PRINCIPAL RESULTS
Hole 1119A
Position: 44°45.33234´S, 172°23.59772´E
Start hole: 0345 hr, 23 August 1998
End hole: 1020 hr, 23 August 1998
Time on hole: 6.58 hr
Seafloor (drill pipe measurement from rig floor, mbrf): 406.50
Distance between rig floor and sea level (m): 11.00
Water depth (drill pipe measurement from sea level, m): 395.50
Total depth (from rig floor, mbrf): 412.50
Total penetration (mbsf): 6.00
Coring totals: type: APC; number: 1; cored: 6.00 m; recovered: 100.17%
Formation: lithostratigraphic Unit I: olive gray silty sand and greenish gray silty clay
Hole 1119B
Position: 44°45.33234´S, 172°23.59772´E
Start hole: 1015 hr, 23 August 1998
End hole: 0020 hr, 24 August 1998
Time on hole: 14.08 hr
Seafloor (drill pipe measurement from rig floor, mbrf): 407.80
Distance between rig floor and sea level (m): 11.00
Water depth (drill pipe measurement from sea level, m): 396.80
Total depth (from rig floor, mbrf): 563.60
Total penetration (mbsf): 155.80 mbsf
Coring totals: type: APC; number: 17; cored: 155.80 m; recovered: 105.56%
Formation: lithostratigraphic Unit I: 0–92 mbsf; olive gray silty sand and greenish gray silty clay
lithostratigraphic Unit II: 92–155.8 mbsf; olive gray silty sand and greenish gray silty clay
Hole 1119C
Position: 44°45.33188´S, 172°23.61420´E
Start hole: 0020 hr, 24 August 1998
End hole: 1915 hr, 26 August 1998
Time on hole: 66.92 hr
Seafloor (drill pipe measurement from rig floor, mbrf): 407.20
Distance between rig floor and sea level (m): 11.00
Water depth (drill pipe measurement from sea level, m): 396.20
Total depth (from rig floor, mbrf): 902.00
Total penetration (mbsf): 494.80
Coring totals: type: APC; number: 17; cored: 160.30 m; recovered: 108.28%
type: XCB; number: 35; cored: 334.50 m; recovered: 80.32%
Formation: lithostratigraphic Unit I: 0–92 mbsf; olive gray silty sand and greenish gray silty clay
lithostratigraphic Unit II: 92–404 mbsf; olive gray silty sand and greenish gray silty clay
lithostratigraphic Unit III: 404–494.72 mbsf; greenish gray silty clay
Site 1119 is located 96 km east of the eastern shoreline of New Zealand's South Island, offshore from Timaru, within the Canterbury Basin. The site was drilled in a water depth of 393 m on the upper slope, 5 km seaward of the edge of the continental shelf. Further seaward the slope levels out onto Campbell Plateau at 800–1000 m. Clinoform reflectors within the Miocene–Holocene represent earlier positions of the prograding shelf-slope. The reflectors define a shore-parallel zone of Pliocene–Pleistocene sediment drifts which prograded landward and accreted to the edge of the shelf.
Site 1119 was drilled to sample the upper slope sediments and underlying sediment drifts. A copious source of sediment is required to build the drifts. Site 1119 samples will allow the provenance of the upper drift sediments to be established, paleocurrent velocities to be inferred, and the late Pliocene–Pleistocene history of the important AAIW water mass to be reconstructed close to its source. The sand-rich intervals encountered in the hole may allow inferences to be made regarding relative sea-level change during this period.
Hole 1119A comprised a single 6.01-m-long core taken for mudline sampling. APC penetration, with essentially full core recovery and little disturbance, was then achieved to a depth of 155.8 mbsf (Hole 1119B) and 160.3 mbsf (Hole 1119C) successively (Table 1). Hole 1119C continued to a depth of 494.8 mbsf using the XCB. Throughout the APC core sections, core voids were common in the sands and silts, resulting from the discharge of gas that caused core expansion. Core recovery was 105% for Hole 1119B and 89% for Hole 1119C.
The 494.8 m of sediment cored is subdivided into three lithologic units (Fig. 7). The upper 246.8 m (Unit I) comprises repetitive, sharp-based, silty sand_silty clay couplets. Silty sand beds are usually <2 m thick and have an olive gray color, coarse texture with shell debris, and small amounts of glauconite. Many microfossils are reworked. The silty clays form thick greenish gray beds (usually 4 m), with mica and scattered macrofossils (including double valves of the subantarctic scallop Zygochlamys delicatula). Nannofossils occur in most samples, radiolarians have sporadic distribution, pyrite is a common accessory mineral, and sponge spicules are prominent. Toward the bottom of lithostratigraphic Unit I, bathyal gastropods appear in the silty muds (e.g., Ellicea), indicating deepening conditions for the sedimentary couplets with depth in the hole: the sequence as a whole indicates shallowing-upward conditions. Foraminifers and nannoplankton indicate deeper, warmer conditions during deposition of the silty sands (sediment-starved upper slope during interglacial highstands), and deposition of silty-clay intervals in relatively shallower, colder water on a nearshore upper slope during glacial lowstands. The basic nature of the Unit I sedimentary couplets was apparently controlled by sea-level change, but seismic records show that all but the uppermost parts of Unit I (shallower than 50 m) have a drift geometry. However, the marked sedimentary and environmental cyclicity of Unit I is similar to that already described from Pliocene–Pleistocene sediments nearby on land.
