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doi:10.2204/iodp.proc.317.101.2011 Site summariesSite U1351BackgroundHole U1351A
Hole U1351B
Hole U1351C
Site U1351 is located on the outer shelf and is the most basinward shelf site of the Canterbury Basin drilling transect. Seismic sequence boundaries U6–U19 were penetrated at Site U1351. Lower Pliocene–upper Miocene sequence boundaries (below U9) feature smooth onlapped paleoshelves and rounded clinoform breaks, or rollovers, with sigmoid internal reflection geometries. In contrast, upper Pliocene–Pleistocene sequence boundaries (above U9) display eroded and incised downlapped paleoshelves and more pronounced breaks with oblique reflection geometries. U8–U19 were penetrated on their paleoshelves, whereas U6 and U7 were penetrated on their paleoslopes. LithostratigraphyStratigraphic changes at Site U1351 on the Canterbury margin are fairly gradual, reflecting progressive differences in sedimentary styles. Two lithologic units were differentiated based on transitional sedimentary facies. Unit I (0–262 m) is heterolithic, mainly dark gray to greenish gray or olive-gray in color, and is composed of mud and sandy mud with lesser shell hash, sand, and muddy sand. In contrast, Unit II (262–1024 m) is composed of mainly dark greenish gray to greenish black sandy mud (sandy mudstone) and muddy sand (muddy sandstone) with lesser sand (sandstone) and shell hash (limestone). Unit I lithologies can be bounded by abrupt to gradational bedding planes, including distinct unconformities, and are locally bioturbated (ichnofabric index of 1–5). Fining- and coarsening-upward beds, lamination, convolute bedding, and carbonate concretions are rare. The diverse assemblage of bioclasts/macrofossils is locally concentrated (shell hash) but is generally dispersed in the core and becomes less common with depth. Coarse shelly beds on the boundaries are overlain by fining-upward sandy mud and are followed by coarsening-upward lithologies. The arrangement of lithologies in Unit I is characteristic of eustatically influenced shelf successions. Tentatively, eight candidate surfaces (U1351-S1 to U1351-S8) were identified. These surfaces are all within the uppermost 250 m and generally have sharp basal contacts, are commonly bioturbated, and separate coarse lithologies from underlying muds. Unit II is generally structureless, becoming more lithified with depth owing to carbonate cementation, as expressed in short pieces of cemented sandy mudstone recovered in the XCB core catcher. Recovery in Unit II was poor, but contrasts across lithologic boundaries appear more gradational downcore (from shelly to sandy to calcareous muds). Unit II comprises mainly dark greenish gray to greenish black sandy mud with an ichnofabric index of 1–3. Mineralogy suggests southerly schist rather than more local graywacke provenance, perhaps reinforcing the importance of northeastward-flowing currents during deposition. Alternatively, the schist detritus may be recycled from more local, uplifted, and eroded units onshore. The uppermost part of Unit II represents the transition from a shelf to slope environment. Below ~300 m the sediments indicate deposition in an upper slope environment, with some intervals possibly influenced by drift deposition. BiostratigraphyThe biostratigraphy of Site U1351 was based on shipboard study of calcareous nannofossils, diatoms, and planktonic and benthic foraminifers in core catcher samples from Holes U1351A and U1351B. Additional calcareous nannofossil samples were taken from within selected cores to address specific age and paleoenvironmental questions. All microfossil groups were present throughout the cored Holocene to upper Miocene section, except for diatoms, which were present in only a few samples. The Holocene to Pleistocene section between Cores 317-U1351B-1H and 18X (0–141.6 m) was primarily dated and divided using calcareous nannofossils into Zones NN21 (Cores 1H through 5H), NN20 (Cores 6H through 10H), and NN19 (Cores 11H through 18X). Benthic foraminifers suggested that water depths were variable throughout the Pleistocene but generally deepened downcore, from inner–middle shelf depths to middle–outer shelf depths. The Pliocene section between Cores 317-U1351B-19X and 94X (151.2–822.3 m) was primarily dated with calcareous nannofossils in the upper part and with planktonic foraminifers in the lower part. Reworked calcareous nannofossils of Miocene age occurred throughout the lower part of the Pliocene, which was close to where planktonic foraminifers indicated a change to deposition on the slope and where the first consistently outer shelf to uppermost bathyal water depths were recorded, the upper part of the Pliocene being shallower. The Miocene section between Cores 317-U1351B-95X and 116X (831.8–1030.6 m) was primarily dated with planktonic foraminifers. A major hiatus was identified between Sample 317-U1351B-113X-CC and Core 114X in the lowermost Miocene and was provisionally correlated with U5 in the seismic interpretation. Planktonic foraminifers and calcareous nannofossils suggested a hiatus of at least 3.4 m.y. Outer shelf to uppermost bathyal water depths persisted throughout the cored Miocene section, although planktonic foraminiferal abundances were consistent with deposition on the slope. The age at the bottom of Hole U1351B was late Miocene (10.60–10.91 Ma). PaleomagnetismNatural remanent magnetization (NRM) was measured on all but the most heavily disturbed cores. Intensities generally range from 10–2 to 10–4 A/m, with some higher intensity zones, particularly at the tops of cores, attributed to cave-in. NRM orientations tend to show steep (~80°) positive inclinations and declinations clustered in the northern hemisphere. Alternating-field (AF) demagnetization was applied at 10 and 20 mT steps and removed ~30% of the NRM. Where magnetic core barrels had been used (in XCB coring from 94.7 m drilling depth below seafloor [DSF]), orientations changed very little with demagnetization. In contrast, where nonmagnetic core barrels were used with APC coring at shallower depths, NRM orientations did change with demagnetization. In the uppermost 65 m of Hole U1351B, inclinations after 20 mT were negative (approximately –70°), suggesting a normal characteristic component. Between 65 and 94 m, core recovery decreased, and when material was available, inclinations shallowed with demagnetization but remained positive, suggesting that the first polarity change occurs between 65.9 and 69.7 m. Poor core recovery and a strong drilling overprint at greater depths limited further magnetostratigraphic interpretations. Physical propertiesSystematic whole-round and/or section-half measurements of magnetic susceptibility, NGR, gamma ray attenuation (GRA) bulk density, and colorimetry revealed patterns of sedimentation characterized by well-defined cyclicity in the uppermost 180 m. At greater depths these patterns seem to be missing, but this may be the result of poor core recovery. Downhole logging suggests that lower amplitude cycles may persist to at least 400 m. Automated vane shear (AVS) and fall cone penetrometer (FCP) sediment strength tests and moisture and density (MAD) analyses reveal interesting trends. The observed shear strength generally reflects the cyclicity seen in other parameters in the uppermost 250 m. Additionally, abrupt changes or offsets in both magnetic susceptibility