carteri, R. pseudoumbilicus, R. minuta, and R. minutula.
Signs of severe dissolution and notable enrichment of Discoaster specimens are observed in the assemblages from Samples 182-1128B-5H-CC (43.7 mbsf) and 6H-3, 98-103 cm (47.68 mbsf), which are placed in Zone NN11 of late Miocene age. The association of common Amaurolithus amplificus, A. ninae, Discoaster intercalaris, D. variabilis, R. pseudoumbilicus, and rare Discoaster quinqueramus in Sample 182-1128B-5H-CC indicates upper Zone NN11. A similar upper Zone NN11 association was also recorded from Sample 182-1128C-5H-5, 45-60 cm (42.95 mbsf), with rare Reticulofenestra umbilicus, reworked from Paleogene sediments.
Amaurolithus amplificus, A. ninae, and D. quinqueramus are not found in Sample 182-1128B-6H-3, 98-103 cm (55.8 mbsf), and instead rare Discoaster berggrenii and common Minylitha convallis together indicate lower Zone NN11. Discoasters in the assemblage below from Sample 182-1128B-6H-CC (53.56 mbsf) are heavily calcified. However, it was possible to identify the index species for Zone NN9, Discoaster hamatus. This suggests that Zone NN10 is either missing or condensed in the interval between 55.8 (Zone NN11) and 53.56 mbsf (Zone NN9).
Samples below 53.56 mbsf (Zone NN9), taken from a lithostratigraphic unit consisting of a series of debrites down to 70.0 mbsf in Hole 1128C (see "Lithostratigraphy"), contain lower-middle Miocene calcareous nannofossil assemblages, although one sample is barren. Samples 182-1128C-6H-CC (55.15 mbsf) and 7H-2, 143-147 cm (58.43 mbsf), contain a mixed assemblage. The dominant elements of this assemblage, including Chiasmolithus altus, Cyclicargolithus abisectus, C. floridanus, D. bisectus, Helicosphaera obliqua, Reticulofenestra lockeri, and Zygrhablithus bijugatus, are derived from Paleogene sediments. The lesser elements are also reworked, but from relatively younger sediments (e.g., Sphenolithus heteromorphus from low in the Miocene). The remaining elements are probably in situ, consisting of C. macintyrei, Dictyococcites antarcticus, D. variabilis, H. carteri, R. pseudoumbilicus, Scyphosphaera spp., and Triquetrorhabdus rugosus. Their abundance and diversity indicate a middle-late Miocene age.
Sample 182-1128B-7H-CC (62.35 mbsf) from the debrite unit contains a poorly to moderately preserved assemblage with heavily calcified discoasters. This assemblage includes Coccolithus miopelagicus, Coronocyclus nitescens, C. floridanus, Discoaster deflandrei, Discoaster trinidadensis, H. carteri, Helicosphaera euphratis, H. obliqua, and S. moriformis, suggesting Zone NN2 of early Miocene age. Minor reworking from Paleogene sediments is indicated by the occurrence of Chiasmolithus oamaruensis.
The evidence of intense reworking and mixing of nannofossils in the interval between 55.15 and 58.43 mbsf is associated with a substantial hiatus in the nannofossil record. The ~9.5-m interval between Samples 182-1128B-6H-CC (53.56 mbsf; Zone NN9) and 7H-CC (62.35 mbsf; Zone NN2) is likely to include at least one substantial disconformity. This interval is too short to accommodate all the middle Miocene and the greater part of the lower Miocene. Sample 182-1128C-7H-CC (64.12 mbsf), less than 2 m below Zone NN2 samples and also from the debrite unit, is barren.
Sample 182-1128B-8H-6, 79-83 cm (70.99 mbsf), contains an assemblage indicative of Zone NP23 of early Oligocene age, whereas the assemblage from Sample 182-1128B-7H-CC is early Miocene in age (Zone NN2). This suggests that most of the basal Miocene and upper Oligocene is either condensed in the intervening ~8.4-m interval or, more likely, partially or completely missing. The main components of the poorly preserved Zone NP23 assemblage in Sample 182-1128B-8H-6, 79-83 cm, include C. altus, C. nitescens, C. abisectus, D. bisectus, D. deflandrei, S. moriformis, and Sphenolithus predistentus.
