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IODP Expedition 329:
South Pacific Gyre Subseafloor Life
Week 3 Report (24-31 October 2010)
PDF file is available for download.
Week 3 of Expedition 329, the
South Pacific Gyre Microbiology, began with the RCB bit at 51 mbsf drilling
down to 71 mbsf in Hole U1365E. At 71 mbsf, the center bit was pulled by
wireline and RCB coring began. Core U1365E-2R began in sediment and crossed the
sediment/basement interface. The first core did not recover any of the sediment
and the basement recovery was poor compared with subsequent basement cores.
Coring continued with Core U1365E-3R and based on the slow penetration rates,
it was decided to proceed with half cores between wireline trips. Given the
delay on our operations schedule caused by the breakdown and repair to the
drill string sheave and the slow penetration rates at Hole U1365E, we decided
to stop RCB coring at 05:00 hours on Wednesday 27 October unless a major change
in basement composition was encountered. Coring ended as planned after
recovering Core U1365E-12R. A total of 11 cores were taken from a cored
interval of 53.2 m and with total recovery of 39.66 m of core (74.6% overall recovery).
Contamination testing was done on all cores after Core U1365E-2R with PFTs.
Given the shallow penetration into basement (~53 m), potentially poor hole
conditions, and time concerns over the overall expedition’s operations
schedule, we decided not to deploy our downhole logging tools and to terminate
the hole. After the last core was recovered, the drill string was tripped to
surface and the rig floor was secured at 21:15 hours on 27 October, ending Site
Thrusters were pulled and the
vessel started the 494 nautical miles sea voyage to Site U1366 (Scientific
Prospectus Site SPG-2A). After a 48.85 hour transit from Site U1365, averaging
10.1 knots, the speed was reduced, and thrusters and hydrophones were lowered.
Speed was less than expected because 2 of the propulsion motors were offline on
the starboard shaft with failed field coils. Dynamic positioning was then
initiated over Site U1366 at 22:15 hours on 29 October. The position reference
was a combination of GPS signals. No acoustic beacon was deployed, but a beacon
remains on standby in the event of a loss of GPS satellite coverage. While
automatic input into the DP system is not possible, it is possible to manually
hold the vessel in position to clear the seafloor with the BHA if necessary.
Rig floor operations commenced at
22:15 hours on 29 October. The top drive was picked up and the drill string was
spaced out and a wash down hole, U1366A, was drilled to determine basement
depth. Mudline was established as 5146.0 mbrf by tagging with the bit. After drilling down, apparent basement
was established at 17.8 mbsf. The bit was pulled back above the seafloor,
clearing the seafloor at 08:45 hours ending Hole U1366A.
After clearing the seafloor, the
center bit was pulled by wireline, the vessel was offset 20 m to the west and
coring operations began. Hole U1366B was spudded at 10:45 hours on 30 October
and the seafloor depth was established with a mudline core at 5141.8 mbrf. APC
coring continued to 17.2 mbsf. A total of 2 cores were taken with a total
recovery of 17.31 m (100.6%). After Core U1366A-2H, the bit was tripped back to
just above the seafloor ending Hole U1366B at 13:00 hours. PFT contamination
testing was done on all cores. Hole U1366C was spudded 20 m north of Hole
U1366B at 13:45 hours and advanced with the APC coring system to 25 mbsf before
APC refusal and after possible basement contact. Contamination testing was done
on all cores with PFTs. A total of 3 cores were taken with a total recovery of
25.42 m or 101.7%. The drill string was then tripped to just above the mudline,
clearing the seafloor at 17:15 hours, ending Hole U1366C. Hole U1366D was
spudded 20 m east of Hole U1366C at 18:00 hours and advanced 2 cores with the
APC coring system to 18.9 mbsf. The first two cores recovered 18.86 m of
sediment (99.8% recovery). After APC refusal without recovery on a third core,
an XCB core barrel was deployed and advanced two meters into the formation
without any recovery. Total recovery for Hole U1366D was 18.86 m with 20.9 m
cored and an overall recovery rate of 90.2%. Contamination testing was done on all cores with PFTs. After
the last core the drill string was then tripped to just above the mudline,
clearing the seafloor at 23:30 hours on 30 October, ending Hole U1366D and Week
three of Expedition 329.
During Week 3 of Expedition 329,
expedition scientists processed and analyzed cores from Sites U1365 and U1366.
All basement cores from Hole U1365E were processed quickly on the catwalk and
immediately after placed in cold storage, where they were examined by the
microbiologists and preliminary described by a petrologist. Basalt samples for
microbiological studies were identified and taken after approval by the Sample
Allocation Committee (SAC). Examined cores then were brought up to the Core
Laboratory for routine core flow processing and description. All cores were
measured for physical properties using the Core Laboratory track systems, split
into working and archive halves and the pieces curated, then imaged and
Basement rocks are light to dark
gray to light yellowish brown aphyric microcrystalline to cryptocrystalline
basalts, highly phyric basalts with large photcrysts, with abundant carbonate
and celadonite veins, reddish brown alteration halos and occasional black
calcite and chert. The wide range of basement lithologies represents different
Expedition geochemists analyzed sediment samples for
interstitial water chemistry and solid phase geochemistry (dissolved inorganic
carbon, alkalinity, oxygen concentration, nitrate, ionic composition, nitrate,
hydrogen, etc), while microbiologists prepared and analyzed samples for cell
enumeration, cultivation and shorebased molecular analyses. Shipboard microbial
cell counts from Site U1365 samples using flow cytometer and fluorescence
microscopy were consistent between the two techniques and show significantly
lower cell numbers in the sediments at Site U1365 than those found in
organic-rich continental margin sediments previously studied.
Toward the end of the week, the JR arrived at Site U1366
(Prospectus Site SPG-2A). The plan for this site was the same as for Site
U1365, to core three holes and dedicate one hole to build the site’s
stratigraphic framework and for sedimentological and petrophysical measurements,
another one for geochemical analyses and a third hole for microbiological
experiments. By week end, five holes were cored due to coring disturbance and
enough adequate material was recovered to conduct all the analyses planned.
Expedition scientists held a science meeting to present and
discuss scientific results from Site U1365 and present the scientific
objectives for Site U1366. The drafts versions of the Site U1365 reports were
finalized and submitted to the Co-Chiefs and EPM for review.
Technical Support and HSE Activities
Technical support staff processed
and curated cores from Sites U1365 and U1366, prepared thin sections, and
helped expedition scientists with laboratory instruments, applications and data
collection and upload. A fire and boat drill was held for all expedition
participants on Sunday October 31.