Core recovery was good throughout Hole 1126C (~90% recovery) and most of Hole 1126B (86% to 160 mbsf), although the continuity of the stratigraphic record was marred by poor core recovery below 160 mbsf in both Holes 1126B (18% recovery below 160 mbsf) and 1126D (13% recovery; the cored interval is mostly below 160 mbsf). Calcareous nannofossils and planktonic foraminifers are generally common to abundant with moderate to good preservation throughout Holes 1126A, 1126B, and 1126C, although preservation deteriorated and abundance declined in conjunction with poor core recovery in Hole 1126D. Benthic foraminifers are few to common with mostly good to moderate preservation in Holes 1126A and 1126B, although their numbers also declined and preservation became poorer downsection, especially in Hole 1126D. Benthic foraminifers, overall, are far less abundant than planktonic foraminifers in all holes.
Sediments recovered from Site 1126 range in age from Quaternary to middle Eocene, with most calcareous nannofossil zones represented except in four intervals, where missing nannofossil zones suggest disconformities. The suspected disconformities lie in the uppermost Pliocene (missing Zones NN18-NN17 at ~57 mbsf), lower Pliocene (missing Zones NN15-NN13 at ~67 mbsf), the upper Miocene (missing Zone NN11 at ~82 mbsf), and the middle Miocene (missing Zones NN9-NN6 at ~118 mbsf). Planktonic foraminifer zones are also missing from the disconformities at ~82 and ~118 mbsf. The foraminifers, however, do not verify the suspected disconformities at ~57 and ~67 mbsf, in part because the low diversity of the temperate planktonic foraminifer assemblages hampered biostratigraphic resolution. Placement of the Miocene/Pliocene boundary is inconsistent between the two data sets. The calcareous nannofossil data suggest that the Miocene/Pliocene boundary is at ~67 mbsf, whereas the planktonic foraminifer data suggest that the boundary lies within the disconformity at ~82 mbsf.
Four main assemblages of benthic foraminifers are identified at Site 1126. The Quaternary to upper Eocene assemblages indicate upper to middle bathyal paleodepths. The middle to upper Eocene assemblage suggests lower to middle bathyal paleodepths and well-oxygenated conditions at the seafloor. A similar assemblage was reported from the early Eocene at Site 747 on the Kerguelen Plateau (Mackensen and Berggren, 1992).
Sedimentation rates are comparatively fast in the Quaternary (31 m/m.y.) and slow in the remainder of the Neogene and Paleogene sections, where rates alternate between 3-8 m/m.y. in the upper Pliocene, the lower Pliocene-upper middle Miocene, the lower Miocene-upper Oligocene, and the lower Oligocene-upper Eocene, and 11-16 m/m.y. in the intervening sections. One interval of nondeposition is indicated in the middle Eocene.
A middle Eocene-upper Pleistocene succession of calcareous nannofossil assemblages showing four possible hiatuses is identified at Site 1126. Several of these hiatuses correspond closely with a sequence stratigraphic boundary (see "Seismic Stratigraphy"). In spite of generally poor core recovery in the lower Miocene, Oligocene, and Eocene, most zones are represented (Fig. F6).
Assemblages of the combined Zones NN21-NN20, including Braarudosphaera bigelowii, Emiliania? huxleyi, Gephyrocapsa caribbeanica, Gephyrocapsa oceanica, small Gephyrocapsa spp. (including G. aperta), and Helicosphaera hyalina are identified in Samples 182-1126B-1H-CC (6.51 mbsf) and 2H-CC (15.63 mbsf). Common Pseudoemiliania lacunosa and abundant small Gephyrocapsa spp. in Sample 182-1126C-2H-CC (17.99 mbsf) indicate Zone NN19. This zone is recognizable down to Sample 182-1126C-6H-CC (56.02 mbsf). Reticulofenestra asanoi appears in the middle of Zone NN19 in Sample 182-1126C-4H-CC (37.23 mbsf). Both Calcidiscus macintyrei and Helicosphaera sellii have their highest occurrences in the lower part of the zone in Sample 182-1126B-6H-CC. Minor reworking from a Paleogene source was found in the lower part of Zone NN19, as shown by the occurrence of Dictyococcites bisectus in Sample 182-1126B-6H-CC. Braarudosphaera bigelowii and Pontosphaera japonica are recorded in Zone NN19 (e.g., in Sample 182-1126B-3H-CC).
Only one Pliocene calcareous nannofossil zone, Zone NN16 of late Pliocene age, is recognized in Holes 1126B and 1126C. The assemblage assignable to this zone is recorded from Samples 182-1126B-7H-CC (63.9 mbsf), 182-1126C-7H-CC (64.96 mbsf), and 182-1126B-8H-3, 32-34 cm (66.82 mbsf). Being heavily calcified, the discoasters in these samples are poorly preserved, although the remainder of the nannofossils are generally moderately to well preserved. The assemblage contains Discoaster brouweri, D. surculus, Calcidiscus leptoporus, C. macintyrei, Coccolithus pelagicus, C. radiatus, Reticulofenestra minuta, Reticulofenestra minutula, and Syracosphaera spp. Whether the two short Zones NN18 and NN17 of the later Pliocene are represented above the core catcher in either or both Cores 182-1126B-7H and 182-1126C-7H was not determined in our shipboard study.
