< Previous week | Next week >
IODP Expedition 324:
Shatsky Rise Formation
Week 2 Report (13-19 September 2009)
PDF file is available for download.
20 September 2009
vessel was positioned on Site U1346 (Prospectus Site SRNH-2) at 0930 hr on 14
September. The 1129 nmi voyage from Yokohama was accomplished at an average
speed of 11.8 knots and was without incident. The four-stand rotary core barrel drilling assembly was made up and deployed as the drilling crew performed the routine first site measuring and internal clearance check of each tubular.
the driller tagged seafloor at 3630.0 m DRF (3.4 m deeper than the corrected
PDR depth), Hole U1346A was spudded with a center bit in place at 0140 hr on 15
September. The hole was advanced to a depth of 71.0 m CSF-A at an average rate
of penetration (ROP) of 20.8 m/hr. During the course of drilling this interval,
hard layers were encountered at 60.0 m, 67.0 m, and 71.0 m and were assumed to
be chert. The worn center bit was
retrieved by coring line and replaced with a wash barrel. The hole was advanced
by drilling ahead from 71.0 m to 100.5 m CSF-A. The 29.5 m advance through
chert layers was accomplished at an average ROP of 8.9 m/hr. The wash barrel
contained 0.21 m of chert including one nicely cored single-piece sample that
was ~15 cm in length.
coring was initiated at a depth of 100.5 m and deepened the hole to a total
depth of 191.8 m by 0915 hr on 18 September. Basaltic basement was contacted at
a depth of 140 m. The total penetration into basement was 51.8 m. The average penetration rate for the
cored interval was 2.0 m/hr with an average recovery of 29.0%. The average
penetration rate for basement coring was 1.3 m/hr with an average recovery of
38.7%. Because of the slow penetration rate combined with the successful
recovery of material suitable to address most of the objectives for this site,
it was decided to end coring at this depth and prepare the hole for logging
operations. An additional factor in the decision to cease coring operations at
this site was the approach of Typhoon Choi-Wan.
a wiper trip and displacement of the hole with 29 barrels of mud, the Triple
Combo tool was deployed on 18 September. The tool was able to log the open hole
to within 10 m of the bottom of the bore. The poor condition of the hole did
not warrant deployment of the FMS-sonic tool suite. Logging was secured by 0845
hr on 19 September.
drilling assembly was pulled free of the seafloor and fully recovered. After
the beacon was recovered from 20-foot seas, the thrusters were retracted, and
the vessel departed for the 370 nmi voyage to Prospectus Site SRSH-3B at 1800
hr on 19 September. Because of the proximity of SRCH-5 and SRSH-6 to Typhoon
Choi-Wan's projected track, it was decided to proceed directly to the more
southerly and higher priority site.
basement of Shatsky Rise was previously cored during ODP Leg 198 at Site 1213
located on the Southern High (TAMU Massif). Most of the igneous cores
(1213B-28R to 33R) recovered from Hole 1213B are available on board and were used to practice workflow and core description using the DESClogik application, the new interface for entering descriptive information to the database.
of the igneous rocks from this site is also of direct relevance to achieving
the scientific objectives of Expedition 324. In the beginning of the second
week, the large group of volcanologists, igneous petrologists, alteration
specialists, and structural geologists onboard Expedition 324 finished their
examination of the basement cores previously recovered at Site 1213. Three
complete massive basaltic flow units were identified based on groundmass grain
size variations, the presence of thin chilled margin zones, and changes in
point-source magnetic susceptibility and color reflectance. All three units are
slightly to completely altered to low-temperature secondary phases that
partially or completely replace the primary phases and the glassy mesostasis.
Two main vein generations were observed with a green clay and calcite vein type
that is dominant and a dark-green clay with minor pyrite vein type.
these cores allowed the scientists and technical staff to practice hard rock
core flow, sampling procedures, core description, database uses and other
onboard protocols. The DESClogik software templates were finalized and all
macroscopic and microscopic thin section descriptions for Site 1213 cores were
completed and entered into the LIMS database. The core describers started on a
short report on the basement samples from Site 1213 that will be added to the
Expedition 324 Proceedings volume.
