IODP Expedition 342:
Paleogene Newfoundland Sediment Drifts
Site U1409 Summary
PDF file is available for download.
Background and objectives
Site U1409 (proposed site SENR-22A; 41° 17.75'N, 49° 14.00'W) is a mid-depth site
(~3500 m; ~3050 m paleodepth at 50 Ma, Tucholke and Vogt, 1979), in the upper
mid-depth end of the Expedition 342 Paleogene Newfoundland Sediment Drifts
depth transect. The site is positioned to capture a record of sedimentation
around 1.5 km shallower than the largely sub-carbonate compensation depth record
drilled at IODP Site U1403. Site U1409, therefore, is located well above the
average late Paleogene carbonate compensation depth and should be sensitive to
both increases and decreases in carbonate burial, whether these reflect
variations in dissolution related to changes in the CCD, changes in carbonate
production, or variations in background non-carbonate sedimentation. Site U1409
is a companion site to Site U1410 where we employ an offset drilling strategy
to obtain APC/XCB records through a thicker section of the same sediment drift
than would be possible by drilling a single site. Our objective at Site U1409,
situated at the edge of the sediment drift, was to penetrate a more condensed
Middle Eocene sequence than anticipated in the mid-section of the drift, making
it possible penetrate Lower Eocene and Paleocene sediments at relatively
shallow burial depth (<250 m).
vessel arrived at Site U1409 (proposed site SENR-22A) at 1010 h (UTC-2.5h) on
16 July 2012, after a 26.3 nmi transit from Site U1408 that took 3.0 hours at
8.8 nmi/hr. The pipe trip to the seafloor was interrupted at 2863.3 m drilling
depth below rig floor (DRF) for a test of the subsea camera system, which had
been damaged at Site U1403, but strong ocean currents led to the early termination
of the test. After completing the pipe trip, Cores U1409A-1H through 16H were
recovered to 127.0 m drilling depth below seafloor (DSF)
using non-magnetic core barrels and the FLEXIT core orientation tool. Core
U1409A-15H experienced the first partial stroke and the APC system was advanced
by recovery to Core U1409A-16H. The XCB system was deployed for Cores
U1409A-17X through 26X to 200.1 m DSF. The seafloor was cleared at 0550 h on 18
July, ending Hole U1409A. Overall core recovery for Hole U1409A was 183.33 m
for the 200.1 m interval cored (92% recovery). The total time spent on Hole
U1409A was 43.5 hours.
vessel was offset 20 m to the east and Cores U1409B-1H through 14H were
retrieved to 122.5 m DSF using non-magnetic core barrels and the FLEXIT core
orientation tool. The XCB system was deployed for Cores U1409B-15X through 19X
to 170.5 m DSF. The seafloor was cleared at 0340 h on 19 July, ending Hole
U1409B. The recovery for Hole U1409B was 167.09 m over the 170.5 m cored (98%
recovery). The total time spent on Hole U1409B was 22.0 hours. The vessel was
offset 20 m to the south and Cores U1409C-1H through14H (124.2 m DSF) were
retrieved using non-magnetic core barrels. Core orientation was not performed
on Hole U1409C. XCB coring continued from Core U1409C-15X through 21X to the
final depth of 160.8 m DSF. The recovery for Hole U1409C was 160.98 m over the
160.8 m cored (100% recovery).
drill string was pulled to ~3200 m DRF and the rig prepared for a transit in
dynamic positioning mode to Site U1410. Poor weather conditions and high
surface currents foiled the recovery of the beacon, which was declared lost at
1515 h on 20 July, ending Hole U1409C. The total time spent on Hole U1409C was
35.5 hours. The overall percentage recovery for Site U1409 was 96%. The total
time spent on Site U1409 was 101.0 hours or 4.2 days.
lithostratigraphic units were described in the ~200 m thick sedimentary
succession of deep-sea pelagic sediments recovered at Site U1409. Unit I
contains alternating brown to reddish brown Pleistocene silty clay and
nannofossil ooze with varying abundances of foraminifers and diatoms and
occasional layers of muddy sand with foraminifers. Both the Unit I/II and Unit
II/III boundaries are erosive contacts.
Unit II is a heavily bioturbated, light yellowish brown Oligocene silty
clay to nannofossil clay, containing manganese nodules, patches of disseminated
sulfides, and rare concentrations of faint red oxide horizons. Unit III contains alternating beds of
light greenish grey nannofossil clay and white nannofossils ooze. Some
intervals are associated with oxide horizons and dampened color contrast
between adjacent beds. Unit IV contains lithologies ranging from pinkish white
nannofossil ooze with varying abundances of radiolarians and foraminifers to
dark brown claystone, siliceous limestone, and chert. The Middle Eocene to
Early Paleocene sediments of Unit IV are subdivided into three subunits.
Subunits IVa–IVc contain i) pinkish white nannofossil oozes with
radiolarians, ii) frequent cherts and highly varied lithologies including pink
to dark brown or grey nannofossil ooze to chalk with interbedded chert,
siliceous nannofossil limestone, and nannofossil claystone, and iii) pink to
pale grey or pale brown nannofossil chalk.
planktic foraminifers and benthic foraminifers are present through most of the
Pleistocene to lower Paleocene succession although all microfossil groups are
absent through a short interval between the Pleistocene and Oligocene.
Radiolarians are only present in the uppermost Pleistocene and the lower middle
Eocene through to the upper Paleocene. Thin Pleistocene and Oligocene sequences
overlie a middle Eocene through lower Paleocene succession with significant
hiatuses between the lower Pleistocene and upper Oligocene (22 my duration) and
lower Oligocene and middle Eocene (8.3 my duration). A short hiatus or
condensed interval is also identified at the Paleocene/Eocene boundary. The
Oligocene is highly condensed and may contain significant hiatuses.