Miocene nannofossil assemblages identified in Holes 1126B and 1126C represent a discontinuous succession of zones (Fig. F6). A distinct lithologic boundary in Section 182-1126B-8H-3 (between 66.51 and 66.82 mbsf) separates upper Pliocene from upper Miocene assemblages. The younger assemblage of Zone NN16 identified from Sample 182-1126B-8H-3, 1-3 cm (66.51 mbsf), is immediately followed downhole by an older assemblage in Sample 182-1126B-8H-3, 32-34 cm (66.82 mbsf). The latter includes Amaurolithus ninae, A. primus, C. leptoporus, C. pelagicus, Dictyococcites antarcticus, Discoaster pentaradiatus, D. variabilis, Helicosphaera carteri, Reticulofenestra pseudoumbilicus, Reticulofenestra minuta, R. minutula, Sphenolithus neoabies, Syracosphaera spp., and Triquetrorhabdus rugosus, indicating lower Zone NN12 (Subzone CN10a) of latest Miocene age. A similar assemblage, also indicating lower Zone NN12, is recorded from Sample 182-1126C-8H-CC (75.76 mbsf). The missing Zones NN13 and NN15 collectively spanned >1 m.y.
Another disconformity is tentatively identified to coincide with a firmground in Section 182-1126C-9H-5 at 85 cm (see "Lithostratigraphy"). Calcareous nannofossils from above and below this firmground suggest a hiatus; the long late Miocene Zone NN11 is apparently missing. Below the firmground the assemblage in Sample 182-1126C-9H-5, 120-125 cm (82.20 mbsf), contains Minylitha convallis and Discoaster neohamatus, which, in the absence of Discoaster quinqueramus, suggests Zone NN10 of early late Miocene age. This zone is also detected in the assemblage from Sample 182-1126B-9H-CC (82.02 mbsf), which also contains reworked components (Cyclicargolithus floridanus, Helicosphaera euphratis, and Discoaster deflandrei "group") from the Paleogene. Assemblages from below the firmground down to Sample 182-1126C-12X-CC (106.96 mbsf) show more pronounced evidence of reworking compared with overlying assemblages, as demonstrated by the occurrence of the Eocene Neococcolithes dubius in Sample 182-1126C-9H-CC and the Paleogene D. bisectus in Sample 182-1126C-10X-CC.
A disconformity close to the lower boundary of lithostratigraphic Subunit IIB (~116 mbsf) (see "Lithostratigraphy") likely is indicated by Zones NN9-NN6 being condensed or missing. The assemblages in Samples 182-1126C-13X-CC through 17X-CC (118.94-148.81 mbsf) are readily assignable to the combined Zones NN5-NN4 on the basis of the consistent presence of the key species Sphenolithus heteromorphus. In contrast to the assemblages from the interval above, the assemblages of the combined Zones NN5-NN4 do not contain any significant reworked component. In addition to S. heteromorphus, the latter assemblages include C. leptoporus, Coccolithus miopelagicus, Coronocyclus nitescens, C. floridanus, D. deflandrei, Discoaster trinidadensis, H. carteri, H. euphratis, Helicosphaera obliqua, R. pseudoumbilicus, and Sphenolithus abies. The hemipelagic taxa B. bigelowii, Micrantholithus pinguis, and Pontosphaera multipora are sporadic in their occurrence, whereas Calcidiscus premacintyrei occurs consistently down to Sample 182-1126B-19H-CC (157.08 mbsf). Helicosphaera ampliaperta, the key species separating Zone NN4 from Zone NN5, is not known to occur in lower Miocene sediments either on the southern margin of Australia (S. Shafik, unpubl. data) or from the Southern Ocean south of Australia. Proxies to the last occurrence (LO) of H. ampliaperta, such as the first occurrence (FO) of Discoaster signus and the end of acme of D. deflandrei, cannot be applied. Discoaster signus is absent, and the abundance of D. deflandrei cannot be satisfactorily determined because of the persistent diluting effect of silicoflagellate debris.
Core recovery in the remainder of the lower Miocene was very poor (see "Operations"). Zone NN2 of early Miocene age is tentatively identified in Sample 182-1126D-5R-CC (185.52 mbsf) because of the presence of a few specimens of Orthorhabus? serratus among an assemblage that includes rare Triquetrorhabdus auritus and Triquetrorhabdulus carinatus, few C. nitescens and Cyclicargolithus abisectus, and abundant B. bigelowii and C. floridanus. Assemblages in Samples 182-1126B-24X-CC and 25X-CC (188.0-197.28 mbsf) are poorly preserved, although the taxa B. bigelowii, C. abisectus, C. floridanus, D. deflandrei, H. euphratis, H. obliqua, Sphenolithus conicus, and T. carinatus are identified. Neither Discoaster druggii nor O. serratus are found, and the abundance of C. abisectus suggests a level above the acme of the species. This evidence is taken to indicate the upper part of Zone NN1 (Subzone CN1b) of early Miocene age. In Hole 1126D the poorly preserved assemblages in Samples 182-1126D-6R-CC and 7-CC (195.30-204.61 mbsf) are datable as early Miocene Zone NN1. The Oligocene/Miocene boundary is well constrained at Site 1126 between Samples 182-1126D-7R-CC and 182-1126B-26X-CC (204.61-205.85 mbsf).