Lower Oligocene assemblages, assignable to combined Zones NN23-NN21, occur in Samples 182-1128C-9H-CC (84.42 mbsf) through to 26X-CC (240.36 mbsf). Nannofossil debris and signs of partial dissolution are abundant in these assemblages, suggesting deposition near the CCD. The assemblage from Sample 182-1128C-9H-CC shows the effects of strong dissolution; it is dominated by Discoaster spp. (the D. deflandrei "group"), C. floridanus and D. bisectus and contains specimens of Chiasmolithus (rims only), S. predistentus (distal spines only), and Coccolithus eopelagicus. Better preserved assemblages occur at a few levels, suggesting fluctuations of the CCD and some transportation from shallower sites, as hemipelagic species are usually present in the better preserved assemblages. One such assemblage, readily assignable to Zone NP22, is found in Sample 182-1128C-15X-CC (84.42 mbsf). It contains Blackites spinosus, Braarudosphaera bigelowii, C. altus, Clausicoccus fenestratus, C. floridanus, D. bisectus, Discoaster scrippsae, Discoaster nodifer, Helicosphaera sp. cf. H. recta, Lanternithus? minutus, Pontosphaera multipora, Reticulofenestra hillae, R. lockeri, R. umbilicus, S. moriformis, and Z. bijugatus. Another example is from Samples 182-1128D-1R-CC (236.73 mbsf) and 2R-CC (243.87 mbsf), where the assemblages (Zone NP21) remain relatively diverse, despite showing signs of severe dissolution. The main elements of these assemblages include B. spinosus, C. altus, C. oamaruensis, C. fenestratus, C. eopelagicus, C. formosus, D. bisectus, D. deflandrei, D. nodifer, Isthmolithus recurvus, Pontosphaera pulcheroides, Reticulofenestra hampdenensis, R. hillae, R. lockeri, R. umbilicus, and Z. bijugatus. In addition to these, Lanternithus minutus, Pontosphaera plana, and Reticulofenestra oamaruensis are present in Sample 182-1128D-2R-CC. The co-occurrence of R. hampdenensis and R. oamaruensis above the extinction of Discoaster saipanensis typifies the lower part of Zone NP21 in southern Australia (S. Shafik, unpubl. data).
Preservation deteriorates rapidly in the upper Eocene section, and most of the lower cores below Sample 182-1128D-12R-CC are barren. Poor preservation is mainly caused by dissolution. The highest occurrence of D. saipanensis is in Sample 182-1128B-28X-CC (254.66 mbsf), in association with C. altus, C. oamaruensis, D. bisectus, I. recurvus, and R. hampdenensis. This indicates upper Zone NP19-NP20. The better preserved assemblages in Samples 182-1128D-4R-CC (263.94 mbsf) and 5R-CC (268.71 mbsf) include the hemipelagic L. minutus and Z. bijugatus. In Sample 182-1128D-5R-CC, D. saipanensis and Cribrocentrum reticulatum co-occur, suggesting the lower part of Zone NP19-NP20.
The assemblage from Sample 182-1128D-6R-CC (284.03 mbsf) is poorly preserved, although C. oamaruensis, C. eopelagicus, D. bisectus, D. saipanensis, and R. umbilicus are identifiable, suggesting Zone NP18 of late Eocene age. A similar assemblage is recorded from Sample 182-1128D-7R-CC (289.01 mbsf).
The assemblage from Sample 182-1128D-8R-2, 5-6 cm, is relatively diverse, and the occurrence of Chiasmolithus grandis, Chiasmolithus solitus, C. reticulatum, D. bisectus, D. saipanensis, Helicosphaera dinesenii/H. reticulata, and Neococcolithites dubius indicate Zone NP16 of middle Eocene age. Poor core recovery coupled with inadequate sampling of Core 182-1128D-8R probably accounts for the absence of Zone NP17 from our record. With the exception of the barren Sample 182-1128D-10R-CC (322.46 mbsf), assemblages of Zone NP16 continue to occur downhole to Sample 182-1128D-13R-3, 110-111 cm.
The assemblage from Sample 182-1128D-8R-2, 5-6 cm, which contains warmer water species such as H. dinesenii/H. reticulata, recalls other assemblages from Zone NP16 recorded at Site 1126 (see "Biostratigraphy" in the "Site 1126" chapter) and in the eastern part of the Great Australian Bight (Shafik, 1990). Coeval assemblages from southeastern Australia (western Otway Basin) lack warm-water indicators (Shafik, 1983), suggesting that the flow of a warm-water surface current in the middle Eocene along the southern Australian margin diminished away from the Indian Ocean (Shafik, 1990).
