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IODP Expedition 342:
Paleogene Newfoundland Sediment Drifts
Week 2 Report (10-16 June 2012)
PDF file is available for download.
vessel arrived at Site U1403 (proposed site JA-1A) at 1708 h (UTC-2.5 h) on 11
June 2012, after a 946 nautical mile transit from Site U1402. The transit speed
averaged 12.6 nmi/hr but ranged up to 15.9 nmi/hr with Gulf Stream assistance. The local vessel time was
advanced ½ hour to the Newfoundland time zone. After deploying the beacon
at 1725 h, the drill string was assembled and prepared for operations. Hole U1403A
(39°56.60'N, 51°48.20'W) was spudded at 1020 h on 12 June. The seafloor was initially
calculated at 4955.7 mbrf (4944.3 m below sea level) based
on a mudline core. However, this water depth was
later suspected to be ~4 m too high, based on the seafloor depth for Hole
U1403B and correlation with physical features found in Hole U1403B. The APC system
recovered Cores U1403A-1H through 17H, where a hard layer was encountered at
~148 mbsf. The XCB system was deployed from Core U1403A-18X through 29X to a final
depth of 253.3 mbsf. The seafloor was cleared at 1240 h on 14 June, ending Hole
U1403A. Overall core recovery for Hole U1403A was 231.82 m for the 253.3 m
interval cored (91% recovery). The total time spent on Hole U1395A was 67.5
vessel was offset 20 m to the east. The bit was spaced out to 4954.5 mbrf in an attempt to recover ~8 m in the mudline core. The 3.9 m core recovery was a surprise. The
seafloor depth was calculated to be 4960.1 mbrf
(4948.7 m below sea level), which is 4.4 m deeper than recorded in Hole U1403A.
This along with other indicators called into question the accuracy of the mud
line core depth calculation in Hole U1403A. Hole U1403B was spudded at 1730 h
on 14 June. The APC coring system was used for Cores U1403B-1H through 16H. The
chert layer identified in the first hole was found to be exactly at the depth
expected for Hole U1403B, confirming the initial error in water depth for Hole
U1403A. The XCB system was deployed for Cores U1403B-17X through 18X, until we
broke through the chert layers at 150.4 mbsf. The APC coring system was again
deployed for Cores U1403B-19H through 22H to a depth of 175.9 mbsf. After a
partial stroke on Core 22H that recovered 2.97 m, the XCB system was again
deployed for Cores U1403B-23X through 32X to a final depth of 265.1 mbsf. Overall,
core recovery for Hole U1403B was 229.81 m for the 265.1 m cored interval (87%
recovery). At the conclusion of coring at 2200h on 16 June, the hole was swept
clean with 30 barrels of high viscosity mud and the drill string was raised up
to to 78.43 mbsf for logging with the triple combo
string and FMS-Sonic-NGR string.
U1403 (proposed site JA-01) is the first and the deepest water site to be
drilled on the J Anomaly Ridge, pinning the deep end of the Paleogene
Newfoundland sediment drifts depth transect. The site is positioned to capture
deep excursions of the calcite compensation depth (CCD) during the Paleogene
and to help improve stratigraphic control on the sediments to be drilled on J
downhole sedimentary progression at Site U1403 reveals a diversity of deep-sea
pelagic sediments comprising foraminifer sandy clay, unfossiliferous
clay, red, brown, and black chert, clay with radiolarians, clay with nannofossils and radiolarians, nannofossil ooze and chalk. Surficial sediments include foraminifer
sand with manganese nodules that overly a succession of unfossiliferous
clay, and clay with nannofossils and radiolarians. Chert is present below 150 m between
intervals of radiolarian clay and nannofossil ooze and chalk. Cherty intervals are
typically poorly recovered while intervening recovered intervals include the
Early Eocene Thermal Maximum 2 ("ELMO"), the Paleocene-Eocene Thermal Maximum
(PETM), and the Cretaceous-Paleogene (K/Pg) boundary.
