Site 1126 is located on the eastern Eyre Terrace upper slope in 783.8 m of water. This site was designed to intersect Cenozoic seismic Sequences 2, 3, and 4, and Lobes 1 and 3 of Sequence 6A and to intersect as much of the upper part of the Cretaceous section as time permitted. The target depth at this site was a high-amplitude reflector of probable Cenomanian age, estimated before drilling (on the basis of stacking velocities) to be at 525 mbsf. Because this was also the first Ocean Drilling Program (ODP) site in this basin, it provided the opportunity to establish a basic stratigraphy for the Cenozoic sequences that could then be refined at later sites.
Five lithostratigraphic units were delineated at Site 1126. Unit I (0-60.2 mbsf) is a calcareous ooze with a gradational alternation between two major sediment types: (1) white-gray nannofossil-rich matrix-supported ooze and (2) light gray grain-supported ooze rich in planktonic foraminifers. Unit II (60.2-116.8 mbsf) is characterized by several intervals of slumped calcareous ooze. Sediment composition in these bodies is the same as in the undisturbed sediments. The first downhole occurrence of silicified layers (porcellanite) subdivides Unit II into an upper Subunit IIA and a lower Subunit IIB. As in Unit I, intervals that are not affected by slumping display a light/dark alternation. In the lower part of Unit II, these cycles are increasingly asymmetric, with the dark portions becoming dominant. Unit III (116.8-166.5 mbsf) consists of calcareous ooze with interbeds of silicified layers in the upper part of the unit. The lower part of the unit is porcellanite free and displays the same type of cyclicity as sediments in the overlying units. Unit IV (166.5-396.6 mbsf) coincides with an interval of low core recovery and thus cannot be described in detail. It consists of an alternation of calcareous ooze to chalk intervals and silicified pelagic limestones with some planktonic foraminifers and bioclasts. Unit V (396.6-455.9 mbsf) consists of black to green sandstones, silty sandstones, clayey siltstones, and minor granule conglomerates.
Nannofossil and planktonic foraminifer biostratigraphies show that Quaternary-middle Eocene sequences were recovered. Sandstones of probable Cenomanian age (Unit V) recovered at the base of the drilled interval are barren of marine microfossils. Sedimentation rates were relatively high in the Quaternary-uppermost Pliocene (31 m/m.y.) and lower Pliocene (24 m/m.y.) and slow in the remainder of the Neogene and Paleogene sections, where rates alternate between 7-8 m/m.y. and 11-15 m/m.y., with faster rates in the upper Miocene, lower Miocene, and upper Oligocene. At least two disconformities or condensed intervals are present at the Miocene/Pliocene and lower/middle Miocene boundaries. Benthic foraminiferal assemblages show a change in benthic environments from lower bathyal to middle bathyal in the upper part of the middle Eocene nannofossil zone (NP16). Slumps between ~55 and 110 mbsf are marked by a mixture of upper Miocene and lower Pliocene planktonic taxa found within an uppermost lower Pliocene assemblage. The slump is also flagged by a mixture of a displaced upper bathyal assemblage of benthic foraminifers found within an in situ middle bathyal assemblage.
The results of paleomagnetic long-core measurements of cores from Hole 1126B and 1126C were disappointing. The NRM was dominated by a vertically downward coring contamination that was largely removed by 20 mT demagnetization, whereupon the signal was almost uniformly reduced to the noise level of the instrument. In addition, there were anomalous peaks in intensity near the tops of most cores and of several sections. These were so large that we interpret them as contamination. Only a single core gave a sequence of reversals that could be interpreted magnetostratigraphically. A comparison between whole-core and archive-half core measurements showed that the two measurements of inclination are not significantly different, but there are systematic differences in declination. The nannofossil chalks gave stronger signals, but poor recovery precluded determination of a useful magnetostratigraphy. In the sandstone recovered toward the base of Hole 1126D (Unit V), normal magnetizations were observed. Their high inclination, giving a paleolatitude of ~50°S, is in accordance with northerly motion of the Australian plate as it moved away from the Antarctic-Australia spreading center. Rock magnetic properties of representative samples from the various sedimentary units differ in a manner that is consistent with the NRM variation. In the nannofossil chalk and in some of the more strongly magnetized nannofossil oozes, the magnetic carrier appears to be single-domain magnetite consistent with a magnetotactic bacterial origin, whereas a different and harder phase dominates in the uppermost nannofossil ooze sediments.
The upper 154.0 m of sediment at Site 1126 was double cored. Construction of the composite section from Holes 1126B and 1126C indicates that a complete record of the sedimentary section was not recovered. Correlation between cores was hindered by significant differential core distortion, particularly at the very top of each core where an expanded record was indicated. Correlations were further hindered by a decrease in core recovery below 100 mbsf, resulting from the presence of multiple chert layers. Below 60 meters composite depth (mcd), large data gaps and the presence of numerous slumps made correlations difficult and highly tentative. The composite section indicates gaps in the record at ~26-27, 64-65, 73-74, 86-87, 109-112, 124-125, and 130-137 mcd.
Only low concentrations of methane and ethane were detected at Site 1126. Methane ranges from 2.2 to 13.6 ppm. Ethane is present in five samples between 186.5 and 236 mbsf (1.1-2.7 ppm) but is not detected at greater depths. The carbonate content is uniformly high (80-91.2 wt%) in the upper 116 mbsf but becomes highly variable (30.6-93.2 wt%) from 116 to 254.2 mbsf. Because of poor core recovery, no samples are available in the interval from 254.2 to 348.6 mbsf. From 348.6 to 389.6 mbsf, the carbonate content returns to high levels within a narrow range (79.5-90.0 wt%), dropping again to very low values in sandstones (0.4-0.6 wt%) from 406.4 to 454.5 mbsf. Total organic carbon is low throughout the cored interval except for the bottommost sample of Hole 1126D, which has 1.33 wt% organic carbon. All other organic carbon values are less than 0.8 wt% and most are less than 0.2 wt%
Site 1126 is characterized by a large increase in salinity that manifests itself as shallowly as 10 mbsf, reaching a maximum of 106 (about three times normal seawater salinity) by a depth of ~100 mbsf. Most of the other geochemical parameters exhibit nonconservative behavior with respect to Cl-, including Ca2+ which shows a net excess, and Mg+, SO42-, and alkalinity, all of which show net losses. The pore waters have a Na+/Cl- ratio close to that of seawater.
Physical properties data closely reflect the location of sequence boundaries and changes in lithology and mineralogy. These data were divided into five units on the basis of shifts in measured parameters. Physical properties Unit (PP Unit) 1 is characterized by high natural gamma radiation (NGR) with a trend of increasing P-wave velocity and bulk-density measurements to the bottom of the unit. The base of PP Unit 1 broadly coincides with the upper Pliocene/Pleistocene boundary. Physical properties Unit 2 is characterized by relatively high NGR that dramatically decreases toward the base of the unit. This decrease occurs because of the downhole disappearance of aragonite. P-wave velocity increases throughout PP Unit 2, as does thermal conductivity. The base of the unit coincides with the upper Pliocene/lower Miocene boundary. Physical properties Unit 3 is characterized by low variability in P-wave velocity and NGR. The base of this unit was not recovered in the sediments, but can be defined at 185 mbsf using downhole logs. Physical properties Unit 4 is characterized by alternations of high-velocity porcellanite and lower velocity oozes. This high contrast in sediment induration was probably the major cause of the low recovery in this unit. The top of PP Unit 5 coincides with a major hiatus at the base of the Tertiary. Physical properties Unit 5 shows much greater NGR values and higher P-wave velocities, reflecting the transition from PP Unit 4 ooze into PP Unit 5 sandstone. This indicates that PP Unit 5 sediments were affected by diagenesis. Thermal conductivity co-varies with water content, bulk density, and P-wave velocity.
Hole 1126D was logged with three tool strings: the triple combination logging tool (triple combo), sonic/geologic high-resolution magnetic tool (GHMT) combination, and the well seismic tool (WST). The FMS tool was not run with the sonic tool as usual because of (1) excessive heave caused by dual swell directions, which was not compensated for by the wireline heave compensator, and (2) a large hole diameter, as indicated by the caliper on the triple combo. The WST was used for recording nine check-shot stations between 420 and 130 mbsf. Several washed-out zones affected readings made by excentric tools (e.g., neutron porosity and density), whereas readings measured by hole-centered tools (e.g., magnetic susceptibility [MS], sonic, and resistivity logs) were little influenced by hole conditions. The MS data were useful for subdividing the measured section into 10 provisional logging units, some of which correlate with the seismic stratigraphic units. In the interval below 160 mbsf where core recovery was poor, changes in several logs provide the detail and continuity necessary to further subdivide the section. The spectral gamma-ray log measured by the triple combo proved very useful for correlating the part of the section measured through pipe (upper 116 mbsf) with core measurements. In the lower siliciclastic part of the section, photoelectric effect (PEF) values indicate the presence of iron minerals.
The check-shot survey showed that the actual time-depth conversion curve fell within the narrow envelope of time-depth curves derived from stacking velocities, so depth estimates for other sites based on stacking velocity curves can be viewed with more confidence. The preliminary biostratigraphic data permitted ages of the regional Cenozoic seismic sequences to be defined, showing that Sequence 2 corresponds to the Pleistocene-latest Pliocene, Sequence 3 is of middle-late Miocene age, Sequence 4 is of early Miocene age, and Sequence 6A is of Eocene-Oligocene age.
Site 1127 was the first and most seaward site of a three-site transect through a spectacular set of upper Neogene clinoforms immediately seaward of the present-day shelf edge. Site 1127, located on the upper slope in 479.3 m of water, intersected an expanded record of the youngest clinoforms as well as the lowest, more condensed portion of the clinoform sequence. The principal objective of this transect was to collect detailed high-resolution profiles through a late Neogene shelf edge (high energy) to upper slope (low energy) succession deposited within a cool-water carbonate environment to determine the response of this type of depositional system to Pliocene-Quaternary sea-level fluctuations.
