< Previous week
IODP Expedition 342:
Paleogene Newfoundland Sediment Drifts
Week 8 Report (21-28 July 2012)
PDF file is available for download.
8 of Expedition 342 began while completing Hole U1410A by retrieving Cores
U1410A-27X and 28X to 259.8 m drilling depth below seafloor (DSF). The seafloor
was cleared at 0500 h on 22 July, ending Hole U1410A. Overall core recovery for
Hole U1410A was 256.88 m for the 259.8 m interval cored (99%). The total time
spent on Hole U1410A was 34.25 hours.
vessel was offset 20 m to the east. Hole U1410B (3398.7 m water depth) was
spudded at 0650 h on 22 July. Cores U1410B-1H through 18H were recovered to
153.8 m DSF using non-magnetic core barrels and the FLEXIT core orientation
tool. The XCB system was deployed for Cores U1410B-19X through 28X to the final
depth of 245.2 m DSF. The seafloor was cleared at 1620 h on 23 July, ending
Hole U1410B. The overall recovery for Hole U1410B was 244.84 m over the 245.2 m
cored (100%). The total time spent on Hole U1410B was 35.25 hours.
vessel was offset 20 m to the south and Hole U1410C (3386.9 m water depth) was
spudded at 1825 h on 23 July. Cores U1410C-1H through 16H were recovered to
146.8 m DSF using non-magnetic core barrels. No core orientation was performed
on cores from Hole U1410C. The XCB system was deployed for Cores U1410C-17X
through 27X to the final depth of 243.8 m DSF. The overall recovery for Hole
U1410C was 238.81 m out of 243.8 m cored (98.0%). The seafloor was cleared and
the vessel was secured for transit at 0915 h on 25 July, ending Hole U1410C.
The total time spent on Hole U1410C was 41.00 hours.
vessel arrived at Site U1411 (proposed site SENR-11A) at 1115 h (UTC-2.5 h) on
25 July after a 19.0 nmi transit from Site U1410, which took 2.0 hours at 9.5 nmi/hr.
The plan for Site U1411 called for three holes to a depth of ~250 m DSF. The first core
for Hole U1411A failed to capture the mudline and the hole was terminated after Core U1411A-1H. A
second hole, Hole U1411B, was successfully cored to 254.2 m DSF. The third hole,
Hole U1411C was piston cored to 9.2 m DSF, then advanced by drilling without
coring by 90.8 m and then cored to a total depth of 223.9 m DSF. Because of a
medical emergency, coring operations were terminated after Hole U1411C. The
overall recovery for Site U1411 was 91%. The total time spent on Site U1411 was
89.75 hours or 3.7 days.
Hole U1411A was spudded at 2320 h on 25 July. Core U1411A-1H was
recovered full (9.87 m) and did not recover the mudline so it was decided
to abandon Hole U1411A. The seafloor was cleared at 2320 h on 25 July, ending
Hole U1411A. Overall core recovery for Hole U1411A was 9.87 m for the 9.5 m
interval recovered (104%). The total time spent on Hole U1411A was 12.0 hours.
vessel was offset 20 m to the east. Hole U1411B (3298.8 m water depth) was
spudded at 0035 h on 26 July. Cores U1411B-1H through 20H were recovered to
177.4 m using non-magnetic core barrels and the FLEXIT core orientation tool.
The XCB system was deployed for Cores U1411B-21X through 28X to a final depth
of 254.2 m DSF. The seafloor was cleared at 1310 h on 27 July, ending Hole
U1411B. The recovery for Hole U1411B was 233.94 m over the 254.2 m cored (92%).
The total time spent on Hole U1411B was 38.0 hours.
vessel was offset 20 m to the south. Hole U1411C (3300.5 m water depth) was
spudded at 1505 h on 27 July. Cores U1411C-1H through 2H were recovered to 9.2
m DSF. After Core U1411C-2H, the hole was advanced by
drilling without coring to 100 m DSF in order to save operational time for
deeper objectives. After the drilling advance, APC coring continued with
Cores U1411C-4H through 9H (100-152.2 m DSF). All APC cores were oriented with
the FLEXIT core orientation tool and were recovered using non-magnetic core
barrels. The XCB system was deployed for Cores U1411C-10X through 17X to a
final depth of 223.9 m DSF. Following Core U1411C-17X, a medical emergency led
to the decision to terminate operations and transit to St. John's, Newfoundland.
The seafloor was cleared and the vessel was secured for transit at 0500 h on 29
July, ending Hole U1411C. The recovery for Hole U1411C was 118.62 m over the
133.1 m cored (89%). The total time spent on Hole U1411C was 39.75 hours.