Assemblages readily assignable to Zone NP25 of late Oligocene age are recorded from Samples 182-1126B-26X-CC through 29X-CC. The moderately preserved assemblage near the top of the zone (Sample 182-1126B-26X-CC) contains a few specimens of Sphenolithus delphix but also includes abundant D. bisectus and common T. carinatus, a transitional form between H. obliqua and Helicosphaera recta, together with typical H. recta. A diverse assemblage in Sample 182-1126B-27-CC includes the key species Sphenolithus ciperoensis, together with B. bigelowii, Chiasmolithus altus, C. abisectus, C. floridanus, D. bisectus, H. euphratis, H. obliqua, H. recta, Micrantholithus flos, Micrantholithus sp. cf. M. procerus, Reticulofenestra lockeri, S. conicus, Sphenolithus dissimilis, and Zygrhablithus bijugatus.
Hole 1126B bottomed in Zone NP24 of late Oligocene age. This age is based on a few specimens of Sphenolithus distentus in association with S. ciperoensis in Sample 182-1126B-32X-CC. Sphenolithus distentus is absent from the samples examined from Hole 1126D, and only atypical forms of this species are observed in Samples 182-1126D-15R-CC and 17R-CC, in association with Sphenolithus predistentus. The assemblage in Sample 182-1126D-15R-CC (281.19 mbsf) is assigned tentatively to the combined zones NP24 and NP23 because of the common presence of C. abisectus. The assemblage in Sample 182-1126D-17R-CC is regarded as upper Zone NP23 (Zone CP18), in the absence of C. abisectus and the presence of Sphenolithus sp. aff. S. distentus. Other species found in Sample 182-1126D-17-CC include B. bigelowii, Chiasmolithus altus, D. bisectus, R. lockeri, and Z. bijugatus. These, in addition to C. miopelagicus, M. flos, and M. pinguis, occur in Sample 182-1126D-15R-CC. The assemblage recovered from Sample 182-1126D-18R-CC (309.9 mbsf) is readily assignable to the lower part of Zone NP23 (Zone CP17), including Chiasmolithus altus, D. bisectus, Discoaster nodifer, R. lockeri, S. predistentus, and Z. bijugatus, and lacking both Sphenolithus sp. aff. S. distentus and Reticulofenestra umbilicus. Zones NP22 and NP21 were recognized in Samples 182-1126D-19R-CC (319.41 mbsf) and 20R-CC (329.89 mbsf), respectively. Coccolithus formosus, Isthmolithus recurvus, and R. umbilicus are recorded in 182-1126D-20R-CC, and R. umbilicus, without the other two species, was identified in 19R-CC.
Abundant Chiasmolithus altus occurs throughout the Oligocene sequence, indicating a cool-water regime, although the presence of S. ciperoensis in the upper part suggests a warm-water influence. The cool-water aspect is supported by macrofaunas and lithologic textures found in sediments of the same age (the Abrakurrie Limestone) on shore (James and Bone, 1991). Shafik (1990) documented nannofossil assemblages from the Great Australian Bight indicative of a cool-water regime, but with an intermittent warm-water influence during the middle and late Oligocene attributed to a surface current intermittently bringing warm water from the Indian Ocean. The consistent occurrence of B. bigelowii and Z. bijugatus throughout the Oligocene sequence suggests shallow-water deposition.
The Eocene/Oligocene boundary lies between Samples 182-1126D-20R-CC and 21R-CC. A sample from the latter (at 338.87 mbsf) recovered a moderately preserved assemblage readily assignable to the upper part of combined Zones NP19-NP20 of late Eocene age based on the presence of Chiasmolithus oamaruensis, C. formosus, D. bisectus, D. nodifer, Discoaster saipanensis, Helicosphaera compacta, Reticulofenestra hampdenensis, R. umbilicus, and Z. bijugatus. Samples 182-1126D-22R-CC and 23R-CC (351.45-370.11 mbsf) contain assemblages, also moderately preserved, which are assigned to Zone NP18. These include the key taxa C. oamaruensis, Cribrocentrum reticulatum, D. bisectus, D. nodifer, and D. saipanensis, as well as the holococcolith Lanternithus minutus.