Samples 182-1128D-13R-CC (355.93 mbsf) to 23R-CC (444.37 mbsf) are barren except for Sample 182-1128D-21R-CC (427.32 mbsf), which yielded C. solitus, C. eopelagicus, Coccolithus formosus, Discoaster barbadiensis, and Discoaster sublodoensis. These indicate Zone NP14, which straddles the lower/middle Eocene boundary.
Planktonic foraminifers indicate that Site 1128 recovered two major biostratigraphic units: upper Miocene-Pleistocene (0-55 mbsf) and Eocene-lower Oligocene (70->290 mbsf). A debrite separates these packages (~55-70 mbsf) and contains clasts of upper Miocene, middle Miocene, and Oligocene sediments, indicating probable upper Miocene deposition from sediment gravity flows. A major unconformity associated with the debrite (see "Lithostratigraphy") is indicated by Miocene Zone Mt9 above and lower Oligocene assemblages beneath the debrite. The hiatus is estimated to be ~20 m.y. in duration. The Pliocene/Pleistocene boundary lies between 15 and 25 mbsf, although the temperate nature of the assemblage means that it is not possible to resolve whether the boundary is a disconformity. Separated by two distinct assemblages, the Pliocene/Miocene boundary falls near 40 mbsf and appears to be gradational. With the exception of several levels, planktonic foraminifers become absent or very rare in lower Oligocene and Eocene sediments further downhole, suggesting a depositional environment near the lysocline and CCD.
Planktonic foraminifers are generally abundant with moderate to good preservation in the upper 36 m of the section. They are common to few with mostly moderate to poor preservation between 36 and 63 mbsf, and they occur only as traces to rare with poor preservation below 63 mbsf (although there are several important exceptions). Select intervals near 135-138 mbsf in both Holes 1128B and 1128C, one sample at 94.63 mbsf in Hole 1128C, and one sample at 243.87 mbsf in Hole 1128D have common planktonic foraminifers with poor to moderate preservation. Core recovery fell from >90% above 240 mbsf to 29% and 36% below 240 mbsf in Holes 1128B and 1128D, respectively, significantly degrading the continuity of the fossil record.
A typical warm temperate Quaternary assemblage is found in the first cores of Holes 1128A, 1128B, and 1128C (Samples 1128A-1H-CC, 7-10 cm, from 9.28 mbsf; 182-1128B-1H-CC, 14-17 cm, from 5.63 mbsf; and from the surface to 182-1128C-1H-CC, 11-13 cm, from 7.93 mbsf). The assemblage is comprised of abundant Globorotalia inflata, Globigerina quinqueloba, Globigerina falconensis, and Globigerinoides ruber with few Orbulina universa, Neogloboquadrina pachyderma (dextral), Globorotalia truncatulinoides, Globorotalia crassaformis, Globigerinella siphonifera, Globigerinita glutinata, and Globigerina bulloides. The section is placed in the subtropical Zone Pt1 on the basis of the presence of G. truncatulinoides. However, the base of the zone as defined by Berggren et al. (1995) could not be applied because Globigerinoides fistulosus and Globigerinoides extremus were not observed. We placed the base at the first appearance of G. truncatulinoides (between 5.63 and 15.50 mbsf at Hole 1128B and between 7.93 and 16.74 mbsf at Hole 1128C), following the definition of Jenkins (1993) and Chaproniere et al. (1995) for the estimated regional base of the Pleistocene.
The upper Pliocene assemblage represents somewhat cooler temperatures than the overlying Pleistocene assemblage. It includes abundant Gt. inflata, Gg. quinqueloba, G. falconensis, and few G. ruber, Globigerinita glutinata, Globigerina bulloides, G. crassaformis, and N. pachyderma (dextral). The upper Pliocene fits the definition of Zone SN13, the Gt. inflata Zone of Jenkins (1985, 1993) because it contains abundant Gt. inflata without G. truncatulinoides. The zone generally corresponds in time to Zones Pl5 and Pl6 of Berggren et al. (1995) (Chaproniere et al., 1995). Samples 182-1128B-2H-CC, 21-24 cm (15.5 mbsf), to 3H-CC, 21-24 cm (23.19 mbsf), and 182-1128C-2H-CC, 15-18 cm (16.74 mbsf), to 3H-6, 24-28 cm (25.24 mbsf), are placed in this zone. The base of the upper Pliocene sequence rests disconformably on a slump (~27-29 mbsf) that contains a lower Pliocene assemblage.