Site U1411 (proposed site SENR-11A; 41°
37.1'N, 49° W) is a mid-depth site (~3300 m; ~2850 m paleodepth at 50 Ma,
Tucholke and Vogt, 1979), in the upper end of the Expedition 342 Paleogene
Newfoundland Sediment Drifts depth transect. The site is positioned to capture
a record of sedimentation around 1.65 km shallower than the largely sub-carbonate
compensation depth record drilled at IODP Site U1403. Our primary scientific
objectives for drilling Site U1411 were (1) to obtain an expanded record of the
upper half of a Miocene-lower Eocene sediment drift to compare directly to the
timing and nature of drift development at the Sites U1407-U1408 drift and the
Sites U1409-U1410 drift; (2) capture fine-scale variations in carbonate
preservation and lysocline shifts in Miocene-Eocene carbonate-rich sediments
that are about 550 m shallower than the Site U1406 Oligocene-Miocene section;
and (3) to evaluate the history of deep water and the carbonate compensation
depth on sediment chemistry, grain-size and provenance. Secondary objectives include the
possible recovery of the Oligocene-Miocene and Eocene-Oligocene boundaries for
comparison with the record of these events elsewhere, particularly Sites
U1404-U1406 along the Expedition 342 depth transect.
At Site U1411, we recovered a 254.5 m
thick sedimentary succession of deep-sea, pelagic sediments of Pleistocene to
Late Eocene age highlighted by an expanded record of the Eocene-Oligocene Transition.
The sedimentary sequence at Site U1411 comprises three lithostratigraphic
units. Unit I is a 13.45 m thick succession of classically Pleistocene
sediments of alternating gray and reddish brown clayey foraminiferal ooze, gray
silty sand with foraminifers, and brown to grayish brown silty clay with
foraminifers. Dropstones and sand-sized lithic grains are prominent in Unit I.
Unit II is a 198.23 m thick succession of silty clay, clay with nannofossils
and silty nannofossil clay of Early Miocene to Late Eocene age. Nannofossil
ooze is also present in Unit II, but only in the interval immediately after the
Eocene-Oligocene Boundary. Small blebs of quartz silt on core surfaces,
interpreted as ice-rafted debris are very common in the Miocene and Oligocene
sediments of Unit II. Unit III is 41.92 m thick and composed of greenish gray
and dark greenish gray nannofossil clay with foraminifers, clayey nannofossil
chalk with foraminifers, and clayey foraminiferal chalk. Laminated intervals,
some of which highly concentrated in foraminifers, are common in Unit III,
which has evidence for significant reworking and winnowing by currents
associated with drift formation.
Biostratigraphy at Site U1411 is based on
nannofossils and planktic and benthic foraminifers throughout the ~255-m thick
Pleistocene to upper Eocene succession of nannofossil ooze with varying amounts
of clay and foraminifers. Nannofossils, planktic foraminifers and benthic
foraminifers are present in all sequences. A short barren interval occurs
between the Pleistocene and lower Miocene-Eocene sequence. Radiolarians are
only present in the uppermost Pleistocene. A relatively thin Pleistocene
sequence overlies a lower Miocene to mid-Oligocene succession with relatively
poor carbonate microfossil preservation, followed by an expanded lower
Oligocene through upper Eocene succession. The Eocene/Oligocene boundary
transition has sedimentation rates of up to ~3 cm/ky.
While preservation of calcareous microfossils in middle to upper Oligocene is
poor as seen in the previous sites on Southeast Newfoundland Ridge, lower
Oligocene contains exceptionally well-preserved fossils.
Paleomagnetic work included routine
demagnetization measurements on archive section halves from Holes U1410A,
U1410B, U1410C, U1411B, and U1411C. For Holes U1410A and U1411B, step-wise
demagnetization, bulk susceptibility and AMS measurements were conducted on
selected samples. Two series of magnetostratigraphies were identified for Site
1410. The first interval spans the Pleistocene, whereas the second interval
spans all but the uppermost of the Middle Eocene. The Site U1410
magnetochronology suggests that average linear sedimentation rates (LSRs) were
~1.5-2.3 cm/ky during the Pleistocene, with higher sedimentation rates during
Chron C2 than during Chron C1. Average LSRs varied from 1.30 cm/ky at the
beginning of the Middle Eocene to 1.98 cm/ky at the end of it. Middle Eocene
LSRs peaked at 2.63 cm/ky during Chron C20n, which is one chron younger than
the interval of peak LSRs at Site U1409. Finally, the geomagnetic field
transitions from C18n.1n to C18n.1r to C18n.2n are recorded in exceptional
detail in Hole U1410B, and show remarkably similar behavior as the same
transitions recorded at Site U1408. For Site U1411, an Oligocene to Early
Eocene magnetostratigraphy was identified. This magnetostratigraphy indicates a
nearly complete and expanded Oligocene record (1.53 cm/ky average LSR, with
peak LSRs of 3.22 cm/ky); a hiatus of <1 m.y. in
the lower Oligocene; a highly expanded Eocene-Oligocene Transition (2.63 cm/ky
average LSR, with peak LSRs of 5.02 cm/ky); and at least three cryptochrons within C13r, one of which occurs in the same
stratigraphic interval as the first downhole appearance of the Eocene marker
foraminifer Hantkenina alabamensis.
