IODP Expedition 318: From Greenhouse to Icehouse at the Wilkes Land Antarctic Margin

Abstract

Integrated Ocean Drilling Program (IODP) Expedition
318, Wilkes Land Glacial History, drilled a transect of sites
across the Wilkes Land margin of Antarctica to provide a
long-term record of the sedimentary archives of Cenozoic
Antarctic glaciation and its intimate relationships with global
climatic and oceanographic change. The Wilkes Land drilling
program was undertaken to constrain the age, nature,
and paleoenvironment of the previously only seismically
inferred glacial sequences. The expedition (January–March
2010) recovered ~2000 meters of high-quality middle
Eocene–Holocene sediments from water depths between 400
m and 4000 m at four sites on the Wilkes Land rise (U1355, U1356, U1359, and U1361) and three sites on the Wilkes
Land shelf (U1357, U1358, and U1360).

These records span ~53 million years of Antarctic history,
and the various seismic units (WL-S4–WL-S9) have been
successfully dated. The cores reveal the history of the
Wilkes Land Antarctic margin from an ice-free “greenhouse”
Antarctica, to the first cooling, to the onset and erosional
consequences of the first glaciation and the subsequent
dynamics of the waxing and waning ice sheets, all the
way to thick, unprecedented "tree ring style" records with
seasonal resolution of the last deglaciation that began
~10,000 y ago. The cores also reveal details of the tectonic
history of the Australo-Antarctic Gulf from 53 Ma, portraying
the onset of the second phase of
rifting between Australia and Antarctica,
to ever-subsiding margins and deepening,
to the present continental and ever-widening
ocean/continent configuration.

doi:10.2204/iodp.sd.12.02.2011

Full text

Scientific Drilling, No. 12, September 2011 15
IODP Expedition 318: From Greenhouse to Icehouse at the
Wilkes Land Antarctic Margin
by Carlota Escutia, Henk Brinkhuis, Adam Klaus, and
the IODP Expedition 318 Scientists
doi: 10.2204/iodp.sd.12.02.2011
6FLHQFH5HSRUWV
Abstract
Integrated Ocean Drilling Program (IODP) Expedition
318, Wilkes Land Glacial History, drilled a transect of sites
across the Wilkes Land margin of Antarctica to provide a
long-term record of the sedimentary archives of Cenozoic
Antarctic glaciation and its intimate relationships with global
climatic and oceanographic change. T he Wilkes Land drill-
ing program was undertaken to constrain the age, nature,
and paleoenvironment of the previously only seismically
inferred glacial sequences. The expedition ( January–March
2010) recovered ~2000 meters of high-quality middle
Eocene–Holocene sediments from water depths between 400
m and 40 00 m at four sites on the Wilkes Land rise (U1355,
U1356, U1359, and U1361) and three sites on the Wilkes
Land shelf ( U1357, U1358, and U1360).
These records span ~53 million years of Antarctic history,
and the various seismic units ( WL-S4–W L -S9) have been
successfully dated. The cores reveal the history of the
Wilkes Land Antarctic margin from an ice-free “green-
house” Antarctica, to the first cooling, to the onset and ero-
sional consequences of the first glaciation and the subse-
quent dynamics of the waxing and waning ice sheets, all the
way to thick, unprecedented “tree ring st yle” records with
seasonal resolution of the last deglaciation that began
~10,000 y ago. The cores also reveal details of the tectonic
histor y of the Australo-Antarctic Gulf from 53 Ma, por-
traying the onset of the second phase of
rif ting between Australia and Antarctica,
to ever-subsiding margins and deepening,
to the present continental and ever-wide -
ning ocean/continent configuration.
Introduction
Polar ice is an important component of
the modern climate system, af fecting
among other things global sea level, ocean
circulation and heat transport, marine pro-
ductivit y, air-sea gas exchange, and plane-
tar y albedo. The modern ice caps are, geo-
logically speaking, a relatively young
phenomenon. Since mid-Permian times
(~270 Ma), parts of Antarctica became
reglaciated only ~34 m.y. ago, whereas full-
scale, permanent Northern Hemisphere
continental ice began only ~3 m.y. ago
(Zachos et al., 2008; Fig. 1). The record of
Antarctic glaciation, from the time of first
ice-sheet inception through the significant
periods of climate change during the
Cenozoic, is not only of scientific interest
but also is of great importance for society.