The lower Pliocene assemblage represents somewhat warmer temperatures than the upper Pliocene assemblage. It includes abundant Globigerinita glutinata and Globigerina juvenilis and few to rare Globorotalia puncticulata, G. crassaformis, G. ruber, Gg. quinqueloba, G. falconensis, and Globigerina bulloides. Also present are Zeaglobigerina decoraperta, Zeaglobigerina apertura, Zeaglobigerina woodi, O. universa, Neogloboquadrina humerosa, Neogloboquadrina acostaensis, Globorotalia scitula, Zeaglobigerina nepenthes, and Globorotalia margaritae.
The section can be divided into subtropical Zones Pl2 and Pl1 on the basis of the last occurrences of G. margaritae in Samples 182-1128B-4H-4, 58-63 cm (29.78 mbsf), and 182-1128C-3H-CC, 0-3 cm (26.61 mbsf), and Z. nepenthes in Sample 182-1128C-4H-CC, 55-58 cm (35.75 mbsf). A combined Zone Pl1-Pl2 is recognized at Hole 1128B where Z. nepenthes is absent, although Z. apertura is present with G. margaritae in Sample 182-1128B-5H-2, 101-105 cm.
The Miocene/Pliocene boundary is placed at the first appearance of Globorotalia sphericomiozea in Samples 182-1128B-6H-3, 98-103 cm (47.68 mbsf), and 182-1128C-5H-CC, 21-24 cm (46.52 mbsf). Berggren et al. (1995) suggested that it is a suitable proxy for the boundary in temperate regions on the basis of the work of Hodell and Kennett (1986). A combined Zone Pl1-Mt10 is recognized in Sample 182-1128C-5H-6, 34-38 cm (44.34 mbsf), where Globoconella conomiozea makes its last appearance in the hole, although G. crassaformis is still present. The presence of fossils with two distinctly different preservation states supports mixing between two assemblages.
The upper Miocene assemblage includes Z. nepenthes, Z. woodi, Z. decoraperta, Sphaeroidinellopsis disjuncta, O. universa, N. acostaensis, G. margaritae, and Globorotalia menardii. The fossils are poorly preserved, with numerous partially dissolved and broken tests. Zones Mt10 and Mt9 are divided on the basis of the first occurrence of Globorotalia conomiozea, and Mt9 is further distinguished by the occurrence of Globorotalia conoidea with neither Globorotalia conomiozea nor Neogloboquadrina mayeri. Samples 182-1128B-5H-CC, 11-13 cm (43.70 mbsf), and 182-1128C-5H-CC, 21-24 cm (46.52 mbsf), are placed in Zone Mt10; Sample 182-1128C-6H-2, 104-108 cm (48.54 mbsf), is assigned to Zone Mt9; and Samples 182-1128B-6H-3, 98-103 cm (47.68 mbsf), and 6H-CC, 19-21 cm (53.56 mbsf), are assigned to a composite Zone Mt10-Mt9.
Four paleontologic samples were taken within the interval of dramatic sediment gravity flow deposits (debrites) observed between 55 and 70 mbsf (see "Lithostratigraphy"). Three samples, each from a different lithology, were placed in different Miocene zones, namely Zone Mt9, composite Zone Mt10-Mt9, and the middle Miocene (Samples 182-1128C-6H-CC, 10-13 cm, from 55.15 mbsf; 7H-2, 143-147 cm, from 58.43 mbsf; and 182-1128B-7H-CC, 21-24 cm, from 62.58 mbsf, respectively). One additional sample (Sample 182-1128C-7H-CC, 29-32 cm, 64.12 mbsf) lay within the debrite. It was barren of foraminifers, but contained abundant siliceous microfossils similar to those observed in the lower Oligocene siliceous unit found beneath the gravity flows. Preliminary results indicate that the various debrite lithologies include discrete packages of Oligocene, middle Miocene, and some upper Miocene sediment. The Quaternary to uppermost Miocene sequence above the debrite appears undisturbed and in proper stratigraphic order.