Sedimentation rates are 0.68-1.31 cm/ky through the middle Eocene, 0.51-1.44
cm/ky through the lower Eocene, and ~0.47-1.80 cm/ky through the Paleocene.
reveals a series of normal and reverse magnetozones between Cores U1409A-1H and
13H (~0-115 m core depth below seafloor [CSF-A]), between Cores U1409B-1H and
13H (~0-120 m CSF-A), and between Cores U1409C-1H and 13H (~0-115 m CSF-A). These
magnetostratigraphies are straightforward to correlate among all three holes
and primarily consist of two time intervals. The first is from lower Chron C6Cr
(~23.9 Ma) through upper Chron C13r (~33.7 Ma); the second is from lower Chron
C19r (~42.3 Ma) through upper Chron C22r (~49.4 Ma). Chrons C9n, C9r, and
C10n.1n are not observed in any hole at Site U1409, indicating a hiatus at
~27.5 Ma. The C13n/C13r chron boundary (33.705 Ma) is tentatively identified in
Section U1409A-5H-2, between Sections U1409B-4H-5 and 4H-6, and in Section U1409C-5H-2.
The magnetochronology suggests that sedimentation rates were ~0.3 cm/ky through
the Oligocene and varied between ~0.5 and ~1.3 cm/ky across the Middle Eocene.
Sedimentation rates were higher before the Middle Eocene Climatic Optimum
(MECO, ~41.5 Ma) than post-MECO, similar to results from Site U1408.
density shows a general increase downhole from 1.40 to 1.95 g/cm3
with a superimposed abrupt step decrease to ~1.5 g/cm3 at the
transition between lithostratigraphic Units I and II.
Grain density averages 2.75 g/cm3 in Hole U1409A. Overall in Hole
U1409A, water content and porosity show a decreasing trend downhole (from 25%
to 60% and from 45% and 80%, respectively). At ~15 m CSF-A, water content and
porosity both show a decrease associated with the major hiatus between the
Oligocene and Eocene. P-wave velocity increases progressively downhole from
1500 to 1800 m/s. Magnetic susceptibility decreases from ~120 to 30 IU at 18 m
CSF-A and remains near-constant (~9 IU) to the bottom of the sediment column
except for three notable peaks within lithostratigraphic Unit III at ~50, ~72, and
~90 m CSF-A corresponding to oxide-rich layers. Color reflectance parameters a*
and b* show very distinct downhole variation throughout the sediment column. Natural
gamma radiation (NGR) and L* show five major peaks at ~38, 47, 70, 100 and 155
m CSF-A, all of which correlate with the major variations in calcium carbonate
content. Almost all physical properties show a shift or a peak at ~155 m CSF-A
associated with the Paleocene Eocene Thermal Maximum (PETM) event.
stratigraphic splice constructed for Site U1409 is stratigraphically continuous
from 0 to ~130 m and 150-190 m core composite depth below seafloor (CCSF). From
~130 m to 150 m CCSF, poor recovery associated with the change to XCB coring
prevented the generation of a continuous splice. Magnetic susceptibility, which
showed clear, correlative cycles, was used for correlation and splice
construction from 0 to 130 m CCSF. NGR was most useful for correlation below
~130 m CCSF, where magnetic susceptibility data was noisy as a result of
drilling disturbance associated with numerous chert layers. The chert
associated with the Paleocene-Eocene boundary was recovered in Cores U1409A-20X
and U1409B-18X, and the boundary appears to fall in the core catcher of Core U1409C-21X.
However, physical properties in the interval preceding the PETM appear quite
different in Hole U1409C compared to Holes U1409A and U1409B.
methane concentrations (1.79–6.43 ppmv) were not above atmospheric
levels. Interstitial pore water profiles display evidence of
compartmentalization with pronounced abrupt downhole shifts in magnesium,
manganese, and potassium at ~125-130 m CSF-A suggesting that the unrecovered
sequence of cherts acts 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.
Potassium and magnesium concentrations decrease and calcium concentrations
increase with depth. The downhole patterns of manganese and sulfate suggest two
zones of organic matter degradation within the recovered sequence, one above
the chert-rich interval and one below. In general, sulfate concentrations are
high, consistent with low total organic content (TOC). A broad downhole peak in
boron concentrations at 59 m CSF-A presumably indicates increased supply from
the terrigenous sediment component in lithostratigraphic Unit II.
content in the whole sediment column at Site U1409 ranges from 0% to 93%. As
with other sites drilled to date on the Southeast Newfoundland Ridge (Sites
U1407 and U1408), the most prominent change is a downhole step increase
(50 to 90 wt%, ~100 m CSF-A) in
sediments of NP14 age (around the Early to Middle Eocene boundary). This step
correlates with shifts in several proxies (e.g., color reflectance, magnetic susceptibility,
NGR, TOC and TN values) and marks a transition from pelagic chalk sedimentation
to clay deposition in the initial stages of sediment drift development. Middle
Eocene sediments appear cyclic, with alternating green clay-rich beds and white
nannofossil ooze layers having carbonate contents of 40% and 85%, respectively.
TOC values are typically 0.1%–0.5% throughout the sediment column.
Organic matter is thermally immature and relatively well preserved with low Tmax
values (380°-420°C). Organic matter is a mixture of Type II (algal and
microbial) and Type III (land plant/detrital) kerogen.