State-of-the-art climate models (DeConto
and Pollard, 2003a, 2003b; Huber et al.,
2004; DeConto et al., 2007; Pollard and
DeConto, 200 9) combined with paleocli-
matic proxy data (Pagani et al., 2005) sug-
gest that the main triggering mechanism
for inception and development of the
6FLHQFH5HSRUWV
Figure 1. Updated Cenozoic pCO2 and stacked deep-sea benthic foraminifer oxygen
isotope curve for 0 Ma to 65 Ma. NB: Updated from Zachos et al. (2008) and converted
to the “Gradstein timescale” (Gradstein et al., 20 04). Mi-1 = Miocene isotope Event 1,
Oi-1 = Oligocene isotope Event 1, ETM2 = Eocene Thermal Maximum 2, PETM =
Paleocene/Eocene Thermal Maximum, ETM1 = Eocene Thermal Maximum 1.
-1
0
1
2
3
4
5
010 20 30 40 50 60
Miocene OligocenePlio.
Plt.
4°
0°
8°
12°
Ice-free temperature (°C)
Full-scale and permanent
Partial or ephemeral
PETM (ETM1)
Atmospheric CO 2 (ppmv)
4000
0
1000
2000
3000
5000
Age (Ma)
CO2 proxies
Boron
Alkenones
010 20 30 40 50 60
Anthropogenic peak
early Eocene
minimum
PaleoceneEocene
Early Eocene
Climatic Optimum
Nahcolite
Trona
Cret.
ETM2
Antarctic ice sheets
N. Hemisphere ice sheets
?
N. Hemisphere sea ice
?
?
Episodic perennial
Seasonal
?
Mid-Miocene Climatic
Optimum
Mid-Eocene Climatic
Optimum
δ18 O (‰)
Oi-1
Mi-1

16 Scientif ic Drilling, No. 12, September 2011
6FLHQFH5HSRUWV
estimates have not been experienced since before the ice
sheets in Antarctica formed.
Since their inception, the Antarctic ice sheets appear to
have been very dynamic, waxing and waning in response to
global climate change over intermediate and even short
(orbital) timescales ( Wise et al., 1991; Zachos et al., 1997;
Pollard and DeConto, 20 09). However, not much is known
about the nat ure, cause, timing, and rate of processes invol-
ved. Of the two main ice sheets, the West Antarctic Ice Sheet
(WAIS) is ma inly mari ne based a nd is considered less stable
(Florindo and Siegert, 2009). The East Antarctic Ice Sheet
(EAIS), which overlies continental terrains that are largely
above sea level, is considered st able and is believed to
respond only slowly to changes in climate (Florindo and
Antarctic ice sheet was the decreasing levels of CO2 (a nd
other greenhouse gases) concentrations in the atmosphere
(DeConto and Pollard, 2003a, 2003b; Figs 1, 2). The opening
of critical Southern Ocean gateways played only a second-
ary role (Kennett, 1977; DeConto and Pollard, 2003a; Huber
et al., 2004). With current rising atmospheric greenhouse
gases resulting in rapidly increasing global temperatures
(Intergovernmental Panel on Climate Change [IPCC], 2007;
ww w.ipcc.ch/), studies of polar climates are prominent on
the research agenda. Understanding Antarctic ice- sheet
dynamics and stability is of special relevance because, based
on IPCC (2007) forecasts, atmospheric CO2 doubling and a
1.8°C–4.2°C temperature rise is expected by the end of this
century. The lower values of these estimates have not been
experienced on our planet since 10–15 Ma, and the higher
Ice-sheet thickness (m)
4000
3500
3000
2500
2000
1500
1000
500
0
Δ Sea level (m)
0204060
Δ δ18 O
0.0 0.2 0.4 0.6
Ice volume (106 km3)
01020
Time (10 6 modely)
2
4
6
8
10 2.0
2.2
2.4
2.6
3.0
3.2
3.4
3.6
2.8
CO2 (PAL)
60°S
70°
80°
PB
WL
LG
0E
0E
0E
0E
Figure 3. Combined IODP Expedition 318 transit and drill sites.