At Site 1127, we recovered a 510.7-m-thick (Table T2) monotonous succession that is dominated by very fine to fine-grained, heavily bioturbated, unlithified to partially lithified, greenish gray wackestones to packstones, made up of three units. Unit I (0-6.0 mbsf) consists of two subunits: an upper nannofossil ooze and a lower foraminiferal ooze. Unit II (6.0-464.5 mbsf) consists of alternating bioclastic wackestone- and packstone-dominated packages with thin grainstone beds divisible into five subunits. These subunits are characterized by a lower portion composed of wackestones to packstones, grading up into wackestones, and dominated at the top by packstones with thin capping grainstones. Shallower water fauna are most abundant near the top of each subunit. The lowermost subunit (~420-464.5 mbsf) has a slumped base with abundant clasts, including bryozoan and large skeletal fragments within an ooze matrix. Unit III (464.5-510.7 mbsf) consists of an upper nannofossil ooze and a lower glauconite-rich bioclastic packstone, with minor capping grainstone beds with intraclasts.
Calcareous nannofossils and planktonic foraminifers indicate an extraordinarily expanded Quaternary-uppermost Pliocene sequence of ~470 m, with a hiatus of ~3 m.y. between basal Quaternary-uppermost Pliocene (Zone NN19) and underlying Miocene sediments. Based on preliminary biostratigraphic datum levels, average sedimentation rates were 240 m/m.y. in the Quaternary and 2-8 m/m.y. in the Miocene. The thin Miocene section contains a strongly mixed planktonic foraminiferal assemblage. A well-preserved benthic Pleistocene foraminiferal assemblage is recognized down to 414.5 m. Between 414.5 and 501.1 mbsf, we identified two benthic assemblages that contain mainly upper bathyal taxa but include large numbers of abraded and corroded tests, indicating extensive mixing or reworking. Quaternary benthic foraminiferal assemblages often display a uniformity in test size and lack of medium to large tests that is consistent with grain-size sorting and downslope redeposition. The cool temperate Quaternary fauna is accompanied by warm-water species at various intervals, probably reflecting a combination of global climatic fluctuations and regional paleoceanographic variations, especially in relation to the flow of the Leeuwin Current.
Paleomagnetic measurements revealed a long section of normal polarity to 343.4 mbsf, which we interpret as the Brunhes Chron. The mean inclination was -49.9° with a standard deviation of 22°. It was only possible to locate a very approximate onset (380 mbsf) and end (395 mbsf) of the Jaramillo Subchron. We found intensity fluctuations within the Brunhes Chron in the NRM after 20 mT demagnetization that appear to correlate with standard records of geomagnetic field fluctuations back to 400,000 yr. The calculated sedimentation rate for the whole Brunhes Chron is 480 m/m.y., whereas the rate for the first 400,000 yr based upon the intensity estimation is 277 m/m.y. Rock magnetism analysis revealed that the dominant magnetic phase was chemically unstable, so that the saturation remanence decayed by as much as 60% within 48 hr. This behavior is typical of the ferromagnetic sulfide greigite, which inverts sluggishly to paramagnetic pyrite. The high ARM/IRM suggests a dominant single-domain grain size and a strong magnetotactic bacteria input. However, if this suggestion is correct, the magnetotactic bacteria synthesize greigite rather than magnetite.
The most striking organic geochemical results at Site 1127 are the very high concentrations of methane and H2S present throughout the section. Gas pockets within the core were common from 47 to 312 mbsf, and these were sampled directly through the core liner with a gas-tight syringe (vacutainer). Methane concentrations in these gas pockets range from 329,000 to 585,000 ppm. Hydrogen sulfide ranges from ~60,000 to 138,000 ppm. Methane is present at lower and highly variable concentrations in headspace samples, with the lowest values at the top and bottom of the drilled interval. Methane/ethane ratios in vacutainer samples decrease downhole from 2728 to 1309, with a decrease in the ratio to 174 in headspace samples. Carbonate content values predominantly range between 85 and 92 wt%, with a trend toward lower values with increasing depth. Organic carbon values are primarily in the range of 0.1-0.6 wt% down to ~250 mbsf and then vary from 0.5 to 1.0 wt% to the bottom of the hole.
Although similarly influenced by high-salinity pore fluids (as much as 100 in Pliocene and older portions of the section), pore-water geochemistry at Site 1127 was fundamentally different than at Site 1126 because of an extended sulfate reduction zone. As a result of the more inshore location, Site 1127 not only had a higher initial organic matter content compared to Site 1126, but more of the organic material was preserved as a result of higher sedimentation rates. As a result of the high sulfate concentration in the deeper, higher salinity fluids, the sulfate reduction zone is enlarged and the consequent production of H2S is much higher than in normal organic-rich sediments. In addition, the relatively iron-poor nature of these sediments precludes the formation of iron sulfide phases that would normally sequester H2S. The greatest amount of carbonate recrystallization appears to occur at the lower interface between the sulfate-depleted zone (~180 mbsf) and the underlying sediments, where sulfate is actively diffusing upward from the higher salinity fluids below. This process produces pore fluids undersaturated with respect to metastable carbonate minerals, causing the precipitation of LMC and dolomite. Striking variations in the amount of LMC, HMC, aragonite, and dolomite also occur throughout the succession, with presumed sea-level lowstands characterized by increased HMC and the presence of dolomite.
As a result of disruption of the sediments during degassing, laboratory physical properties measurements are of limited value for developing a downhole stratigraphy. However, the NGR measurements were only affected to a minor extent and can be used to define three PP units. Physical properties Unit 1, from 0 to 130 mbsf, is characterized by three high-amplitude cycles superimposed on a rising trend. Physical properties Unit 2 occurs from 130 mbsf to the base of the uppermost Pliocene-Quaternary unit at 467 mbsf, which is marked by a sudden decrease in NGR values. This unit is characterized by low-amplitude, high-frequency cyclicity in NGR values. Physical properties Unit 3 corresponds to the lower Pliocene sediments below the seismic Sequence 2 boundary, which are also significantly denser than the Quaternary sediments.
Hole conditions were excellent for logging, with most caliper readings within 10 cm of bit size. Hole 1127B was logged with three tool strings: the triple combo and FMS/sonic to the mudline, and the GHMT to 59 mbsf. The triple combo was run without the nuclear source in the hostile environment lithodensity sonde because of safety concerns; consequently, density logs are not available for this site. During and after logging, close examination showed that there was no obvious damage to either the logging cable or tools from the limited H2S exposure. Cycles and surfaces seen in the high-quality FMS data correlate well with conventional logs (gamma ray, sonic, and resistivity) and indicate the presence of high-frequency cycles (10-20 m thick) in the lower part of the Quaternary-uppermost Pliocene succession. Simultaneous peaks on gamma-ray, resistivity, sonic, and susceptibility logs may reflect changes in sediment lithification throughout the logged section. Because of the high quality and uniform response of the sonic log, the WST was not deployed at this site. We anticipate that a check-shot survey at one of the other sites in this transect will provide appropriate drift control on the integrated sonic log.
Site 1128, the deep-water site of the Leg 182 shelf-to-basin transect, is located on the upper continental rise in 3874.4 m of water. The primary goals of this site were to (1) recover pelagic ooze from the upper continental rise to compile a paleoceanographic record of the Cenozoic opening of the Southern Ocean and development of the Circum-Antarctic Current, (2) determine the history of Cenozoic and Late Cretaceous CCD fluctuations and deep-water mass variations during the evolution of the Southern Ocean, and (3) determine depositional and diagenetic facies on the upper continental rise.
The sedimentary succession intersected at Site 1128 was divided into four major lithostratigraphic units. Unit I (0-95.6 mbsf) is a pink to brown, bioturbated, calcareous nannofossil ooze punctuated by numerous thin glauconite and planktonic foraminiferal sand calciturbidites and conglomeratic sediment gravity-flow deposits. A chaotic zone of debrites and slumped sediment (54.4-70.0 mbsf) separates this succession into three subunits containing variable proportions of resedimented material. Unit II (95.6-281.9 mbsf) is a thick section of uniform, green, variably calcareous clay and claystone that is locally interrupted, particularly in the upper parts, by several centimeter-thick turbidites composed of planktonic foraminiferal and nannofossil ooze. The relatively few carbonate particles in the sediment are etched and corroded, suggesting accumulation near the carbonate lysocline. The lower parts of this unit contain numerous well-preserved trace fossils (Planolites, Chondrites, Zoophycos, Terebellina, and Thalassinoides) and numerous thin chert horizons. A thin unit of green glauconitic sand to carbonate nannofossil ooze turbidites forms Unit III (281.9-284.0 mbsf) and marks a sharp change in sedimentation compared with the coarser, green, carbonate-free silts and clays of Unit IV (284.0-452.6 mbsf). Unit IV was subdivided into an upper Subunit IVA (284.0-358.4 mbsf) composed of bioturbated clayey siltstone with minor chert and glauconitic sand turbidites and Subunit IVB (358.4-452.6 mbsf) made up of pervasively burrowed sandy siltstone that grades to green silty sandstone at the base. The well-preserved siliceous microfossils and almost total lack of calcareous microfossils indicate accumulation below the CCD. The burrowed green sediment points to accumulation in dysoxic bottom waters.
Two major biostratigraphic successions were recovered at Site 1128 and dated by calcareous nannofossils and planktonic foraminifers as late Miocene-Quaternary (0-55 mbsf) and early Eocene-early Oligocene (72-427 mbsf). These intervals are separated by a debrite (55-72 mbsf) containing mixed upper Paleogene and Miocene nannofossils and planktonic foraminifers. Calcareous nannofossil data indicate four possible hiatuses within the Neogene succession, one of which is confirmed by planktonic foraminifer data at the upper/lower Pliocene boundary. A major unconformity beneath the debrite removed middle Miocene-upper Oligocene sediment (~15 m.y.). Below 72 mbsf, nannofossils and planktonic foraminifers show increasing signs of dissolution and are absent at some levels, suggesting deposition near the lysocline and CCD. Sedimentation rates were 10-12 m/m.y. through the Neogene, 50-60 m/m.y. in most of the early Oligocene, and 4 m/m.y. in the late Eocene. Although characterized by poor core recovery and barren intervals, datum levels from the older Eocene succession suggest a sedimentation rate of 40-45 m/m.y. Five benthic foraminiferal assemblages are distinguished: (1) a diversified Quaternary and Pliocene assemblage indicating abyssal paleodepths above the CCD, (2) a mixed assemblage of displaced faunas in the debrites, (3) an impoverished lower Oligocene-lower upper Eocene assemblage indicating lower bathyal to abyssal paleodepths close to the lysocline, (4) an impoverished lower upper to upper middle Eocene calcareous assemblage indicating lower bathyal to abyssal paleodepths close to the lysocline, and (5) an impoverished upper middle to upper lower Eocene agglutinated assemblage indicating deposition below the CCD.
