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IODP Expedition 339:
Week 5 Report (12-18 December 2011)
PDF file is available for download.
The fifth week of Expedition 339 started while deploying the RCB coring
assembly and the underwater camera system down to the seafloor. Once the video
images provided by the underwater camera confirmed that the seafloor was clear
of obstructions, the driller tagged the seabed with the bit at 569.8 mbsf
(558.4 mbsl) at 1640 hr on
11 December. Following the retrieval of the underwater camera, Hole U1387C was
spudded with the RCB at 1850 hr. The hole was drilled with a wash barrel in
place to 290 mbsf where continuous RCB coring was initiated.
Rotary coring proceeded to a final depth of 870 mbsf by 0930 hr on 16 December. The results of the hole were 580 m cored
with a recovery of 71%. The average rate of penetration for the cored interval
was ~12 m/hr. The drilled portion of the hole was 290 m and the total
penetration (cored plus drilled) was 870 m. While penetrating the cored
interval, the drillers pumped 11 each 20-barrel and 2 each 30-barrel high
viscosity mud flushes to keep the hole clean of cuttings.
Near the end of the week we carried out downhole logging operations in Hole
U1387C. Following a wiper trip and a hole conditioning exercise, Hole U1387C
was displaced with 290 barrels of 10.5 ppg
mud to prepare the hole for downhole logging. The open end of the pipe was
placed at a logging depth of 104 mbsf. The Triple Combo tool string descended
through the seafloor at 0310 hr on 17 December and
was run down to 1220 mbrf (651 mbsf) where it was
blocked from further downhole progress by an obstruction in the hole. At this
depth, a bridge or ledge had already been noted during the hole
preparation from 649 to 653 mbsf. Logging started at 0539 hr
and the tool string was back on deck by 0830 hr.
The Versatile Seismic Imager (VSI) tool was run as a second tool string
during daylight. Marine mammal watch for conducting the vertical seismic
profile experiment (VSP) started at ~1000 hr. The airguns
(2-gun cluster, 7 m below sea level on the port side) had been ramped up in a
soft start procedure initiated at 1115 hr. The VSI tool started its descent
down Hole U1387C at 1120 hr and reached an
obstruction at 824 mbrf (255 mbsf) at 1205 hr. The
shallow penetration for this tool run indicated that the hole was closing
quickly with time. Despite the large diameter of the borehole
and the soft formation, good first arrival times were obtained for five
stations. The last log was made with the FMS-sonic, which was deployed at 1610 hr and could not go deeper than 334 mbsf. The FMS-sonic was
recovered and disassembled by 2300 hr. The drilling equipment was secured and
the vessel departed for Site U1388 (proposed site GC-04D) at 0230 hr on 18 December. The total time on site was 9.3 days.
The sedimentary sequence in Hole U1387B is essentially the same as that
cored in Hole U1387A. It is dominated by the three lithofacies
described previously as Lithologic Unit I at Site
U1386: (1) nannofossil mud, (2) silty
mud with biogenic carbonate, and (3) silty sand with
biogenic carbonate. Although the
overall abundance of the coarser lithologies is less
in the upper ~350 m of Holes U1387A and U1387B than at Site U1386, variations
in the relative abundances of the nannofossil mud vs.
the coarser lithologies are similar to the pattern of
relative abundance variations in Lithologic Unit I at
Site 1386. That is an upper zone with relatively higher abundances of sands and
silts, an intermediate zone with fewer sands and silts, and a lower zone with
higher abundances of sands and silts.
The deeper interval cored in Hole U1387C included lithofacies
and lithofacies sequences not encountered previously
at this site; these include:
1) A 59 cm-thick bed of dolomitic mud in Core U1387C-19R and another one
12 cm-thick in Core U1387C-20R. These are massive beds composed of fine-grained
dolomite. Their origin is still being discussed; in particular, whether they
are detrital, represent hardgrounds, or are diagenetic.
2) A recurrent stacking pattern of the three lithofacies
observed in the upper part of Site U1387, with shell-rich silty
sand to sand grading up into silty mud, relatively
lighter nannofossil mud, and relatively dark nannofossil mud, with a distinctive pattern of bioturbation in the upper 10-20 cm of each cycle. The
lighter color lithofacies are interpreted as
turbidites, whereas the darker muds are potentially contourites.
This pattern is well-developed in Cores ~U1387C-19R
3) Contorted/convolute bedding in several intervals from Core U1387C-34R
(~600 mbsf) to Core U1387C-43R (~685 mbsf). These intervals are interpreted as
recording submarine slumping events.