Figure 2. Simulated initiation of East
Antarctic glaciation in the earliest
Oligocene using a coupled general
circulation model (GCM) ice-sheet
model (from DeConto and Pollard,
2003a). These results are principally
forced by gradual lowering of
atmospheric levels of CO2 in the
simulated atmosphere. Note that the
glaciation takes place in a “two -step”
fashion reminiscent of the two-step
į18O increase recorded in benthic
foraminiferal carbonates across the
Eocene– Oligocene transition (Coxall
et al., 2005). The first step results in
glaciation in the Antarctic continental
interior, discharging mainly through
the Lamber t Graben (LG) to
Prydz Bay (PB). The second step
results in the initial connection and
subsequent rapid expansion of the
ice sheet, reaching sea level in the
Wilkes Land (WL) at a later stage.
PAL = Preindustrial Atmospheric
Level.

Scientific Drilling, No. 12, September 2011 17
-1012345
0
10
20
30
40
50
60
MioceneOligocene Plio.
Plt.
δ18O (‰)
U1359
4°0° 8° 12°
Ice-free temperature (°C)
Full-scale and permanent
Partial or ephemeral
PETM (ETM1)
Age (Ma)
Paleocene Eocene
Early Eocene
Climatic Optimum
Cret.
ETM2
Antarctic ice sheets
N. Hemisphere ice sheets
?
N. Hemisphere sea ice
?
?
Episodic perennial
?
Mid-Miocene Climatic
Optimum
U1355
U1357
U1360
U1358
U1356
U1361
Shelf sites Rise sites
Seasonal
WL-U8?
IcehouseGreenhouse
WL-U5
WL-U4
WL-U3
51.06 Ma
51.90 Ma
Clay/Silt
Sand
Diatom ooze
Nannofossil ooze
Sandy mud
Limestone
Lithology
Rise
Site
U1356
Rise
Site
U1359
Rise
Site
U1361
Shelf
Site
U1358
Shelf
Site
U1360
Clast-rich
sandy diamict
Clast-poor
sandy diamict
Timescale
25
30
35
40
45
50
55
Age (Ma)
0
5
10
15
20
Eocene Oligocene
Paleo-
cene Miocene
Plio-
cene
cene
Holocene
C18
C17
C16
C15
C13
C12
C11
C10
C9
C8
C7A
C7
C6C
C6B
C6AA
C6A
C26
C25
C24
C23
C22
C21
C20
C19
C5E
C5D
C5C
C5B
C5A
D
C5A
C
C5AB
C5AA
C5A
C5
C4A
C4
C3B
C3A
C3
C2A
C2
C1 C1n
C3n
C2An
C3An
C4n/C4An
C5n
C5r.2n
C5An
C5An
C3An
C2An
C3n
C1n
C2n
C5n
1000
975
950
925
900
875
850
825
800
775
750
725
700
675
650
625
600
575
550
525
500
475
450
425
400
375
350
325
300
275
250
225
200
175
150
125
100
75
50
25
0
Depth (mbsf)
C24n
C12n
C9n
C8n
C7An
C5Dn
C5Cn
C5AAn
C5ABn
C5ACn
C5ADn
C23n.2n
C11n.1n
C10n
C5Bn.2n
600
575
550
525
500
475
450
425
400
375
350
325
300
275
250
225
200
175
150
125
100
75
50
25
0
375
350
325
300
275
250
225
200
175
150
125
100
75
50
25
0
25
0
Insucient paleomagnetic data
C5AB
C5AA
C5A
C5
C4A
C4
C3B
C3A
C3
C2A
C2
C1
0
5
10
Miocene Plio-
cene Pleisto-
cene
Holo-
cene
1
2
3
7
8
9
6
4
13
11
12
h
h
Pleist.
Plio.