Long-core measurements established a magnetostratigraphy for the uppermost 40 mbsf, spanning the Brunhes Chron, Matuyama Chron, and part of the Gauss Chron. Below this, the interval characterized by debris flows disrupts the record, and it is not possible to recognize a magnetostratigraphy until a depth of ~60 mbsf, where the record was correlated with the early Oligocene magnetic polarity time scale. A nonmagnetic APC coring assembly was used at this site and produced significant improvement in the declination record in shallow APC cores. Excellent records were obtained both with and without the nonmagnetic assembly toward the bottom of the intervals cored by the APC.
Construction of a composite depth section from Holes 1128B and 1128C indicates that a complete Quaternary through upper Miocene sedimentary record was recovered at Site 1128. A break in the record occurs at ~68 mcd, corresponding to the 17-m-thick debrite separating upper Miocene from lower Oligocene sediments. The numerous turbidites in the section aided correlation. The primary lithologic parameters used to create the composite section were MS, gamma-ray attenuation (GRA), wet bulk density, NGR emissions data acquired by the multisensor track (MST) on whole cores, and color reflectance data (400 nm) measured on split cores.
Only low concentrations of methane were detected (maximum of 6.0 ppm), with most samples having less than 3 ppm. Calcium carbonate content has a bimodal pattern with generally high values (75-90 wt%) present in the upper 50 mbsf, followed by a decrease to a low of 2.1 wt% at 138 mbsf. Between 138 and 240 mbsf, carbonate content increases to a second mode with a maximum value of 68 wt%, and then decreases downhole with very low values (0-1 wt%) below 353 mbsf. Organic carbon concentrations are generally less than 0.16 wt% down to the base of Hole 1128B. Organic carbon values are 0 wt% from 200 to 276 mbsf, and headspace methane concentrations in this depth range are near background. Sulfur is present in only five samples in Hole 1128B, with values ranging from 0.05 to 0.21 wt%. Nitrogen is not detectable in any sample.
Site 1128 does not appear to be influenced by the high-salinity pore fluids observed at Sites 1126 and 1127. With the exception of the lower part of the cored interval, salinities are close to normal seawater values throughout. As a consequence of slow rates of deposition and low concentrations of organic material, pore fluids are not significantly depleted in sulfate in the upper sediments, and rates of carbonate recrystallization are relatively low. Two significant changes in pore-water chemistry occur at Site 1128: the first at 20-40 mbsf, and the second between 236.8 and 253.3 mbsf. The change in pore-water chemistry at the shallow depth is manifest as an abrupt decrease in silica concentration from values of ~570 to 350 mM, corresponding to a slump unit. Seismic imagery indicates that this unit outcrops at the seafloor, so it is possible that bottom water has infiltrated the formation to cause this effect. The second major change in pore-water chemistry, accompanied by a decrease in salinity, is evident in most of the major and minor cations and occurs in the interval between lithostratigraphic Units II and IV. Concentrations of Mg2+, K+, SO42-, and Na+ show a marked decrease, whereas Li+, alkalinity, and Ca2+ increase. Although the change in salinity is accompanied by a decrease in Cl-, this decrease is not of the magnitude expected from the salinity decrease alone, indicating that a portion of the salinity decrease is a result of the removal of cations and anions through precipitation and adsorption. Downhole logs indicate the presence of numerous relatively impermeable layers in the interval between lithostratigraphic Units II and IV, which would effectively limit vertical diffusion between these two units and allow them to geochemically evolve relatively independently of each other. The sediments in lithostratigraphic Unit IV contain very low concentrations of carbonate minerals, and reactions leading to the enrichment and depletions in the pore-water constituents principally involve clay minerals.
Sediment physical properties data at Site 1128 closely reflect lithologic variations observed in the recovered sediments and provide essential data for core-log correlation. Physical properties data were divided into five units on the basis of trends in the measured parameters. Physical properties Unit 1 (0-70 mbsf) is characterized by high variability in all datasets, corresponding to the lithologic sequence of turbidites and debris flows interbedded with nannofossil ooze. The base of this unit is marked by abrupt shifts in all parameters measured. Physical properties Unit 2 (70-139 mbsf) is characterized by low variability in all datasets, punctuated by a number of distinct data offsets (1-5 m thick) corresponding to sharply bounded intervals of redeposited nannofossil ooze. Physical properties Unit 3 (139-231 mbsf) is an interval characterized by relatively low and nearly constant values for all parameters, corresponding to a sequence of monotonous clays. An increase in NGR, MS, GRA, and discrete P-wave velocity and a decrease in porosity is observed at the upper boundary of PP Unit 4 (231-363 mbsf), below which all parameters display increased variability reflecting alternations of indurated and nonindurated sediments. The upper boundary of PP Unit 5 (363-452 mbsf) is marked by a negative shift in GRA, MS, and NGR, corresponding to the transition into lithostratigraphic Subunit IVB. Other than porosity, which decreases through the unit, the parameters measured show constant downhole trends for the remainder of the recovered interval.
Site 1128 was successfully logged with the triple combo and FMS/sonic tools. As a result of time constraints, the GHMT and WST tools were not run. Downhole logging data were divided into four units, with trends closely correlating with lithologic and sediment physical properties data. Logging Unit 1 (0-242 mbsf) is characterized by uniform values, punctuated by sharp decreases in gamma-ray values and increases in density and resistivity apparently corresponding to intervals of redeposited nannofossil ooze. Logging Unit 2 (242-295 mbsf) is characterized by high variability in all data sets, corresponding to an interval of high variability in sediment physical properties data and an interval of variable lithification in cores. The lower part of this unit corresponds to lithostratigraphic Unit III and consists of nannofossil ooze interbedded with variably indurated sandstone turbidites. These interbedded sediments are reflected in logging data as alternations of low gamma-ray, high-density, and resistive intervals corresponding to calcite-rich layers, and high gamma-ray, low-density, and conductive intervals corresponding to sandstones. Logging Unit 3 (295-362 mbsf) has low variability and nearly constant values on all logs except the gamma ray, which increases downcore. Increased concentrations of thorium and potassium correspond to an increased concentration of terrigenous sediment. Logging Unit 4 (363-414 mbsf) has minimal variability in most parameters, with the exception of cyclic variations in gamma-ray values. Downhole measurements from Unit 5 indicate the presence of clays and quartz through the unit.
Site 1128 provided the first opportunity to sample and establish a seismic stratigraphy for this thick (containing more than 10 km of sediment) and laterally extensive continental rise basin. Seismic imagery shows that the thin (72 m), relatively condensed Neogene section (largely corresponding to lithostratigraphic Unit I) was deposited in a small perched sub-basin lying within a thick Paleogene and Mesozoic succession and that the Neogene sequence is thin or absent over much of the basin. Exposed Mesozoic sediments on the middle and lower slope are the presumed source of lithified material commonly present within resedimented intervals. Although not intersected because of operational time constraints, a prominent angular unconformity ~150 m below total depth at Site 1128 almost certainly marks the base of the Cenozoic succession. Apart from hiatuses between the lower and middle Eocene and the Oligocene and Miocene, Site 1128 results indicate that the upper part of this basin contains a thick, almost continuous biosiliceous record of Southern Ocean development through the Paleogene.
Site 1129 was the third and proximal site of a three-site transect through a set of upper Neogene clinoforms immediately seaward of the present-day shelf edge. Site 1129, located just seaward of the shelf edge in 202.5 m of water, intersects a more expanded record of the oldest part of the clinoform sequence. The principal objective of this transect was to collect detailed, high-resolution profiles through a late Neogene shelf edge (high energy) to upper slope (low energy) succession deposited within a cool-water carbonate environment, to determine the response of this type of depositional system to Pliocene-Quaternary sea-level fluctuations.
The succession recovered at Site 1129 is 604.2 m thick (Table T2) and was divided into three lithostratigraphic units. Unit I (0-149.8 mbsf) consists mainly of unlithified bryozoan floatstone to rudstone and bioclastic packstone to grainstone, with abundant bryozoan fragments. The floatstone and rudstone are pale yellow to light gray, with a poorly sorted, very fine to medium sand-sized bioclastic packstone matrix. The floatstone and rudstone contain abundant granule- to pebble-sized bryozoan fragments exhibiting highly diverse growth forms. The bioclastic packstone to grainstone is pale yellow, light gray, and light olive gray and consists of very fine to fine sand-sized bioclasts together with coarse sand- to granule-sized bryozoan fragments. The unit is divided into five subunits, each forming a package grading upward from bioclastic packstone at the base to bryozoan floatstone and rudstone at the top. We infer that each subunit represents an individual mound-building episode. Unit II (149.8-556.7 mbsf) consists of light gray, light olive gray, and gray bioturbated bioclastic packstone and minor grainstone and wackestone with four nannofossil chalk intervals. Lithification increases from unlithified sediments at the top of Unit II to partially lithified sediment with well-lithified chalk intervals at the base. The upper part of Unit II is dominated by very fine to fine sand-sized, generally well-sorted, massive bioclastic packstone with subordinate grainstone and wackestone. The lower part is characterized by muddy bioclastic mudstone, wackestone, and packstone with abundant well-defined burrows. Unit II therefore exhibits an overall coarsening-upward trend. Unit III (556.7-604.2 mbsf), with very poor recovery, consists of dolomitized, fine sand-sized bioclastic grainstone and chert fragments. It is likely that the chert fragments represent thin beds and lenses of preferentially silicified wackestone/ooze. The boundary between Units II and III is sharp and represents a major hiatus.
