The micropaleontological biostratigraphy of Site 1119 is mostly based on the onboard study of core-catcher samples. Hole 1119B samples were used for the upper part of the section and Hole 1119C samples for the lower part. Additional samples were taken from within selected cores to address specific age and paleoenvironmental questions. The absolute ages assigned to biostratigraphic datums follow the references listed in Tables T2, T3, T4, and T5, all in the "Explanatory Notes" chapter.
There are no obvious long hiatuses in Site 1119. Using our best fit from the constraining datum levels from all four microfossil groups, we conclude that Site 1119 cored a near-complete section of late Pliocene and Pleistocene sediments (Table T3). The Pliocene/Pleistocene boundary (1.8 Ma) is near 300 mbsf, and the base of the section, at 494 mbsf, approximates the middle/late Pliocene boundary (~2.6-2.8 Ma), or is somewhat older (~3.8 Ma) on foraminiferal evidence.
The nannofossil content is variable throughout the site but is generally common or abundant (Table T4). The preservation is generally good to moderate in the lowermost part of the section (Cores 181-1119C-46X to 52X) and from Core 181-1119C-33X to the top. The preservation is moderate to poor between Samples 181-1119C-34X-CC and 45X-CC, displaying dissolution, overgrowth, and recrystallization; Samples 181-1119C-40X-CC and 41X-CC are almost barren.
Emiliania huxleyi is abundant in the uppermost part of the section and dominates the nannofossil assemblages in Samples 181-1119C-1H-CC and 2H-CC. The first occurrence (FO) of this species (0.24 Ma) occurs in Sample 181-1119C-5H-CC. The acme of the same species is recorded in the two uppermost core-catchers. The age of the bottom of this acme zone in the Pacific has been estimated to be at 0.12 Ma or 0.085 Ma (Table T1). Pseudoemiliania lacunosa has a sporadic distribution and very low abundance throughout the section. The last occurrence (LO) of this species (0.42 Ma) occurs in Sample 181-1119C-9X-CC.
Medium-sized Gephyrocapsa (which includes specimens with a maximum length between 3.5 and 5.5 µm and diagonal bridge: Gephyrocapsa oceanica s.s., Gephyrocapsa caribbeanica, Gephyrocapsa sinuosa) are common or abundant from the top of the section down to Sample 181-1119C-17X-CC. Gephyrocapsiids with a crossbar aligned to the short axis of the central opening, identified as Gephyrocapsa parallela in this study, occur in intervals from Samples 181-1119B-14X-CC to 17X-CC. The FO of G. parallela has been calibrated to the uppermost Matuyama Chron around the Jaramillo Event (Takayama, 1993). The top of the acme of G. parallela is reported as 0.78 Ma, around the Matuyama/Brunhes boundary in the northwestern Pacific.
The nannofossil assemblage is dominated by small Gephyrocapsa (specimens <3.5 µm in size) in the interval between Samples 181-1119C-18X-CC and 26X-CC; in this interval medium-sized Gephyrocapsa are virtually absent. A major change occurs in Sample 181- 1119C-27X-CC, where large Gephyrocapsa (specimens >5.5 µm) are abundant. Large Gephyrocapsa occur from Samples 181-1119C-27X-CC to 29X-CC (~1.24 to ~1.46 Ma). Medium-sized Gephyrocapsa are common again below Sample 181-1119C-29X-CC.
The LO of Helicosphaera sellii occurs in Sample 181-1119C-27X-CC. Different values for the absolute age are given for this event (all between 1.2 and 1.65 Ma). The last appearance of H. sellii appears to be time transgressive from tropical to mid-latitudes, with a range from 1.5 to 1.2 Ma. For the time being, we have adopted an age of 1.26 Ma for the LO of H. sellii.
The FO of medium-sized Gephyrocapsa is recorded in Sample 181-1119C-32X-CC. This event should correspond to the FO of Gephyrocapsa oceanica s.l. (1.7 Ma), the FO of G. caribbeanica (1.66 Ma), the FO of Gephyrocapsa >4 µm (1.71 Ma), and to the FO of Gephyrocapsa sinuosa (~1.75-1.8 Ma). This event has been detected to be slightly above the top of the Olduvai Event, and has been used as a good marker for the Pliocene/Pleistocene boundary (1.81 Ma).
Dictyococcites productus is common or abundant throughout the section, but becomes dominant in the lower part, below the FO of medium-sized Gephyrocapsa. The genus Calcidiscus, represented mostly by C. leptoporus, is sporadic throughout the section. Calcidiscus macintyrei is present only in two samples (Samples 181-1119C-29X-CC and 49X-CC), and thus in this section the LO of this species cannot be used for biostratigraphic correlation.