A prominent lithologic change from carbonate-rich to clayey siliceous sediments occurs at ~70 mbsf. Planktonic foraminifers are sparse, and many samples are barren or contain only a trace of tests. The site probably lies alternately near and below the CCD during deposition of this siliceous ooze. A few intermittent intervals contain some age-diagnostic planktonic foraminifers, indicating that the interval from 70 to >200 mbsf mainly belongs in the lower Oligocene. The core-catcher samples from Cores 182-1128C-8H (73.95 mbsf), 182-1128B-8H (72.47 mbsf), and 9H (81.82 mbsf), and Sample 182-1128B-11H-2, 93-97 cm (93.63 mbsf), contain a poorly preserved assemblage with Catapsydrax dissimilis, Chiloguembelina sp., Globorotaloides suteri, and Subbotina angiporoides. Samples 182-1128C-11H-1, 113-117 cm (94.63 mbsf), 13H-2, 14-18 cm (114.14 mbsf), and the core-catcher samples from Cores 182-1128B-15H (137.76 mbsf), 182-1128C-15H (138.30 mbsf), 16X (148.10 mbsf), and 17X-5, 43-47 cm (152.53 mbsf), contain a typical lower Oligocene assemblage characterized by Tenuitella gemma, Tenuitella munda, Tenuitella angustiumbilicata, Tenuitella juvenilis, Tenuitella praestainforthi, S. angiporoides, Globorotaloides testarugosa, Globorotaloides suteri, Globigerina officinalis, Chiloguembelina cubensis, Globigerina euapertura, Guembelitria triseriata, and Zeaglobigerina ampliapertura.
Samples between 236 and 244 mbsf at Site 1128 contain an assemblage that cannot be positively distinguished as either Oligocene or Eocene. The assemblage includes poorly preserved specimens of Tenuitella spp., Subbotina gortanii, C. dissimilis, Globorotaloides suteri, S. angiporoides, G. officinalis, C. cubensis, and G. testarugosa. No planktonic foraminifers were found deeper than 285 mbsf at Site 1128. Biostratigraphy from most of the section in Hole 1128D relied on calcareous nannofossils, which indicate that the lower part of the sediment sequence at Site 1128 was mainly middle-late Eocene in age.
Benthic foraminifers were studied from every core-catcher sample at Holes 1128B and 1128D. Additional samples were also analyzed from core-catcher samples at Hole 1128C and from selected intervals at Holes 1128B and 1128C, where the lithology differed markedly from core-catcher samples. Benthic foraminifers are generally abundant and well preserved in the upper parts of Hole 1128B and Hole 1128C (Cores 182-1128C-1H through 7H). However, abundance and diversity decrease dramatically and preservation is generally poor below Core 182-1128C-7H (63 mbsf) and in all samples examined from Hole 1128D. The following core-catcher samples were found to be barren: Samples 182-1128D-4R-CC and 13R-CC through 15R-CC, and Section 182-1128D-21R through Sample 182-1128D-23R-CC. Approximately 100-300 benthic foraminifers were picked from the >63-µm fraction, except in samples in which benthic foraminifer abundance was low. The benthic foraminiferal assemblages studied include mainly calcareous taxa. However, an assemblage containing only agglutinated taxa with organically cemented tests was found in the lower part of Hole 1128D (Cores 182-1128D-16R through 20R). Five benthic foraminiferal asssemblages are distinguished within the Cenozoic succession at Site 1128.
This diversified assemblage is characterized by the occurrence of few to common Pyrgo murrhina and the rare to few occurrence of Melonis sphaeroides and Melonis barleeanum. Also present as rare to common constituents are Planulina wuellerstorfi, Globocassidulina subglobosa, Oridorsalis umbonatus, Cibicidoides mundulus, Uvigerina hispidocostata, Pullenia bulloides, Eggerella bradyi, Stilostomella lepidula, Triloculina trihedra, Astronion pusillum, Bulimina alazanensis, Stilostomella spp., Loxostomum spp., Bolivina spp., Cibicidoides spp., and Pleurostomella spp., as well as various nodosariids. Tests within this assemblage are generally well preserved, showing no obvious sign of partial dissolution. Included within Assemblage 1 are useful bathymetric indicators such as M. sphaeroides, which provides a reliable index for abyssal depths (Hasegawa, 1984; van Morkhoven et al., 1986), P. wuellerstorfi, considered to be primarily a lower bathyal to abyssal dweller (van Morkhoven et al., 1986), and P. murrhina, characteristically found in middle bathyal to abyssal deposits (van Morkhoven et al., 1986). The composition of Assemblage 1 indicates deposition above the CCD, which is in accordance with the consistently high CaCO3 values recorded in this interval (see "Organic Geochemistry"). Heterogeneous bathyal faunas are also recorded between Cores 1H and 6H at Holes 1128B and 1128C in Samples 182-1128B-4H-4, 58-63 cm; 182-1128B-4H-CC; 182-1128B-6H-CC; 182-1128B-6H-3, 98-103 cm; and 182-1128C-6H-2, 104-108 cm. These obviously displaced faunas are interpreted as having been transported by turbidity flows. More detailed work will clarify the provenance and the frequency of such flows.