Site 1129 contains two biostratigraphic units: (1) an expanded Quaternary section more than 554 m thick that is underlain by a thin and conformable uppermost Pliocene section, and (2) a middle-lower Mio-cene section. These units are separated at 556 mbsf by an unconformity representing ~12 m.y., marked by a bryozoan turbidite overlying indurated sediments and chert layers. Calcareous nannofossils are generally abundant and moderately well preserved in the upper part of the section, but below 371 mbsf the preservation is poor. The preservation and abundance of planktonic foraminifers degrade more rapidly downhole than that of the nannofossil assemblages. Below ~68 mbsf, most characteristic features of foraminifers are obscured by carbonate cement and recrystallization. Benthic foraminifers are generally abundant and well preserved in the upper part of Hole 1129C. At a depth of ~140 mbsf, preservation and abundance deteriorate markedly. Three main assemblages are recognized at Site 1129: (1) a distinctive, well-preserved Quaternary assemblage found in bryozoan-rich accumulations (down to ~140 mbsf), (2) a Pleistocene-upper Pliocene assemblage (140-557 mbsf) that includes a variable redeposited neritic component, and (3) a sparse Miocene assemblage below ~560 mbsf. The two Quaternary-upper Pliocene assemblages indicate upper bathyal paleodepths, whereas the Miocene assemblage indicates an upper to middle bathyal paleodepth.
Long-core measurements of Hole 1129C sediments revealed an extensive interval of normal magnetization to a depth of ~340 mbsf. Sediments record reverse polarity magnetizations below that depth, with the boundary best defined by measurements on discrete samples. This reversal is interpreted as the Brunhes/Matuyama boundary. In Hole 1129D, a long interval of predominantly reverse polarity magnetizations to a depth of ~540 mbsf is interpreted as the upper part of the Matuyama Chron (C1r). The Jaramillo Subchron (C1r1n) is recorded in both holes at depths of ~400-440 mbsf. Normal polarities are recorded again in Hole 1129D at depths of 540-550 mbsf, possibly representing the Olduvai Chron (C2n). This would indicate a variable sedimentation rate, with the late Quaternary sedimentation rate nearly triple that of the early Pleistocene-latest Pliocene. Rock magnetic characteristics, such as near saturation with inductions of 400 mT and median destructive fields of the IRM of 20-40 mT, suggest that magnetite and possibly magnetic sulfides are the principal remanence carriers. ARM/IRM indicate a high relative abundance of single-domain grains, possibly biogenic magnetite.
High concentrations of CH4 and H2S through much of the section are a major feature at Site 1129. Methane and H2S concentrations at this site fall between the levels found at Sites 1127 and Site 1131. Calcium carbonate content is uniformly high, primarily in the range of 86-94 wt%. Organic carbon concentrations generally vary from 0.4 to 0.7 wt%.
Site 1129, like many other sites drilled during Leg 182, is influenced by the presence of high-salinity pore fluids within and below the cored interval. Within the cored interval, the presence of pore waters with Na+/Cl- ratios significantly higher than seawater indicates the influence of fluids that have been involved in the precipitation and dissolution of halite. Site 1129 was characterized by high rates of SO42- reduction of organic material and consequent production of alkalinity. The absence of significant iron concentrations resulted in a pH less than 6. Although high concentrations of H2S and high alkalinity values were measured at relatively shallow depths, significant SO42- reduction did not occur until below 100 mbsf. This suggests that H2S is diffusing from the underlying sediments into the overlying oxic sediments, where it is oxidized to SO42-. Rates of carbonate alteration reflected in the Sr2+ concentration (>2 mM) were the highest yet observed during Leg 182. Dolomite is ubiquitous below a depth of 70 mbsf and reached values as high as 24 wt%.
Physical properties measurements at Site 1129 correlate well with lithologic changes observed in the sedimentary section and provide an important data set for core-log correlation. In general, Site 1129 is characterized by significant variations in NGR and GRA bulk density. In general, variations are less marked in P-wave velocity, porosity, and other physical properties data. A well-defined cyclicity is present in the NGR record and can be correlated with the downhole gamma-ray logs and NGR records from Site 1127 and 1131. Physical properties data were divided into three major units. Physical properties Unit 1 (0-40 mbsf) is characterized by a rapid increase in NGR, as observed at most other Leg 182 sites. The base of this unit coincides with the top of the three bryozoan mound sequences, which form the lower part of litho-stratigraphic Unit I. P-wave velocity and bulk density also increase with depth toward the base of this unit. Physical properties Unit 2 (40-258 mbsf) is characterized by a uniformly high NGR with some cyclic variations and by a slight increase in GRA bulk density and P-wave velocity. A significant offset to higher values of P-wave velocity and bulk density can be seen at 90 mbsf in PP Unit 2. Physical properties Unit 3 (258-558 mbsf) is characterized by increasing P-wave velocity (1650-2450 m/s) and bulk density and decreasing porosity, which reflects the increasing induration of the succession. Below 558 mbsf, core recovery was too low for physical properties characterization of the deeper part of the sedimentary section.
Hole 1129D was successfully logged with three logging-tool strings. The triple combo produced very good results, except for the interval between 360 and 460 mbsf where the porosity log was affected by excessive borehole rugosity. The log patterns are very similar to those from Hole 1131A; the uranium gamma-ray log showed distinct cyclicity in the lower part of the Quaternary sequence with 18-20 individual cycles, each measuring 10-20 m in thickness. Chalk layers and firmgrounds in the Quaternary succession, as indicated by the conventional logs, are clearly imaged by FMS data. The FMS data also provide a detailed picture of the thickness distribution of thinly bedded cherts (~20 cm) and carbonates (1-2 m) in the middle upper Miocene succession, where recovery was very poor.
The high-resolution site survey seismic data at Site 1129 clearly images the bryozoan mound complex within lithostratigraphic Unit I and shows that this or similar mound complexes have existed at and immediately below the shelf edge throughout the Pleistocene. A combination of the results from Sites 1129 and 1131, now correlated with the recognition of a distinctive motif on seismic data, confirms that development of extensive bryozoan mound complexes has been one of the characteristic features of Quaternary cool-water carbonate sedimentation across a large area of the western Great Australian Bight.
Site 1130 was located to intersect and characterize Neogene cool-water carbonate shelf edge sequences and the nearshore portion of a Paleocene?-middle Eocene progradational siliciclastic wedge (seismic Sequences 2, 4, and 6A). The principal objectives were to (1) recover a detailed record of siliciclastic progradation and aggradation to evaluate the complex interaction among Paleogene sea-level fluctuations, accommodation space, and subsidence; (2) determine the facies characteristics, sea-level response, and paleoceanographic history of a Neogene cool-water carbonate succession in a shelf edge setting; and (3) evaluate diagenetic history and processes within the Neogene facies in a shelf edge setting.
The sediments recovered at Site 1130 were divided into four major lithostratigraphic units. Unit I (0-261.43 mbsf) is a light gray to pale olive, strongly bioturbated, unlithified to partially lithified bioclastic packstone. This succession is punctuated by unlithified bioclastic wackestone layers and occasional nannofossil foraminiferal ooze to chalk intervals. The upper part of this unit is characterized by a repetitive uphole textural change from matrix-supported to grain-supported sediment. Lighter intervals in the otherwise monotonous packstones are fine grained and foraminifer rich, whereas the generally coarser and darker intervals contain more bioclasts. The lower part of Unit I is typified by gradual color changes ranging from light gray to olive gray with a few abrupt transitions. Soft sediment deformation structures interpreted as slumps are present at the base of Unit I. Unit II (261.43-328.86 mbsf) is dominated by strongly bioturbated, white to light gray nannofossil foraminiferal chalk with a wackestone to packstone texture. Disseminated black grains (pyrite, glauconite, and other unidentifiable grains) are scattered throughout the unit. Unit III (328.86-369.50 mbsf) consists of chert layers (silicified nannofossil planktonic foraminiferal ooze) interbedded with intervals of white nannofossil planktonic foraminiferal ooze. The light to dark gray, partially translucent chert fragments contain burrows filled with white, fine-grained, lithified planktonic foraminiferal packstone to grainstone. Unit IV (369.50-386.51 mbsf) is dominantly a calcareous sandstone, but with compositional and textural variability encompassing red bioclastic glauconitic wackestone; sandy bryozoan grainstone; pink, coarse-grained bivalve grainstone; and red, very coarse grained calcareous sandstone.
Calcareous nannofossils and planktonic foraminifers indicate that three biostratigraphic successions were recovered at Site 1130: (1) Quaternary-upper Miocene (0-327 mbsf), (2) upper-middle Oligocene (327-~355 mbsf), and (3) a sandy limestone of unknown age from the bottom of Holes 1130A and 1130C. Preliminary results indicate that the upper part of the lower Pliocene is missing (>1 m.y.) and that the major disconformity between upper Miocene and Oligocene sediments represents a hiatus of at least 15 m.y. The sedimentation rate for the middle-upper Oligocene was 10-30 m/m.y., although this should be viewed with caution because of poor core recovery. The rate fluctuated between 15 and 30 m/m.y. during the Pliocene-Miocene and reached as high as 240-260 m/m.y. during most of the Quaternary. The three benthic foraminiferal assemblages recognized correspond respectively to the Oligo-cene, early Pliocene-late Miocene, and Quaternary-late Pliocene, and indicate a shallowing-upward trend during these time periods. The Oligocene and lower Pliocene-upper Miocene assemblages are typically cosmopolitan, middle bathyal assemblages, whereas the Quaternary-upper Pliocene contains a mixed assemblage representing upper bathyal paleodepths and containing many well-sorted specimens from shelf environments.
Long-core measurements revealed an extended interval of normal magnetization and then a sharp reversal to normal polarity at 199.9 mbsf, interpreted as the Brunhes/Matuyama boundary. Intensities of magnetization varied from 0.01 to 1 mA/M with an overall decreasing trend downhole. Within this general trend are fluctuations with dominant wavelengths of a few tens of meters. The ratio of ARM/IRM, a measure of the relative importance of single-domain to multidomain behavior, decreases downcore, suggesting that the role of biogenic magnetite diminishes. Coupled with the decrease in magnetization, this strongly suggests that fine-grained magnetite of biogenic origin is preferentially dissolved.
An experimental nonmagnetic cutting shoe was used for alternate cores between Cores 182-1130A-3H and 7H, and an entire nonmagnetic core-barrel assembly was used on Cores 182-1130B-3H to 7H. Both the nonmagnetic shoe and core-barrel assembly produced reductions in radial component contamination, but the effects were not as dramatic as at Site 1128.