U1346, the first drill site of Expedition 324, is located on the Northern High
(Shirshov Massif) of Shatsky Rise and was chosen to yield information about the
late stage of this large igneous plateau.
first six cores from this site contained sedimentary material. The first three
cores (including one wash core) recovered small isolated pieces of dark-colored
chert. Cores U1346A-4R to -6R recovered approximately 3.5 m of lithified
sediments, including limestones and mudstones. Core U1346A-4R is an intriguing
mixture of basaltic rock associated with calcareous sediments. The basalt
appears to have intruded into soft, clay-bearing calcareous sediments,
intermingling with the sediment at the margins and deforming the original
depositional bedding. Stratigraphically below, there is a well-preserved
laminated, graded sandstone to mudstone interval interpreted as turbiditic in
origin. Beneath this, clayey limestone pieces in Core U1346A-5R and -6R contain
abundant, angular volcaniclastic grains and bivalve shell fragments, suggesting
a relatively shallow depositional marine environment in close proximity to a
volcanic sediment source.
nannofossils occur through all the recovered carbonate sediment intervals. Ages
estimated from calcareous nannofossils remain inconclusive, ranging from the Berriasian to Campanian, yet two samples from the uppermost part of Core U1346A-4R and Section U1346A-5R-CC can be narrowly constrained to Zone NC4a (131.2129.6
Ma) of the Hauterivian. Foraminifera successfully retrieved from two levels in
Section U1346A-4R-CC are composed entirely of benthic forms and the planktonic
group is completely absent, possibly due to the pre-Aptian age (i.e., prior to
major diversification of planktonic foraminifera) and/or because of an
ecological bias induced by overwhelmingly large population of radiolaria.
Benthic foraminifera are diverse and predominante the upper bathyal assemblage.
one of the highlights at this site is the recovery of the 2.9 m long
spectacular succession of highly vesicular lava intermixed with calcareous
sediment in Core U1346A-4R, which has been interpreted as possible peperite but
further detailed studies are needed for confirmation. Below this "peperite" and
the short sediment succession described above, we recovered a seemingly
continuous sequence of numerous small 0.3 to 4 m basalt pillows (U1346A-6R to
-16R). In total more than 40 individual inflation units could be identified on
the presence of pillow contact zones, chilled glassy margins, vesicle
abundance, banding and filling, cm-long pipe vesicles, non-vesicular pillow
cores, and so on. These basalts are all aphyric containing a large proportion
of very fine-grained plagioclase laths set in a variolitic matrix. The pillow
basalts are generally vesicular in nature and have zones that are moderately
vesicular (30%-50% vesicles).
of the igneous rocks is highly variable and in some places pervasive, ranging
from relatively fresh dark gray basalts in the pillow units at the bottom of
the hole, to completely altered and oxidized brown vesicular basalts. Green and
brown clays are the main secondary phases of the highly altered basalts and
replace the primary phases as well as the glassy mesostasis. Minor pyrite and
calcite have also been observed associated with the groundmass clays, as well
as in veins. We are awaiting onboard geochemistry and XRD data to evaluate the
extent of the alteration. The first thin sections were produced and are now
being studied, photomicrographed and described.
examinations confirmed the interpretation that the lower igneous units
recovered at this site are formed by pillow basalts. Many pieces show typical
pillow structures, having heterogeneously and/or radially distributed cracks
and veins. Many vesicles, dominantly filled with calcite, are layered parallel
to the rim of pillows. Some of the vesicles, on the other hand, form elongated
pipe structures pointing towards the rim.
types of vesicles are generally concentrated along the rim of the individual
pillow units resulting in lower vesicularity in the center. Only longer pipe
vesicles (>1 cm), however, are also found in the central portion of the
to analyze both sedimentary and igneous samples were completed in the chemistry
lab this week. A test run of the CHNS analyzer was conducted, and preparation
of samples for CaCO3 and total organic carbon analysis was complete
and analysis of a set of samples began. Modification and development of Excel
spreadsheets for the reduction of shipboard ICP-AES major and trace element
data was completed, and a group of standards was analyzed. The results were
used to verify that the machine was working properly and to refine the spreadsheets. Processing of samples of igneous rocks and vein-filling material from the Site U1346 cores is underway.