and shear strength suggest the presence of unconformities. A gradual increase in bulk density with depth was matched by a similarly subtle decrease in porosity from an average of ~45% at the surface to ~37% at 1000 m. Thermal conductivity variations seemed to follow these trends. GeochemistryHigh-frequency sampling established the midpoint of the SMT at 16 m, based on the dissolved sulfate and methane gradients. The maximum alkalinity at the SMT was 10 mM, with marked cation depletions of 17 mM for Mg2+ and 5 mM for Ca2+. The apparent levels of carbon oxidized and low levels of ammonium and phosphate generated suggest that sulfate reduction is fueled primarily by AOM. The initial gas present beneath the SMT contains ethane at relatively high levels (C1/C2 = 500–800), but absolute gas contents were low (3,000–20,000 ppm C1 in headspace or 1–6 mM in pore space). This suggests preferential loss of methane due to AOM (possibly when the shelf at Site U1351 was emergent) or gas loss from sands during core recovery and sampling. The gas did not show any major deviations from established trends at greater depths to 1000 m. The pore waters in the uppermost 250 m have moderately elevated Cl– and Na+ (~10% greater than seawater). Ca2+ increases from 16 to 40 mM, whereas Mg2+ decreases from 30 to 20 mM over the interval between 200 and 250 m. There are also marked differences in the sediment geochemistry, with higher carbonate, higher nitrogen, and lower sulfur above 200 m. Organic carbon contents range from <0.1 to 1.5 wt%, with more frequent higher values in the uppermost 200 m. Pyrolysis characterization suggests that the organic matter is dominated by degraded higher plant debris. Heat flowOnly one out of five temperature measurements taken at this site was of acceptable quality based on conductive cooling curves over >300 s. Using all five temperature measurements yields a poorly fit geothermal gradient of 14.1°C/km, much lower than the 40°–50°C/km obtained at the Clipper well (Reyes, 2007) and almost certainly in error. Thermal conductivity measured in the laboratory (0.962–2.233 W/[m·K]) was corrected to in situ conditions (0.959–2.215 W/[m·K]). The resulting values increase linearly with depth. Use of a Bullard plot yields a heat flow of 20.1 mW/m2. However, as with the estimated geothermal gradient, heat flow values are suspect because of insufficient reliable temperature measurements. Downhole loggingDownhole logging took place in Holes U1351B and U1351C. Two tool strings were deployed in Hole U1351B: (1) the triple combo tool string, which measures gamma radiation, bulk density, porosity, and electrical resistivity, was run from the seafloor to 1032 m WSF; (2) the FMS-sonic tool string, which measures electrical resistivity images and sonic velocities, could not reach the total depth of the hole and acquired data from 74 to 488 m WSF. In Hole U1351C, only the triple combo tool string was deployed, recording gamma radiation and resistivity during its descent between the seafloor and 801 m WSF. The tool was trapped by hole collapse, preventing logging of the deeper section of Hole U1351C. The complete tool string was later recovered after a 36 h recovery effort. Three logging units were identified in the logs. Logging Unit 1 (83–260 m WSF) is characterized by relatively high amplitude variations in gamma ray values, which increase overall with depth. In this unit, gamma ray minima associated with high resistivity and sonic velocities are consistent with sand layers alternating with clay. Logging Unit 2 (260–510 m WSF) is defined by low-amplitude variability in all logs and trends of decreasing gamma radiation and resistivity. Three distinct intervals of uphole-increasing gamma radiation within this unit suggest fining-upward transgressive sequences. Caliper readings consistently higher than 19.5 inches in Units 1 and 2 show that the formation has little cohesion. The top of Logging Unit 3 (510–1032 m WSF) is defined by significant downhole increases in gamma radiation, density, and resistivity, which remain variable with no distinct trends in this unit. The borehole diameter was slightly smaller (12–18 inches) but was irregular, suggesting a change to more cohesive sediments. Site U1352BackgroundHole U1352A
Hole U1352B
Hole U1352C
Hole U1352D
Site U1352 is located on the upper slope within the Canterbury Bight and is the most basinward site of the Canterbury Basin drilling transect. Seismic sequence boundaries U6–U19 were penetrated at Site U1352, where sediments are finer grained and pelagic microfossils are more abundant than at shelf sites, providing good age control for sequences drilled on the shelf. An additional target, requiring deep penetration, was recovery of the early Oligocene Marshall Paraconformity. The paraconformity is presumed to record intensified current erosion or nondeposition at all water depths that accompanied the development of a partial Antarctic Circumpolar Current system following the opening of the seaway south of Tasmania. There are indications from Leg 181 drilling that the paraconformity developed in deep (bathyal) water ~1–2 m.y. earlier than in shallow water. Dating the paraconformity in the offshore Canterbury Basin at Site U1352 tests this hypothesis by sampling it where paleowater depths were intermediate. Because of time constraints, drilling into one of the large, elongate sediment drifts of the Canterbury Basin became a secondary contingency objective. However, it is likely that insights into sediment drift deposition and paleoceanography will be obtained from Site U1352 cores. Current reworking of sediments is evident at Site U1352, even though distinctive large-scale drift seismic geometries are absent. LithostratigraphyFour holes were drilled at Site U1352, reaching a total depth of 1927 m and spanning the Holocene to late Eocene. This site contains a gradual lithologic transition between the Holocene and Miocene and a major unconformity between the early Miocene and early Oligocene at 1853 m. The succession is divided into three lithologic units. Unit I (0–711 m) spans the Holocene to middle Pliocene and contains predominantly mud-rich sediment consisting of calcareous sandy mud, interbedded sandy mud and clay, interbedded sand and mud, massive sand, mottled sandy mud, homogeneous mud, shelly mud, and marl. The ichnofabric index is 1–5. Unit I is divided into three subunits. Subunit IA (0–98 m) is dominated by interbedded mud, sand, and clay lithologies, with frequent greenish gray sharp-based muddy sand or sandy mud beds. Subunit IB (98–447 m) contains more homogeneous mud and less frequent sharp-based greenish gray muddy sand or sandy mud beds. Subunit IC (447–711 m) represents a transition between the mud-dominated lithologies of Unit I and the calcareous lithologies of Unit II. This gradual transition reflects a progressive change in water depth to deeper slope depositional environments. Unit II (711–1853 m) spans the middle Pliocene through lower Miocene and contains hemipelagic to pelagic sediment consisting of calcareous sandy mud, sandy marls, chalk, sandy marlstone, and sandy limestone with minor amounts of calcareous mudstone and sandstone. The ichnofabric index is 1–5. The unit is divided into three subunits. Subunit IIA (711–1189 m) ranges from homogeneous marl (in Hole U1352B) to bioturbated marlstone (in Hole U1352C). Occasional mudstone, muddy sandstone, and chalk