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IODP Expedition 317:
Canterbury Basin Sea Level
Site U1354 Summary
PDF file is available for download.
3 January 2010
Position: 44° 50.8281' S Latitude, 171° 47.2096' E Longitude
Water Depth: 109.8 m (based on mudline recovered with APC)
Penetration Depth: 85.4 m DSF
Recovered Core: 84.43 m (101%)
Time on Hole: 28 December, 2345 h through 29 December, 2300
Position: 44° 50.8367' S Lat, 171° 47.2069' E Long (20m
south from Hole U1354A
Water Depth: 113.4 m (based on mudline recovered with APC)
Penetration Depth: 77.2 mbsf
Recovered Core: 77.52 m (10%)
Time on Hole: 29 December, 2300 h through 30 December, 1245
Position: 44° 50.8487' S Lat, 171° 47.2080' E Long (20m
south from Hole U1354B)
Water Depth: 113.4 m (adopted from Hole U1354B)
Penetration Depth: 384.2 m DSF
Advanced without Coring: 65.0 m
Cored Interval: 319.2
Recovered Core: 133.37 m (42%)
Time on Hole: 31 December, 0700 h through 30 December, 1245
Site U1354 (proposed Site CB-02A; 110 m water depth) is located
on the mid-outer shelf within the Canterbury Bight between landward shelf Site
U1353 (proposed Site CB-01A) and outer shelf Site U1351 (proposed Site CB-03B)
within the Canterbury Basin drilling transect. Site U1354 occupies an
intermediate position in the shelf portion of the Expedition 317 transect.
Lithologies and paleoenvironments should therefore be intermediate between
those found at Sites U1351 and U1353.
Site U1354 penetrates a middle Miocene to Pleistocene section
containing seismic sequence boundaries U8 to U19. All sequence boundaries are
penetrated landward of their rollovers, or paleo-shelf edges with the goal of
recovering proximal facies, yielding evidence of shallow-water deposition, and
providing optimal paleo-water depths from benthic foraminiferal biofacies.
The principal objectives at Site U1354 were:
1. Sample facies landward of rollovers of progradational sequence
boundaries U8-U19. A particular goal is to use benthic foraminiferal biofacies
to estimate paleo-water depths both above and below sequence boundaries. This
information will be used to calculate eustatic amplitudes using two-dimensional
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.
After a 7 nm transit from Site U1353, the vessel was positioned
over Site U1354 (proposed site CB-02A) at 2320 h (UTC+13h) on 28 December 28.
Three holes were cored with the APC/XCB coring system at Site U1354. The third
hole was drilled with a center bit installed to 65 m DSF to advance the hole
after severe weather ended Hole U1354B. Logging of Hole U1354C was successfully
completed with a special tool configuration that minimized risk and maximized
logging data return. The SET temperature tool was deployed twice without
success. The type of formation encountered proved too difficult for our
temperature measurement tools. Overall recovery for Site U1354 was 100% with
the APC coring system and 39% with the XCB system. The total cored interval for
Site U1354 was 479.8 m with 294.50 m (61%) of recovery.
Coring in Hole U1354A began at 0415 h on 29 December and APC
coring continued through Core U1354A-19H to a depth of 85.4 m DSF using
non-magnetic coring assemblies. A 2-m section (64.9 - 66.9 m DSF) had to be
drilled to advance through a section of shells and shell fragments. Core
orientation was measured on the first three cores, but hard formation and
incomplete piston strokes prompted a decision to remove the tool. Temperature
measurements were not attempted on this hole because of poor hole conditions.
Waiting for 10 minutes without circulation in shallow water was deemed too
risky. Overall recovery for Hole U1354A using the APC coring system was 100%.
The vessel was offset 20 m south of Hole U1354A and Hole U1354B
was piston cored to a depth of 77.2 m DSF with a total recovery of 77.52 m
(100%). Because of the rough piston coring conditions noted in Hole U1354A, the
core orientation and downhole temperature tools were not deployed. Coring was
terminated at 77.2 m DSF because highly variable winds from the south caused
positioning problems. Unable to keep the vessel within the required watch circle,
the decision was made to wait on the weather to improve. The drill string was
tripped back to just above the sea floor and the bit cleared the sea floor at
1245 h on 30 December, ending Hole U1353B.
Operations in Hole U1354C began at 0700 h on 31 December when the
vessel was again able to maintain its watch circle over the new location. The
ship was offset 20 m south from Hole U1354B. The hole was drilled to 65 m DSF
with the center bit installed before two APC cores were taken. The core liner
shattered on the second attempt and the APC system was replaced with the XCB
system to core through a particularly dense layer of shells. Core recovery with
the XCB was initially very good but deteriorated downhole. Coring with the XCB
continued to 384.2 m DSF (Core U1354C-36X). The total penetration for Hole
U1354C was 384.2 m. The total cored interval for Hole U1354C was 319.2 m, with
133.37 m of core recovered (42%).