Unit II comprises Subunits IIA from 246.8 to 318.4 mbsf and IIB from 318.4 to 428 2 mbsf. It also contains sedimentary rhythms that differ from the couplets of Unit I. The upper part, Subunit IIA, contains doubly-graded silty-sand/silty-clay units (A-Bt-A), with continuous gradation between components. The sands have increased calcite content and sometimes show incipient cementation. Nannofossils are more frequent than in Unit I. The lower part of Unit II (IIB) contains sharp-based sand-silty clay couplets (A-Bc) similar to those of Unit I, but in which the sandstones have less terrigenous material, and include significant amounts of broken shell, benthic foraminifers, and nannofossils. The sands have sharp bases beneath which are muds displaying sand-filled burrows of Thalassinoides and Chondrites. Whole-valve molluscs, conspicuous in the overlying unit, are rare.
The lowest gradational A-Bt-A motif occurs in the bottom part of Core 181-1119C-34X (the base of Subunit IIA), below which the sharp-based sand-mud couplets continue downhole intermittently to the base of Core 181-1119C-43X (428.2 mbsf, base of Subunit IIB). We interpret the double graded-motif as the deeper water manifestation of the climatic and sea-level changes that produced the sharp-based silty sand-silty clay couplets in Unit I. The sharp-based silty sand-silty clay couplets of Subunit IIB are more difficult to interpret. They may have a similar origin to their counterparts in Unit I, or they may be redeposited (i.e., turbidites). X-radiography will be a great help in making this distinction.
Unit III occurs from 428.2 mbsf to the bottom of the hole and comprises mostly massive, pale olive gray silty clay with occasional burrows, which is similar to the inferred glacial silty clays of Units I and II. Unit III contains very thin beds and laminae of light gray sediments that smear slides suggest are mud turbidites. The trace fossil Zoophycos occurs scattered throughout, macrofossils and shell fragments are almost absent, and interbeds of olive sand are completely absent. This unit corresponds with the presence of a large sediment drift on the deep seismic line through Site 1119, and we interpret Unit III sediments as deposits of the deeper slopes of the Canterbury drifts. Microfaunas from Unit III are consistent with deeper water depths than are those from Units I and II.
Preliminary paleontological data indicate that the Unit I/II boundary is ~1 Ma (early Castlecliffian), the Unit II/III boundary ~2 Ma (early Nukumaruan), and the bottom of hole ~2.6 Ma (late Pliocene, perhaps as old as late Waitotaran) old. These ages are drawn from cycle counting and faunal evidence. A shipboard paleomagnetic reversal chronology could not be determined unambiguously because of a combination of low intensities and magnetic overprints. The average sedimentation rate across the section is therefore ~20 cm/k.y., with lower rates during interglacials (sand), and considerably higher rates during glacials (silt and clay).
Despite the widely varying sedimentation rates and the presence of random core gaps resulting from degassing, an excellent spliced MST record for the two APC cores was achieved for Site 1119, based on magnetic susceptibility and natural gamma records. Cyclicity that matches the observed sediment couplets is apparent in both the smoothed magnetic susceptibility and, to a lesser degree, the natural gamma ray records. In other physical property data a distinct increase in vane shear strength is noted at ~85 mbsf, which may correlate with an observed seismic discontinuity and indicate a hiatus.
Carbonate concentrations are in the wide range of 0.5% and 75%, indicating strongly variable environmental conditions during sediment deposition (Fig. 7). In contrast, the average concentration of total organic carbon is 0.34% with small variations, which is low for coastal sediments. This may be a result of dilution either by carbonate or, during times with low carbonate supply, by enhanced terrigenous clastic material.
Interstitial water profiles show that the sulfate reduction zone occurs at 20 mbsf. There are increases in alkalinity, ammonium, and phosphate concentration in this zone. These increases are controlled by the degradation of sedimentary organic matter in a shallow marine environment. Sulfate concentrations are near zero from 20.15 through 472.3 mbsf, suggesting enhanced diagenetic processes, including the dissolution of magnetic minerals throughout the sequence. The decreases in calcium and magnesium concentrations in the sulfate reduction zone suggest the precipitation of diagenetic carbonate promoted by the rapid increase in alkalinity.
Downhole logging at Site 1119 included runs of the following tools: triple combination, Geologic High-Resolution Magnetic Tool (GHMT), and Formation MicroScanner (FMS-sonic). Downhole conditions were irregular below 160.3 m because of damage to the wall during drilling, and some data dropouts occur. After the GHMT tool run, the bottom 20 m of the hole collapsed because of cavings or swelling mud, and, as a result, the data from the two later tool strings do not contain this portion of the hole. The poor hole conditions affected the lithodensity and neutron porosity tools, making interpretation of the data difficult. The sonic tool was also affected by the poor conditions, but to a lesser degree, and the data obtained from it were used to create integrated travel times for interpretation of seismic survey data at this site. The resistivity, susceptibility, and gamma ray tools recorded good logs with cyclic signals.