lithologies also occur. Subunit IIB (1189–1694 m) contains abundant dark-colored mudstone beds in the upper part and more frequent occurrences of current bedding, especially toward the base of the unit. The frequency of mudstone bed occurrence decreases below 1392 m, in concert with other changes in mineralogy and an unconformity detected by biostratigraphy. Packages of recumbent and isoclinal folds, tilted beds, contorted strata, and fluid escape features are present both above and below this unconformity. Subunit IIC (1694–1853 m) contains a gradual progression from marlstone to limestone, with frequent glauconitic laminae and beds. A ~12 m.y. unconformity occurs at the base of Unit II, with an abrupt change into lithologic Unit III (1853–1924 m [total depth]) consisting of hemipelagic to pelagic foraminifer-bearing nannofossil limestone of early Oligocene to late Eocene age with an ichnofabric index of 1–5. Except for minor abundances of quartz and clay, Unit III lacks siliciclastic components. This unit is correlative to the onshore Amuri Limestone. Site U1352 represents an upper Eocene to lower Oligocene and nearly complete Neogene continental slope sedimentary record dominated by pelagic to hemipelagic sedimentation with minor traction and gravity flow sediments. The sediments were deposited along a passive continental margin characterized by large volumes of sediment from a tectonically and climatically evolving hinterland. The site represents a unique downhole record from unlithified sediments to lithified carbonates at depth. The gradual downhole transition in lithofacies from more siliciclastic-rich Pleistocene–Holocene muddy facies into pelagic limestones and glauconitic marlstones and marls appears to reflect the downhole transition, seen on seismic profiles, from an upper slope location on a clinoformal margin with a sharp shelf-slope break in the Pleistocene–Holocene toward a toe-of-slope location on a more ramplike margin in the Miocene. The lower carbonate content in the upper part of this interval may be linked to higher terrigenous supply, possibly related to the uplift of the Southern Alps and/or Neogene climate change. BiostratigraphySite U1352 recovered a Holocene–upper Eocene succession. Fifty-five bioevents were recognized and used to provide a detailed biostratigraphic framework. Calcareous nannofossils were the primary dating tool in the Pleistocene, whereas planktonic foraminifers provided robust age control in the Pliocene–middle Miocene section. Both fossil groups were integral for biostratigraphic assessment of the lower Miocene–upper Eocene succession. Diatoms were sparse but provided two useful Pleistocene datums. Analysis of benthic foraminifer assemblages yielded detailed estimates of paleowater depths throughout the succession. A ~500 m thick progradational Holocene–Pleistocene section was recovered, and 16 bioevents were distinguished. The Pliocene/Pleistocene boundary was constrained between 492 and 525 m and is potentially unconformable. Sediments below the boundary were dated at 2.45–3.04 Ma, suggesting that most, if not all, of the upper Pliocene was missing. Pleistocene nannofossil abundances fluctuated dramatically across predicted seismic sequence boundaries (most notably from 0.8 Ma to recent). Similar fluctuations in planktonic foraminifer abundances were also noted near seismic surfaces interpreted as sequence boundaries. The progradational Pliocene interval was also thick (~785 m) and spanned Cores 317-U1352B-58X through 73R (500–1285 m). As at Site U1351, all standard nannofossil zonal markers (except Reticulofenestra pseudoumbilicus) were absent. The Miocene/Pliocene boundary was identified between 1266 and 1284 m and is conformable, although potentially condensed toward the base of the Pliocene. Twenty-six foraminifer and nannofossil datums were observed within the cored Miocene succession (1275–1851 m). The Miocene interval contained three biostratigraphically defined unconformities: a lower upper Miocene unconformity between Cores 317-U1352C-90R and 91R (1395–1410 m), an unconformity within the upper to middle Miocene transition between Cores 101R and 102R (1487–1497 m), and the Marshall Paraconformity between Cores 139R and 140R (1848–1853 m). The latter separated lower Miocene sediments (~18–19 Ma) from underlying lower Oligocene sediments (30.1–32.0 Ma), with ~12 m.y. absent. The Oligocene and Eocene intervals were relatively thin (1851–1910 and 1910–1924 m, respectively). Microfossil preservation was generally poor in Oligocene sediments and moderate in the Eocene. This boundary was recognized between Cores 317-U1352C-146R and 147R (1903–1917 m) and was unconformable, with ~2.3 m.y. missing. The bottom-hole age was constrained between 35.2 and 36.0 Ma in Core 148R (1924 m). Pleistocene and Pliocene sediments were dominated by inner to outer shelf benthic foraminiferal taxa, although the rare but persistent presence of bathyal marker species suggested that the shallower shelfal taxa were possibly reworked. Paleodepths generally increased downhole to lower bathyal depths in the lower part of the cored succession. Middle to deep bathyal taxa occurred in lower Pliocene and older sediments, which is consistent with the generally increasing downhole abundance of planktonic foraminifers through the progradational foreset sequence into the bottom sets and basin floor facies and coincides with the change from suboceanic to fully oceanic conditions. PaleomagnetismNRM was measured on all but the most disturbed cores from all four holes at Site U1352. Intensity ranged from 10–2 to 10–3 A/m in the upper half of the drilled interval and decreased to 10–4 A/m in the lower half of the record (consistent with an increase in carbonate). One AF demagnetization step at peak fields of 20 mT was routinely applied. Where nonmagnetic core barrels were used with APC coring (the uppermost 27 cores in Hole U1352B [to 246 m]), inclinations after 20 mT demagnetization are well grouped around –60.1°. The uppermost 18 cores (to 166 m) are azimuthally oriented and show a mean declination of 27.7° after correction. These values are close to the orientation of the present-day magnetic field (inclination –70°, declination 25°). The relatively shallower inclination of this component suggests that it may be a primary magnetization. The change to magnetic barrels occurred within the interval where the Brunhes/Matuyama boundary was anticipated (from biostratigraphic age determinations), and the boundary was not unambiguously identified at this site. A pervasive drilling overprint hampered further magnetostratigraphic interpretation. Rock magnetic experiments and demagnetization of discrete specimens indicate that a low-coercivity mineral is the main magnetization carrier. Thermal demagnetization of NRM showed unblocking temperatures in the range of 320° to 340°C and an increase in susceptibility at ~400°C, suggesting the presence of iron sulfides. Physical propertiesCore physical properties change with depth broadly, as anticipated, with decreasing overall trends in magnetic susceptibility and NGR and an increasing trend in bulk density obtained from GRA and MAD methods. The uppermost 275 m exhibits regular cyclicity in magnetic susceptibility and NGR, similar to the NGR record at Site 1119. For example, three peaks between 50 and 70 m in Hole U1352B correlate with peaks in Holes 1119B and 1119C (between 36 and 46 