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IODP Expedition 318:
Wilkes Land Glacial History
Week 9 Report (28 February-8 March 2010)
PDF file is available for download.
6 March 2010
week consisted of (1) the continuation of APC/XCB coring at Site U1361
(WLRIS-05A) on the continental rise and (2) the end of expedition transit to
After we had
recovered Core U1361A-41X that reached to 388.0 mbsf, we had to deploy a
Free-Fall Funnel (FFF) due to an approaching iceberg. We raised the bit to 90
mbsf and deployed the FFF at 0700 hr on 28 February. At that time, the iceberg
was 5.5 nmi away and continuing to move toward the ship. We waited until around
0900 hr to see if it would change course, but it was still heading toward us.
At 0945 hr, we pulled the bit out of the hole and started moving the ship to the
north and out of the icebergs path.
wide iceberg passed directly over the hole at 1245 hr. Once the iceberg had
cleared the site and was no longer a threat, we moved back over the hole by
1500 hr and the reentry camera/sonar system was deployed. At 1555 hr, the video
failed when the system was 200 meters below the ship. When we recovered the
camera system we found that water had entered the cable head assembly on the
main umbilical cable. As soon as it was repaired we lowered it to the end of
the drill string.
Hole U1361A at 2137 hr on 28 February after 15 minutes of searching and
positioning the drill bit over the FFF. We lowered the drill string into the
hole as the camera system was retrieved and by 0130 hr on 1 March the bit had
reached the bottom of the hole at 388.0 mbsf without having experienced any
significant drag while running into the hole. Because of the little time
remaining before we had to depart for Hobart, we decided not to continue coring
and prepare the hole for the downhole logging.
The hole was
flushed with 50-barrels of sepiolite mud and then displaced with 179 barrels of
10.5 ppg heavy mud. The drill string was raised up to 88.6 mbsf for logging. We
conducted two successful logging runs with the triple combo and the FMS-sonic
tool strings with both reaching the bottom of the hole. Once logging was
concluded, the bit was pulled free of the seafloor and the vessel offset 50 m
north of Hole U1361A.
APC coring in
Hole U1361B started at 0840 hr on 2 March and established the water depth at
3466.9 mbrf. We only had time for two piston cores before the operational time
for the expedition ran out – in part due to a delay caused by ice buildup
on the APC piston rod. APC Cores U1361B-1H to 2H penetrated to 12.1 mbsf and
recovered 12.0 m (100%). We recovered the drill string, disassembled the bottom
hole assemble into component parts, and started our transit to Hobart,
Australia at 0030 hr on 3 March.
We are scheduled to arrive at the Hobart pilot station at 1000 hr on 8 March.
Site U1361 (WLRIS-05A) is located in the continental rise at 3466 m water depth.
Similar to Site U1359, the main objective at Site U1361 was to provide a
history of climate and paleoceanographic variability record from the middle
Miocene to the Pleistocene and to test the stability of the East Antarctic Ice
Sheet during extreme warm periods (e.g., Miocene Climate Optimum, early
Pliocene, and Pleistocene Isotopic Stages MIS 31 and MIS 11). Drilling at this
site targeted the timing and nature of deposition of the upper seismic units
(i.e., above the WL-U6 unconformity) defined on the Wilkes Land margin. Within
these units a shift in sedimentary depocenters from the continental rise to the
outer shelf is observed, possibly corresponding with the transition from a
dynamic wet-based to a more persistent cold-based EAIS, which is inferred to
occur during the late Miocene–Pliocene. At Site U1361 unconformities
WL-U6, WL-U7 and WL-U8 lie at about 5.13s, 5.03s, and 4.78s two way travel time
(TWTT), respectively (about 385, 300 and 100 mbsf, respectively).
Site U1361 is
located on the eastern levee of the Jussieau submarine channel downstream from
Site U1359. The levee relief at Site U1361 is about 195 m. The fine-grained
components of the turbidity flows traveling through the channel and hemipelagic
drape are inferred to be the dominant sedimentary processes building these
levees. Bottom-currents can further influence sedimentation in this
setting. The record from Site U1361 should be complementary to the record from
Site U1359. Similar depositional environments were cored during ODP Leg 178 in
the Antarctic Peninsula and ODP Leg 188 in Prydz Bay.
Two holes were
drilled at Site U1361. Hole U1361A reached a total depth of 388.0 meters below
sea floor (mbsf), using the Advanced Piston Corer (APC) system to refusal at
151.5 mbsf, followed by Extended Core Barrel (XCB) drilling to the bottom of
the hole at 388.0 mbsf. Hole U1361B reached 12.1 mbsf using the APC. Five
lithofacies (designated A through E) were identified at Site U1361 and, based
on their distribution in Hole U1361A, two lithostratigraphic units are defined.