Only one specimen, not well preserved, of Discoaster asymmetricus, is recorded in Sample 181-1119C-52X-CC. Its LO is reported to be close to that of D. tamalis, tied to at an absolute age of ~2.8 Ma. Nevertheless, the paucity of discoasterids in the temperate and subantarctic area in the Southwest Pacific during the Pliocene (Lohman, 1986) hampers the recognition of any reliable markers to date the Pliocene sequences below Core 181-1119C-32X.
Reworked nannofossils are sporadic throughout the section--Cyclicargolithus floridanus, C. abisectus, Dictyococcites bisectus, and Discoaster deflandrei, from the late Eocene-early Miocene--are the most common. Miocene species, such as Helicosphaera ampliaperta, Reticulofenestra pseudoumbilicus, Sphenolithus moriformis, S. neoabies, and S. heteromorphus, occur in a few samples.
Foraminiferal assemblages are generally rich and well preserved, and planktonic forms compose 60%-95% of the total. Less well-preserved, slightly recrystallized, and glauconite-filled assemblages occur in the sandy, micritic horizons lower in the section (e.g., in Sample 181-1119C-38X-1, 64-68 cm) (Tables T5, T6). Throughout the section the assemblages are dominated by Globigerina bulloides, G. quinqueloba, and other small Globigerina species. Neogloboquadrina pachyderma (mostly sinistrally coiled) is present throughout, generally being more common higher in the section. Globorotalia scitula is present in low numbers throughout most of the section. One specimen of Globorotalia hirsuta (FO 0.45 Ma) is present in Sample 181-1119B-1H-CC and it occurs no lower.
Typical 3- to 3.5-chambered Globorotalia inflata is the dominant globorotaliid down to Sample 181-1119C-18X-CC; below this level the morphotype becomes more rounded and smaller, with the taxon present in lower numbers. The highest occurrence of a compressed form of Globorotalia puncticulata, locally called Globorotalia puncticuloides, is in Sample 181-1119C-18X-CC. It replaces G. inflata as the most common globorotaliid from Sample 181-1119C-19X-CC to almost the bottom of the section. The LO datum of G. puncticuloides in this region is not well tied to an absolute age (~2 Ma in DSDP Hole 593; ~0.7-0.8 Ma in DSDP Hole 284; ~0.8 Ma in DSDP Hole 594). It is just above the Brunhes/Matuyama boundary (0.78 Ma) at Site 1122.
Globorotalia truncatulinoides occurs sporadically in low numbers down to 181-1119C-18X-CC, but no lower. Although the Atlantic and Pacific FO datum of G. truncatulinoides morphotypes is 2.6 Ma, it is known to be sparse or absent at southern, austral latitudes through most of the Pliocene and in the lower Brunhes Chron interval in DSDP Holes 284 and 594 (Hornibrook and Jenkins, 1994). Thus, a local FO at Site 1119 near 0.8 Ma is not surprising. No specimens of its ancestor, Globorotalia tosaensis, were found. Similar to nearby DSDP Site 594, the LO of G. puncticuloides overlaps one core with the FO of G. truncatulinoides, at the base of the local G. truncatulinoides zone (Hornibrook and Jenkins, 1994) and near the base of the Brunhes polarity interval (0.78 Ma).
Globorotalia crassula (FO 2.6 Ma) occurs in low numbers down to Sample 181-1119C-41X-CC. The FO of related G. crassacarina, as far as may be determined from its rare presence, is in Core 31X, confirming an age younger than 2.6 Ma (late Pliocene). Unkeeled sinistral Globorotalia crassaformis morphotypes occur sporadically throughout the lower half of the section with a narrow dextral zone (2.1-3.0 Ma) in Sample 181-1119C-41X-CC. Thus, this sample is dated as late Pliocene (2.1-2.6 Ma, early Nukumaruan Stage). Unit III (Cores 181-1119C-43X to 52X) appears to be below the dextral A. crassaformis zone (2.1-3.0 Ma) but all, except 52X-CC, are dominated by Globorotalia puncticuloides (FO 3.6 Ma) and are dated as mid-Pliocene (3.0-3.6 Ma). The lowest sample (Sample 181-1119C-52X-CC) has dominant Globorotalia puncticulata (LO 3.7 Ma) and is presumably ~3.7-4.0 Ma, mid-Pliocene (late Opoitian Stage).