mbsf), which have been recognized as signals of MIS 5. Magnetic susceptibility, NGR, GRA bulk density, and color reflectance b* show unexplained but conspicuous negative peaks between 555 and 630 m, followed positive peaks at 665 m. Below the Marshall Paraconformity (~1853 m), magnetic susceptibility switches to negative values, consistent with diamagnetic limestone. Excellent P-wave velocity measurements were obtained using the P-wave caliper (PWC) method on discrete samples from cemented sediments in RCB cores from Hole U1352C. PWC values increase slightly below 1255 m (averaging ~2500–3500 m/s) and increase strongly between 1500 and 1670 m (averaging ~3500–4000 m/s). Below ~1795 m P-wave velocity increases again to 5900 m/s, and an additional slight increase in P-wave velocity was observed below the Marshall Paraconformity. The unexpected high velocities below 1255 m may require a revision of the traveltime/depth conversion of seismic records. Reflectance spectrometry measurements on split cores revealed clear trends in both reflectivity and color. Variations in color were observed to correlate with similar variations in magnetic susceptibility. Results from MAD analyses revealed downhole trends in sediment compaction and lithification. Lithologic Subunit IA shows little downhole variability, but porosity begins to decrease and bulk density begins to increase in Subunit IB. Cementation begins at this level and increases downcore toward lithologic Subunit IIB, which is almost fully cemented. Grain density varies little with depth. AVS and FCP sediment strength tests indicate that sediments range from very soft (0–20 kN/m2) to very stiff (150–300 kN/m2). Sediment strengths correlate well in very soft and soft sediments, but AVS tests appear to underestimate shear strength in firm to very stiff sediments. The pronounced cyclicity in shear strength seen at Site U1351 was not observed at Site U1352. GeochemistryThe SMT occurs between 15 and 17 m. The apparent level of carbon oxidized relative to sulfate reduced suggests that sulfate reduction is driven by both methane oxidation and organic matter oxidation. The initial gas below the SMT contains ethane (2 ppmv) with C1/C2 of ~16,000. Gas composition changes regularly with increasing depth, reaching C1/C2 of ~60 near the bottom of Hole U1352C at 1920 m. C3–C5 hydrocarbon abundance also generally increases with depth. At an apparent unconformity near 1390 m, gas content is very low (40 ppmv methane) and C1/C2 drops as low as 7, mainly because of the near absence of methane. Below the unconformity the gas resumes the normal trend. The initial predominance of branched C4 and C5 alkanes in the gas decreases with depth. Below the unconformity the normal/(normal + iso) C4 and C5 ratios show a large and consistent decrease followed by an increase, which so far remains unexplained but most likely reflects the mixing of different gas generations. Analyses of sediment samples distinguish the clay-rich lithologic Unit I from the carbonate-dominated Unit II. Organic carbon content is generally low (<0.6 wt%), with only a few samples having >1 wt% TOC. The character of the organic matter changes from relatively labile volatile material in the shallower sediments to more stable proto-kerogen downhole, with evidence for increasing thermal maturity at total depth. The organic matter appears to be mainly terrestrial plant in origin. Interstitial water analyses were conducted to 1400 m. Initial reductions in calcium and magnesium in the SMT are related to microbial processes (sulfate reduction and methanogenesis). Below 400 m, calcium, magnesium, and strontium concentrations in interstitial water increase and alkalinity decreases, consistent with dissolution of carbonates and the poor preservation of microfossils. Potassium and sodium concentrations decrease markedly below 300 m, possibly related to glauconite formation, whereas fluctuations in silica concentrations point to dissolution of siliceous fossils. Increasing boron concentrations below 200 m may reflect a diagenetic opal-A/opal-CT transition and microbial degradation of organic matter. A lithium increase below 500 m can be explained by dehydration reactions that remove lithium from clay interlayer exchange sites. Eleven whole-round samples were taken between 1630 m and the bottom of Hole U1352C at 1927 m for microbiological and organic geochemical characterization of in situ microbial communities. Onshore investigation of these samples could potentially extend the maximum known depth of habitable sediments. Heat flowFour good-quality temperature measurements out of six measurement attempts in the depth interval from 94 to 313 m yielded a geothermal gradient of 46.2°C/km. Laboratory thermal conductivity measurements from 8 to 1920 m, with a range of 0.849–3.440 W/(m·K), reveal a trend of increasing thermal conductivity with depth except in the topmost 90 m, where a decreasing trend was observed. Two individual trends were recognized: one for unlithified sediment from 90 to 800 m and another for hard rock from 600 to 1920 m. Thermal conductivity shows positive and negative relationships with bulk density and porosity, respectively. Heat flow was calculated as 57.8 mW/m2 within the depth interval where the geothermal gradient was established. Assuming steady-state heat flow, the temperature profile yields a bottom-hole temperature of ~60°C, but this would be higher if a constant geothermal gradient were assumed. Downhole loggingDownhole logging at Site U1352 took place in Holes U1352B and U1352C. Two tool strings were deployed in Hole U1352B: (1) the triple combo tool string, which measures natural gamma ray, bulk density, porosity, and electrical resistivity, was run from the seafloor to 487 m WSF, below which an obstruction prevented it from reaching total depth, and (2) the FMS-sonic tool string, which measures electrical resistivity images and sonic velocities, encountered the same blockage and acquired data from 82 to 442 m WSF. In Hole U1352C, hole conditions were unstable, and only a modified triple combo (without radioactive sources) tool string was deployed, recording gamma ray and resistivity between the seafloor and 207 m WSF. Below 207 m WSF the tool string encountered a blockage that prevented it from reaching total depth. Two logging units were identified. Logging Unit 1 (82–250 m WSF) is characterized by relatively low amplitude variations in gamma radiation, resistivity, and acoustic velocities. A distinct uphole-increasing and then uphole-decreasing trend in gamma radiation is consistent with gamma ray logs at Site 1119 and may be associated with variations in clay content. Resistivity decreases with depth in this unit, whereas velocity increases with depth. Caliper measurements consistently higher than 19.5 inches indicate an enlarged borehole in this interval. Logging Unit 2 (250–487 m WSF) is defined by a change to higher amplitude variations in gamma radiation, resistivity, and acoustic velocities. Gamma radiation and velocity show increasing trends with depth, whereas resistivity varies around a relatively constant value. Sharp peaks in P-wave velocity associated with variations in density or lithology may correlate with significant seismic reflections in this unit. The borehole diameter is smaller but highly irregular (6–19.5 inches) and may reflect the appearance of more cohesive marls within the formation. Site U1353BackgroundHole U1353A