Construction of the composite section from Holes 1130A and 1130B indicates that a continuous sedimentary record was not recovered at Site 1130. Low recovery in Core 182-1130A-3H and no recovery in Core 182-1130B-3H produced a gap at 22-24 mbsf. The record below this is apparently continuous to ~191 mcd (all Quaternary), at which depth core overlap becomes minimal to nonexistent, disrupting continuity of the spliced section. The primary lithologic parameters used for correlation at Site 1130 were NGR emissions and the 700:400 nm ratio of color reflectance data.
Only low concentrations of CH4 were detected, with most samples containing <7 ppm (maximum = 11.3 ppm). Calcium carbonate content ranges from 80.9 to 93.2 wt% in lithostratigraphic Units I and II, with most samples varying between 85 and 90 wt%. No carbonate analyses were conducted in Units III and IV (328.9-386.51 mbsf) because of low core recovery.
Site 1130 is influenced by high-salinity pore fluids, as was the case at Sites 1126 and 1127. The maximum rate of salinity increase, 5.7/m, is the highest observed during Leg 182. The steep gradient down to ~32 mbsf and then the constant salinity concentration (83) below suggest nonsteady-state conditions. In contrast to Site 1127, the SO42- reduction zone is incomplete and confined to the upper part of the profile, and the degree of SO42- reduction is ~40% less than at Site 1127. These differences are probably caused by a lower initial organic carbon content at Site 1130. As a consequence of the decreased sulfate reduction activity, interstitial waters are saturated with respect to SrSO4 (celestite), limiting pore-water Sr2+ concentrations.
Sediment physical properties data closely reflect Oligocene-Holocene lithologic variations observed in recovered sediments and downhole logging data. Three physical properties units were recognized, primarily on the basis of trends in NGR. The homogenous bioclastic packstones of PP Unit 1 (0-43 mbsf) are characterized by low variability in all measured parameters. The large increase in NGR from 5 to 35 cps at the base of PP Unit 1 does not correlate to any lithologic change but is roughly coincident with an increase in P-wave velocity variability, suggesting that it results from diagenesis. Physical properties Unit 2 (43-254 mbsf) is dominated by cyclic variations in NGR that appear to be related to Milankovitch cyclicity on a 100-k.y. frequency from 43 to 175 mbsf and on a higher 41-k.y. frequency for the remainder of the unit. This change in frequency occurs near the Brunhes/Matuyama boundary and is clearly seen in downhole logging data from this site. From 199 to 254 mbsf in PP Unit 2, increased variability in P-wave velocity reflects the presence of a series of firmgrounds observed in the recovered sedimentary section. The upper boundary of PP Unit 3 (254-335 mbsf) correlates well with a distinct change in lithology (lithostratigraphic Unit II) from packstone/wackestone to nannofossil oozes and chalks. NGR and P-wave velocity show low variability within PP Unit 3, whereas bulk density shows a general increasing trend.
Three large-scale units were identified in downhole logging data from Hole 1130C, based on shifts in conventional and FMS logs, with boundaries at 258 and 329 mbsf. The interval above 258 mbsf is characterized by a near-constant background level of gamma radiation of 20 American Petroleum Institute (API) units, with individual spikes reaching 40-45 API. The boundary at 260 mbsf is defined at a sharp downhole decrease in the uranium gamma-ray log, and the boundary at 329 mbsf corresponds to the change from carbonate sediments above to siliciclastic deposits below.
Integration of the various data sets with the regional seismic stratigraphic interpretation provides a sequential record consisting of the seismic Sequence 7 Eocene? progradational wedge deposited at shelf water depths; overlain after an indefinite hiatus by deep-water, seismic Sequence 6A upper Oligocene oozes that have since been irregularly silicified. The record then contains another hiatus of ~20 m.y., before deposition of upper Miocene-lower Pliocene seismic Sequence 3 oozes, capped by a packstone unit, as a continuation of a shallowing-upward trend. A further short hiatus was then followed by rapid deposition of a thick sequence of seismic Sequence 2 Quaternary wackestones and packstones at upper slope/shelf edge depths.
Site 1131 was the second and intermediate site of a three-site transect through a spectacular set of upper Neogene clinoforms immediately seaward of the present-day shelf edge. Site 1131, located on the upper slope in 332.4 m of water, intersected a more expanded record of the middle part of the clinoform sequence. The principal objective of this transect was to collect detailed, high-resolution profiles through an upper Neogene shelf edge (high energy) to upper slope (low energy) succession deposited within a cool-water carbonate environment, and to determine the response of this type of depositional system to Pliocene-Quaternary sea-level fluctuations.
Three major lithostratigraphic units were identified at Site 1131. Unit I (0-25.0 mbsf) consists dominantly of bioclastic packstone, floatstone, and rudstone. The upper part of Unit I is composed of a massive, homogeneous, light gray to olive gray, unlithified bioclastic packstone that includes a significant bryozoan component. The lower part of Unit I is a heterogeneous interval of unlithified bryozoan floatstone and rudstone punctuated by thin (decimeter scale) layers of wackestone, packstone, and grainstone. Unit II (25.0-531.7 mbsf) consists of a very thick (>500 m), homogeneous succession of light gray to olive-gray bioclastic packstone, grainstone, and wackestone. In general, lithification and diversity of the bioclastic component increase downhole. Unit III (531.7-607.4 mbsf) is separated from Unit II by an unconformity representing a major hiatus. Below the unconformity, recovery was incomplete in a succession consisting of dark gray, silicified nannofossil ooze beds or lenses within olive-gray partially to strongly lithified bioclastic grainstone containing blackened grains and glauconite.
Two biostratigraphic successions were identified at Site 1131: (1) an expanded Quaternary interval more than 510 m thick underlain by a thin and conformable uppermost Pliocene interval and (2) a middle and lower Miocene section lacking hiatuses within the resolution of available biostratigraphic data. These successions are divided by a disconformity at 532 mbsf that spans ~10 m.y. An environmental crisis produced an unusual nannofossil assemblage dominated by B. bigelowii near the base of Zone NN19 at ~522 mbsf. A similar event was observed in the same stratigraphic interval at Site 1127. Carbonate microfossils, especially foraminifers, were strongly affected by overgrowths, cementation, and recrystallization below 60-100 mbsf. These effects are consistent with the pore-water geochemistry and the onset of lithification. One main Quaternary-uppermost Pliocene upper bathyal assemblage of benthic foraminifers is recognized above 100 mbsf. This assemblage also contains a large proportion of small neritic tests (63-150 µm), probably redeposited from the shelf. Well-preserved benthic foraminifers, including a high proportion of large specimens (>1 mm), are found together with well-preserved bryozoans down to 25 mbsf. Poor preservation prevented detailed faunal analysis below 100 mbsf.
Magnetic measurements of archive-half cores established a magnetostratigraphy to a depth of 320 mbsf, which includes the Brunhes and uppermost Matuyama Chrons. Below this, drilling disturbance disrupted the record and no further magnetostratigraphic data were obtained. Rock magnetic properties show minimum downhole variability and are consistent with single-domain biogenic magnetite, except for cores between 70 and 150 mbsf that display the typical behavior of ultrafine-grained (superparamagnetic) greigite. Magnetic susceptibility is dominated by contributions from the diamagnetic carbonate matrix.
Composite section construction from Holes 1131A and 1131B indicates that a continuous record was not recovered. Overlap between cores in adjacent holes was maintained to ~55 mcd, until poor recovery in Core 182-1131C-6H resulted in a short (few centimeters) data gap. Below 70 mbsf, low recovery from extended core barrel cores resulted in reduced core overlap and prohibited splicing below 78 mcd. The primary parameters used for correlation were NGR emissions, GRA bulk density, and color reflectance. Comparison of data between holes revealed a low degree of similarity, making correlations difficult.
The most striking organic geochemical results from Site 1131 were the high concentrations of CH4 and H2S in the upper part of the section. In comparison to Site 1127, gas pockets were less abundant, and the concentration of CH4 in both gas pockets and headspace samples at Site 1131 was lower. Hydrogen sulfide concentrations, however, were comparable at both sites. Atypically, C1/C2 ratios first increase then decrease with increasing depth in Hole 1131A, essentially mirroring the methane profile as C2 varies little throughout the section. Calcium carbonate content is uniformly high (86-94 wt%). Organic carbon is less than 0.4 wt% down to 125 mbsf, with higher values (as much as 1.0 wt%) at greater depths.
Site 1131 exhibited inorganic geochemical features similar to those at Site 1127, with the exception of more extreme changes in pore-water geochemistry profiles because of increased degradation of organic material. For example, alkalinity reached a maximum value of 137 mM, compared to 106 mM at Site 1127. In contrast to Site 1127, although there was significant depletion in the concentration of SO42-, measurable concentrations remained even in the zones of highest alkalinity, suggesting that organic material was the limiting factor in the production of H2S at Site 1131. Excess SO42- in the upper portion of the core suggests that the oxidation of H2S originated lower in the section. In the upper 300 m, depletion in the concentrations of Ca2+ and Mg2+ and enrichment in Sr2+ indicate a recrystallization of aragonite and HMC. This was confirmed by mineralogical analyses, which showed that HMC had disappeared by 50 mbsf. Aragonite gradually decreased with increasing depth and vanished at the Pliocene/Pleistocene boundary. Ratios of Na+/Cl- were in excess of the ratio in seawater throughout the Quaternary section, indicating that the high-salinity fluids had participated in the precipitation and dissolution of halite.