The hole was swept clean with a 50-barrel high viscosity mud
sweep and displaced with 320 barrels of high viscosity 10.5 ppg logging mud. A
special logging string was made up in order to get all basic sensors without
nuclear sources into a single run. The string provided resistivity (DIT), sonic
compressional and shear (DSI), and natural gamma ray spectroscopy (HNGS) tools.
The tool string tagged the bottom of the hole at ~505 m WRF. After a short
"repeat section" was recorded from TD up to ~440 m WRF, the tool
string was returned to TD and then recorded a main pass up to the seabed. The
drill string was tripped back to 275 m DRF and a 12-barrel, 14-ppg cement plug
was pumped. The logging tools were rigged down, the drill string was tripped to
surface and the bottom hole assembly was broken down and secured for transit. After
the beacons were recovered and the rig was secured for transit, operations at
Hole U1354C, at Site U1354, and on Expedition 317 ended at 1200 h on 2 January
and the vessel departed for the 24-h transit to Wellington.
Site U1354 drilled Quaternary to Early Pliocene sediments located
in water depths and position between Site U1351 on the outer shelf, and Site
U1353 on the mid-shelf. It provides an excellent sedimentary record of
deposition through the Holocene-Quaternary period of eustatic sea-level
fluctuation. Hole U1354C penetrated some of the older Early
Pleistocene-Pliocene seismic reflectors in the offshore Canterbury Basin, which
at this site, are at relatively shallow sub-bottom depths. Core recovery was
reduced below 175 m CSF, which hindered lithostratigraphic 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 the other shelf sites. Cores recovered from Holes U1354A,
U1354B, and U1354C show a downhole transition from a heterolithic upper section
between 0 – 250.81 m CSF with abrupt contacts (Unit I), to a more
featureless mud-dominated succession below 250.81 m CSF (Unit II). Unit I is
further subdivided into an upper Subunit IA (0 – 145.8 m CSF), and a
lower Subunit IB (145.8 – 250.81 m CSF).
Subunit IA is more heterolithic, containing dark greenish gray to
olive gray calcareous muddy sand, sandy marl, and homogeneous marl and very
dark gray massive quartz-rich very well-sorted very fine – fine sand. It
also contains examples of sharp, bioturbated contacts between very fine muddy
sand, sometimes calcareous, above and silty mud below. In contrast, Subunit IB
lacks the aforementioned olive gray marls and massive sands, and is
characterized by more repetitive assemblages of facies that consist of
homogeneous greenish gray mud, which appears to be more clay-rich than Subunit
IA and also contain a minor calcareous component, and greenish gray to gray
calcareous sandy mud to sandy marl that often contains calcareous concretions.
The dominant lithology of Unit II 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 (bioturbation indices of 1 to 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 for Unit I, appears to represent a
shallower-water, inner shelf setting both in relation to Sites U1351 and U1353.
This is surprising in respect to Site U1354, which is today in shallower water.
Evidence for shore face and sub-tidal deposition, including potential
paleosols, suggest that Unit IA at Site U1354 might represent a shoaled region
of deposition. Several sharp and also subtle contacts, along with
biostratigraphic evidence for hiatuses, are evidence that sea-level variations
controlled depositional facies of Unit I. Unit II represents inner- to
mid-shelf depositional settings during the Pliocene at the site. Potential
lithologic expression of seismic sequence boundaries can be matched between all
three shelf sites.
The Holocene to late early Pliocene biostratigraphy of Site U1354
was based on the shipboard study of calcareous nannofossils, diatoms, and
planktic 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 section in Hole U1354A (3.78-85.4 m),
Hole U1354B (4.1-77.3 m), and Hole U1354C (0-127.8 m) was primarily dated and
subdivided with calcareous nannofossils into zones NN21-NN19. Two hiatuses were
identified from nannofossil dating: an intra-Pleistocene hiatus at 57.7-62.4 m
in Hole U1354A and at 73.7-73.9 m in Hole U1354B, where ~0.3 m.y. was missing;
and 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 at Holes U1354A and
U1354B, at 69.9 m and 64.8 m, respectively. Benthic foraminifers were generally
indicative of subtidal to middle shelf depths through the Pleistocene, and
planktic foraminifers suggested deposition was generally under sheltered inner
neritic conditions, except for short-lived excursions to outer neritic and
The Pliocene section between 133 and 375 m was poorly dated,
although calcareous nannofossil and planktic foraminifers dating suggest the
age of the section is middle Pliocene (>2.78 Ma, calcareous nannofossils) to
late early Pliocene (>4.3 Ma, planktic foraminifers). There was no
biostratigraphic evidence for the late Pliocene and it is probably missing at
the level of the basal Pleistocene hiatus. Pliocene deposition was generally in
inner shelf water depths, ranging possibly to middle shelf depths at times,
under sheltered inner neritic conditions. The age at the bottom of Hole U1354C
(357.3 m), as constrained by calcareous nannofossils and planktic foraminifers,
was late early Pliocene–Miocene (3.7-4.3 Ma).
