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IODP Expedition 342:
Paleogene Newfoundland Sediment Drifts
Week 4 Report (24-30 June 2012)
PDF file is available for download.
Week 4 of
Expedition 342 began with the completion of Hole U1404B (Cores U1404B-22H
through 27H), to a depth of 228.7 m driller's depth below seafloor (DSF), at
1200 h on 24 June. Cores U1404B-21H through 27H were all partial strokes as the
formation began to firm up. A total of eight core liners were either collapsed
or broken and three of those had to be pumped out of the core barrel with a
high-pressure pump. The bit cleared the seafloor at 1310 h on 24 June, ending
Hole U1404B. A total of 27 piston cores were taken over a 228.7-m interval,
with a total recovery of 228.04 m (100%). The total time spent on Hole U1404B
was 40.5 hours.
The vessel was
offset 20 m to the south and Hole U1404C was spudded at 1445 h on 24 June and
drilled without coring to a depth of 16 m, based on the seafloor depth from Hole
U1404B (4759.1 mbrf; 4747.6 m water depth). Cores U1404C-2H through 4H were
recovered to a final depth of 44.5 m. A total of 28.98 m were recovered (102%).
The bit cleared the seafloor at 1945 h on 24 June, ending Hole U1404C. The
total time spent on Hole U1404C was 6.5 hours.
The drill floor
was secured and the vessel moved to the next site, Site U1405 (proposed site
JA-14A), in dynamic positioning (DP) mode at a speed of 0.8 nmi/hr. Cores
U1405A-1H through 26H were recovered to a depth of 241.9 m DSF using non-magnetic
core barrels and the FLEXIT core orientation tool. Advanced Piston Corer
Temperature (APCT3) measurements were taken on Cores U1405A-4H, 7H and 10H with
good results. Core U1405A-26H experienced the first partial stroke and the
liner and core had to be pumped out of the core barrel. The XCB system was deployed
for Cores U1405A-27X through 33X to a final depth of 308.6 m DSF. Overall core
recovery for Hole U1405A was 270.34 m for the 308.6 m interval cored (88%
recovery). The seafloor was cleared at 1120 h on 27 June, ending Hole U1405A. Total time spent on Hole U1405A was 51.50 hours.
The vessel was
offset 20 m to the east. The bit was spaced out to 4296.0 mbrf in an attempt to
recover ~8 m on the mud line core. Hole U1405B was spudded at 1305 h on 27 June.
Based on the 9.5-m (full barrel) recovery, the seafloor depth was determined to
be 4296.0 mbrf (4284.5 m water depth). Cores U1405B-1H through 24H were
recovered to a total depth of 223.5 m DSF using non-magnetic core barrels and the
FLEXIT core orientation tool. One 5-m interval was drilled ahead without coring
for stratigraphic correlation. The bit cleared the seafloor at 1610 h on 28
June, ending Hole U1405B. A total of 24 piston cores were taken over a 218.5-m
interval with a recovery of 219.84 m (101%). The total time spent on Hole
U1405B was 29.0 hours.
The vessel was
offset 20 m to the south and Hole U1405C was spudded at 1915 h on 28 June. Cores
U1405C-1H through Core 25H were recovered to a depth of 232.0 m DSF using
non-magnetic core barrels and the FLEXIT core orientation tool. The 25 piston
cores were taken over a 232.0-m interval with a total recovery of 227.77 m (98%).
The total time spent on Hole U1405C was 33.75 hours. The seafloor was cleared
at 0200 h on 30 June, ending Hole U1405C.
Overall at Site
U1405, 74 APC cores recovered 693.59 m of sediment (100% recovery) and seven
XCB cores recovered 24.12 m of sediments (36%). The overall recovery for Site
U1405 was 95%. The total time spent on Site U1405 was 114.25 hours or 4.8 days.
The drill floor was secured and the vessel began moving in DP mode to the next site at 1.4 nmi/hr.