Middle Eocene nannofossil assemblages (Zones NP17 and NP16) were recovered from Sample 182-1126D-24R-CC through 27-CC (370.1-396.63 mbsf). Assemblages assignable to Zone NP16 occur in Samples 182-1126D-25R-CC through 27-CC (380.38-396.63 mbsf). These are characterized by common Chiasmolithus grandis, Chiasmolithus solitus, C. reticulatum, D. nodifer, and D. saipanensis. Chiasmoliths are markedly more abundant than discoasters, indicating a cool-water regime, although subtle evidence for warm-water influence in the lower cores is detected: S. predistentus in Sample 182-1126D-26R-CC (390.38 mbsf), and Helicosphaera dinesenii and H. reticulata in Sample 182-1126D-27R-CC (396.63 mbsf). Samples from Cores 182-1126D-28R (409.75 mbsf) down to 32R (total depth at 444.35 mbsf) lack any calcareous microfossils.
Shafik (1990, and references therein) suggested the existence of warm-water masses during the mid-middle Eocene in the region, attributed to a proto-Leeuwin Current. The current's influence along the Australian southern margin was strong in the western Great Australian Bight and diminished in an easterly direction. Middle Eocene assemblages from the eastern part of the Great Australian Bight (immediately to the west of Kangaroo Island), coeval with those in Samples 182-1126D-26R-CC and 27-CC, contain S. predistentus, H. dinesenii, and H. reticulata. In contrast, middle Eocene assemblages from the western Otway Basin to the east lack these warm-water species (Shafik, 1983), suggesting no significant effect of the proto-Leeuwin Current (Shafik, 1990). Shallow-water deposition during most of the Eocene at Site 1126 is suggested by the occurrence of L. minutus and Z. bijugatus.
The quality of the foraminifers at Site 1126 was excellent overall. The preservation was ranked from very good to moderate throughout the Quaternary to Oligocene sections, and poor only in the Eocene section of Hole 1126D. Abundance was ranked from abundant to common throughout Holes 1126B, 1126C, and 1126D, and the single core from Hole 1126A. Eleven core-catcher samples recovered only pieces of chert and porcellanite when drilling difficulties washed away the soft and probably fossiliferous sediments. The basal sandstone of Hole 1126D (396.61-455.91 mbsf) was barren of foraminifers except for a few contaminated specimens in Sample 182-1126D-28R-CC, 15-17 cm (409.75 mbsf).
The Cenozoic subtropical and temperate zonations of Berggren et al. (1995a, 1995b) were partly applicable to the fossil succession at Site 1126 in the Pleistocene, Pliocene, and Miocene. We found that the zonal definitions of Jenkins (1993, 1985) best described two assemblages from the early Pleistocene-late Pliocene and late Miocene (Fig. F6). The Oligocene and Eocene successions were correlated to the standard "P" zones of Blow (1969) and Berggren and Miller (1988), on the basis of the species ranges of Toumarkine and Luterbacher (1985) and datum levels developed for the region as compiled in Chaproniere et al. (1995) and McGowran et al. (1997).
The foraminifer-bearing sections recovered most biostratigraphic zones within the Quaternary through the middle Eocene. Several zonal boundaries occur near seismic boundaries, and many indicate hiatuses (see "Seismic Stratigraphy"). The slumping in the interval between Cores 7H and 13X in Holes 1126B and 1126C (see "Lithostratigraphy") mixed lower Pliocene and upper Miocene sediments to various degrees. In this interval Zone Pl1 rests on Zone Mt9 at ~82 mbsf, with an apparent loss of ~3 m.y. Zone Mt9 rests on Zone Mt6, indicating a loss of ~4 m.y. at ~118 mbsf. Several zones were not positively identified from the middle and lower Miocene at Holes 1126B and 1126C, indicating either disconformities or insufficient sampling.
The planktonic foraminifer assemblage is dominated by Globorotalia inflata and Globigerinoides ruber (principally the white form), with lesser amounts of Globigerina bulloides, Globigerina quinqueloba, Globigerina falconensis, Orbulina universa, dextral Neogloboquadrina pachyderma, and Globigerinita glutinata. There are traces of warmer water taxa, such as Globigerinoides sacculifer, Neogloboquadrina dutertrei, and Pulleniatina obliquiloculata.
The subtropical zonation of Berggren et al. (1995b) was applied in part to the Quaternary succession. Globorotalia truncatulinoides persisted throughout the interval, and Globorotalia tosaensis made its last appearance at 15.63 mbsf (182-1126B-2H-CC, 17-22 cm) and 27.28 mbsf (182-1126C-3H-CC, 13-15 cm), dividing the Quaternary zone into Pt1a and Pt1b (Fig. F6). Globorotalia hirsuta makes its first appearance in Subzone Pt1b (Berggren et al., 1995a) in Sample 182-1126B-1H-CC, 11-16 cm (6.51 mbsf). The base of the zone as defined by Berggren et al. (1995b) could not be applied because Globigerinoides fistulosus and Globigerinoides extremus were not observed. We placed the base of Pt1 at the first appearance of G. truncatulinoides, following the definition of Jenkins (1993) and Chaproniere et al. (1995).
A distinctly cool temperate assemblage underlies the interval assigned to Pt1 and includes dextral N. pachyderma, Globigerina bulloides, G. falconensis, G. ruber, Globorotalia inflata, Globorotalia crassaformis, Globorotalia crassula, and G. tosaensis. The assemblage fits the definition of Zone SN13, the Globorotalia inflata Zone of Jenkins (1985, 1993), because it contains abundant Globorotalia inflata without G. truncatulinoides. On the basis of correlation to the calcareous nannofossil zones, we suspect that this zone includes part of the early Pleistocene and may extend into the late Pliocene, although this remains unconfirmed.