C12r
C23n.2n
50
25
0
Pleist.
C12r
14.3 m
h
h
U5
U3
Timescale
A
B
Figure 4. [A] Stacked deep-sea
benthic foraminifer oxygen isotope
curve for 0–65 Ma (updated from
Zachos et al., 2008) converted into
“Gradstein timescale” (Gradstein
et al., 2004) and combined with
chronostratigraphy of the sites drilled
during Expedition 318. ETM2 =
Eocene Thermal Maximum 2, PETM =
Paleocene/Eocene Thermal Maximum,
ETM1 = Eocene Thermal Maximum 1.
[B] Chronostratigraphic framework for
sites drilled during Expedition 318.
Timescales are those of Gradstein et
al. (2004). [11x17 landscape]

18 Scientif ic Drilling, No. 12, September 2011
6FLHQFH5HSRUWV
Wilkes Land margin also includes sites with ultrahigh accu-
mulation rates of sediments that document the Holocene
deglaciation and subsequent climate and sedimentological
variabilit y extending over the past 10,000 y. In general, our
strategy was to core and analyze sedimentary records along
the inshore-offshore transect to constrain the age, nature,
and environments of deposition, until now only inferred from
seismic surveys of the Wilkes L and continental shelf, rise,
and abyssal plain (Escutia et al., 1997; De Santis et al., 2003;
Escutia et al., 2005).
The Expedition
IODP Expedition 318 (January–March 2010; Wellington,
New Zealand, to Hobart, Australia), occupied seven sites
(Fig. 3) across the Wilkes Land Margin at water depths be-
tween ~400 mbsl and 4000 mbsl. Together, we retrieved
~2000 meters of high-qualit y upper Eocene–Quaternary
sedimentary cores (Fig. 4a, b). Sites U1355, U1356, U1359,
and U1361 are on the Wilkes Land rise, and Sites U1358,
U1360, and U1357 are on the Wilkes Land shelf. The cores
span ~53 m.y. of Antarctic histor y, revealing the history of
the Wilkes Land Antarctic margin from an ice-free “green-
house Antarctica,” to the first cooling, to the onset and ero -
sional consequences of the first glaciation and the subse-
quent dynamics of the wax ing and waning ice sheets (Fig. 4).
Furthermore, we also were able to capture the record of the
last deglaciation in terms of thick, unprecedented “tree ring
style” records with annual to seasonal resolution taken in the
Adélie depression (U1357) (Fig. 5).
Initial studies now
also reveal details of the
tectonic history of the
Australo-Antarctic Gulf
(at 53 Ma), the onset of
the second phase of
rif ting between Australia
and Antarctica (Colwell
et al., 2006; Close et
al., 2009), ever-subsiding
margins and deepen-
ing, to the present
ocean/continent configu-
ration. Tectonic and cli-
matic change turned the
initially shallow, broad
subtropical Antarctic
Wilkes Land offshore
shelf into a deeply
subsided basin with
a narrow ice-infested
margin (Fig. 6).
Siegert, 2009). However, reports of beach gravel deposited
20 m above sea level in Bermuda and the Bahamas from
420 ka to 360 ka indicate the collapse of not only the WAIS
(6 m of sea-level equivalent, SLE) and Greenland ice sheet
(6 m of SLE), but possibly also 8 m of SLE f rom East Antarct ic
ice sources (Hearty et al., 1999). Therefore, during episodes
of global warmth, with likely elevated atmospheric CO2 con-
ditions, the EA IS may contribute just as much or more to
rising global sea level as the Greenland ice sheet. In the face
of rising CO2 levels (Pachauri, R.K., and Reisinger, A., 2007),
a better understanding of the EAIS dynamics is therefore
urgently needed from both an academic as well as a societal
point of view.