Natural remanent magnetization was measured before and after
demagnetization at 20 mT peak fields, where possible at this site. Persistent
flux jumps in the 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 non-magnetic core barrels throughout the overlapping
Holes U1354A and U1354B allowed the identification of sediments holding reverse
polarity from about 69.9 m and 65 m CSF downhole, respectively. The B/M
boundary lies within an unconformity marked by a sharp lithological boundary in
both holes. Hole U1354C began coring just beneath this boundary, and revealed
sediments with reverse polarity of Matuyama age at its top. Biostratigraphic
constraints indicate that the Jaramillo normal Chron (C1r.1n, 0.998-1.072 Ma)
has not been recorded in sediments from Site U1354. Below 78.1 m CSF coring in
Hole U1354C used the XCB system, which imparted a pervasive drilling overprint
not fully removed during shipboard analyses.
Magnetic susceptibility, natural gamma radiation and color
records show pronounced variations in the upper ~170 m in all three holes, and
these variations are similar to the patterns observed at previous Expedition
317 sites. Changes in magnetic susceptibility, natural gamma radiation and
color can be linked to change in lithology. Color changes in particular
highlight the utility of this parameter for distinguishing between low gamma
ray and magnetic susceptibility sands and marls. Abrupt changes in these
records at 34 and 54 m also coincide with two observed also with two observed
sulfate–methane transitions in Hole U1354A.
P-wave measurements yielded good results over the upper 217 m.
Good results were also gained from measurements made at Site U1353. At both
sites 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 in
Hole U1354A and between 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 the natural gamma radiation, magnetic susceptibility, and color data.
Porosity and void ratio decrease and bulk density show changes
compatible with the porosity trends seen at the other three Expedition 317
sites. The grain density shows some scatter, reflecting the variable lithology.
Sediment strength measurements show a similar pattern to that observed at all
Expedition 317 sites.
Gaseous hydrocarbon monitoring at Site U1354 showed two peaks in
methane content, one at 33-75 m, where HS methane increased to a peak of 23
ppmv at 46 m, and below about 200 m where HS methane increased above 20,000
ppmv. Where sulfate is zero, methane starts to build up, then decreases to near
background concentrations at 60 m, the depth where 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
fast by both organic matter oxidation (one-third) and anaerobic methane
oxidation (two-thirds). In the 60-178 m depth interval the stochiometry suggest
that sulfate reduction was driven almost exclusively by anaerobic methane
oxidation, and apparently the 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 U1354 is the lack of a low-salinity zone, which was seen at the more
on-shore site U1353 at about 50 m. This helps clarify the origin of this
low-salinity zone. As the water depth at Site U1354 is only slightly deeper
than at Site U1353, there is no reason to believe that these sites have had a
significantly different exposure during lowstands caused by glaciation. Therefore,
the presence of this 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 anaerobic
methane oxidation. 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 in Site
U1354, such as the increases in barium, lithium and boron with depth.
Only eighteen sediment samples were analyzed for carbonate
content and by the elemental analyzer due to time constraints at the end of the
expedition. 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 a depth of 50 m. The ratio of total
organic carbon to total nitrogen generally decreases with depth, with the
exception of some of the high carbonate samples in the 73-76 m depth interval.
Two temperature measurements were made using the SET with Core
U1354C-14X and -16X, but results were poor due to the harsh coring conditions.
Accordingly, it was impossible to determine the geothermal gradient and heat
flow at U1354. Thermal conductivity ranged from 1.183-1.873 W/m∙K
showing constant profile with depth. Overall thermal conductivity correlated
negatively with porosity and positively with bulk density. However, the highest
values above 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 high thermal conductive material such as quartz.
Downhole logging of Hole U1354C took place on January 2,
2010. Based on the potential for
unstable hole conditions, our previous experience logging shelf sites, and time
constraints at the end of the expedition, it was decided that a single logging
run without radioactive sources was the most reasonable approach for the last
site. A modified "Sonic Combo" toolstring was deployed, measuring natural gamma
ray, sonic velocities, and electrical resistivity from seafloor to a total
depth of 383 m WSF (wireline depth below seafloor).
Two units were identified in the logs. Logging Unit 1 (110-285 m
WSF) is characterized by an increasing trend in gamma ray 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 ray 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 cores. Preliminary synthetic seismograms show that
the two most prominent of these sand-rich intervals coincide with seismic
reflectors U10 and U11. Logging Unit 2 (285-384 m WSF) is characterized by
slightly decreasing trends in gamma ray 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.