Facies A and B consist of clays and silty clays with common diatoms and
foraminifera, and rare dm-scale sets of mm- to cm-scale silt and clay laminae.
These facies are restricted to the interval between 0.0 and 34.9 mbsf
(Lithostratigraphic Unit I). Facies A and B were deposited in hemipelagic
depositional environments, with isolated sets of silt and clay laminae indicating
occasional sedimentation from low-density turbidity currents or saline density
flows in a distal levee setting (Escutia et al., 2008). Facies C and D are
strongly bioturbated silty clays and diatom/nannofossil oozes with intervals
containing dispersed clasts. Facies E consists of laminated clays. Facies C
through E are present between 34.9 and 386.3 mbsf (Lithostratigraphic Unit II)
and are typical of contourite facies associations, although downslope currents
possibly contributed sediment as well.
U1361A-1H-CC through -41X-CC (1.5 to 386.31 mbsf) were analyzed for
microfossils. Diatoms and radiolarians provide good age-control for Hole
U1361A, resolving an uppermost Pleistocene through uppermost Middle Miocene
sedimentary succession with no major breaks in sedimentation.
assemblages at Site U1361 are indicative of productive, seasonally variable,
open marine conditions. Fluctuations in the abundance of marine benthic
and tychopelagic taxa such as Cocconeis spp., Diploneis spp., Paralia sulcata,
stephanopyxids and Trinacria excavata may indicate pulses of shelfal material
to the drill site. The presence of well preserved benthic foraminifers in
Sample U1361A-34X-CC (321.07 mbsf) suggests that depositional settings were
favorable for calcite preservation (i.e., not corrosive) for brief intervals in
the Miocene. The persistent presence of reworked Mesozoic/Paleozoic sporomorphs
within the palynological associations suggests ongoing erosion in the
diatom assemblages from sediments drilled at Site U1361 are typical Southern
Ocean open water taxa, with variable abundances of benthic, neritic and sea
ice-associated diatoms, indicating a high nutrient-high productivity, sea
ice-influenced setting throughout the late Neogene. High abundances of reworked
sporomorphs within the palynological associations indicates strong erosion in
the hinterland. Dinocysts are absent during this interval. The preservation of
planktonic foraminifers in the Pleistocene indicates that bottom waters were
favorable to the preservation of calcium carbonate.
investigations at Site U1361 document a complete section from the top of Chron
C2n to the top of Chron C3n. Below Chron C2n the recovered core was quite
disturbed and there is no complete analysis of the discrete samples as of yet.
The lower portion of Hole U1361A can plausibly be correlated to the
bottom of Chron C5n to C5An.
from Hole U1361A were taken for analyses of percent carbonate, carbon, nitrogen
and sulfur content, as well as major and trace element analyses. CaCO3
contents for most samples are well below detection limit (<1 wt%). Between
313.96 and 342.04 mbsf, however, carbonate contents increase to 12.1 - 24.8
wt%. This matches the recognition of nannofossil-bearing clays constituting one
of three major facies below 313.2 mbsf (Unit IIb). Carbon, nitrogen and sulfur
contents were measured on 15 selected samples covering the full range of CaCO3
contents (0 – 24.8 wt%). All concentration levels are very low (i.e.,
<0.5 wt% C, <0.03 wt % N, <0.02 wt% S), except for the four samples
with high calcium carbonate contents. Taken together with the CaCO3 measurements, these samples yield total organic carbon concentrations below 0.3 wt%, which is within the error or the respective measurements.
susceptibility data exhibit relatively high amplitude variations and this
apparent cyclicity at several scales occurs especially in the upper 165 mbsf
and between 305 mbsf and the bottom of the hole. There are two intervals with
relatively lower magnetic susceptibility units between 165 to ~185 mbsf and
between 265 to 305 mbsf. The variations in GRA density reflect the regular
fluctuations in lithology and porosity. The relative moisture content varies
between 63 to 22 wt% and porosity from 82 to 42% with gradual decrease with
increasing depth and overburden pressure.
operations started after a successful reentry of Hole U1361A. Runs with the
triple combo, followed by the FMS-sonic in Hole U1361 were successful. The
downhole logs at Hole U1361A have high-amplitude 1-5-m-scale variability
superimposed on a downhole compaction trend. It is likely that Milankovitch
band variability at eccentricity and possibly obliquity periods is recorded at
Site U1361. The downhole measurements at Site U1361 included four APCT-3
deployments in Hole U1361A that document a heat flow of 58.2 mW/m2.
Technical Support and HSE Activities
focused on the processing of the final cores from Site U1361 and spent the
remaining time conducting end of expedition activities (preparing sample and
other shipments, backing up data, and cleaning laboratories). A fire and boat
drill along with abandon ship drill was held on 4 March for the entire ship's complement.