The positioning beacon of Hole U1405C was left on site due to the risk of
losing it during recovery in difficult weather conditions. The plan is to
return to Site U1405 and recover the beacon after operations at Site U1406.
arrived on Site U1406 (proposed site JA-6A) at 1430h on 30 June. The APC system
was deployed and recovered two water cores until the third attempt recovered a 6.25-m
long mudline core. Seafloor depth was calculated to be 3826.3 mbrf. By week's
end Cores U1406A-1H through 4H were recovered to a depth of 34.7 m.
lithostratigraphy of IODP Site 1405 consists of an expanded record of
Oligocene-Miocene sediments recovered in Holes U1405A, U1405B, and U1405C under
a thin veneer of Pleistocene sediment. The dominant lithology is greenish grey
clay with various biogenic components like diatoms, radiolarians, and
calcareous nannofossils. This package, seems to correlate in age, lithology,
and seismic profile to Unit II at Site U1404, and appears to make up the
majority of the acoustically homogenous and largely transparent drift sediments
on J Anomaly Ridge. The Oligocene-Miocene boundary section drilled at this site
is perhaps the most expanded recovered to date from the oceans.
The green clay
and nannofossil-biosiliceous ooze of Site U1405 yield relatively abundant
microfossils providing a biozonation scheme for almost the entire succession.
Nannofossils are predominantly abundant and moderately well preserved. Planktic
foraminifers are generally common and well preserved throughout the sediment
column. Except for the top and bottom of the hole, radiolarians occur
consistently from lower Miocene to late Oligocene. As at Site U1404, abundant
diatoms and well-preserved infaunal benthic foraminifers at Site U1405 suggest
high productivity in the lower Miocene. According to the nannofossil
biostratigraphy, this high productivity interval is similar in age to the one
observed at Site U1404.
biostratigraphic analyses suggest a continuous, lower Miocene-upper Oligocene
interval with comparatively high sedimentation rates (1.4 cm/ky), and an
Oligocene/Miocene transition with high sedimentation rates (~10 cm/ky).
transition appears to be stratigraphically complete and contains at least one
carbonate-rich layer with common to abundant Braarudosphaera. Similar layers
have been described from the lower Oligocene of the North and South Atlantic
Ocean. Braarudosphaera is normally restricted to shelf seas and so these range
expansions may be caused by unusual paleoceanographic conditions, such as
increased upwelling or climatic-driven shifts in the position of boundary
work focused on routine demagnetization measurements on archive section halves
from Holes U1404B, U1404C, U1405A, U1405B, and U1405C. For Hole U1405A,
step-wise demagnetization behavior was also measured for approximately
every-other discrete paleomagnetic sample collected. Bulk susceptibility and
AMS measurements were completed on each discrete sample from Cores U1404A-1H through
9H. We chose to abandon measurements on every discrete sample for Hole U1404A
because we were faced with 18 hours of trouble-shooting the SRM, which lost
measurement sensitivity due to strong electromagnetic interference on the ship.
The solution to the SRM problems has resulted in greater sensitivity for the
SRM and the ability to extract a fairly clear reversal stratigraphy for Site
1405. Continuing work on Site U1404 shows a semi-continuous series of
magnetozones that can be correlated to Chrons 12r to C19r (31.034- 41.390 Ma).
Our age model agrees well with nannofossil biostratigraphy and provides a
magnetostratigraphic framework for Late Eocene carbonate accumulation events
and the Eocene-Oligocene transition.
stratigraphic correlation shows that "fast-track" (special task multisensor
logger [STMSL]) physical property data of Site U1404 and U1405 are inadequate
for real-time depth-adjustments to monitor and direct drilling operations. The
development of a reliable complete splice in the clay-rich biosiliceous
sediment recovered at both sites U1404 and 1405 will require combination of
shipboard physical property data, biostratigraphy and magnetostratigraphy
together with initial shore-based high-resolution measurements.
of Site U1404, several observations suggested the presence of methane hydrates
in the upper sediment column (~22-40 m core depth below seafloor [CSF-A]),
including 1) the presence of effervescent sediment, 2) expelled section caps
due to pressure, 3) bulging core liners, 4) low bulk density values, and 5) the
presence of massive pyrite. High-resolution sampling was conducted to test for
the existence of methane hydrates by drilling Cores U1404C-2H to 4H. Following imaging with a thermal imaging
device, headspace samples and 5 cm-long whole rounds for interstitial water
(IW) samples were taken on the catwalk, both at a sampling interval of one per
section. After logging Cores U1404C-2H through 4H on the STMSL, rhizon sampling
commenced at an interval of 50 cm through Hole U1404C.