In on-land sections from New Zealand of late Neogene age, a number of benthic foraminifer first and last occurrences have been documented (Hornibrook et al., 1989), which are of potential stratigraphic value, although undoubtedly diachronous because of local paleoenvironmental changes that are difficult to gauge. One of the best documented biostratigraphic datums is the FO of Saidovina karrerianum (Haweran [Wq]-Holocene, <0.4 Ma); unfortunately, the species appears not to be present at Site 1119. Of a number of species documented with LO datums in the Nukumaruan Stage (Wn, 2.6-1.1 Ma), five are recorded in Site 1119 samples: Plectofrondicularia pellucida (LO in Sample 181-1119B-13H-CC), Bolivina affiliata (LO in Sample 181-1119B-15H-CC), Anomalinoides parvumbilius (LO in Sample 181-1119C-18-CC), Haeuslerella pliocenica (LO in Sample 181-1119C-36X-CC), and Karreriella cylindrica (LO in Sample 181-1119C-38X-1, 64-68). We consider that the first three events are probable upward extensions of their local stratigraphic ranges into the Castlecliffian Stage (Wc, <1.1 Ma). Haeuslerella is an endemic New Zealand genus that is common in shelf to uppermost bathyal facies in the Neogene, and its on-land absence from Castlecliffian strata is well tested and probably reliable. We are therefore confident that the LO of Haeuslerella in Sample 181-1119C-36X-CC is not younger than latest Nukumaruan (Wn, >1.1 Ma). An examination of its recorded occurrence in the New Zealand fossil record system indicates that it becomes extinct within the Nukumaruan at a level estimated by G.H. Scott (pers. comm., 1998) of ~2 Ma, an age remarkably coincident for this level with the evidence from other microfossil groups.
The extinction of Plectofrondicularia advena (~0.62 Ma) is one of the events recorded worldwide in the Stilostomella Extinction Event. Its last occurrence here is in Sample 181-1119B-10H-CC.
In Unit II (Cores 181-1119C-28X through 1119C-44X), the Globigerina ooze assemblage is more indurated, with micritic aggregates, encrusted mollusk and echinoid stems, and much glauconite. This level possibly reflects a brief stratigraphic hiatus or condensed section in the late Pliocene.
Diatoms are present in varying amounts through the Pliocene and Pleistocene sedimentary record recovered at this relatively shallow site (Table T7). Their overall abundance is low because of strong dilution with terrigenous detritus at this location. The preservation of the diatoms is generally good.
Species used in the low-latitude zonal scheme are completely absent from the sediments at this site. Of those species used in zonal schemes for the Antarctic-subantarctic region, only three species were encountered. Actinocyclus ingens is present below Sample 181-1119B-15-CC, giving an age for these sediments of >0.65 Ma. A single, poorly preserved specimen of Nitzschia weaveri was found in Sample 181-1119C-48-CC, which suggests an age older than 2.74 Ma. The third species is Nitzschia praeinterfrigidaria. It occurs only in Sample 181-1119C-38-CC, though in this sample relatively frequently. Following Harwood and Maruyama (1992), this species indicates an age between 3.7 and 4.9 Ma. The preservation of the valves and the composition of the diatom assemblage does not indicate that these specimens of N. praeinterfrigidaria are reworked. Nevertheless, the presence of this species at this core depth definitely disagrees with the other fossil datums found for this Hole.
Throughout the section, radiolarians are rare, and, because of terrigenous dilution, numbers per slide do not exceed 50. Radiolarian faunas are more prevalent in the upper part of the section, but diversity is consistently low (Table T8). Samples from the section lower than Core 181-1119C-23X are mostly barren, except Samples 181-1119C-25X-5, 111-113 cm, and 181-1119C-38X-2,110-111 cm.
In the upper part of the section, the predominant species are those characteristic of Antarctic/subantarctic waters (e.g., Antarctissa strelkovi, A. cylindrica, and A. denticulata). Spongotrochus glacialis, Triceraspyris antarctica, and Phorticium clevei are also present high in the section.
Lithelius nautiloides (FO 1.93 Ma) occurs sporadically from Samples 181-1119B-4H-CC to 181-1119C-31X-CC. Pterocanium trilobum (LO 0.83 Ma) occurs in Sample 181-1119C-25X-5, 111-113 cm. A typical form of Eucyrtidium calvertense (LO 1.92 Ma) is present in Sample 181-1119C-38X-2, 110-111 cm.
Throughout the core, the nannofossil assemblages consist mainly of subantarctic flora with a few temperate forms. Subtropical species are virtually absent. The ratio of Calcidiscus leptoporus + Helicosphaera spp. to Coccolithus pelagicus appears to be a good indicator of sea-surface temperature in the subantarctic waters in this area: the higher the ratio, the warmer the sea-surface water mass (Hiramatsu and De Deckker, 1997a).