Physical properties measurements at Site 1131 correlate well with lithologic changes observed in the sedimentary section and provide the basic data for core-log correlation to reconstruct poorly recovered intervals. Correlation of downhole gamma-ray logs with NGR data from the MST indicates that moderate to poor recovery at Site 1131 may have aliased and concealed in cores the cyclic fluctuations that are clearly visible on downhole logs. Physical properties data indicate that the cored interval is divisible into two units. Physical properties Unit 1 (0-31 mbsf) is mainly defined by a large increase in NGR toward the base of the unit, corresponding to the lower limit of the bryozoan floatstone/rudstone comprising lithostratigraphic Subunit IA. This NGR peak is also observed on downhole logs, with spectral gamma data indicating that it reflects uranium content and, accordingly, is either the result of increased organic matter content or carbonate diagenesis. P-wave velocity and bulk density also increase toward the base of this unit. Physical properties Unit 2 (31-532 mbsf) is characterized by gradual increases in porosity, P-wave velocity, and bulk density, primarily reflecting increased compaction, but also showing data excursions corresponding to coarser and more lithified horizons. More indurated layers within the generally homogenous sediments of PP Unit 2 have increased velocities and bulk densities and generally lower NGR. Below 532 mbsf, core recovery was too low for physical properties characterization of the deeper part of the sedimentary section.
Three logging-tool strings were deployed in Hole 1131A. Downhole logging data indicate that the uppermost part of the cored section (0-28 mbsf) correlates with bryozoan-rich horizons described in core. As was noted with the physical properties data, a uranium peak at the base of this unit reflects increased organic content and/or carbonate diagenesis and may represent a firmground. The remainder of the cored section to 575 mbsf contains porosity-density crossovers that coincide with low PEF values and high resistivity and sonic values. These crossovers are interpreted as probable chert layers. In contrast, low-porosity peaks associated with density, PEF, sonic, and resistivity peaks may represent possible firmgrounds.
Integration of coring results with high-resolution site survey seismic data at Site 1131 confirms that the mounded features visible in the uppermost part of the seismic section are in fact bryozoan-dominated mounds. The spectacular clinoform geometry corresponding to the remainder of the cored interval consists of bioclastic packstone, grainstone, and wackestone, with variable lithification as the dominant factor controlling seismic data amplitude and impedance variability. The lithostratigraphic and biostratigraphic boundary toward the base of the section coincides with a major regional unconformity and the base seismic Sequence 2 sequence boundary.
Site 1132 was located to intersect and characterize Neogene cool-water carbonate shelf edge sequences and the nearshore portion of a Paleocene?-middle Eocene progradational siliciclastic wedge (seismic Sequences 2, 3, 4, and 6A). The principal objectives were to (1) recover a detailed record of siliciclastic progradation and aggradation to evaluate the complex interaction among Paleogene sea-level fluctuations, accommodation space, and subsidence; (2) determine the facies characteristics, sea-level response, and paleoceanographic history of a Neogene cool-water carbonate succession in a shelf edge setting; and (3) evaluate the diagenetic history and processes within the Neogene facies in a shelf edge setting.
The recovered succession was divided into six lithostratigraphic units. Unit I (0-113.5 mbsf) consists of bryozoan floatstone and rudstone, alternating with bryozoan packstone and, in the lower part, also bioclastic wackestone with bryozoans. The abundant bryozoan fauna are highly diverse and include a great variety of growth forms. The sediments are unlithified and burrow mottled, and the color is dominantly light gray with thinner pale olive and white intervals. This unit represents a major bryozoan mound complex. Unit II (113.5-158.3 mbsf) consists of uniform bioclastic packstone with a great diversity of bryozoan growth forms. The color is light gray, with minor light olive gray and white intervals. The sediment is burrow mottled and mainly unlithified, but thin, partially lithified beds are present between 130 and 140 mbsf. Unit III (158.3-250.70 mbsf) consists of unlithified bioclastic packstone and minor wackestone and grainstone, with an interbedded thin package of foraminiferal ooze and chalk. The unit is strongly burrowed and mainly unlithified down to 168 mbsf and partially lithified below that level. The color is dominantly light olive gray with thinner olive, pale olive, and white intervals. Several prominent firmgrounds are the basis for subdivision into five subunits. Unit IV (255.80-437.33 mbsf) was poorly recovered; however, available data suggest that it consists of bioclastic packstone and grainstone with an interval of nannofossil foraminiferal chalk partially replaced by nodular, light to dark gray chert. Unit V (441.50-517.70 mbsf) is also characterized by poor recovery, but recovered material indicates that it consists of bioclastic packstone and grainstone and lacks chert. Glauconite is abundant, and the colors vary between very pale brown and pale yellow. Unit VI (517.70-555.95 mbsf) is topped by a prominent mineralized hardground and consists of lithified bioclastic packstone and wackestone. It differs from overlying units in its color, prominent firmgrounds and hardgrounds, solution seams, and centimeter-sized bioclasts. The color is pale yellow at the top and passes downward into light gray, pale yellow, red yellow, to pale red and dark red at the bottom. The lowest recovered bed contains pebbles of siliciclastic sandstone rich in lithic fragments.
Calcareous nannofossils and planktonic foraminifers indicate that drilling at Site 1132 recovered a thick Quaternary-Eocene sequence (~550 m thick) overlying a relatively thin, barren section (~45 m). Calcareous nannofossils from the basal Quaternary-uppermost Pliocene unit registered a nannofossil event, the "Braarudosphaera Event" previously recorded at Sites 1127, 1130, and 1131, indicating a dramatic short-lived change in surface-water conditions over a large geographic area. The thick Quaternary-uppermost Pliocene section (~235 m) contains combined Zones NN21-NN20 and Zone NN19, and the thick middle Miocene section (~300 m) contains Zones NN6 and NN5-NN4. These sections are separated by a thin interval (~20 m) with poor core recovery. Hiatuses are likely within this thin interval, where the recovered nannofossils and planktonic foraminifers suggest late Miocene age. Another similarly thin interval (~20 m) with poor core recovery, which is also likely to contain hiatuses, is recorded between the middle Mio-cene section and the underlying mainly lower Oligocene section. Fossils of early Miocene age were reported in this condensed unit. An Eocene age is indicated for the section underlying the lower Oligocene, based on thin-section analysis of two samples at ~530 and ~547 mbsf, respectively. A sharp change in sedimentation rates corresponds to the condensed interval between Quaternary-upper Pliocene and middle Miocene sections. The Quaternary-uppermost Pliocene section registered an average sedimentation rate of 175 m/m.y., whereas the middle Miocene showed an average rate of 20 m/m.y. Another condensed section between the middle Miocene and Oligocene successions is indicated by the sparse biostratigraphic datums through this interval. Four main benthic foraminiferal assemblages are identified. These indicate an upper to middle bathyal paleodepth for the Pleistocene-Oligocene section. In the Pleistocene, a striking, well-preserved assemblage characterized by many large (>1 mm) agglutinated foraminifers is found within bryozoan-rich accumulations. This assemblage probably reflects a diverse, highly dynamic ecosystem that became established at the seafloor at various times during the Quaternary, corresponding to episodes of bryozoan mound growth. Changes in the composition of this assemblage may relate to sea-level or circulation fluctuations.
The Brunhes/Matuyama boundary was found at ~180 mbsf, yielding a sedimentation rate of ~230 m/m.y. above this level. There were indications of the same intensity fluctuations observed at earlier sites; therefore, there is a possibility of high-resolution stratigraphy within the Brunhes Chron after further shore-based work. The top of the Jaramillo Subchron was found at 230 mbsf, which is consistent with this sedimentation rate. Magnetic anomalies were found associated with hardgrounds with mineralized crusts and with lithified skeletal limestones. In some cases, this suggests that diagenesis occurred extremely early, within 100,000 yr after deposition.
As at Sites 1126, 1128, and 1130, only low concentrations of CH4 were detected at Site 1132. Of the four sites, Site 1132 has the highest CH4 content, with a maximum value of 54 ppm. Unlike the other low-methane sites, H2S is present at Site 1132 in low concentrations. Calcium carbonate content is between 85 and 95 wt%, with values at the higher end of the range near the surface and declining gradually toward the lower end of the range with depth. Organic carbon values are primarily in the range of 0.3-0.6 wt%. Nitrogen concentrations are all less than 0.1 wt%, and sulfur is present at low concentrations in only a few samples in the upper 90 mbsf.
Site 1132 is influenced by the presence of high-salinity fluids, as is the case with all previous Leg 182 sites except 1128. However, unlike the adjacent Site 1130, the rate of salinity increase with depth is uniform and shows no evidence of nonsteady-state conditions. Site 1132 possibly had an initially higher organic carbon content, producing slightly higher SO42- reduction rates and a more extended SO42- reduction zone. As a result, carbonate diagenesis is more active, causing carbonate precipitation in the upper part of the profile, whereas the lower part is characterized by carbonate dissolution. As with Site 1131, Site 1132 displays a Na+/Cl- anomaly in the upper part of the profile. Site 1132 is characterized by a constant seawater composition of both conservative and nonconservative interstitial water constituents in the upper 30 mbsf, suggesting active flushing with seawater. With the completion of the slope transect from Site 1130 to 1132, we can draw initial conclusions about the horizontal distribution of brine in this area. It appears that salinity values at Sites 1130 and 1132 stabilize at about the same depth below the sea surface, suggesting a horizontal top of the main brine body at ~520 mbsl.
High-quality NGR and GRA bulk density data were obtained from the MST. Variations of NGR and GRA bulk density, supplemented by index properties measurements of porosity and thermal conductivity, form the basis for the five physical properties units recognized at Site 1132. Physical properties Unit 1 (0-5 mbsf) is characterized by very low (<5 cps) NGR and a high initial bulk density (>1.9 g/cm3), which declines rapidly with depth. This unit corresponds to a thin package of grainstones that caps lithostratigraphic Unit I. Physical properties Unit 2 (5-140 mbsf) displays an overall increase in bulk density with depth (1.65-1.90 g/cm3). There is a corresponding decrease in porosity from 55% to 43%, but with considerable variation probably associated with lithologic variability. High-amplitude cyclic variation in both NGR (>20 cps) and bulk density (0.2 g/cm3) is also observed throughout this unit. Physical properties Unit 3 (140-248 mbsf) is characterized by a decline with depth in GRA bulk density and porosity and by a continued but more regular cyclicity in both NGR and GRA bulk density. Physical properties Unit 4 (~248-520 mbsf) is recognized solely on the basis of a change in NGR from 25 to <5 cps at 248 mbsf. Similar characteristics are present in limited core recovery from 516 to 520 mbsf, with cherts showing the anticipated high values of P-wave velocity. Physical properties Unit 5 (>520 mbsf) is poorly characterized because of limited recovery and drilling disturbance. NGR shows a shift back to higher values (10-20 cps), but there are considerable fluctuations associated with the much greater variety of lithologies present.