Analysis of the
Hole U1404C headspace samples yielded methane concentrations of 1.82 to 2.99
ppmv, within the range of atmospheric concentrations. No other hydrocarbon traces were
detected. Results of manual titrations for alkalinity, pH, chloride, and
salinity from Hole U1404C IW samples illustrated uniform depth profiles. Based on the headspace analysis of gas
compounds and pore fluid data from whole round IW samples a decision was made to
archive the high-resolution rhizon samples from Hole U1404C without analyzing
their chemical components. Shipboard geochemical analysis of Hole U1404C samples
does not suggest the presence of methane hydrates at Site U1404.
At Site U1404,
downhole profiles of pore-water components reflect a combination of: 1) organic
matter degradation, 2) sorption/desorption reactions with clay minerals and
chemical exchange involving other minerals undergoing diagenetic reactions, 3)
up-section percolation of pore water during sediment compaction, and 4)
diffusion-related gradients produced by exchange with deep sources/sinks for
chemical constituents. Measured total carbon and nitrogen, and calculated total
organic carbon and C/N ratios were obtained for the remainder of Site U1404. We
estimated organic carbon by subtracting the inorganic carbon in wt% from the
total measured carbon in wt%. The acidification protocol for direct measurement
of organic carbon via flash EA was attempted and rejected. We observed unexpected
leakage from the silver capsules used in the acidification process leading to
sample loss and under-reporting of organic carbon and nitrogen content in the
samples in the process. To account for high CaCO3, we switched to
the La Luna Shale standard. Carbonate contents in Hole U1404A revealed
significant increases in CaCO3 content in middle to upper Eocene
strata as well as in the uppermost Oligocene to lower Miocene.
Hole U1405A, headspace gas, interstitial water (IW) and bulk elemental analyses
(IC, TOC, TC and TN) were routinely carried out. The recognition of prominent
increases in CaCO3 content in lowermost Miocene to uppermost
Oligocene sediments prompted sampling for additional analyses in the
corresponding lithostratigraphically distinct layers in Holes U1405B and
U1405C. Correlative intervals of elevated carbonate burial in the early Miocene
appear to exist at both Sites U1404 and U1405.
properties measurements at Site U1405 reveal an abrupt drop in magnetic
susceptibility, natural gamma radiation and color reflectance at ~15 to 20 m
CSF-A in all three holes. Bulk density gradually increases downhole from 1.30
to 1.60 g/cm3 below 20 m, while water content and porosity gradually
decrease from 70% to 60% and from 85% to 70%, respectively. P-wave velocity
also displays a gradual increase downhole. Most of these downhole trends
reflect the thick greenish, biosiliceous clay unit below 20 m.
Education and Outreach
three Ship-to-Shore broadcasts this week with the Birch Aquarium at Scripps
(San Diego), the National Marine Educators Conference (Alaska), and with scientist
Howie Scher's children and their fellow campers at Camp Gan Israel (South
Carolina). Five test calls were conducted to prepare for broadcasts in the
first weeks of July. Five blog posts were added to joidesresolution.org. The
most read was a post about plastic debris in the ocean seen from the JR. We
held a contest on Facebook to define ELMO and win a JR t-shirt, and posted lots
of popular pictures of the stormy weather. Dan Brinkhaus' second video,
Expedition 342: Core on Deck was posted on YouTube (http://www.youtube.com/watch?v=IgouMVdqLDI) and already has been viewed 800 times.
Dan is busy working on the third video. We are in the planning stages to do a
TV spot for the television station KBTX (College Station, TX), to do a
broadcast with the website BoingBoing, and an interview with Deep-Sea News.
Technical Support and HSE Activities
labs were busy processing cores. The antifreeze injection system was prepared
for VSP work on the next expedition. A new amplifier was installed in the movie
room. The fire drill due Friday, 29 June, was cancelled due to weather. The eye
wash stations were tested Monday June 25.