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IODP Expedition 330:
Louisville Seamount Trail
Week 3 Report (27 December 2010 to 2 January 2011)
PDF file is available for download.
This week begun with the scheduled drill bit change at
Hole U1372A after the bit had accumulated 64.4 hours of rotation. Once a new
bit and a rebuilt mechanical bit release were made up, the Bottom Hole Assembly
(BHA) was deployed with an extra stand of drill collars. The Free Fall Funnel (FFF) was reentered at 0100 hr on 27 December and by 0430 hr rotary coring was
resumed at a depth of 145.0 mbsf.
Coring advanced to 175.4 mbsf where ~3 hours was
expended working tight hole conditions by pulling back from 174 to 163 mbsf
with a maximum overpull of 40,000 pounds (40 Kips) and circulating frequent mud
flushes. Once the drill string was free, rotary coring then advanced from 175.4
to 232.9 mbsf, where the drill string again had to be worked free over a duration
of 5.5 hours. Coring then resumed and advanced slowly and smoothly from 228.9
to 232.9 mbsf. At this juncture, the hole was flushed with a 20-barrel mud
sweep in preparation for a wiper trip.
The drill string was pulled back from 232.9 to 204.5
mbsf where it became irretrievably stuck. Unlike the previous stuck pipe
episodes where both circulation and rotation were maintained, the top drive stalled
out at 800 amperes, making extrication even more problematical even though
circulation was still possible. From 2130 hr on 29 December until 0800 hr on 30
December all attempts to free the drill string and salvage the hole failed. The
only remaining course of action was to sever the first 5-1/2" joint of
drill pipe directly above the tapered drill collar in the BHA at a depth of 83
mbsf. This was successfully accomplished at 1950 hr on 30 December. Left in the
hole were one 9-7/8" core bit, one mechanical bit release, two modified
head subs, 11 controlled length drill collars, one modified top sub, one
tapered drill collar, and the lower end of one joint of 5-1/2" drill pipe.
Above the severed BHA there could have been a short open hole section of around
40 m available for downhole logging. After considering the probable condition
of the hole following the use of explosives and the potential risk to the
logging tools, downhole logging was not attempted in Hole U1337A.
In summary, coring in Hole U1372A penetrated 232.9 m
with an average recovery of 60.0%. The total penetration into basement was
187.7 m with an average recovery of 55.8% and an average rate of penetration of
2.2 m/hr. There was one bit change during the 227 hours (9.5 days) on site.
After the pipe was recovered and the beacon retrieved,
the vessel departed for approved alternate site LOUI-6A at 0300 hr on 31
December. The site is located on a similar age seamount (working name "28.6°S guyot") just 146 nautical miles to the SE. By 1730 hr on 31 December, the vessel was positioning on the new site. The voyage was accomplished at an average speed of 10.1 knots.
A new rotary core barrel BHA with a C-4 bit and
mechanical bit release was made up and deployed. The corrected PDR depth for
this site is 1455 mbrf. The VIT camera was deployed with the drill string and
by 0200 hr on 1 January 2011 a seafloor strewn with large boulders and outcrops
of hard rock was visible. From 0230 hr to 0445 hr a VIT survey was made around
the periphery of the site until a clear area was found that appeared to be able
to support a FFF deployment. After the driller tagged the seafloor at 1458.0
mbrf, the top drive was picked up and Hole U1373A spudded at 0700 hr on 1
January. By midnight on 2 January, the RCB coring assembly had penetrated 32.7
m with an average recovery of 52.9%.
Although operations started at the Site U1373 at the end of this
week, all of the analyses and observation summarized below were carried out on
core material and samples retrieved from Site U1372.
Core and thin section observations in Unit II of Hole U1372A (previously
defined as a single interval predominantly composed of basalt breccia and
conglomerate between the overlying pelagic sediments and the igneous basement)
allowed definition of five lithological subunits based on clast angularity and
composition of inter-cobble and boulder spaces: (1) Subunit IIA, a multicolor
basalt breccias; (2) Subunit IIB, a foraminiferal limestone with basalt clasts,
manganese incrustations and abundant Inoceramus fragments; (3) Subunit IIC, a
multicolor basalt breccia; (4) Subunit IID, a multicolor basalt conglomerate;
and (5), Subunit IIE, a bluish gray basalt conglomerate that was deposited on
top of the volcanic basement. Occurrences of Inoceramus fragments defined a Cretaceous
age for Subunits IIB to IIE. Bioclasts of shallow water origin (annelid and
calcareous alga) and well-rounded basalt clasts occur throughout Unit II. These
observations and the absence of rudist-coral limestone in retrieved sediments
indicate that the drilled seamount sequence represents a rocky shore
environment in the Cretaceous. Increasing clast roundness and increasing amounts
of shallow water bioclasts, in combination with decreasing amounts of
planktonic fossils (foraminifera and calcisphere) with depth downhole, support the interpretation that Unit II includes a deepening upward sequence developed
during the subsidence of the drilled seamount.