A thin, graded, green spherule horizon is present at the K/Pg
boundary and interpreted as debris from the Chicxulub
impact event. Underlying sediments largely consist of color banded nannofossil
chalk to a depth of ~262 m.
The sediments recovered at Site U1403 are Pleistocene to Campanian in age. Quaternary nannofossils and planktonic
foraminifers are present in the uppermost 2 m of the section, but from 2 to 70 m
the sediments contain no age-diagnostic fossils. Nannofossils
and radiolarians indicate a middle Eocene (44.5 Ma) and lower Eocene to K/Pg boundary sequence from ~70 to 220 m. Preliminary biostratigraphic analysis suggests that there may be minor
hiatuses in the lower Eocene and middle-upper Paleocene. Fossiliferous
sequences of both the PETM and ETM-2 hyperthermal
events were recovered and include "excursion" nannofossil assemblages. The K/Pg boundary section appears to be biostratigraphically
complete. A high diversity uppermost Maastrichtian
nannofossil assemblage occurs below the K/Pg impact ejecta bed and very low diversity, post-mass-extinction
assemblages occurs above this bed. These earliest Danian
assemblages are dominated by calcareous dinoflagellates
and a handful of Cretaceous nannofossil survivor species, and are followed up-section
by a record of nannoplankton recovery and
diversification. Hole U1403B bottomed at ~262 m in upper Campanian
sediments consisting largely of nannofossil chalk. Planktonic foraminifera are
absent or very poorly preserved through most of the succession, except for an
interval of well-preserved assemblages in the lowermost Danian
and uppermost Maastrichtian. Benthic foraminiferal assemblages characterized by agglutinated
species, and sporadic occurrence of calcareous taxa, are present throughout the
Paleocene to Cretaceous. Planktonic foraminifera are mainly restricted to the
basal Danian and the Maastrichtian.
Paleomagnetic data reveal a sequence of possible
reversals below ~60 m in Hole U1403A. Non-magnetic core barrels were used during
APC coring at Site U1403 but a strong vertical overprint is persistent
in most cores even after 20mT demagnetization. Reductive
dissolution and the absence of age-diagnostic fossils are additional issues
that make the identification of magnetozones difficult, particularly between Cores U1403A-2H and -5H. Core
orientations provided by the FlexIt tool system, as
well as demagnetization data from discrete samples, substantially help clarify
the identification of polarity transitions. XCB coring obscured the declination
record of polarity reversals, as anticipated, but the inclination component
after 20 mT demagnetization seems to be
useful for recognizing some magnetozones. Bulk
susceptibility of discrete samples shows similar 1° and 2° cycles as those observed in the whole round magnetic susceptibility measurements.
partially spliced composite depth record was produced for Holes U1403A and U1403B.
The mudlines could not be reliably aligned owing to
an inconsistency in the apparent seafloor depths between the two holes.
However, based on real time analysis of density and magnetic susceptibility
data, the drillers were directed to pull up twice before taking Cores U1403B-3H
and 4H and this resulted in a good offset between between
successive cores in Holes U1403A and U1403B between ~20 and 150 m CCSF (core
composite depth below seafloor). Below 150 m CCSF, where chert layers were
encountered in both holes, floating composite sections for the ELMO, PETM, and the K/Pg boundary were constructed.
Age-depth relationships are based largely upon biostratigraphic datums for
radiolarians and calcareous nannofossils in Hole
U1403A. The upper ~80 m of the sediment column at Site U1403 is undated other
than an ~2 m-thick layer of Pleistocene sediment. The first dated record below
this barren interval is a 40.65 Ma radiolarian datum at 82 m CSF-A. Average
linear rates of sedimentation of ~0.6 cm/ky are
relatively stable to ~148 m CSF-A.