This assemblage is found within a lithostratigraphic unit that includes a series of debrites in intervals 182-1128B-7H-1, 125 cm, through 8H-2, 55 cm, and 182-1128C-7H through 8H-4, 55 cm (see "Lithostratigraphy"). Nannofossil and planktonic foraminiferal assemblages within this unit contain mixed Miocene and Oligocene taxa, which reflect the exotic provenance of some of the clasts. The following displaced benthic foraminifers are recorded: P. wuellerstorfi, Siphonina tenuicarinata, Rectuvigerina multicostata, Rectuvigerina striata, Bulimina alazanensis, Bulimina aculeata, Hanzawaia ammophila, G. subglobosa, O. umbonatus, Cibicidoides mundulus, U. hispidocostata, Pullenia bulloides, Karreriella bradyi, Stilostomella subspinosa, Laticarinina pauperata, Pullenia spp., Cibicidoides spp., Stilostomella spp., Uvigerina spp., Bolivina spp., and Trifarina spp., as well as various nodosariids. It is interesting to note that M. sphaeroides, the indicator for abyssal paleodepths, is absent from any of the samples examined. Most of the taxa recorded within this interval are typical of lower to upper bathyal paleodepths. However, a more detailed study is needed to determine the provenance of the clasts within the debrites and to establish the timing of deposition within a regional framework.
A major lithologic change from carbonate-rich sediments to calcareous claystones occurs within Core 8H from Holes 1128B and 1128C. This represents a major unconformity spanning a gap of at least 18 m.y. between the Miocene and lower Oligocene, as shown by nannofossil and planktonic foraminifer data. Below a transitional unit composed of calcareous clay and clayey nannofossil ooze (intervals 182-1128B-8H, 55 cm, through 11H and 182-1128C-8H4, 55 cm, through 11H-2, 60 cm), the dominant lithology consists of green, variably calcareous claystones with minor calcareous turbidites, decreasing in frequency downhole. The washed residues from the green claystones contain abundant sponge spicules and radiolarians, as well as a poorly preserved, impoverished benthic foraminiferal assemblage. The benthic foraminiferal assemblage consists of rare specimens of Cibicidoides subhaidingeri, Astronion pusillum, O. umbonatus, Stilostomella subnodosa, Stilostomella aculeata, K. bradyi, G. subglobosa, L. pauperata, Pleurostomella spp., Cibicidoides spp., Stilostomella spp., Pullenia spp., Gyroidinoides spp., and some nodosariids. Samples from the base of the interval (Cores 182-1128D-3R through 5R) also contain fragments of thick-walled Rhabdammina sp. The major faunal change observed between Assemblages 2 and 3 is probably coincident with sequence boundary 1C_2 recognized on seismic lines (see "Seismic Stratigraphy").
The composition of the assemblage suggests that it originated from a lower bathyal to abyssal environment, probably near the lysocline, as shown by evidence of strong dissolution in the planktonic foraminifer tests and nannofossils from this interval. The benthic foraminifers from Assemblage 3 tend to have robust, heavily calcified tests and are thus probably resistant to dissolution, even in close proximity to the lysocline. The fluctuating but generally low CaCO3 values recorded within this interval (see "Organic Geochemistry") also suggest paleodepths near the lysocline for this site. The paucity of benthic foraminifers in Assemblage 3 may be caused by dysoxic conditions at the seafloor, as indicated by the green color of the sediment (see "Lithostratigraphy"), and/or may reflect high sedimentation rates. Interestingly, biosiliceous radiolarian-rich sediments are commonly associated with impoverished benthic foraminiferal assemblages in the deep sea during the Cretaceous and Paleogene (Kuhnt et al., 1989; Kaminski et al., 1992).