The paleontology laboratory group investigated the
carbonate matrix between the volcanic clasts of Unit II by preparing smear
slides from Intervals U1372A-4R-1W, 38-40 cm and -5R-1W, 30-32 cm. In addition,
two thin sections were prepared with 10 Ám thickness from Intervals
U1372A-5R-1W, 31-34 cm and -2W, 1-3 cm. Unfortunately, both smear slides and
the 10 Ám thin sections proved to be totally barren of nannofossils. Additional thin sections with normal
thickness (~30 Ám) from Cores U1372A-4R, -5R, and -6R were produced and
analyzed for planktonic foraminifer content. The preliminary results suggest
that the consolidated breccia in Section U1372A-4R-1 is correlated to the
Danian and Section U1372-5R-1 can be assigned to the late Campanian to early
Maastrichtian. No age diagnostic species are found so far from samples below Section U1372-5R-1.
Also during this week, the investigation of the
uncemented, pelagic carbonate sediments of uppermost Unit I (Cores U1372A-2R
and -3R) continued. The top of each section was sampled resulting in 8 samples
in total. Unfortunately both cores were homogenized owing to the RCB drilling
disturbance and the soupy nature of the sediment. Preliminary ages for the six
samples taken from this Core U1372A-2R are from biostratigraphic zones CN13 to CN15
corresponding to Pleistocene - Recent. Examinations of 2 samples from Core
U1372A-3R are preliminarily assigned to CN11a based on the common abundance of Reticulafenesta psuedoumbilica and Sphenolithus neoabies. There is an inferred discomformity above and below
CN11a in the column due to the presence of species in the mixed assemblage that
do not share a concurrent interval with all members of the assemblage. This is
taken to be an artifact of the drilling disturbance.
Below Unit II, drilling recovered igneous rocks. Lava
flows dominate the hole down to 128.9 mbsf with hyaloclastite making its first
appearance at 92.4 mbsf. The 36.5-meter interval between these two depths
represents a period of transition from subaerial to submarine volcanism
downhole. Hyaloclastite dominates the volcanic succession from 128.9 to 228.4
mbsf and includes several (up to 2.2 m) short intervals of massive basalt
representing pillows or submarine flow lobes. The hyaloclastite deposits can be
divided into seven individual eruptive packages on the basis of the phenocryst
content of the basaltic clasts. Three of these packages were terminated by
short (0.13, 0.16 and 3.3 m) intervals of vitric-lithic volcanic sandstone,
implying periods of quiescence or more distant eruption sites. Drilling
terminated in a beautifully fresh and thick (4.3 m penetrated), massive,
olivine-augite-plagioclase-phyric basalt lava flow.
The division of the igneous part (Units III-XVII) of
Hole U1372A into an upper subaerial and lower submarine stage is confirmed by
examinations of the Alteration Petrology group. A "reddish" alteration is
distinguished indicating oxidizing conditions for the upper portions of the
hole and a more "greenish" alteration from reducing conditions in the deeper
portions in the hole.
Three main secondary minerals were identified. Clay
minerals are among the most abundant alteration minerals. They were principally
identified using optical microscopy and X-ray diffraction (XRD). But because of
large amounts of associated calcite dominating the XRD patterns, it was
difficult to identify the more specific clay minerals without more detailed on-shore
XRD studies. Clays are often found as a coating in vesicles or are commonly
intergrown with carbonate and zeolite. Carbonate is the second-most abundant
secondary mineral and was found in vesicles, veins, and as cement in breccias.
XRD measurements on carbonate samples revealed that they are mostly calcite or
Mg-calcite, but some siderite is also present in the core. The third mineral is
zeolite, which is predominant in vugs and veins. Another major alteration phase
appears because of are the alteration of olivine to iddingsite, which is
present throughout the entire core.
Structural Geology group completed the identification and description of veins,
joints, geopetals, and aligned vesicles within core and thin sections. It was
observed that fractures and veins are relatively common in lava flows, but are
rare to absent in hyaloclastites. This distribution is likely due to
differences in rock rheology, with lavas being comparatively impermeable and
strong, but brittle, thus concentrating strain (i.e., fractures) and fluids
(i.e., veins) along zones of weakness. In contrast, the porous hyaloclastites
are able to deform via compaction, with the high porosity enabling easy fluid
flow, negating any significant flow through veins. If veins are present within
hyaloclastite units they are strongly concentrated along unit boundaries.