Hole U1353B
Hole U1353C
Site U1353 is located on the middle shelf within the Canterbury Bight and is the most landward shelf site of the Canterbury Basin drilling transect. As a result, Site U1353 was considered the most challenging site, both because the water depth at the site (85 m) is the shallowest of all Expedition 317 sites and also because the lithologies at this inboard setting were likely to be particularly coarse grained. Site U1353 penetrates a middle Miocene–Holocene section containing seismic sequence boundaries U5–U19. All sequence boundaries were penetrated landward of their rollovers, or paleoshelf edges, with the goal of recovering proximal facies, yielding evidence of shallow-water deposition, and providing optimal paleowater depths from benthic foraminiferal biofacies. Cores from Site U1353 include upper Miocene to lower Pliocene sequence boundaries (below U10) that feature smooth onlapped paleoshelves and rounded rollovers with middle Pliocene to Pleistocene sequence boundaries (U10 and above), which display eroded and incised downlapped paleoshelves and more pronounced rollovers. LithostratigraphySite U1353 provides an excellent and unique sedimentary record of deposition through the Holocene–Pleistocene period of global sea level fluctuations. Hole U1353B also penetrated some of the older early Pleistocene–Miocene seismic reflectors in the offshore Canterbury Basin, which at this site are at relatively shallow subbottom depths of <500 m. Poor core recovery, however, hindered lithologic interpretation in deeper portions of the hole. Cores recovered from Holes U1353A and U1353B show a downhole transition from a heterolithic upper section with abrupt contacts (Unit I) to a more featureless, mud-dominated section with depth (Unit II). These changes suggest a progressive and gradual change in sedimentary style as the margin evolved. Unit I (Hole U1353B, 0–151 m) is characterized by its overall muddy character, the dominant lithology being a dark greenish gray homogeneous mud with a few percent very fine sand. Shells are either rare and scattered or locally concentrated in layers as thick as 15 cm. Bioturbation is common, with ichnofabric indexes of 3–4. Subordinate lithologies include shelly mud to shell hash, micaceous well-sorted very fine sand, clay, and sandy marl. The dominant lithology of Unit II (Hole U1353B, 151–614 m) consists of dark greenish gray, micaceous very fine sandy mud and mud, typically with shells. Both types of sediment are slightly to heavily bioturbated (ichnofabric indexes of 2–4). Sand and cemented intervals were recovered sporadically throughout the unit as minor lithologies. Close similarities were noted between Site U1353 and Sites U1354 and U1351 (located 13 and 20 km, respectively, to the southeast). Comparable Unit I and II subdivisions and constituent lithotypes were recognized at these sites, and potential lithologic expression of seismic unconformities can also be matched between the sites. Site U1353 was interpreted to represent a slightly more shoreline-proximal equivalent of Sites U1354 and U1351. Deposition is dominated by shelf processes, characterized during Unit I (Holocene–Pleistocene) by frequent sea level variations and preceded by inner to middle shelf depositional settings through Unit II (early Pleistocene–Miocene). BiostratigraphyCalcareous nannofossil, planktonic and benthic foraminifer, and diatom assemblages from Site U1353 core catcher samples were used to create a shipboard biostratigraphic framework. Benthic foraminifers were also used to estimate paleowater depths. Diatoms were sparse to absent at this site. Site U1353 contained a Holocene to Miocene succession. Thirteen biostratigraphic events were recognized, most of them in the Pleistocene. Pleistocene microfossil abundances were high, and assemblages exhibited good preservation, which allowed for robust age control, particularly with nannofossils. A hiatus was recognized within the middle-lower Pleistocene section between Samples 317-U1353B-12H-CC and 14X-CC (80.12–80.77 m), where ~0.8 m.y. was missing. The Pliocene/Pleistocene boundary was biostratigraphically picked between Samples 317-U1353B-21H-CC and 23H-CC (121.16–135.71 m) and is unconformable, missing most, if not all, of the upper Pliocene. Biostratigraphic analysis of Pliocene and Miocene sediments at this site was particularly problematic for all microfossil groups because of either low abundances and/or the absence of biostratigraphic markers. Below Sample 60H-CC (257.69 m), nannofossil abundances dropped sharply and remained low for the rest of the downhole succession. Samples below this level were nearly barren of planktonic foraminifers, but shelfal benthic foraminifers were present, albeit without reliable age-diagnostic markers. Nevertheless, several important datums allowed for biostratigraphic constraint and critical correlation with Sites U1351 and U1352. The early/middle Pliocene boundary was distinguished on the basis of a nannofossil datum (3.7 Ma) between Samples 317-U1353B-27H-CC and 28H-1, 124 cm (149.68–150.64 m). In combination with a planktonic foraminifer datum (<4.3 Ma) it constrained the interval from 150.64 to 256.04 m to the lower Pliocene between 3.7 and 4.3 Ma. The Miocene/Pliocene boundary could not be picked biostratigraphically. Although Site U1353 yielded no biostratigraphic evidence for upper Miocene sediments, the extrapolation of correlative seismic reflectors from outermost shelf Site U1351 supported the presence of an upper Miocene interval at Site U1353. A nannofossil marker constrained between Samples 317-U1353B-88X-CC and 89X-CC (510.52–518.66 m) was dated older than 12.03 Ma, indicating a substantial hiatus above this interval, although the amount of time missing is unknown. Samples below 90X-CC were barren of calcareous nannofossils and planktonic foraminifers, except for the bottommost core catcher (98X-CC [604.60 m]), which contained sparse nannofossils with an assemblage age of middle to early Miocene. Paleowater depths derived from benthic foraminifers ranged from subtidal to outer shelf environments throughout the Holocene to Miocene section but were no deeper than outer shelf. Pleistocene paleowater depths fluctuated between subtidal and middle shelf water depths, although a notable deepening to outer shelfal depths (correlated to the interval just above the early/middle Pleistocene hiatus) was noted in Samples 317-U1353B-10H-CC and 11H-CC (67.5–73.19 m). Pliocene water depths were generally subtidal to inner shelf but ranged down to outer shelf in the early Pliocene. Middle–early Miocene paleowater depths could not be interpreted because of low numbers of benthic foraminifers. PaleomagnetismNRM was measured on all but the most disturbed cores from Site U1353. NRM intensities are on the order of 10–3–10–2 A/m and decrease to 10–4–10–3 A/m by AF demagnetization at peak fields of 20 mT. A steep, northerly, positive drilling overprint was removed by AF peak demagnetization at 20 mT from APC cores recovered using nonmagnetic core barrels (Hole U1353B, 0–67.6 m). After demagnetization, remanence direction was oriented upward, or negative (normal), with a mean inclination around –60°, consistent with a Brunhes age for this component. The overprint persisted (with declinations clustered at north) where standard steel core barrels were used at greater depths. Consequently, no reversals