The differentiation of upper Miocene from lower Pliocene sections is complicated at Site 1126 by the slumps and debris flows throughout lithostratigraphic Unit II between Core 182-1126B-7H and Section 182-1126B-14H-5 and between Core 182-1126C-7H and Section 182-1126C-13X-5 (Fig. F6). The sedimentary disturbance mixed together various proportions of Miocene and lower Pliocene taxa. In general, samples from Cores 182-1126B-7H to 9H and Cores 182-1126C-7H to 9H are dominated by lower Pliocene taxa with minor occurrences of Miocene taxa, whereas samples from Cores 182-1126B-10H to 14H and 182-1126C-10H to 13H are dominated by upper Miocene taxa with some middle Miocene elements.
The lower Pliocene assemblage from Cores 182-1126B-7H to 9H and 182-1126C-7H to 8H is warm temperate to subtropical and includes such warm-water elements as Globorotalia tumida, Globorotalia plesiotumida, Globorotalia exilis, and Globorotalia menardii with Sphaeroidinella seminulina s.l., Globigerinoides quadrilobatus, and Globigerinoides trilobus. Important lower Pliocene zone markers and/or datum levels fall in this interval, such as the last appearance of Zeaglobigerina nepenthes in Samples 182-1126B-9H-CC, 15-18 cm, and 182-1126C-8H-CC, 43-46 cm, indicating the top of Pl1, and the last appearance of Globorotalia margaritae in Samples 182-1126B-7H-CC, 12-15 cm, and 182-1126C-6H-CC, 26-29 cm, indicating the top of Pl2. Although Zones Pl1 and Pl2 were referred to this interval, the disjunct range of many species reflects disturbance caused by slumping in lithostratigraphic Unit II (see "Lithostratigraphy"); hence, the zonal assignments are tentative.
Other species that make their last appearances in the temperate late Miocene are Globoconella conoidea and Globoconella miozea, which last occur in Sample 182-1126B-9H-CC and Section 182-1126C-9H-5, and several menardine taxa, including G. menardii (Samples 182-1126B-8H-CC to 10H-CC and 182-1126C-10X-CC) and Globorotalia cf. praemenardii (Sections 182-1126B-11H, 12H, and 182-1126C-9H-5). This interval is placed in Zone Mt9 or SN10.
The position of the Miocene/Pliocene boundary was tentatively placed between Cores 182-1126B-8H and 9H and 182-1126C-8H and 9H, and occurs within a disconformity. The range of the upper Miocene species Globoquadrina dehiscens is truncated at the disconformity, and distinctly Pliocene taxa overlie the contact (Samples 182-1126C-8H-CC, 43-46 cm, and 182-1126B-8H-CC, 13-16 cm). The Pliocene taxa include Globoconella sphericomiozea, G. tumida, G. crassaformis, and Globorotalia pliozea, all of which make their first appearances near the base of the Pliocene in Zone Pl1. The Miocene taxa include Globoconella miozea, G. dehiscens, and Globoconella conoidea, which occur together in lower Zone Mt9. A hiatus of at least 1.3 m.y. is indicated between the last appearance of G. dehiscens (last appearance datum is 5.8 m.y.) and the first appearance of G. crassaformis (first appearance datum is 4.5 m.y.). This hiatus is probably more than 2.6 m.y. (between the top of Mt9 at 7.12 Ma and the first appearance of G. crassaformis, which is 4.5 Ma). The contact of Pl1 on Mt9 suggests that the Miocene/Pliocene boundary lies within the disconformity at ~82 mbsf. Calcareous nannofossils, however, indicate that the Miocene/Pliocene boundary lies at the contact between Zones NN16 and NN12 at ~68 mbsf (see "Calcareous Nannofossils"). Postcruise study is needed to resolve the discrepancy.
The first undisturbed sediments below the slumped interval (116.75 mbsf at Hole 1126B and 116.32 mbsf at Hole 1126C) are early middle Miocene in age in Zone Mt6, indicating a hiatus of ~4 m.y. in the later middle Miocene (Fig. F6). The middle Miocene assemblage includes Globigerinoides sicanus, Orbulina suturalis, Praeorbulina glomerosa, and Fohsella peripheroronda, in addition to significant percentages of several long-ranging Neogene species such as G. quadrilobatus, G. triloba, G. dehiscens, and G. quinqueloba. Temperate Zone Mt6 was delineated from Samples 182-1126B-14H-CC, 12-15 cm; 15H-CC, 0-4 cm; and 182-1126C-12X-CC to 15X-CC. Zone Mt5 was recognized in Samples 182-1126B-17H-CC; 18H-CC; 19H-CC, 23-26 cm; 20H-CC, 6-9 cm; 182-1126C-16H-CC, 10-12 cm; and 182-1126C-17X-CC, 25-27 cm.
