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IODP Expedition 317:
Canterbury Basin Sea Level
Week 4 Report (22-28 November 2009)
PDF file is available for download.
30 November 2009
week began while coring on Core U1351B-70X at a depth of 611 m DSF. Because
core recovery with the XCB system was poor, the coring system was again
switched to the APC for Cores U1351B-78H and 85H, but recovery was <1 m in
each case. Coring was terminated at 1030.6 m DSF after the Core U1351B-116X
barrel became stuck. The hole was cleaned and then displaced with mud in
preparation for logging. The drill string was tripped back to 80 m DSF and the
triple combo was rigged up and run to bottom. Drilling conditions in the hole
prior to logging were good. However, the first logging run revealed a hole that
was oversized for logging over much of its length. The triple combo was rigged
down and the FMS-sonic tool string was deployed but failed to pass 618 m WSF.
Indications were that the hole collapsed and bridged at around 618 m WRF. The
hole was logged from that point upwards and the logging equipment was rigged
down. A cement plug was pumped at 283 m DSF and the drill string was tripped
back to surface.
bottom hole assembly was made up with a 9-7/8 inch tri-cone bit fitted with a
mechanical bit release. Drilling in the dedicated logging Hole U1351C began at
2335 h on 25 November and ended in the evening of 27 November at 1100 m DRF.
1915 h on 27 November, while sweeping the hole clean with mud in preparation
for logging, a sudden wind change forced the vessel outside the maximum positioning
offset (8% of water depth, or ~10 m). The vessel lost power to three of the six
forward thrusters while trying to respond to the sudden shift. Position and
power were re-established within 15 minutes. The maximum excursion from the
hole was 38 m. With all drilling parameters still normal, Hole U1351C was
displaced with logging mud in preparation for logging. The drill string was
tripped to 80 m DSF and the section of drill pipe that was located at the
seabed during the excursion was inspected after it was recovered at the
surface. No damage to the drill string was visible.
triple combo logging string was assembled and run into Hole U1351C. With the
tool at ~912 m WSF, the winch lost weight, indicating that the tool got stuck.
At that point the tool could not be moved either up or down. The decision was
made to cut the logging line and trip in with drill pipe over the logging line
in an attempt to recover the triple combo logging string. The week ended while
still performing recovery operations to free the stuck logging tools.
at Hole U1351B proceeded using the XCB, although occasional attempts with APC
coring were made. Core recovery was generally low and decreased with depth.
Often only the core catcher was recovered and several cores were completely
empty. However, recovery was also highly variable: a number of longer cores
(2-7 m) were obtained even near the bottom of the hole. Coring operations in
Hole U1351B were completed at 1030 m (CSF) (U1351-B-116X) when the XCB drill bit
finally yielded to the increasingly hard formation. Average recovery for the
interval cored this week was 21%, average recovery for the entire hole was 31%.
Cores U1351-B-32X to -116X are composed mainly of sandy mud and very fine sand. Very fine sand dominates above ~300 m (CSF), while mud and sandy mud dominate below ~300 m.
Pleistocene/Pliocene boundary is near 150 m and the Pliocene/Miocene boundary
is at ~750 m, based on planktic foraminifers. Nannofossils lack definitive
markers. Benthic foraminifers indicate that the paleoenvironment deepens
downhole from outer shelf to upper slope. The last cores contained grayish
green mud with an estimated age of 10.6 to 11.0 Ma based on planktic
foraminifers. Therefore, ~150 m of Pleistocene, ~600 m of Pliocene and ~300 m
of late Miocene strata were recovered. Recovery of thick Pleistocene and
Pliocene intervals will provide high-resolution data on Pleistocene-Pliocene
sea-level and environmental fluctuations.
boundaries U11-U7, interpreted using the EW00-01 seismic profiles, are
represented as gaps in recovery because of the presence of coarse material at
these boundaries. It is therefore difficult to determine the exact positions of
the sequence boundaries. A sequence boundary might be at 1014-1024 m.
laboratory measurements of magnetic susceptibility, natural gamma radiation,
bulk density and colorimetry were supplemented with discrete measurements of
thermal conductivity, sediment strength, and density and porosity. Internal consistency among different measurement tools and methods was used to provide verification or error estimates. These measurements were used by stratigraphers to help them identify and characterize lithologic units.
measurements concentrated on performing full (0-80 mT) alternating field (AF)
and thermal (only up to 140°C) demagnetization on a selection of discrete
plastic cubic samples distributed throughout Hole U1351B. In addition, some
rock magnetic experiments were also performed (isothermal and anhysteretic
remanent magnetization acquisitions followed by AF demagnetization) in order to
establish the magnetic carriers.
samples from Site U1351 were analyzed for interstitial water constituents. In
addition to the well-defined sulfate-methane transition at 16 m, the upper ~200
m of sediment contain moderately high-salinity (10% greater than seawater)
brine along with higher carbonate, organic carbon, and nitrogen contents.
Dissolved calcium and magnesium show major changes over the depth interval 200
to 230 m, with calcium increasing (from 16 to 38 mM) while magnesium decreases
(from 33 to 24 mM), possibly representing dissolution of biogenic calcite and
re-precipitation of diagenetic carbonate. Potassium, silica, and sodium all decrease with depth, possibly associated with glauconite formation.
gamma ray, density, porosity and resistivity logs (triple combo) were run
throughout the entire depth of Hole U1351B. However the caliper indicated that
the condition of the hole was poor after 5 days of coring with long intervals
beyond the maximum caliper reading (>20 inches in diameter). Furthermore, a
cave-in at ~490 m (WSF) prevented the FMS-sonic tool from being run below this
depth. It was therefore decided to drill a dedicated logging hole at this site
(Hole U1351C) with the goal of providing improved logs.
Technical Support and HSE Activities
support staff processed cores and samples from Site U1351. The G-gun cluster
was set up in preparation for vertical seismic profiling (VSP). Prior to the
scheduled VSP operation a tool-box meeting was held with technical staff, the
crane operator and roustabouts for the safe handling of the guns and to prepare
for marine mammal watch.
fire and boat drill was held on 22 November for the entire ship's complement. A
safety meeting was held on 27 November with the Captain, Offshore Installations
Manager, Doctor, Operations Superintendent, Expedition Project Manager, and
Laboratory Officer to discuss protocols for the use of HF for microbiological
sample preparation. On 28 November, a 1% HF working solution was prepared in
the paleontology lab safely hood.