Several of the recovered lava flows (particularly in the upper subaerial
portion of the lava pile) have moderate to strong macro- and microscopic flow
addition to the predominately optical observation of the igneous rocks of Units
III-XVII by the three petrological laboratory groups, archive halves from Core
U1372A-14R through to the bottom of Hole U1372A have been also measured by the
Paleomagnetism group during this week. The section halves were AF demagnetized
in the cryogenic magnetometer system up to a peak field of 70 mT over 8 steps,
and the remanent magnetization measured at 2 cm intervals. These data have been
processed and directions picked for oriented pieces greater than 9 cm. In
addition, average directions for each continuous archive half-piece have also
been calculated. AF demagnetization has been carried out on further 41 discrete
8 cm3 cubes up to a peak field of 160 mT using the D-Tech AF demagnetizer,
and 32 discrete cubes have been thermally demagnetized in batches of eight up
to a temperature of 675°C. To monitor thermal alteration during thermal
demagnetization, magnetic susceptibility measurements were made using the
Bartington point susceptibility meter after each heating step. The last batch
of five discrete cubes is currently being thermally demagnetized. AF and
thermally demagnetized samples from the same lava pieces exhibit very similar
characteristic directions. These in turn show good agreement with the
directions derived from archive half-cores at the same interval.
The Physical Properties group continued running tests this
week on whole core and discrete samples from Units III-XVII. Whole round and
split half measurements have been completed for Cores U1372A-21R to -38R, along
with natural gamma ray testing with total count times between one hour and one
and a half hours, depending on the overall core flow speed. A total of 14 non-destructive
thermal conductivity tests were performed on selected intervals from Cores
U1372A-11R to -38R. Discrete samples were chosen in collaboration with the
Paleomagnetism group, and the large majority of them have been already subjected
to the entire set of paleomagnetic, P-wave, and moisture and density
measurements. The automated data filtering program for processing whole round
multi-sensor and section half multi-senor data was completed this week and has
been successfully implemented for Expedition 330 data. The group also performed
additional programming during this week that was needed to display data results
for use in presentations and site reports.
Also this week, the Geochemistry group completed ICP-AES
analyses of 22 igneous rock samples from this site. The initial run of these
samples through the ICP-AES machine revealed minor instrument problems, which
were subsequently addressed by the chemistry technician. Data reduction and
interpretation are underway after a successful second run. In addition, eight
samples of foraminiferal ooze from Cores U1372A-2R and -3R were analyzed for
total carbon, total nitrogen, carbonate as CaCO3, and total organic
whole round samples were collected for microbiological analysis; four from Site
U1372 and one already from the Site U1373. The standard suite of sampling,
which includes preservation for cell counts, DNA analysis, and 34S
and 13C stable isotope analyses, was conducted on each sample. For
one sample from Hole U1372A and for the first sample collected from Hole U1373A
(from Section U1373A-2R-1), culturing experiments were innoculated. During the
downtime between microbiology sampling, a rigorous blank (negative control) for
cell counts was developed, and some samples needed to be recounted after the
new cell count method was devised.
Education and Outreach
The educator or "Teacher at Sea" continued posting daily
blogs on the JR website and facebook page. The JR website had 763 visits
between December 26 and January 1. Of those, 287 were new visitors. The JR
Facebook page had over 12,000 page views per day during the week and has
increased its followers from 2,235 fans on December 26 to 2,245 fans on January
1. Several video conference tests were performed during this week in
preparation for the videoconferences beginning next week. The videographer has
written a draft script for a 330 Expedition Mission video, started creating
animations, collecting premade graphics, and laying in scratch narration. She
interviewed the Schlumberger Logging Engineer as he prepared to blast off the lower part of the drill string. She also shot and edited a "New Years" video, which will
be released shortly. In addition, she recorded a new song "Calm Before the
Core," with a click track and sent it to her band in San Francisco, hoping
they have time to kick it up.
Technical Support and HSE Activities
Technical staff engaged in providing full support for
coring operations at Sites U1372 and U1373. No HSE incidents to report. Other
activities included the following:
1. Deployed magnetometer during transit from Site U1372 to U1373.
2. Initiated work on relocating whole core track amplifiers to reduce NGR electrical interference.
3. Continued effort on minor software upgrades to various applications.
4. Continued software development for the core liner engraver.