Several samples from fine-grained calcareous turbidites within this interval were also analyzed in an attempt to determine the origin of the turbidites (Samples 182-1128B-11X-CC; 26X-4, 94-98 cm; 27X-3, 100-103 cm; 15X-CC; 182-1128C-15-3, 100-104 cm; 17X-5, 43-47 cm; and 182-1128D-2R-CC). In contrast to samples from the green claystones, these yielded relatively well-preserved benthic foraminiferal assemblages with few to abundant small specimens (63-150 µm) of Patellina corrugata, Spirillina spp., Stilostomella spp., Bolivina spp., Trifarina spp., and various nodosariids. The uniformity in test size and the presence of typically shallow-water indicators such as P. corrugata and Spirillina spp. indicate that the tests were originally derived from the shelf, before being redeposited into the basin and sorted by distal turbidity currents.
This impoverished, poorly preserved assemblage is characterized by the occurrence of few to common Rhabdammina sp. and Cibicidoides spp. and by the rare presence of Nuttallides truempyi, O. umbonatus, Glomospira charoides, Pullenia spp., and some nodosariids. Also found in the samples are abundant radiolarians and sponge spicules. According to Tjalsma and Lohmann (1983), N. truempyi had a bathymetric range from middle or lower bathyal to abyssal during the Eocene. Nuttallides truempyi was also recorded within the same stratigraphic interval in Assemblage 4B at Site 1126, but in a more proximal setting than at Site 1128. Paleodepths at Site 1128 were much greater than at Site 1126 in the middle and upper Eocene, as shown by the strong dissolution of nannofossils and the virtual absence of presumably dissolved planktonic tests. However, the presence of calcareous benthic foraminifers within Assemblage 4 indicates deposition near the lysocline, although not below the CCD. The rarity of benthic foraminifers within this assemblage may be caused by dysoxic conditions at the seafloor, perhaps related to high biosiliceous productivity in surface waters and/or to high sedimentation rates causing dilution of benthic foraminiferal tests. Nuttallides truempyi, with a last occurrence in the upper Eocene in Zone P17 (Berggren and Miller, 1989), is a stratigraphically significant taxon within Assemblage 4.
Assemblage 5 is found between two barren intervals at the base of Hole 1128D and represents a very impoverished assemblage containing only thick-walled Rhabdammina fragments. Preservation is generally poor and abundance is low. Also present within the same samples are abundant radiolarians and sponge spicules. The lack of calcareous tests within this interval indicates deposition below the CCD. This is supported by the extremely low CaCO3 values (0-0.99 wt%) recorded within this interval (see "Organic Geochemistry"). Dysoxic conditions at the seafloor, indicated by the green sediment color (see "Lithostratigraphy"), and/or an increased siliciclastic flux into the restricted basin during the middle and lower upper Eocene (see "Lithostratigraphy") may account for the scarcity of benthic foraminifers within this assemblage.
Sediment accumulation rates were calculated from preliminary biostratigraphic and paleomagnetic data from Site 1128, and the results are presented in Figure F12. The datum levels used to calculate sedimentation rates are listed in Table T2.
The Pleistocene-Pliocene registered a sedimentation rate of ~11 m/m.y. This is a relatively low rate when compared with sedimentation rates averaging between ~240 m/m.y. and ~31 m/m.y. recorded for coeval sections at Sites 1127 and 1126, respectively. There is a sharp decrease in sedimentation rates from ~10-15 m/m.y. for the lower Pliocene-upper Miocene section. A thin debrite (~14 m thick) containing clasts bearing upper Miocene, middle Miocene, and Oligocene assemblages separates the upper Miocene section above from the Paleogene unit below. The gravity-flow event apparently removed most of the basal Miocene and upper Oligocene, an interval spanning more than 18 m.y.
Sedimentation rates are low (~18 cm/m.y.) in the upper lower Oligocene and increase to 50-67 m/m.y. in the lower Oligocene. In contrast, the rate for the upper Eocene is 4 m/m.y. Because of poor recovery for the remainder of the Eocene and the occurrence of barren intervals, the sedimentation rate calculated for this part of the section (40-45 m/m.y.) should be considered with caution.