Two logging runs were attempted at Site 1132. The triple combo successfully logged 560 m, whereas hole conditions limited the FMS/sonic tool to only 70 m. Logging data closely reflect lithologic variations observed in the upper 245 mbsf of the section. Below this depth, downhole logs enable the characterization of sedimentary sequences in low recovery intervals and assist in intersite correlations. Logging data were divided into four units on the basis of variations in the collected datasets. Logging Unit 1 (0-242 mbsf) is characterized by an increase in the magnitude and variability of gamma-ray values that are mainly the result of increased uranium concentrations. High and variable uranium contents continue for the remainder of the unit, with an abrupt decrease at the boundary with logging Unit 2. In the open-hole logged interval below 104 mbsf, separation of the porosity and density curves indicates a somewhat higher noncarbonate fraction than is present higher in the hole. This noncarbonate fraction is only slightly enriched in K and Th. The base of logging Unit 1 correlates well with the base of lithostratigraphic Unit III. Logging Unit 2 (242-437 mbsf) is characterized by a return to low gamma-ray values and increased variability in the magnitude of density and porosity variations, possibly caused by chert layers. In addition, resistivity logs from logging Unit 2 indicate that drilling fluid invasion occurred within this partially lithified packstone interval, suggesting higher porosity than in surrounding units. In the lower part of logging Unit 2, both porosity and density values increase, as does the degree of fluid invasion. The base of logging Unit 2 correlates well with the base of lithostratigraphic Unit IV and is characterized by increases in resistivity and decreases in gamma-ray values, porosity, and density. Logging Unit 3 (437-524 mbsf) is characterized by nearly constant density and gamma-ray values and variable porosity. Resistivity logs show low variability and indicate that drilling fluid invasion occurred in this interval, although to a lesser extent than in the units above and below. Logging Unit 3 correlates well with lithostratigraphic Unit V, which, despite low recovery, appears to be dominated by a homogenous interval of lithified bioclastic grainstones. The upper boundary of logging Unit 4 (524-537 mbsf) is marked by a sharp increase in all parameters. Within the limited section logged, resistivity measurements show increased drilling fluid invasion. The gamma-ray increase in logging Unit 4 is dominated by increased Th and K, indicating the presence of terrigenous minerals within the carbonate sediments. Logging Unit 4 correlates with lithostratigraphic Unit VI.
Regional seismic stratigraphic correlation shows that the Quaternary bryozoan mound complex, represented on seismic imagery by a distinctive mounded facies, occurs in a narrow band immediately below the shelf edge along much of the western Great Australian Bight. Litho-stratigraphic data indicate that bryozoans are also important constituents of underlying nonmounded packstone and grainstone facies corresponding to the lower parts of seismic Sequence 2. Seismic Sequences 3 (middle-late Miocene) and 4 (early Miocene) are characterized by bioclastic grainstones, packstones, and wackestones, with minor foraminiferal ooze. Increased amplitudes toward the base of Sequence 3 probably represent increased impedance contrast associated with interbedded silicified horizons, and disconformity surfaces visible on the high-resolution seismic within both sequences appear to correlate with firmgrounds and hardgrounds. Lithostratigraphic and biostratigraphic data show that the small mounds immediately overlying the distinctive Sequence 7 progradational wedge are composed of lithified bioclastic packstone and wackestone of Eocene age. The only samples recovered from Sequence 7 are carbonate-cemented sandstone fragments forming the uppermost sequence boundary, with the underlying friable sandstones being too poorly cemented for recovery.
Site 1133 is located on the middle upper slope in 1037.2 m of water. It was one of two paleoceanographic sites located to intersect pelagic sections that collectively span the entire Cenozoic succession and form the deeper water component of the shelf-to-basin transect. The principal objectives at this site were to (1) recover pelagic ooze from the middle upper slope to construct a Cenozoic paleoceanographic record of the opening of the Southern Ocean and the development of the Circum-Antarctic Current, (2) determine the history of Cenozoic CCD fluctuations and intermediate water mass variations, and (3) determine depositional and diagenetic facies on the middle upper slope. Drilling difficulties severely restricted the extent to which these objectives could be met.
Sediments recovered at Site 1133 were divided into two major litho-stratigraphic units. Unit I (0-28.55 mbsf) consists of gray and white, moderately to strongly bioturbated calcareous ooze with varying amounts of calcareous nannofossils and planktonic foraminifers. This unit was divided into three subunits based on color changes, textural differences, firmgrounds, and a scoured surface. The boundary between Unit I and II is marked by a firmground that separates overlying white nannofossil ooze from underlying unlithified bioclastic wackestone. Unit II (28.55-142.59 mbsf) consists mainly of (1) gray to light gray, poorly sorted, unlithified bioclastic wackestone, with very fine grained silt- to sand-sized particles; (2) gray, light gray to light olive-gray, unlithified to partially lithified bioclastic packstone with poorly to well-sorted silt- to sand-sized grains; and (3) gray to dark gray chert/porcellanite (silicified wackestone). Most of the recovered sediments are pebble- to cobble-sized fragments. Some porcellanite/chert fragments are draped with a thin layer of unlithified to partially lithified bioclastic packstone. It is likely that the entire unit consists of bioclastic packstone or wackestone containing beds or lenses of preferentially silicified limestone (formerly nannofossil planktonic foraminiferal ooze/chalk).
Drilling at Site 1133 revealed the presence of two major biostratigraphic units, dated by nannofossils and planktonic foraminifers as Quaternary and middle-early Miocene. The Quaternary sequence extends down to 21.49 mbsf and overlies a thin, highly condensed interval with upper Miocene assemblages. This disconformity represents a hiatus of at least 3 m.y., and a second disconformity at 28.55 mbsf separates upper Miocene from lower-middle Miocene sediment and spans ~6 m.y. Three main benthic foraminiferal assemblages are recognized--a diversified Quaternary calcareous assemblage, a diversified upper Mio-cene assemblage, and an impoverished middle-lower Miocene assemblage. All three assemblages indicate middle to lower bathyal paleodepths.
Magnetic measurements of archive-half cores establish a tentative Quaternary-late Pliocene? magnetostratigraphy to 40 mbsf in Hole 1133B, which includes the Brunhes Chron (0-12 mbsf), Matuyama Chron (12-24 mbsf), and Gauss Chron (24-? mbsf). The interpretation is problematic because the same result was not reproduced in Hole 1133A, which yielded uniform normal polarity magnetizations to a depth of 20 mbsf and anomalously shallow magnetizations of both polarities below this depth. Intensities are low; after demagnetization to 20 mT, median values are ~7 × 105 A/m. Intensity fluctuations are closely correlated with lithology in both holes but appear to be inversely correlated with MS. Anomalously high intensities and susceptibilities are observed in both holes at ~30 mbsf. Rock magnetic properties are consistent with single-domain biogenic magnetite or greigite as the remanence carrier. Magnetic susceptibility is dominated by contributions from the diamagnetic carbonate matrix.
Construction of the composite and spliced section from Holes 1133B and 1133C indicates that a complete record of the cored interval between 0 and 39 mcd (34 mbsf) was recovered. This depth interval includes sediments of Quaternary-early Miocene age. Distinctive high-amplitude events occur in the reflectance and GRA density records, enabling easy correlation between holes. Difficulties in correlation result from a slumped interval at ~20-32 mcd; however, the base of the slumped interval is clearly defined and provides a good correlation horizon.
Except for two samples with slightly higher methane contents, generally low concentrations of methane (<12 ppm) were detected at Site 1133. Calcium carbonate content ranges from 78.5 to 94.4 wt%, with most samples between 85 and 92 wt%. Organic carbon values are <0.4 wt%.
Seven interstitial water samples were collected at Site 1133. These data indicate that Site 1133 may be, as was the case with most other sites, underlain by high-salinity fluids, although the maximum salinity value measured was 41 at 123.4 mbsf. Compared to shallower sites, the sulfate reduction rate is substantially reduced and the resulting maximum alkalinity values are <5.2 mM. This, together with the small variations in excess calcium, suggests that the rate of carbonate diagenesis is slower than at other Leg 182 sites in shallower water.
Physical properties measurements at Site 1133 were limited because of poor core recovery. Data were divided into two units, with the boundary correlating with the base of the Quaternary section. Physical properties Unit 1 (0-21.8 mbsf) is characterized by increasing NGR (5-22 cps), bulk density (1.65-1.95 g/cm3), velocity (1.57-1.62 km/s), and decreasing porosity (62%-45%). At the top of PP Unit 2, NGR values decrease to 5 cps, bulk density decreases to 1.8 g/cm3, and porosity shows a general increase to 58%. Physical properties Unit 2 (21.8-152.1 mbsf) is mainly composed of neritic carbonate with low NGR values (~5 cps), variable density, and variable velocities, correlating with an alternation between high-velocity silicified limestones and packstones and lower velocity partially lithified/unlithified packstones.
Regional seismic stratigraphic correlation shows that the youngest interval, of Quaternary age, corresponds to seismic Sequence 2. The remainder of the succession corresponds to seismic Sequence 3. The hiatus recognized at 28.55 mbsf correlates with one of the intrasequence disconformities apparent on the high-resolution site-survey seismic data.
Site 1134 is located on the eastern Eyre Terrace upper slope in 701.0 m of water. This site was designed to intersect Cenozoic seismic Sequences 2, 3, and 4 and Lobes 2 and 3 of Sequence 6A (Feary and James, 1998, reprinted as Chap. 2), and as much of the upper part of the Cretaceous section as time permitted. The principal objectives at this site were to (1) collect a detailed record of Paleogene-early Neogene temperate to subtropical midlatitude sedimentation in an upper slope environment and (2) recover a record of marine flooding of the evolving rift basin in the Cenomanian. The target depth at this site was just below a high-amplitude reflector of probable Cenomanian age, estimated before drilling to be at 520 mbsf (on the basis of stacking velocities).