A detailed study of Core 181-1119C-25X's succession of nannofossil assemblages in a depositional cycle spanning ~6 m was conducted. At the base of the cycle, sediments consist mainly of silt enriched in carbonate particles. Nannofossils are generally abundant and diverse. They are dominated by the subantarctic flora, but species that are more or less characteristic of temperate water masses, such as Helicosphaera carteri, H. sellii, and Syracosphaera spp. (Hiramatsu and De Deckker, 1997b), have been added to the assemblage. The sizes of small placoliths (Reticulofenestra, Dictyococcites) are bigger than those deposited in the finer sediments within the cycle. The coarseness of the sediments, the occurrence of tunicate spicules, and bioclastic materials imply that the sediment was transported downslope from the edge of the adjacent continental shelf. However, very few reworked nannofossils are present. We interpret the basal part of the cycle (characterized by coarser sediment) as being deposited during a warmer interglacial period when sea level was at a highstand.
In contrast, in intervals of fine sediment, nannofossil assemblages are enriched with cold-water-dwelling species, such as Coccolithus pelagicus, Calcidiscus leptoporus, and small gephyrocapsids (Hiramatsu and De Deckker, 1997a). The assemblages show low abundance and low diversity of indigenous species but contain reworked Cenozoic nannofossils, such as Cyclicargolithus floridanus, Dictyococcites bisectus, Reticulofenestra pseudoumbilica, and occasionally discoasterids as well as sphenoliths. The low abundance of nannofossils is considered to be a result of the dilution effect of the increased influx of terrigenous sediments during glacial periods. Pontosphaera species generally only occur in the fine-sediment intervals. The size of small placoliths (Reticulofenestra minutula, R. minuta, Dictyococcites productus, D. perplexa) is smaller than those deposited during the warm sea-level highstand. The small-sized placoliths are generally considered to be r-selected species, indicative of eutrophic conditions (Young et al., 1994). Some of the fine sediment samples contain abundant pyrite and/or rhombohedral dolomite plates, indicative of strong sulfate reduction. The low diversity and r-selected nannoflora, together with high degree of sulfate reduction (and, therefore, high content of organic matter) suggests that the sediments were deposited in a nearshore setting with high nutrient content. We consider that this part of the cycle was deposited during glacial intervals while sea level was low. The nannoflora is indicative of a coastal eutrophic environment.
Foraminifer assemblages at Site 1119 consistently are rich in planktonic taxa (60%-95% of foraminifer faunas), indicative of the open-marine, normal salinity environment expected at the site, which at present is situated ~96 km from land. Throughout the section, globigerinid taxa prevail; turborotaliids are rare to common; semi-keeled to keeled globorotaliids and also Orbulina are rare; Globigerinoides is absent. Hence, the assemblage overall is indicative of a cool to temperate surface water mass (see below). At many levels, the assemblage, and in fact the sediment as a whole, may be characterized as a Globigerina ooze, with a consistent admixture of silt-sized, angular quartz, and mica wafers. The most common globigerinid taxa include Neogloboquadrina pachyderma (mostly sinistrally coiled), Globigerina quinqueloba, G. umbilicata, G. bulloides, and "nondescript" Globigerina spp., with less common Globigerinita glutinata, G. uvula, and rare Globigerinella aequilateralis.
In lithostratigraphic Units I and II (between 181-1119B-1H and 181-1119C-27X-CC), there is an alternation between assemblages that are characterized by (1) globigerinid-dominant fauna with micromollusks and quinqueloculinid benthic forms (including large Pyrgo anomala) and, at Sample 181-1119B-17H-CC, masses of siliceous sponge spicules, and (2) the same globigerinid assemblage with consistently more temperate water mass indicators like Orbulina universa, Globorotalia inflata, G. truncatulinoides, G. crassula, and G. scitula. The latter assemblage also contains (benthic) Planulina wuellerstorfi, Discanomalina semipunctata, and common Globocassidulina curvata, indicative of upper bathyal or deeper conditions. This contrasting alternation of the two assemblages is seen in core-catcher samples between Cores 181-1119B-1H to 181-1119C-19X, with the warmer and deeper marine component in the coarser lithologies, and the colder and likely shallower assemblage, more tolerant of a neritic water mass and coastal conditions, in the finer lithologies. The finding suggests a systematic pattern reflecting shallower and colder glacial conditions alternating with warmer and deeper interglacial ones in an outer shelf to upper bathyal setting, consistent with the seismic geometry of the site.