could be detected at Site U1353. Rock magnetic experiments reveal lithology-dependent changes in magnetic behavior between gray muds and green silty/sandy intervals in Hole U1353B. Gray muds show relatively higher coercivities (~80 mT) and lose ~80% of their remanence between 250° and 360°C heating steps. Green, coarser grained sediments have coercivities of ~40–50 mT and lose only 40%–50% of their remanence between the same heating steps. Rock magnetic parameters are consistent with the presence of magnetic iron sulfides throughout the sediments and indicate the presence of an additional remanence carrier, likely magnetite, particularly in the greenish intervals. Physical propertiesIn the uppermost 260 m, systematic whole-round and/or section-half measurements of magnetic susceptibility, NGR, GRA bulk density, and P-wave velocities, as well as colorimetry and MAD measurements, revealed patterns of sedimentation characterized by cyclic variations as well as evidence suggestive of unconformities. Two abrupt excursions in magnetic susceptibility, NGR, and color occur between 13 and 17 m and between 27 and 36 m and are associated with thick sandy units. These peaks may correlate with the two most recent glacial–interglacial cycles, MIS 1–5 and 6–7, and provide tentative age estimates for the Holocene and latest Pleistocene. Overall, magnetic susceptibility decreases, and P-wave velocity and bulk density increase downhole. Several abrupt shifts were observed in these trends. These shifts correspond to intervals where biostratigraphic evidence indicates a hiatus, and those intervals could be related to erosion or a missing section. A number of prominent peaks in magnetic susceptibility in the uppermost 80 m may be linked to caved-in shell-hash material observed at the top of each core, as observed previously at Site U1351. These findings indicate that the noisy magnetic susceptibility signal below ~100 m may also be mainly caused by the drilling process, including material that fell down onto the tops of cores (cave-in) or material that was sucked into the bottoms of core liners (flow-in). Caution is required before additional onshore analyses confirm or reinterpret tentative shipboard observations. Good P-wave velocity results were obtained in the muddy portions of the sediment to >585 m. This contrasts with Sites U1351 and U1352, where high gas content in unlithified sediments destroyed the P-wave signal below the top ~20 m of soft sediments. AVS and FCP sediment strength tests correlate well in very soft and soft sediments, but AVS test values are about three times lower than FCP test values in firm to very stiff sediments. These findings, consistent with those at Sites U1351 and U1352, suggest that the applicability of the AVS test in firm to very stiff sediments is limited in that it underestimates the strength of such sediments. GeochemistryGaseous hydrocarbon monitoring at Site U1353 did not show significant levels of hydrocarbons above the background laboratory air concentration of ~2 ppmv. Sulfate levels are never strongly depleted and no SMT is apparent, suggesting that either (1) methanogenesis did not occur in the sediments, (2) previously generated methane was lost when the shelf was emergent, or (3) methane was oxidized when sulfate was replenished by diffusion after a subsequent sea level rise. Interstitial water chemistry in the uppermost 150 m is dominated by a salinity minimum, reaching values of 2.4, or 70% of seawater, at ~50 m. Below this depth salinity increases again to seawater values and reaches a value slightly higher than that of seawater in the deepest sample at 586 m. The presence of this less saline lens can be explained by either modern intrusion of meteoric water from land or by the historic remains of freshwater that was emplaced when the shelf was emergent and is now being slowly replaced by the downward diffusion of seawater. The profiles of chloride, sodium, sulfate, and, to some extent, potassium closely track the salinity trend and also show minima at ~50 m. Normalization of alkalinity, sulfate, calcium, and magnesium profiles to seawater chloride concentrations allows the evaluation of changes due to reaction rather than dilution with freshwater. Chloride-normalized alkalinity increases from 3.2 mM near the seafloor to 9 mM at 54 m, which co-occurs with a depletion of 8 mM in chloride-normalized sulfate. This implies that some sulfate reduction occurred and that alkalinity is affected by additional processes such as carbonate precipitation and dissolution. The normalized calcium concentrations increase with depth to 16 mM and possibly reflect dissolution of calcareous microfossils. The chloride-normalized magnesium profile shows a steady decline downhole and levels out at 45 mM. Increasing boron concentrations indicate release of a desorbable boron fraction and degradation of organic matter. Similarly, the increasing lithium amounts can be explained by desorption reactions. Barium concentrations seem to be coupled to the sulfate profile and increase slightly when sulfate concentrations decline, possibly related to dissolution of barite. Average carbonate content is highly variable but is lower below 300 m. The decrease of TOC over the uppermost 100 m can be correlated with the intervals of alkalinity increase and sulfate decrease and might represent active biological oxidation. Pyrolysis characterization of organic matter suggests a major contribution from terrestrial plants, whereas C/N ratios from elemental analysis are consistent with a significant marine influence. Heat flowOne in situ temperature measurement was attempted with the third-generation advanced piston corer temperature tool (APCT-3), but it yielded poor results. Additional temperature measurements were not obtained because of difficult drilling conditions, and therefore heat flow could not be determined. Laboratory thermal conductivity measurements for the depth interval 5.2–413.5 m provide a range of 1.122–1.840 W/(m·K) and show two downhole-increasing trends: an increasing trend in the 0–32 m interval, with a local maximum at ~30 m, and a subsequent drop followed by another increasing trend to 413 m. The origin of the local maximum at ~30 m is unclear because porosity and bulk density are constant in the 20–50 m interval. In general, thermal conductivity varies positively with bulk density and negatively with porosity. Thermal conductivity measurements are unreliable below 414 m. Downhole loggingDownhole logging of dedicated logging Hole U1353C took place on 28 December 2009. Two tool strings were deployed: (1) a modified triple combo tool string (without radioactive sources because of unstable hole conditions at this site), which measured natural gamma ray and resistivity from the seafloor to a total depth of 528 m WSF, and (2) the FMS-sonic tool string, which measured electrical resistivity images and sonic velocities from 105 to 249 m WSF. Below 249 m WSF the FMS-sonic tool string encountered a blockage that prevented it from reaching total depth. Two units were identified in the logs. Logging Unit 1 (105–260 m WSF) is characterized by an increasing trend from the top of the unit to 180 m WSF. Below that interval the gamma ray trend decreases downhole to ~250 m WSF. These trends are interrupted by abrupt high-amplitude lows in gamma radiation and peaks in resistivity and velocity that are interpreted as sandy intervals, many of which coincide with sand or gravel at corresponding depths in Hole U1353B. These features also show good correspondence to significant seismic reflections. Logging Unit 2 (260–528 m WSF) is characterized by overall decreasing trends with depth in gamma radiation and resistivity, with low variability. The top of the unit is roughly the same depth as the onset of low core recovery in Hole U1353B and the point at which the FMS-sonic tool string was unable to descend deeper into the hole, suggesting a change in the properties of the formation across the unit boundary. Site U1354BackgroundHole U1354A