Following the completion of drilling
operations, a composite depth scale and splice were constructed for Site U1410.
Due to the presence of clear astronomical cycles in magnetic susceptibility,
the splice is continuous down to ~228 m core composite depth below seafloor
(CCSF). Hole U1411A failed to recover a mudline and
only extended to 9.2 m DSF. Hole U1411B cored to a total depth of 254.2 m DSF.
Due to time constraints, Hole U1411C was advanced without recovery from 9.2 to
100 m DSF. Real-time correlation was possible between Holes U1411B and U1411C
from ~100 m CCSF to the base of Hole U1411C at ~220 m CCSF. Drilling
successfully recovered a spliced record, including the Eocene-Oligocene
transition, from ~103-169 m CCSF. XCB coring achieved poor recovery of Cores
U1411B-21X and 22X as well as Cores U1411C-13X and 14X, so there is a large gap
in the spliced record from ~180 to 201 m CCSF.
The geochemistry program this week completed
routine shipboard analyses for headspace gas samples, interstitial pore water
geochemistry, and bulk sediment geochemistry for Site U1410 (reported here) and
Site U1411 (to be reported in Site U1411 summary). At Site U1410, methane concentrations
(2.11 to 4.12 ppmv) were not above atmospheric levels. As with our other
Southeast Newfoundland Ridge drill sites (Sites U1407-U1409), interstitial pore
water profiles display evidence of compartmentalization with pronounced abrupt
downhole shifts in magnesium, manganese and potassium at ~220-230 m CSF-A,
suggesting that the unrecovered sequence of cherts functions as an aquiclude.
Overall, interstitial pore water profiles of potassium, calcium, and magnesium
are consistent with those resulting from exchange with, and alteration of
basaltic basement at depth. Downhole patterns of manganese, iron and sulfate
indicate modest organic matter degradation. Alkalinity, ammonium and manganese
concentrations are low and sulfate concentrations are high. A broad downhole
peak in boron concentrations at ~30 m CSF-A presumably indicates increased
supply from the terrigenous sediment component in lithostratigraphic
Carbonate content in the sediment column at Site U1410 ranges from ~0.7% to 93%.
The most prominent changes are 1) the downhole transition from Pleistocene nannofossil
ooze of lithostratigraphic Unit I (~40 wt% average) to Late Miocene to Oligocene clay of
lithostratigraphic Unit II (~10 wt%); 2) the downhole
transition (70 m CSF-A) from lithostratigraphic Unit
II to Unit III, a Middle Eocene sequence made up of alternations of clay and
white nannofossil ooze (carbonate content ~30 and 80 wt%, respectively); and 3)
a downhole step-decrease in carbonate content associated with the Middle to
Lower Eocene boundary (~92-46 wt%, ~210 m CSF-A). As observed in the previous
Southeast Newfoundland Ridge sites, this step correlates with excursions in
several proxies (e.g., color reflectance, magnetic susceptibility, NGR, TOC and
TN values) and marks a transition in time from pelagic chalk sedimentation to
clay deposition in the initial stages of drift development.
TOC values are typically 0.01%–0.57%
throughout the sediment column. Organic matter is thermally immature and
relatively well preserved with low Tmax values (380°-420°C).
Organic matter throughout the sediment column is a mixture of Type II (algal and
microbial) and Type III (land plant/detrital) kerogen.
In the middle of the week, we began to
measure pore fluid constituents from Hole U1411A samples. Measurements on
interstitial water, solid sediments, and organic matter characterization are
During week eight, a full physical
properties program was run on cores from all three holes at Site U1410 and for
Hole U1411A, including Whole-Round Multisensor Logger (WRMSL) measurements for
magnetic susceptibility, bulk density, P-wave velocity, and natural gamma
radiation (NGR), followed by discrete measurements on section halves for color
reflectance, magnetic susceptibility, moisture and density properties, and
compressional wave velocity.
Education and Outreach
The combined viewership for the
Expedition 342 YouTube videos has exceeded 8,000 views. Expedition 342 Episode
1 is now listed in the top 10 most viewed videos on the Ocean Leadership
YouTube channel. Episode 5 was uploaded this week and is already very popular. The
shipboard videographer is busy producing Episode 6. Ship-to-Shore broadcasts
involved campers in Florida and a teen center in San Antonio, Texas. The highlight
of the week was participating in the annual Bryce Canyon National Park Geology
Festival and the broadcast was a special ranger program. Posts continue on
Facebook, Twitter, and tumblr.
Technical Support and HSE Activities
shipboard labs were busy processing cores. End of expedition shipment requirements
were updated. A fire and boat drill was held on 28 July. Eye wash stations were
tested Monday 23 July.