IODP Expedition 307:
Modern Carbonate Mounds: Porcupine Drilling
Week 1 Report
PDF file is available for download.
May 2, 2005
Operations
Port Call: The ship arrived dockside at Ocean Pier, Berth 32, Dublin, Ireland from
Expedition 306 at 1551 hr 25 April. Aside from the normal on/off loading of
freight the ship also took on 1044 metric tons of marine gas oil by truck.
Other port call activities included ODL and IODP/TAMU crew change/crossover,
offloading of all Expedition 306 frozen and "keep-cool" core/samples,
the dispatching of all Expedition 306 scientists, and the boarding of all
Expedition 307 scientists.
Port
Call Security & Safety: During the Dublin port call the ship operated under
a security level of MARSEC Level 1 (Yellow) and appropriate security measures
were in effect. All personnel were required to register with the
shipıs staff before being allowed on the ship and were also required to wear
proper identification at all times. All personnel who had not sailed within the
last 6 months were given safety briefings and participated in a safety drill
upon their arrival.
Transit
to Site U1316 (Prospectus Site PORC-4A): The last line away from Berth 32,
Dublin, Ireland was at 2057 hr on 28 April ~2.5 days ahead the scheduled
departure time. The pilot was dispatched at 2230 hrs and the vessel was
underway at full speed for Site U1316. The transit was relatively benign with
the ship rolling/pitching moderately while averaging 9.7 knots over the 302 nmi
distance. During the transit preparations were made for oriented non-magnetic APC
coring operations. Thrusters were lowered at 0343 hr 30 April. The vessel was
placed in dynamic positioning mode by 0403 hr and hydrophones were lowered.
Hole
U1316A: A positioning beacon was deployed at 0410 hr officially marking the
beginning of operations for Hole U1312A. However, the beacon failed shortly
thereafter and was recovered followed by deployment of a 2nd beacon.
After deploying the drill string to 6.4 m above bottom (based on precision
depth recorder), the first attempt to spud the hole returned a water core. The
drill string was lowered 7 m, and Hole U1316A was spudded at 1120 hr 30 April
and returning a 7.3 m of core.
Hole
U1316A was intended to be the logging hole and the target depth was set for
162.0 mbsf so that the tools could log the intervals of interest. APC coring
was routine from Cores 1H through 6H to 54.8 mbsf with recovery averaging over
100%. APC temperature measurements were taken on Cores 3H and 6H, and
orientation was taken on APC cores 3H through 7H. Core 7H short-stroked with a
3.24 m core. After Core 7H, the Tensor tool was removed and the non-magnetic
core barrel was replaced with a standard steel barrel. Core 8H short-stroked
and became stuck. The driller picked up with 80 klbs over-pull with no success
and the core barrel was finally released after over-drilling 1.5 m. The coring
assembly was switched to XCB. We encountered difficult coring conditions during
XCB Cores 9X through 21X. The coring times were long and recovery
erratic. The XCB shoe on Core 18X failed in torsion, but remained on the
core barrel, and heat checking was evident on other shoes. The average
penetration rate was less than 3 m/hr. Coring was suspended at 2015 hr on 1 May
because the time required for further advancement had reached a diminishing
return.
Preparations
began for logging Hole 1316A. A wiper trip was run from bottom to 30 mbsf and
back down to bottom using the top drive. One meter of fill was found and the
hole was displaced with 45 bbls of sepiolite mud. The top drive was used to
pull up to 98 mbsf and then set back. The bit was then pulled up to logging
depth of 30 mbsf. Schlumberger commenced rigging up for logging.
Science Summary
Port call:
For the shipboard scientific party, Expedition 307 began with a pre-cruise workshop
in Dublin, Ireland on April 26th and 27th, hosted by the Geological Society of
Ireland and organized by Jean-Pierre Henriet, the chief proponent of the
proposal to drill the Porcupine Bight Carbonate Mounds. The aim was to provide
a background on previous work on the Porcupine Mounds, introduction of
individual scientists' work and plans for the expedition, and discussion of
sampling plans. This enabled the science party to concentrate on learning their
laboratory equipment and tasks once they had boarded the ship on April 27th.
Sedimentary
strata recovered from Hole U1316 A are mostly siliciclastic and divided into
two distinct units, in terms of consolidation, color and biostratigraphic age.
Cores U1316A-1H to 5H are brown-gray partly bioturbated silty clay of late
Pleistocene age (Brunhes normal magnetic polarity), and contain dropstones. Two
coral rudstone/floatstone layers occur in Core 6H (55.1-59.1 mbsf), and
preliminary biostratigraphy indicates that they are late Pliocene to early
Pleistocene in age. Cores 7H to 21X (59.1-134.0 mbsf) are early Miocene in age
and are greenish gray siltstone, with grain size generally decreasing downhole.
The siltstone is rich in glauconite and yields microfossils (calcareous
nannofossils and foraminifers) and mollusks.
Interstitial
water sulfate decreased with increasing depth to a final concentration of about
5 mM at 130 mbsf. Methane was first detected at 80 mbsf and increased with a
concave up profile through the rest of the hole. Low concentrations of ethane
were also detected at 80 mbsf and increased in concentration with depth to the
bottom of the hole. The C2/C1 ratio of ethane to methane
decreased from a peak at 80 mbsf to low values at the bottom of the hole, and
was indicative of preferential oxidation of methane in the sulfate zone. Beyond
ethane, no higher hydrocarbons were detected. In the first tens of meters of
sediment, the total prokaryote counts were low, which is consistent with the
apparently reworked nature of the sediment (it contains many Cretaceous
microfossils).
Technical Support Activities
The
Expedition 307 technical staff boarded the vessel on April 26. Crossover took
place with the off coming crew and training started for the new staff in the
Physical Property, Paleomagic, Thin Section and Underway laboratories. There
was a service call for the microscopes. The chemistry labortories had an
Aglient service call. Two trucks of surface freight were loaded and the off
going air shipment picked up. The off going surface shipment was left onboard
to be shipped at Mobile; it contained no time-critical items. On April 27 cores
were off-loaded and the cold and frozen shipments picked up for shipment. Tours
of the vessel were conducted. On April 28 an introduction meeting was held with
the science crew. Both the scientists and the technicians were given an H2S safety course. The vessel sailed in the evening.
During
the short one day transit to the first site, the technical crew prepared the
shipboard laboratories for the commencement of coring. The scientific staff was
introduced to the laboratories and technical staff, and the laboratories were
prepared for the start of coring. A pre-site meeting was held and the marine
mammal policy reviewed to prepare for the upcoming VSP logging.
HSE Activities
A fire and H2S
drill was held on 29 April for the entire ship's complement. The technical
staff was instructed in the use of the Scott air packs and fixed air systems in
preparation for H2S should it be encountered.
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