The lower Miocene assemblage is characterized by Catapsydrax dissimilis, Catapsydrax unicavus, Globoconella incognita, Jenkinsella semivera, Jenkinsella bella, Zeaglobigerina brazieri, Zeaglobigerina woodi, and Zeaglobigerina connecta. Zone Mt4, which spans only 300,000 yr, was absent from the site, probably because of inadequate sampling. Zone Mt3 was delineated from Samples 182-1126B-21X-CC, 18-20 cm (160.48 mbsf); 22X-CC, 17-20 cm (168.35 mbsf); and 182-1126D-3R-CC, 4-6 cm (166.69 mbsf). Zone Mt2 was recognized in Samples 182-1126B-24X-CC, 23-26 cm (188 mbsf); and 25X-CC, 15-18 cm (197.28 mbsf).
Sample 182-1126B-26X-CC, 15-18 cm (205.85 mbsf), contains, among other Oligocene/Miocene species, typical specimens of Globigerinoides primordius that indicate the latest Oligocene. This further suggests that the Miocene/Oligocene boundary lies between 197.28 and 205.85 mbsf.
Overall, the Oligocene section at Site 1126 is poorly represented because of poor core recovery. At Hole 1126D Oligocene sediment was recovered in the core catchers of Cores 182-1126D-8R, 12R, 16R, and 20R at 217.69, 252.68, 290.98, and 329.89 mbsf, respectively. The intervening cores contain only chert coated by thin rinds of sediment suitable only for nannofossil analysis. Core recovery was also poor at Hole 1126B, averaging 18% below 160 mbsf. However, a core-catcher sample from every core was successfully prepared for foraminifers. The Oligo-cene foraminifers included C. dissimilis, Chiloguembelina cubensis, Dentoglobigerina galavisi, Globigerina ciperoensis, Globigerina euapertura, Globigerina officinalis, Globigerina ouachitaensis, Globigerina praebulloides, Globigerinita juvenilis, Paragloborotalia opima nana, Globoquadrina vene-zuelana, G. suteri, Globorotaloides testarugosus, and Zeaglobigerina labiacrassata. Zone P22, equivalent to SP15 of Jenkins (1993) and containing most of these species except C. cubensis and Z. labiacrassata, occurs from Cores 182-1126B-27X to 31X and in Samples 182-1126D-8R-CC, 21-23 cm; and 12R-CC, 18-20 cm. In Sample 182-1126B-32X-CC, 26-28 cm, P. opima nana and Paragloborotalia opima opima indicate Zone P21 (Subzone P21b) according to Berggren et al. (1995b). Sample 182-1126D-16R-CC, 38-39 cm, contains abundant small specimens, particularly those of C. cubensis and tenuitellid forms. In the absence of Pseudohastigerina, the association of these forms with Z. labiacrassata indicates an early Oligocene age equivalent to Zone P19 (Berggren et al., 1995b; McGowran et al., 1997) (Fig. F6).
Upper and middle Eocene sediments were recovered from Hole 1126D, although core recovery was low (~13%). The upper Eocene assemblage, which occurs in samples from 334.38 ± 4.49 mbsf to 360.78 ± 9.33 mbsf, consisted of C. cubensis, Globigerina cryptomphala, Globigerinatheka index, Globoconella nana, Globorotaloides suteri, Globorotaloides testarugosa, Pseudohastigerina micra, Subbotina angiporoides, Subbotina eocaena, Subbotina lineaperta, and Turborotalia increbescens. Lacking typical middle Eocene taxa such as Acarinina, the association was correlated to Zone P16 in Samples 182-1126D-21R-CC, 18-19 cm (338.87 mbsf), and 22R-CC, 15-17 cm (351.45 mbsf). The middle Eocene association is comprised of Acarinina aculeata, Acarinina bullbrooki, Acarinina collactea, Acarinina primitiva, Acarinina spinuloinflata, C. cubensis, G. index, Globigerinatheka subconglobata luterbacheri, P. micra, S. angiporoides, Subbotina linaperta, and Turborotalia cerroazulensis. On the basis of the successive last appearances of A. collactea, Acarinina primitiva, and A. bullbrooki (Table T1), Samples 182-1126D-24R-CC, 30-33 cm (370.11 mbsf), and 25R-CC, 15-17 cm (380.38 mbsf), were assigned to P15; Sample 182-1126D-26R-CC, 23-25 cm (390.38 mbsf), was assigned to Zone P14; and Sample 182-1126D-27R-CC, 0-2 cm (396.63 mbsf), was assigned to Zone P12.
Benthic foraminifers were studied in all core-catcher samples from Holes 1126B and 1126D, except in Cores 182-1126B-13H and 16W, 182-1126D-13R through 15R, and 182-1126D-17R through 19R, which recovered only hard chert fragments. Additional samples from Hole 1126C were also analyzed (Samples 182-1126C-9H-5, 45-50 cm, and 9H-5, 120-125 cm). Abundant chert layers were found during drilling between ~160 and 400 mbsf, leading to poor core recovery. Abundant sponge spicules and radiolarians in many samples from that interval indicate an extended episode of high biosiliceous sedimentation.