A key region for analysis of the long- and short-term beha-
vior of the EAIS is the eastern sector of the Wilkes Land mar-
gin, located at the seaward termination of the largest East
Antarctic subglacial basin, the Wilkes subglacial basin. The
base of the portion of the EA IS draining through the W ilkes
subglacial basin is largely below sea level, suggesting that
this portion of the EA IS can potentially be less stable than
other areas of the EAIS (Escutia et al., 2005). Numerical
models of ice-sheet behavior (Huybrechts, 1993; DeConto
and Pollard, 2003a, 2003b; DeConto et al., 2007; Pollard and
DeConto, 2009) provide a basic understanding of the cli-
matic sensitivity of particular Antarctic regions for early
ice-sheet formation, connection and expansion, and eventual
development of the entire ice sheet. For example, in these
models glaciation is shown to have begun in the East
Antarctic interior, discharging mainly through the Lambert
Graben to Prydz Bay. These models imply that the EAIS did
not reach the W ilkes Land margin until a later stage. These
models can only be validated through drilling and obtaining
direct evidence from the sedimentary record.
Scientic Objectives
The overall objectives of Expedition 318 were to date the
identified seismic units and to obtain long-term records of
Antarctic glaciation to better understand its relationships
with global paleoclimate and paleoceanographic changes.
Of particular interest is testing the sensitivity of the EAIS
to episodes of global warming and detailed analysis of criti-
cal periods in Earth’s climate history, such as the
Eocene –Oligocene and Oligocene–Miocene glaciations, late
Miocene, Pliocene, and the last deglaciation. During these
time s, the Ant arctic c ryosphere evol ved in a step -wise fash ion
to ultimately assume its present- day configuration, charac-
terized by a relatively stable EAIS. Conceivably even more
important than the histor y of the A ntarctic glaciations are
past lessons of deglaciations and periods of exceptional
warmth. We therefore planned to core several sequences
from the Pleistocene and Pliocene that formed during inter-
glacial intervals of exceptional warmth, periods that may pro-
vide valuable information about A ntarctica’s response to
warming predicted in the centuries ahead. Furthermore,
seismic reflection and shallow coring data indicate that the
Figure 5.Example of a core section
from Holocene diatomaceous ooze,
Site U1357. Note the distinct seasonal
laminations.
cm
125
115
120
110

Scientific Drilling, No. 12, September 2011 19
activity related to the commencement of rapid sea floor
spreading in the Australia-Antarctic Basin (A A B), reported
to initiate around the same time (~50 Ma; Colwell et al.,
2006). Also, combined Site U1356 and ODP L eg 189 dinocyst
distribution patterns suggest earliest through-flow of South
Pacific Antarctic waters through the Tasmanian Gateway to
be coeval with this tectonic phase. Sedimentological and
microfossil information from this interval from Hole U1356A
also suggest some deepening during the early middle
Eocene.
At Site U1356, the upper middle Eocene to the basal
Oligocene is conspicuously missing in a ~19-m.y. hiatus at
~890 bsf (~47.9–33.6 Ma) marking unconformity W L-U3
based on dinocyst and paleomagnetic evidence. Despite
ongoing tectonic reorganizations, it appears likely that the
erosive nature of unconformity WL -U3 is notably related to
the early stages of EA IS formation. T he impact of ice-sheet
growth, including crustal and sea-level response, and major
erosion by the ice sheets, is proposed as the principal mecha-
nism that for med u ncon formi t y W L-U 3. T his is suppor ted by
the abrupt increase in benthic foraminiferal į18O values and
coeval sea-level change globally recorded
in complete marine successions (Oligocene
isotope event Oi-1; Miller et al., 1985; Coxall
et al., 2005). Progressive subsidence—the
large accommodation space created by ero-
sion in the margin (300–6 00 m of missing
strata; Eittreim et al., 1995)—and partial
eustat ic recovery allowed sediments of
early Oligocene age to accumulate above
unconformity WL-U3.
Microfossils, sedimentology, and geo-
chemistry of the Oligocene sediments
from Site U1356, at present occupying a
distal setting (i.e., lowermost rise-abyssal
plain) and immediately above unconfor-
mity WL-U3, unequivocally reflect ice-
house environments with evidence of ice-
berg activity (dropstones) and at least
seasonal sea-ice cover. The sediments,
dominated by hemipelagic sedimentation
with bottom current and gravity flow
influence, as well as biota, indicate deeper
water settings relative to the underlying
middle Eocene environments. These find-
ings imply significant crustal stretching,
subsidence of the margin, and deepening of
the Tasman R ise and the Adélie Rift Block
(ARB) between 47.9 Ma and 33.6 Ma
(Fig. 6).