Between 148 and 149 CSF-A, an ~three million year-long
interval from 50.5 to 53.7 Ma is recorded by a series of chert horizons. The
lower Eocene to the PETM sequence accumulated at average linear sedimentation rates
of ~1.4 cm/kyr. Immediately underlying the PETM, a
highly condensed chert-rich interval comprising at least one hiatus between 182
and 189 m CSF-A corresponds to ~56-62 Ma. Average linear sedimentation rates of
~0.8 cm/ky are recorded in the interval spanning the
K/Pg boundary (~62-69 Ma).
Headspace gas, interstitial water (IW) and bulk
elemental analyses (IC, TOC, TC and TN) have been routinely carried out for
Hole U1403A. The sampling resolution was one sample per core for headspace gas,
typically one sample per core for IW analysis, and one sample per section for
sediment analysis. Additional sediment samples for carbonate analysis were
collected from the PETM, ETM2, and K-Pg transition sediments
to conduct higher resolution analysis (one sample per 20 cm). In headspace gas analysis for the purpose
of safety monitoring, methane was detected in low concentration and gradually increased
to 17 ppmv with depth. Other higher hydrocarbon gases
were not detected. TOC content was quite low in the upper 34 m in Hole U1403A, ranging from 0.14 to 0.46 wt %, except for the interval
27-31 m where TOC content ranged from 1.4 to 1.7 wt%.
Carbonate content varied between 0.04 and 0.80 wt% in
Cores U1403A-1H to 13H.
In the bottom of Core U1403A-13H (~137 m) carbonate
increases to 60% and fluctuates between about 2 and 40% to the bottom of the recovered sequence.
property data show downhole variations in sediment color, bulk density,
magnetic susceptibility and P-wave velocity. Discrete measurements of bulk
density focused on Hole U1403A. Thermal conductivity was not measured owing to
unresolved problems with the instrument's sensitivity to the environment. The uppermost
20 m of sediments recovered at Site U1403 are brown in color with high magnetic
susceptibility (80-20 instrument units [IU]) and moderate to low bulk density (1.5
g/cm3). Between 20~130 m, sediments are green,
blue or brown with low to moderate bulk density (1.1-1.5 g/cm3) and average magnetic susceptibility of
~20-30 IU. A transition into pink and tan sediments occurs at 130-140 m, an
interval in which carbonate and biogenic silica both make an appearance. Another
step in P-wave velocity (from 1500 to 1600 m/s) occurs below 160 m. This
transition is also reflected by increases in magnetic susceptibility and bulk
density. Below 160 m, bulk density gradually increases from 1.7 to 1.9 g/cm3, magnetic susceptibility shows
fluctuations between 20-140 IU, and color ranges from pale green, reddish brown
to pale brown. A step increase in P-wave velocity occurs at ~220 m. Color and
magnetic susceptibility cycles are evident in parts of the record that may
reflect various orbital periods.
Education and Outreach
The highlight of
week two in the vigorous Expedition 342 education and outreach program was the posting of Dan Brinkhuis' Expedition 342: Departure video on
the Ocean Leadership YouTube page. It has been viewed over 650 times in just
three days. Departure introduces Expedition 342 to the public and includes the
first installments of "Titanic Tales" with Richard Norris and "Eocene Invasion"
with Caitlin Scully and her cohort of Eocene stuffed animals. Currently there
is a naming contest for the Eocene mammals running on Facebook. We continue to
post stories and pictures on JR.org, Facebook, Twitter, and tumblr.
Seven new blog entries were posted on JR. org including a new Q&A interview
format, which was the most popular post this week. We had three Ship-to-Shore
broadcasts: Palmerton, New Zealand, and Pittsburg, USA (2). Shipboard
scientists across a wide spectrum of career stages, scientific specialties and
nationalities (Diederik Liebrand, Sandy Kirtland Turner, Chris Hollis, and Pincelli Hull) fielded student questions.
Technical Support and HSE Activities
The technical staff supported core processing and shipboard laboratory activities.
A fire drill was held on Tuesday, 12 June.