Hole U1354B
Hole U1354C
Site U1354 (110 m water depth) is located on the mid-outer shelf within the Canterbury Bight between landward shelf Site U1353 and outer shelf Site U1351 within the Canterbury Basin drilling transect. Site U1354 occupies an intermediate position in the shelf portion of the Expedition 317 transect. Lithologies and paleoenvironments were thus expected to be intermediate between those at Sites U1351 and U1353. Site U1354 penetrates a middle Miocene to Pleistocene section containing seismic sequence boundaries U8–U19. All sequence boundaries were penetrated landward of their rollovers, or paleoshelf edges, with the goal of recovering proximal facies, yielding evidence of shallow-water deposition, and providing optimal paleowater depths from benthic foraminiferal biofacies. The principal objectives at Site U1354 were to (1) sample facies landward of rollovers of progradational seismic sequence boundaries U8–U19 and in particular to use benthic foraminiferal biofacies to estimate paleowater depths both above and below these sequence boundaries in order to calculate eustatic amplitudes using two-dimensional backstripping and (2) investigate the facies, paleoenvironments, and depositional processes associated with the sequence stratigraphic model in a proximal setting on a prograding continental margin where sequence architecture is well constrained by seismic imaging. LithostratigraphyAt Site U1354, Holocene to lower Pliocene sediments were drilled at a water depth and location intermediate between Site U1351 on the outer shelf and Site U1353 on the middle shelf. This site provides an excellent sedimentary record of deposition throughout the Holocene–Pleistocene period of eustatic sea level fluctuation. Some of the older lower Pleistocene–Pliocene seismic reflectors in the offshore Canterbury Basin were penetrated at this site at relatively shallow subbottom depths. Core recovery was reduced below 175 m, which hindered lithologic interpretation of the deeper parts of the section. Lithologic changes suggest a progressive and gradual change in sedimentary style as the margin evolved and are consistent with similar observations made at other shelf sites. Cores recovered from Holes U1354A, U1354B, and U1354C show a downhole transition from a heterolithic upper section between 0 and 251 m with abrupt contacts (Unit I) to a more featureless, mud-dominated succession below 251 m (Unit II). Unit I is further divided into Subunits IA (0–146 m) and IB (146–251 m). Subunit IA is more heterolithic, containing dark greenish gray to olive-gray calcareous muddy sand, sandy marl, and homogeneous marl (e.g., Cores 317-U1354A-1H and 317-U1354B-10H) and very dark gray, massive, quartz-rich, very well sorted very fine–fine sand (e.g., Cores 317-U1354A-7H and 317-U1354B-7H). The ichnofabric index ranges between 1 and 5. Subunit IA also contains examples of sharp bioturbated contacts between very fine muddy sand (sometimes calcareous), above, and silty mud, below (e.g., Section 317-U1354B-13H-2). In contrast, Subunit IB lacks the aforementioned olive-gray marls and massive sands and is characterized by more repetitive assemblages of facies (e.g., Cores 317-U1354C-19X and 21X) consisting of homogeneous greenish gray mud, which appears to be more clay rich (e.g., Sections 317-U1354C-18X-1 and 12X-2) than that of Subunit IA and which contains a minor calcareous component, and greenish gray to gray calcareous sandy mud to sandy marl that often contains calcareous concretions (e.g., Sample 317-U1354C-21X-CC). The ichnofabric index ranges between 1 and 5. The dominant Unit II lithology consists of very dark and dark greenish gray to gray micaceous, very fine sandy mud and mud, typically with shells. Both types of sediment have variable degrees of bioturbation ranging from absent to moderate (ichnofabric indexes of 1–3). Muddy very fine sand with shells occurs as a minor lithology. Site U1354 is interpreted to represent a slightly more shoreline-proximal equivalent of Site U1351, but Unit I appears to represent a shallower water inner shelf setting compared to Sites U1351 and U1353. This is surprising because Site U1354 is today in shallower water. Evidence for shoreface and subtidal deposition, including potential paleosols, suggests that Subunit IA at Site U1354 might represent a shoaled region of deposition. Several sharp, subtle contacts, along with biostratigraphic evidence for hiatuses, are evidence that sea level variations controlled the depositional facies of Unit I. Unit II represents inner to middle shelf depositional settings during the Pliocene. Potential lithologic expression of seismic sequence boundaries can be matched between all three shelf sites. BiostratigraphyThe Holocene to early Pliocene biostratigraphy of Site U1354 was based on the shipboard study of calcareous nannofossils, diatoms, and planktonic and benthic foraminifers in core catcher samples from Holes U1354A, U1354B, and U1354C. Additional intra-core samples were taken from selected cores to address specific age and paleoenvironmental questions using calcareous nannofossils. All microfossils groups were represented throughout the cored section, except for diatoms, which were only found in a few Pleistocene samples. The Holocene to Pleistocene sections in Holes U1354A (0–85.4 m), U1354B (0–77.3 m), and U1354C (0–127.8 m) were primarily dated and divided with calcareous nannofossils. Two hiatuses were identified with nannofossil dating: (1) an intra-Pleistocene hiatus at 76.2–80.2 m in Hole U1354A and 73.7–73.9 m in Hole U1354B, where ~0.3 m.y. was missing, and (2) a hiatus at the base of the Pleistocene at 122.2–133.4 m in Hole U1354C, where ~1 m.y. was missing. Another potential hiatus was identified on the basis of calcareous nannofossil dating and magnetostratigraphic data in Holes U1354A and U1354B at 69.9 and 64.8 m, respectively. Benthic foraminifers were generally indicative of subtidal to middle shelf depths throughout the Pleistocene, and planktonic foraminifers suggested deposition generally occurred under sheltered inner neritic conditions, except for short-lived excursions to outer neritic and extraneritic conditions. The Pliocene section between 133 and 375 m was poorly dated, although calcareous nannofossils and planktonic foraminifers suggested that the age of the section was middle Pliocene (>2.78 Ma, calcareous nannofossils) to late early Pliocene (>4.3 Ma, planktonic foraminifers). There was no biostratigraphic evidence for upper Pliocene sediments, which were probably missing at the level of the basal Pleistocene hiatus. Pliocene deposition occurred generally in inner shelf water depths, possibly ranging at times to middle shelf depths, under sheltered inner neritic conditions. The age at the bottom of Hole U1354C (375.3 m) was late early