Site 1134 contained a 397.1-m-thick succession (Table T2) of Quaternary-middle Eocene sedimentation that was divided into six units. Unit I (0-33 mbsf) consists of calcareous nannofossil ooze with varying amounts of planktonic foraminifers. In general, whitish matrix-supported intervals consisting of planktonic foraminifers, sponge spicules, bioclasts, benthic foraminifers, radiolarians, and minor tunicate spicules in the >63-µm fraction alternate with darker, grainier, light gray intervals that contain echinoid spines as well as rare glauconite, pyrite, and unidentified black grains. Unit II (33-66 mbsf) is characterized by soft-sediment deformation interpreted as slumping. Two slumped intervals were identified, with the lower interval defining the boundary between Units II and III. Unit II consists of white to light gray, calcareous nannofossil ooze and calcareous nannofossil foraminifer ooze, as well as unlithified wackestones, packstones, floatstones, and rudstones. The light gray wackestones to rudstones contain a wide variety of coarse components, including various bryozoans (robust and delicate branching, arborescent, and fenestrate growth forms), bioclasts, sponge and tunicate spicules, and pellets. Pebble-sized lumps of calcareous nannofossil ooze, which are interpreted to be reworked clasts, occur in the packstones and floatstones. Unit III (66-152 mbsf) consists of calcareous nannofossil ooze and calcareous nannofossil foraminifer ooze. In the lower part of the unit, alternations between unlithified and lithified sediment are unlikely to be solely related to sediment compaction. The lower limit of alternating lithification corresponds to the base of Sequence 3 and thus may reflect condensed sedimentation related to this sequence boundary. The lower limit of Unit III is marked by a change from the dominantly pelagic sediments of Unit III to the partially lithified wackestones of Unit IV. Unit IV (152-214.3 mbsf) consists of unlithified to partially lithified wackestone/packstone, foraminifer chalk, and very minor packstone. The style of deposition is uniform throughout the unit, characterized by meter-scale alternations of light gray foraminifer chalk and light gray to gray wackestone/packstone. The unlithified to partially lithified wackestone/packstone contains similar components to the chalk, but it is richer in glauconite and dominated by bioclasts. Some of these layers have a sharp base and are normally graded, and they are interpreted to be turbidites. The lower boundary of Unit IV has been placed at the top of a white foraminifer chalk. Two main lithologies were recovered in Unit V (214.3-368.2 mbsf): (1) strongly bioturbated calcareous nannofossil chalk and (2) fragments of porcellanite and chert. The white chalk matrix is dominated by calcareous nannofossils with common sponge spicules as well as trace amounts of bioclasts and dolomite, whereas the coarse fraction consists of planktonic and benthic foraminifers. The gray and green porcellanite fragments are silicified chalk. Only 30 cm of core was recovered from Unit VI (368.2-397.1 mbsf), principally from the lowermost part of the unit. The sediments within this unit are coarse sand-sized, brown limonitic sandstones with quartz, limonite, glauconite, mica, and abundant skeletal grains, as well as minor planktonic foraminifers.
Calcareous nannofossils and planktonic foraminifers indicate that sediments recovered at Site 1134 range from Quaternary to middle Eocene in age. Two hiatuses are indicated: the first is within the Pliocene (nannofossil Zones NN18-NN13 missing at ~57 mbsf) and the second in the middle-upper Miocene (nannofossil Zones NN9-NN7 missing at ~114 mbsf). Planktonic foraminifers also indicate hiatuses at approximately the same depths. A third hiatus may be present in the Eocene section because nannofossil Zone NP17 was not recognized; however, poor core recovery makes confirmation of this hiatus difficult. Calcareous nannofossils are moderately well preserved above ~200 mbsf, with decreasing preservation below this level. Planktonic foraminifers are moderately well preserved throughout most of Hole 1134A, with preservation deteriorating only in the lowermost 30 m of the hole. Benthic foraminifers are generally rare compared to planktonic foraminifers, decreasing in abundance in the lower 130 m of Hole 1134A. Preservation of benthic foraminifers is comparable to that of the planktonic foraminifers. The five main assemblages of benthic foraminifers can be correlated with coeval assemblages at Site 1126 and indicate middle bathyal paleodepths. The benthic foraminifer record at Sites 1126 and 1134 appears excellent for evaluating changes in deep-water circulation in the Great Australian Bight during the Oligocene and Mio-cene.
Long-core measurements at Site 1134 indicate that the intensity of magnetization is extremely weak in the uppermost 100 mbsf, similar to that at Site 1126. However, discrete measurements revealed that a stable remanence is present, and the Brunhes/Matuyama boundary was identified in both holes. Magnetization intensity decreases to a minimum near 110 mbsf in a manner characteristic of the dissolution of fine magnetic particles. There is a marked increase in intensity to 120 mbsf, which coincides with the first appearance of chert at Site 1134. A brief magnetostratigraphy was determined within the Anomaly 5 sequence. Whole-core measurements and nonmagnetic coring experiments were conducted at this site, but the intensity of magnetization was so weak that further analysis is required from shore-based work.
Construction of a composite section for Site 1134 indicates that recovery of Holocene-middle Miocene sediments was complete to a depth of 151.7 mcd. The composite section was constructed primarily using 400-nm color reflectance, the 700:400 nm color reflectance ratio, and GRA bulk density data from Holes 1134A and 1134B. The mcd scale at Site 1134 is expanded by ~6% relative to the mbsf scale. The upper 35 m of sediment (lithostratigraphic Unit I) exhibits cyclic oscillations in color reflectance that are sufficiently distinctive to permit easy correlation between holes. Lithostratigraphic Unit II (34.7-68.9 mcd) contains two slumped intervals that yield excellent correlative horizons at their tops and bases. Lithostratigraphic Unit III (>68.9 mcd) is more difficult to correlate because of dissimilarities in the records from each hole, which may be a result of differential lithification and diagenesis.
Methane concentrations at Site 1134 were low, with maximum concentrations of 7.7 ppm and average concentrations less than 5 ppm. Calcium carbonate contents range from 58 to 94 wt%, averaging 80-92 wt%.
Site 1134 was characterized by a very steep gradient in pore-water salinity, reaching values of 97 by 65.90 mbsf. This salinity gradient is similar to that measured at Sites 1130 and 1126, and is consistent with the suggestion that the brine has a common level below the sea surface at all sites and is controlled by the level of the hydrostatic head during sea-level lowstands. Because of the low rate of accumulation of organic material at Site 1134, oxidation rates of organic material and carbonate diagenesis are reduced compared to the more proximal (shallower water) sites. Significant geochemical reactions appear to take place only in the upper 40 mbsf at Site 1134. In this interval, there is a decrease in the concentration of metastable minerals (e.g., aragonite and HMC) and the appearance of small concentrations of dolomite. As a result, there is only a small increase in Sr2+ with depth--an increase that is quickly swamped by increases associated with greater salinity. The concentration of iron in interstitial waters from Site 1134 is higher than at shallower water, H2S-dominated sites, reaching concentrations >60 mM.
Sediment physical properties measurements closely reflect lithologic variations and provide essential data for core-log correlation. These data were divided into four units based on variations in measured parameters. Physical properties Unit I (0-33 mbsf) is characterized by a sharp decrease in porosity (50%-30%) downhole, together with an increase in bulk density (1.7-2.0 g/cm3) and P-wave velocity (1.6-1.8 km/s). This unit corresponds to the nannofossil ooze succession of lithostratigraphic Unit I. The top of PP Unit 2 is defined by an abrupt increase in bulk density and NGR and correlates with the transition from nannofossil ooze to unlithified bioclastic wackestone. Physical properties Unit 2 (33-66 mbsf) is typified by high variability in P-wave velocity, bulk density, and NGR that correlates with intervals of soft sediment deformation interpreted as slumps. Physical properties Unit 3 (66-145 mbsf) is characterized by a gradual decrease in bulk density and P-wave velocity, and a sharp decrease in NGR (10-2 cps) downhole. The lower part of the unit shows a marked increase in MS (negative values to ~10 × 10- 6 SI units) and porosity. The base of PP Unit 3 is defined by an increase in NGR and a sharp decrease in MS. Physical properties Unit 4 (145-368 mbsf) shows highly variable P-wave velocity, bulk density, and porosity, which result from alternation of nannofossil oozes and wackestones/packstones in the upper part and alternation between chalk and chert in the lower part.
Three logging strings were successfully deployed in Hole 1134A. Overall, downhole measurement trends are similar to those at Site 1126C, but gamma-ray values at Site 1134 are markedly higher than at Site 1126C. The sedimentary succession at Site 1134 was divided into six logging units based on data trends that reflect lithologic alternations among the calcareous ooze, wackestone, grainstone, and thin chert interbed lithologies. Positive density and porosity separation and relatively high PEF values indicate the presence of dolomite toward the top of logging Unit 1. Narrow separation of density and porosity and relatively low PEF values indicate the presence of quartz in the carbonates of logging Unit 2. The presence of blackened grains in recovered cores coincides with higher gamma-ray values, indicating a possible phosphatic and/or glauconitic component. Downhole logs also identify an interval of unusually low potassium concentrations in logging Unit 3, the significance of which is still to be established. Density, PEF, caliper, and resistivity were the only logs acquired within the sandstones at the base of the succession (logging Unit 6). High density and high PEF peaks are consistent with the small amount of limonitic sandstone recovered from this horizon, which may correspond to logging Unit 8 at Hole 1126C. Seven check-shot stations were recorded, with individual stations situated near the estimated depths of significant reflectors.
Correlation of Site 1134 data with the regional seismic grid permits further refinement of the Eucla Basin Cenozoic seismic stratigraphy (Feary and James, 1998, reprinted as Chap. 2). Data from Site 1134 confirm the Pleistocene-upper Pliocene age of the seismic Sequence 2 nannofossil ooze and nannofossil foraminifer ooze, the middle-late Miocene age of the nannofossil ooze and nannofossil foraminifer ooze of Sequence 3, and the early Miocene age of the alternating foraminifer chalk and unlithified to partially lithified wackestone/packstone lithologies of Sequence 4. It also establishes that the uppermost Lobe 3 component of seismic Sequence 6A is of late Oligocene age, consisting of partially silicified, bioturbated, calcareous nannofossil chalk. The middle Lobe 2 part of Sequence 6A has a similar lithology, and spans the upper Eocene-lower Oligocene. The middle Eocene limonitic sandstone poorly recovered at the base of Site 1134 is assigned to seismic Sequence 7.