To further test this finding, a set of samples was taken from within Core 181-1119C-25X, from fine and coarse horizons:
The analysis of samples at the bottom and top of a fining-upward sediment cycle was repeated in a sample pair from Core 181-1119C-38X. Here the coarse horizon (Sample 181-1119C-38X-1, 64-68 cm) is a green, micritic, glauconitic, foraminiferal sand with a rich and diverse, though less well preserved, planktonic and benthic foraminiferal fauna. The fine horizon (Sample 181-1119C-38X-2, 100-107 cm) is a gray hemipelagic mud from near the top of a thick, fining-upward unit and has a sparse fauna of small planktonic and benthic foraminifers. These faunal differences are very similar to those documented in the higher cycle. We conclude that the coarser beds represent higher energy, deeper marine, sediment-starved, well-oxygenated, interglacial conditions, with the fining-upward muddy part of the sediment cycle indicating colder and shallower marine conditions, with higher sedimentation rates, when sea level dropped toward the peak of each glacial period.
In lithostratigraphic Unit III, in the lower parts of the section (below Core 181-1119C-44X), the sediment is dominantly hemipelagic clay containing low concentrations of a rich and diversified planktonic and benthic foraminiferal assemblage, very similar to the coarse intervals of Unit II (above), with the consistent addition of Cibicidoides pachyderma and C. aff. pachyderma (LO in Core 181-1119C-41X-CC). The benthic fauna is dominated by a mixture of Astrononion novozelandicum, Cassidulina carinata, Discorbinella bertheloti, Epistominella exigua, Nonionellina flemingi, and Notorotalia spp. In late Pliocene time, a deeper upper bathyal (~300-600 m water depth) setting is inferred for Unit III at Site 1119.
The dominant diatom species found are cosmopolitan neritic species. Subantarctic species are subordinate and generally occur in higher numbers only in samples rich in diatoms from the gray, clayey silts deposited during glacial periods (compare the species in Samples 181-1119C-16H-8, 60-61 cm, 17H-5, 97-98 cm, 18X-CC, 21X-CC, 22X-CC, 28X-CC, 31X-CC, 32X-CC, 35X-CC, 38X-CC, 48X-CC). Occurrence of subantarctic species in the olive-gray, sandy interglacial sediments (e.g., Sample 181-1119C-17H-CC) is rare and restricted to intervals with generally higher biogenic silica. The abundance of diatoms is controlled by productivity. As productivity is highest during periods of increased terrigenous input, the changes in diatom abundance can be expected to reflect changes in overall sedimentation rates. Using this relationship, higher sedimentation rates can be postulated for the times documented in core intervals between 130-210, 240-260, and 310-390 mbsf at Site 1119 (Fig. F12).
A study of the diatoms in five samples through one sedimentary cycle in Core 181-1119C-25X showed the following pattern. Diatoms were absent from the glauconitic, interglacial sands at the base of the cycle. A low-diversity flora, dominated by neritic, cosmopolitan taxa with just a few subantarctic species, occurs in the gray clayey silts. It is inferred to have been deposited during a glacial period with increased productivity. Higher up in the gray silty clays, the abundance of diatoms in the sediment decreases. The samples from the upper part of the cycle contain only traces of diatoms.
Fossil mollusks occur commonly throughout the upper parts of cores from Site 1119, especially in Units I and II. Single valves of Tawera spissa and, at deeper levels, Limposis peteri, are the dominant macrofossil in the inferred interglacial (highstand) sand intervals, and in situ double valves of Zygochlamys delicatula occur frequently in the inferred glacial (lowstand) silt beds. The glacial silts also contain archibenthal gastropods, including Cominella (Eucominia) alertae, Aeneator (Ellicea) recens, Provocator mirabilis, and Pliconacca denticulifera (Table T9). This molluscan fauna is similar to the upper bathyal fauna that occurs today on mud substrates on the New Zealand upper slope.
Site 1119 microfossils appear to document a slight overall shallowing through the late Pliocene and Pleistocene, from deeper upper bathyal (300-600 m) to uppermost bathyal-outer shelf (100-400 m) depths. The cycles of coarse and fine sedimentation in the upper two-thirds of the section contain alternating assemblages. The fine-grained intervals contain assemblages with dominantly cool, neritic, shallow-water affinities and were presumably deposited in glacial periods. The coarse-grained intervals contain similar assemblages, but with variable additions of temperate planktonic taxa and benthic foraminiferal indications of slightly deeper water; these were presumably deposited in interglacial periods.