Benthic foraminifers are moderately abundant in core-catcher samples from Holes 1126B and 1126D, although they are rare in comparison with planktonic foraminifers. Benthic foraminifer abundance drops significantly in the carbonate rocks near the base of Hole 1126D in Cores 22R-27R. The lowermost cores from Hole 1126D (Cores 28R-33R) are barren, below the major lithologic change from light carbonate rocks into dark micaceous sandstones, siltstones, and mudstones. The absence of foraminifers and nannofossils from any of the core-catcher samples examined from this interval suggests that it probably represents an episode of nonmarine deposition.
Between 100 and 300 specimens were picked from the >63-µm fraction, except in samples where benthic foraminifer abundance was very low. Preservation is good to moderate, except in samples from Cores 182-1126B-12H through 18H that contain a significant proportion of abraded and corroded specimens, and in samples from Cores 182-1126B-24X through 25X and Cores 182-1126D-20R through 24R that contain mainly small, thin tests of benthic foraminifers, showing signs of partial dissolution. Relative abundances of species were determined in all samples (see "Benthic Foraminifers" in the "Explanatory Notes" chapter). The benthic foraminiferal assemblages studied include mainly calcareous taxa and only few species and specimens of agglutinated taxa. The benthic foraminifers generally represent well-known "deep-water" taxa, which have a well-documented cosmopolitan distribution (van Morkhoven et al., 1986; Miller and Katz, 1987; Thomas, 1990; Katz and Miller, 1991; Mackensen and Berggren, 1992; Mackensen, 1992). The following benthic foraminiferal assemblages are recognized in the Cenozoic succession of Holes 1126B, 1126C, and 1126D.
This is a well-diversified assemblage, characterized by the few or common occurrence of Planulina wuellerstorfi, Uvigerina hispidicostata, Stilostomella lepidula, Bulimina aculeata, Cibicidoides spp., and Loxostomoides spp. Also present are Plectofrondicularia vaughni, Uvigerina proboscidea, Bigenerina nodosaria, Sigmoilopsis schlumbergeri, Laticarinina pauperata, Triloculina spp., Pleurostomella spp., Lenticulina spp., and Pullenia spp. Middle bathyal paleodepths are indicated for this interval by the presence of P. vaughni, L. pauperata, and P. wuellerstorfi, generally found in water depths exceeding 500 m, and by the lack of deeper water indicators. Fluctuations in the relative abundance of some taxa such as Cibicidoides spp. and Uvigerina spp., observed in some of the samples, may reflect cyclic changes in surface-water productivity or circulation. However, the low time resolution of the present study does not permit the frequency of these changes to be resolved and clearly shows the need for high-resolution studies to elucidate benthic foraminiferal distribution patterns in relation to paleoceanography.
Assemblages 2A and 2B are characterized by the few to common occurrence of P. wuellerstorfi, U. proboscidea, and Rectuvigerina striata (Assemblage 2A). From Core 182-1126B-14H downward, fluctuating abundances of Patellina corrugata are observed (Assemblage 2B). Also present within the assemblage are Spirillina minima, Stilostomella modesta, Stilostomella spp., Cibicidoides mundulus, Sphaeroidina bulloides, Lagena sulcata, Uvigerina spp., Lenticulina spp., Cibicidoides spp., Siphonina tenuicarinata, B. aculeata, Globocassidulina subglobosa, Vulvulina spinosa, Hanzawaia mantaensis, S. schlumbergeri, Karreriella bradyi, and L. pauperata. Sample 182-1126B-12H-CC contains some large, abraded, and corroded tests, which are indicative of reworking. The presence of P. corrugata and Spirillina minima in Cores 182-1126B-14H to 22X within a typically middle bathyal assemblage (as shown by the presence of G. subglobosa, S. schlumbergeri, L. pauperata, and P. wuellerstorfi) suggests that sediments from shallower depths were redeposited into deeper water. Below Core 182-1126B-18H R. striata becomes common or abundant in all samples. The changes observed in the relative composition of Assemblage 2B may be associated with global hydrographic or climatic changes in the early-middle Miocene (McGowran et al., 1997).
Assemblage 2C is a very impoverished assemblage dominated by small, thin, poorly preserved tests of Bolivina spp. Also present as minor constituents of the assemblage are L. sulcata, Oridorsalis umbonatus, Astrononion pusillum, C. mundulus, Cibicidoides spp., S. tenuicarinata, L. pauperata, Stilostomella spp., and various nodosariids. The assemblage includes species indicative of upper to middle bathyal paleodepths. However, the presence of P. corrugata and Spirillina minima and the dominance of small bolivinid tests within the assemblage indicate that the sediment may have been partly derived from the shallow shelf.