Pliocene (3.7–4.3 Ma), constrained by calcareous nannofossils and planktonic foraminifers. PaleomagnetismWhen possible, NRM was measured before and after demagnetization at 20 mT peak fields. Persistent flux jumps in the superconducting rock magnetometer (SRM) rendered measurement difficult, and in some cases impossible, in the time available. In spite of this, a good, unambiguous record was recovered. The use of nonmagnetic core barrels throughout the overlapping Holes U1354A and U1354B allowed the identification of sediments holding reversed polarity from ~69.9 and 65 m downhole, respectively. The Brunhes/Matuyama boundary lies within an unconformity marked by a sharp lithologic boundary in both holes. Coring in Hole U1354C began just beneath this boundary and revealed sediments with reversed polarity of Matuyama age. Biostratigraphic constraints indicate that the Jaramillo Subchron (C1r.1n, 0.998–1.072 Ma) was not recorded in sediments from Site U1354. Below 78.1 m, coring in Hole U1354C used the XCB system, which imparted a pervasive drilling overprint not fully removed during shipboard analyses. Physical propertiesMagnetic susceptibility, NGR, and color records show pronounced variations in the uppermost ~170 m in all three holes, and these variations are similar to the patterns observed at other Expedition 317 sites. Changes in magnetic susceptibility, NGR, and color can be linked to changes in lithology. Color changes, in particular, highlight the utility of this parameter for distinguishing between sands and marls with low NGR and magnetic susceptibility. Abrupt changes in these records at 34 and 54 m also coincide with two changes in sulfate–methane abundances in Hole U1354A. P-wave measurements yielded good results over the uppermost 217 m. Good results were also gained from measurements made at Site U1353. At both Sites U1353 and U1354, the long record of good P-wave data can be ascribed to the absence of sediment fracturing caused by high gas content. A change between ~68 and 70 m in Hole U1354A and 64 and 65 m in Hole U1354B marks both a hiatus and the position of the Brunhes/Matuyama boundary. This boundary can also be recognized in NGR, magnetic susceptibility, and color data. Decreases in porosity and void ratio and changes in bulk density are compatible with the porosity trends seen at the other sites. Grain density shows some scatter, reflecting the variable lithology at this site. Sediment strength measurements have a similar pattern to that observed at all Expedition 317 sites. GeochemistryGaseous hydrocarbon monitoring at Site U1354 revealed two peaks in methane content, one at 33–75 m, where headspace methane increases to a peak of 23 ppmv at 46 m, and one below ~200 m, where headspace methane increases to >20,000 ppmv. Where sulfate is zero, methane begins to increase and then decreases to near background concentrations at 60 m, the depth at which sulfate reappears in the cores. Sulfate is also fully depleted below 200 m. The upper methane zone corresponds to a zone of rapid sedimentation, above which sulfate was depleted quickly by both organic matter oxidation (one-third) and AOM (two-thirds). In the 60–178 m depth interval the stoichiometry suggests that sulfate reduction was driven almost exclusively by AOM and that apparently sediments in this depth interval were deposited at a rate slow enough to permit continuous replenishment of dissolved sulfate by diffusion from overlying seawater. One notable aspect of the shallow pore water chemistry profiles at Site U1354 is the lack of a low-salinity zone like that seen at ~50 m at the more landward Site U1353. This helps clarify the origin of this low-salinity zone. Because the water depth at Site U1354 is only slightly deeper than at Site U1353, there is no reason to believe that these sites experienced significantly different exposure during lowstands caused by glaciation. Therefore, the presence of a less-saline lens at Site U1353 is most likely explained by modern intrusion of meteoric water from land rather than by the historic remains of freshwater emplaced when the shelf was emergent. Other changes in pore water chemistry at Site U1354 are probably related to carbonate diagenesis and possible contributions from deeper basinal brines. The main decreases in dissolved calcium and magnesium occur within the depth intervals characterized by sulfate reduction, methanogenesis, and AOM. These processes are commonly associated with precipitation of authigenic carbonates with distinct carbon isotopic compositions. The increase in sodium and chloride from 0 to 60 m, possibly related to an influx of saline fluid, may also account for some of the other changes seen at Site U1354, such as the increases in barium, lithium, and boron with depth. Because of time constraints at the end of the expedition, only 18 sediment samples were analyzed for carbonate content by the elemental analyzer. Calcium carbonate contents range from 1.3 to 52 wt% in the sediments analyzed down to burial depths of 81 m. Organic carbon ranges from 0.02 to 1.1 wt%, with the highest value at 50 m. The ratio of TOC to TN generally decreases with depth, with the exception of some of the high-carbonate samples in the 73–76 m depth interval. Heat flowTwo temperature measurements were made using the Sediment Temperature (SET) tool, but results were poor because of harsh coring conditions. Accordingly, it was impossible to determine the geothermal gradient and heat flow at Site U1354. Laboratory thermal conductivity ranges from 1.183 to 1.873 W/(m·K), showing a constant profile with depth. Overall thermal conductivity correlates negatively with porosity and positively with bulk density. However, the highest values (>1.700 W/[m·K]) came from very fine–fine sand layers in Holes U1354A and U1354B that were not associated with low porosity and high bulk density, probably because the sand layers consist mainly of highly thermally conductive material such as quartz. Downhole loggingDownhole logging of Hole U1354C took place on 2 January 2010. Based on the potential for unstable hole conditions, our previous experience logging shelf sites, and time constraints at the end of the expedition, we decided that a single logging run without radioactive sources was the most reasonable logging strategy for this site. A modified "sonic combo" tool string was deployed to measure natural gamma ray, sonic velocities, and electrical resistivity from the seafloor to 383 m WSF. Two units were identified in the logs. Logging Unit 1 (110–285 m WSF) is characterized by an increasing trend in gamma radiation from the top of the unit to ~185 m WSF, followed by a generally decreasing trend to the base of the unit, punctuated by abrupt high-amplitude lows in gamma radiation and peaks in resistivity and velocity. This unit is identical to logging Unit 1 at Site U1353, and the high-amplitude features at both sites correspond to coarser grained intervals in the cores. Preliminary synthetic seismograms show that the two most prominent sand-rich intervals coincide with U10 and U11. Logging Unit 2 (285–384 m WSF) is characterized by slightly decreasing trends in gamma radiation and resistivity, with limited variability and increasing velocity. Unit 2 at this site is similar to logging Unit 2 at Site U1353, which is characterized by low core recovery associated with sandy sediments. |
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