Record of EAIS Variability
Drilling at continental rise Site U1356
also recovered a thick section of Oligocene
“Pre-Glacial” Regional Unconformity WL-U3
and the Timing, Nature, and Consequences
of the First Major Phase of EAIS Growth
Prior to the expedition, the prominent unconformity
WL -U3 had be en interpret ed to separat e pre-gla cial (Eo cene)
strat a from (Oligocene) glacial-influenced deposits (Escutia
et al., 1997, 2005). Drilling and dating of WL -U3 at continen-
tal rise Site U1356 and shelf Site U1360 (Fig. 3) confirmed
that this surface represents major erosion related to the
onset of glaciation at ~34 Ma (early Oligocene), with immedi-
ately overly ing deposits dated as 33.6 Ma (Fig. 7). Below
unconformit y WL-U3 at Site U1356, we recovered a record
that is late early to early middle Eocene in age and that inclu-
des peak greenhouse conditions and likely some of the early
Eocene hyperthermals (Fig. 8). We infer subtropical shal-
low-water depositional environments for this section based
on dinocysts, pollen and spores, and the chemical index of
alteration, among other indicators. A hiatus spanning ~2 m.y.
separates the lower Eocene from the middle Eocene record
at Site U1356 according to dinocyst and magnetostrati-
graphic evidence. This hiatus may be related to tectonic
Figure 6. Conceptual illustration of tectonic, geological, sedimentological, and climatic
evolution of the Wilkes L and margin since the middle early Eocene (~54 Ma). U3, U4, and U5
refer to seismic unconformities WL-U3, WL-U4, and WL-U5, respectively. Oi-1 = Oligocene
isotope Event 1, CPDW = Circumpolar Deep Water, ACSC = Antarctic Circumpolar Surface
Water, UCPDW = Upper Circumpolar Deep Water, LCPDW = Lower Circumpolar Deep
Water, AABW = Antarctic Bottom Water. MTD = mass transport debris flows.
500 km
Antarctic Counter Current
Proto-Leeuwin Current
Wilkes Shelf
53–48 Ma
0
200
400
Wilkes Shelf
15–0 Ma
0
800
1600
Rifting ~50 Ma
X
0
250
400
Icebergs and
seasonal sea ice
Sea level
Sea level
Wilkes Shelf
33 Ma
(Oi-1)
onset of glaciation
Wilkes Shelf
30–15 Ma
0
1
2
U3
U3
U4
U3
U4
U5
U3
U3
U5
ACSC
X
X
X
X
CPDW
Sea level
Sea level
X
AABW
UCPDW
X
X
Current coming out of page
Current going into page
Wilkes Land
U3
Deepwater production
Wilkes
Contourites and turbidites
Contourites and turbidites
MTDs, contourites, and turbidites
Neritic/Upper slope deposits
Basement
Wilkes Land
Wilkes Land
Wilkes Land
LCPDW
ACSC
CPDW
Depth (m) Depth (m)
Depth (m)
Depth (km)

20 Scientific Drilling, No. 12, September 2011
6FLHQFH5HSRUWV
Ocean open cold-water taxa, with variable abundances of
sea-ice -associated diatoms were recovered, indicating a
high-nutrient, high-productivity sea-ice-influenced set ting
throughout the Neogene. Combined sedimentological and
microfossil information indicates the ever-increasing
influence of typical Antarctic Counter Current surface
waters and intensifying AABW flow. Furthermore, the
preser vation of calcareous microfossils in several intervals
indicates times when bottom waters were favorable to the
preservation of calcium carbonate. These observations point
to a very dynamic ice -sheet/sea-ice regime during the late
Miocene through the Pleistocene. Detailed postcruise
studies in sediments from the late Neogene will provide a
history of glacial-interglacial climate and paleoceano-
graphic variability, including a history of AABW produc-
tion that can be linked to sea-ice variations in this margin.