This is a well-diversified, generally well-preserved assemblage that is characterized by the relatively common abundance of O. umbonatus, Cibicidoides praemundulus, R. striata, V. spinosa, S. tenuicarinata, Stilostomella subspinosa, S. modesta, S. bulloides, Cibicidoides spp., Pullenia spp., G. subglobosa, V. spinosa, and Hanzawaia ammophila. Also present in the assemblage are K. bradyi, U. proboscidea, L. pauperata, Cibicidoides mexicanus, Cibicidoides micrus, Lenticulina spp., Bulimina spp., Bolivina spp., Uvigerina spp., Tritaxia spp., Anomalinoides semicribratus, L. sulcata, and various nodosariids. The presence of S. bulloides, S. tenuicarinata, R. striata, L. pauperata, V. spinosa, and U. proboscidea in the assemblage indicate upper to middle bathyal paleodepths. This paleobathymetric interpretation is also supported by the absence of either shallower (neritic) or deeper water (lower bathyal to abyssal) indicators within Assemblage 3. Stratigraphically significant species within Assemblage 3 are Cibicidoides mexicanus, with a stratigraphic range from the upper Eocene (P16) to lower Miocene (N5), C. micrus with a LO in the upper Oligocene (P21b), S. bulloides with a FO in the upper lower Oligocene (P19), and L. pauperata with a stratigraphic range from the lower Oligocene (P18 or P19) to the Pleistocene (N23).
Assemblage 4A is dominated by numerous small tests of S. subspinosa, Stilostomella subspinescens, and Stilostomella spp. Many of the tests are poorly preserved and partially dissolved. Also present as minor elements of the assemblage are O. umbonatus, C. praemundulus, Cibicidoides spp., Lenticulina spp., Pullenia, spp., G. subglobosa, V. spinosa, H. ammophila, and various nodosariids. The absence of Nuttallides truempyi from the assemblage suggests that the site remained above this species' upper depth limit (lower to middle bathyal) during the early late Oligocene to early Oligocene. This assemblage shows close similarity to the assemblage (PC1) dominated by Stilostomella spp. and Lenticulina spp. recorded by Mackensen and Berggren (1992) from lower-middle Eocene sediments at Site 748 on the Kerguelen Plateau. These authors noted that the Stilostomella-Lenticulina assemblage disappeared in the late Eocene at Site 748, to be replaced by an assemblage characterized by newly evolved Oligocene species.
Assemblage 4B is characterized by the presence of N. truempyi, O. umbonatus, H. ammophila, Cibicidoides mexicanus, C. praemundulus, and Cibicidoides spp. In addition, G. subglobosa, Lenticulina spp., and Pullenia spp. also occur within this assemblage. The presence of N. truempyi suggests a well-oxygenated environment at middle to lower bathyal paleodepths. In a study of Paleocene and Eocene assemblages from the southern Atlantic Ocean, Tjalsma and Lohmann (1983) concluded that the bathymetric range of N. truempyi had been restricted to abyssal depths during most of the Paleocene, but became extended to lower and middle bathyal depths in the latest Paleocene. The change in composition between Assemblage 4B and Assemblage 4A suggests that the site was at deeper bathyal depths in the middle-early late Eocene than in the early late Eocene-earliest Oligocene. Assemblage 4B is very similar to the lower Eocene assemblage (PC IV) from Site 747 on the Kerguelen Plateau described by Mackensen and Berggren (1992). The N. truempyi-dominated assemblage was only observed at Site 747 in the early Eocene, whereas an assemblage dominated by Stilostomella and Lenticulina spp. was recorded at Site 748 in the lower and middle Eocene. Mackensen and Berggren (1992) suggested that, in contrast to Site 747 during the early Eocene, Site 748 was situated above the upper paleodepth limit of N. truempyi during the early and middle Eocene.
Sediment accumulation rates were calculated from preliminary biostratigraphic data from Site 1126; the results are presented in Fig. F7. The biostratigraphic datum levels used to calculate sedimentation rates are listed in Table T2.
The sedimentation rate is ~31 m/m.y. in the Pleistocene section and slows to 24 m/m.y. in the lower Pliocene. Rates alternate between 11-15 m/m.y. and 7-8 m/m.y., with the faster rates in the upper Miocene, lower Miocene, and upper Oligocene, and slower rates in the intervening sections. The sedimentation rate curve clearly delineates three hiatuses suggested by disjunct biozones (see "Calcareous Nannofossils" and "Planktonic Foraminifers"), however, the youngest hiatus is not discernible on Figure F7 (missing Zones NN18-NN17 at ~56 mbsf). The second hiatus occurred between 2 and 3.8 Ma, between the LOs of D. brouweri and R. pseudoumbilicus at ~67 mbsf, where Zones NN15-NN13 are missing. The third hiatus occurred between 4.5 and 7.8 Ma, between the FO of G. crassaformis and the LO of M. convallis at ~118 mbsf, where Zone NN11 is missing. Reworked Paleogene nannofossils (such as the Eocene N. dubius) were found near this disconformity. The oldest hiatus occurred between 10.80 and 13.60 Ma between the LOs of C. miopelagicus and S. heteromorphus, with the upper middle Miocene missing (Zones NN9-NN6). There is no obvious paleontologic evidence of hiatuses in the Oligocene and Eocene sections, as all nannofossil zones and most foraminifer zones are present. The continuity of the record, however, is in question because of poor core recovery.