4) Partially cemented to heavily cemented sandstones in an interval of
low recovery, from Core U1387C-43R (~685 mbsf) to Core -47R (~722 mbsf), and
from Core U1387C-49R-CC (~748 mbsf) to Core -50R-1 (~751 mbsf). These include a
gray, strongly cemented, well sorted sandstone with abundant subrounded quartz grains, shell fragments, and dissolution
molds of shell fragments and a dark greenish gray weakly cemented, poorly
sorted silty/muddy sandstone. Additional information about these
sandstones will be derived from thin sections presently being prepared.
Below ~722 mbsf, the section is dominated by nannofossil
muds and silty muds with biogenic carbonate, with nannofossil muds becoming even more abundant in the last three to four cores, and tending toward muddy nannofossil ooze.
As was true in Holes U1387A and U1387B, the sediments in Hole U1387C are
dominated by colors of gray to greenish gray to dark gray to very dark
gray. Macrofossil debris is relatively common, especially as shell fragments.
Bioturbation intensity ranges from sparse to
slight, and recognizable ichnofauna are more common
than at Site U1386.
Core catcher samples from Holes U1387B and U1387C were prepared for nannofossil, planktonic and benthic foraminifer, and ostracod analyses. Pollen content was also examined in some
samples of Hole U1387C. Additional samples from the lower section of Hole
U1387C were also analyzed to provide supplementary biostratigraphic
control at Site U1387. Based on various calcareous nannofossil
and foraminifer events, we estimate that the recovered section at Site U1387 spans
from the Holocene to c. 5.8 Ma. The compilation of the final version of the
biostratigraphy report of Site U1387 is still in progress.
All routine physical properties measurements have been completed on all
cores from Holes U1387B and U1387C. These include magnetic susceptibility,
natural gamma radiation, bulk density, colorimetry, thermal
conductivity, sediment strength, moisture and density; as well as natural remanent magnetization and associated rock magnetic
experiments. Physical property records show very complex patterns that reveal changes in sand composition and major variations in the detrital content of the
The remanent magnetization of archive-half
sections of APC/XCB and RCB cores from all holes at Site U1387 was measured
before and after 20 mT
alternating field demagnetization. Detailed measurements of the demagnetization
behavior of discrete samples are currently in progress. Below ~100 mbsf in
Holes U1387A and U1387B and ~430 mbsf in Hole U1387C magnetic polarity is
mostly obliterated by a strong normal overprint and by coring disturbances.
With the exception of the top part of the Brunhes Chron, and the termination of Chron
C2n (Olduvai, 1.778 Ma) at ~410 mbsf in Hole U1387C the magnetostratigraphy
cannot be resolved without the pending results from discrete samples.
A nearly complete composite stratigraphic record was constructed down to
about 350 mbsf from the three holes cored at Site U1387. This site is only 3.8
km from Site U1386. Correlation of the composite sections from Sites U1386 and
U1387 aid in assessing the completeness of the records and provides an
opportunity to examine differences in sedimentation rates and processes that
occur between the sites.
Standard gas analysis from headspace samples were
performed for Hole U1387A from 0 to 352 mbsf and Hole U1387C from 354 to 865
mbsf. Methane, ethane, ethane and propane were detected. Bulk sediment analysis
of CaCO3, total and organic carbon, and total nitrogen have been
completed for Holes U1387A and U1387B, and are ongoing for Hole U1387C.
were taken one per core from Hole U1387A for interstitial water analysis to a
depth of 350 mbsf. We did not take
pore water samples below this level because of severe bisquiting
caused by XCB coring disturbance and drill water contamination of the
interstitial whole rounds during RCB drilling. Interstitial water measurements
of alkalinity, chloride, ammonia, sulfate, and major and minor seawater
elements for Site U1387 were completed. We also completed high-resolution water
isotopic analysis for Hole U1386B to a depth of 83 mbsf.
Education and Outreach
Expedition participants continue to share their experience aboard the JOIDES Resolution on the JR's website
(http://joidesresolution.org/blog) and other blogging sites. The expedition's Education Officer
continued to post daily updates on the JR Facebook page and Twitter account.
ship-to-shore interactive video conferences program were conducted: on Tuesday
with 5th graders from the Agrupamento no 1
de Escolas de Portalegre that were visiting the Centro Ciência Viva de Estremoz (Alentejo, Portugal); on
Wednesday and Friday with the two 10th graders classes of our
Education Officer from the Escola Secundária
de Loulé (Algarve, Portugal); and on Thursday with
Undergraduate 'Ocean Sciences' students from the Universidade
do Algarve (Portugal). Three other videoconferences are scheduled for next
Technical Support and HSE Activities
Activities of the USIO marine technical staff included laboratory and
instrument support, catwalk core processing, curation
and storage of core sections from Site U1387. They also carried out marine
mammal watch during the vertical seismic profile (VSP) experiment conducted at
Site U1386. A H2S Gas Alert and Boat Drill were held for all
expedition participants on December 17.