contrast to chemical analyses, requiring long preparation time and
time-consuming instrument set-up, physical property measurements could start
thermal conductivity setup was tested with the basaltic samples from ODP Leg
198 available on board and the Macor disc standard. All recovered material
(sediment and igneous sections) from Cores U1346-1R to -16R have been run
through the whole round multisensor logger for measurement of gamma ray
attenuation (GRA) density and magnetic susceptibility at 2 cm intervals; and
through the Natural Gamma Ray logger (NGR) in two positions with a count time
of 1800-5400 seconds, depending on available time between core recovery.
Density measurements of basaltic material is generally 2.22.3 g/cm3,
which is slightly lower than the range of 2.42.7 g/cm3
measured on Leg 198 Shatsky Rise basalts. This could be due to the pervasive
alteration observed in the Hole U1346A cores. Sixteen discrete physical
property samples were taken from cores 4R-11R, and determination of moisture
and density, and compressional wave velocity in three directions are underway.
discrete physical property samples are being shared with the paleomagnetists
who spent the first part of this week testing the software (both for long core
sections and discrete samples) for the 2G-Cryomagnetometer. It was found that
the long-core software is reliably stable while the discrete-sample software
needs further improvement. Several sections from Leg 198 cores (Sections
1213B-28R-1 and 3, Sections 31R-1 through 4, Sections 32R-3 and 4, and Section
33R-2) were re-measured. Magnetic remanence of the cores with 0, 30, and 40 mT
AF demagnetization steps were measured. Remanence inclinations and declinations
from Leg 198 cores were found to be 0 and 90 degrees, respectively, and the
remanence magnetization intensities are much higher than the previously
documented values from Leg 198 after 30 mT demagnetization. Remanence
magnetization intensity values increase over time (within 12 hrs or 3 days) up
to 1 A/m even after demagnetized to 40 mT. Since this puzzling behavior seems
to be restricted to the Leg 198 samples, it was planned to investigate this
issue in more detail with shore-based measurements. Next, several sections
recovered from Hole U1346A were demagnetized and measured (Sections U1346A-6R-1
and -6R-2, -7R-1 and -7R-2, -9R-3, -10R-1 and -10R-2). These basalt archive
halves were stepwise AF-demagnetized up to about 40 mT. When demagnetized to
higher fields, all the basalt cores regained some magnetization and their
natural remanent magnetization (NRM) inclination tended towards 90 degrees.
This behavior is somewhat similar to that observed in the Hole 1213B cores.
Until it can be determinated if this is due to the samples or the magnetometer,
it was decided to stop the AF demagnetization by the 2G magnetometer.
Preliminary determinations of characteristic remanent magnetization (ChRM) are
being processed on discrete samples by using DTech AF demagnetizer and Molspin
eventful week was concluded by logging operations in Hole U1346A. Despite high
sea state one logging run was successfully completed and provided gamma ray,
density, and resistivity measurements from this hole including the sediment
basement interface. The results show a variable size hole, several distinctive
resistivity units, and uranium anomalies near the sediment basement contact
that could indicate zones of focused hydrothermal fluid flow. The FMS-sonic
tool string was not run due to poor borehole conditions. The wireline heave
compensator was tested in heave conditions ranging from 4 to 5 m with
occasional excursions up to 6 m.
Technical Support and HSE Activities
arrival of the first core on deck on September 16 the shipboard labs were busy
processing cores and samples. The ALOs met with the marine technicians on their
shifts and explained how to handle and curate hard rock cores. Dr. Sager gave a
presentation about the expedition objectives at Shatsky Rise for the ship's
crew and technical staff.
A fire and boat drill was held on September 18 for the entire ship's complement. The safety showers and eyewash stations were tested.