Ultrahigh Resolution Holocene Record of
Climate Variability
Coring at Site U1357 yielded a 186-m section of contin-
uously laminated diatom ooze as well as a portion of the
underlying Last Glacial Maximum diamict. Based on much
shorter piston cores recovered from adjacent basins and
banks, the onset of marine sedimentation during the degla-
cial interval began bet ween 10,400 y and 11,000 y ago. T he
site was triple cored, providing overlapping sequences that
will aid in the construction of a composite stratigraphy span-
ning at least the last 10,000 y. The Site U1357 sediments are
unusual for Antarctic shelf deposits because of their high
accumulation rate (2 cm y
-1), lack of bioturbation, and excel-
lent preservation of organic matter as well as calcareous,
opaline, phosphatic, and organic fossils. The sediments are
profoundly anoxic, with levels of H2S as high as 42,000 ppm
at 20 mbsf. Larger burrowing organisms are completely
to upper Miocene sediments (Figs. 4, 8) indicative of a rela-
tively deep-water, sea-ice-in fluenced setting. Oligocene to
upper Miocene sediments are indicative of episodically redu-
ced oxygen conditions either at the seafloor or within the
upper sediments prior to ~17 Ma. From t he late early Miocene
(~17 Ma) onward, progressive deepening and possible inten-
sification of deep-water flow and circulation led to a transi-
tion from a poorly oxygenated low-silica system (present
from the early to early middle Eocene to late early Miocene)
to a well-ventilated si lica-enriched system a kin to the modern
Southern Ocean. This change coincides with one of the
major regional unconformities in the Wilkes Land margin,
unconformity WL-U5, which represents a ~3 m.y. latest
Oligocene–early Miocene hiatus (Figs. 4, 8). This unconfor-
mity marks a change in the dominant sedimentary proces -
ses at this site, which are dominated by mass transport pro-
cesses below the unconformity and by hemipelagic, turbidity
flow, and bottom-current deposition above.
A complete record with good recovery of late Miocene
to Pleistocene deposits was achieved at continental rise
Sites U1359 and U1361 (Figs. 4, 9), drilled on levee deposits
bounding turbidity channels. We successfully dated the
seismic units between unconformities WL-U6 and W L -U8,
and the sedimentological, wireline logging, and magnetic
susceptibility data exhibit relatively high amplitude varia-
tions, indicating strong potential for this record to reveal
EAIS dynamics down to orbital timescales (100 k.y. and
40 k.y. cyclicity) (Fig. 10). This cyclicity likely documents
the successive advances and retreats of the ice- sheet and
sea-ice cover, as well as the var ying intensity of cold saline
density flows related to bottom water production at the
Wilkes Land margin (e.g., high-salinity shelf water flowing
from the shelf into the deep ocean to form Antarctic
Bottom Water [AABW ]). In general, typical Southern
Figure 7. Multichannel seismic reflection profile across Site U1356 showing regional unconformities WL-U3, WL-U4, and WL-U5. Red rectangle =
approximate penetration achieved at Site U1356.
WL-U3
WL-U4
WL-U5
WL-U5b
5.0
5.5
6.0
6.5
Site
U1356
GA229-07
SP 7374
10 km
Levee
Levee
Channel
Channel
Two-way traveltime (s)
Shotpoint
8500.0 8400.0 8300.0 8200.0 8100.0 8000.0 7900.0 7800.0 7700.0 7600.0 7500.0 7400.0 7300.0 7200.0 7100.0 7000.0 6900.0 6800.0 6700.0 6600.0 6500.0 6400.0 6300.0

Scientific Drilling, No. 12, September 2011 21
Miocene
Pliocene
elddimetalearly
Pleist.
late
25 m m.y.-1
69 m m.y.-1
37 m m.y.-1
Age
(Ma)
Lithology
Hole U1361A
Depth (mbsf)
1H
2H
3H
4H
5H
6H
7H
8H
9H
10H
11H
12H
13H
14H
15H
16H
17X
18X
19X
20X
21X
22X
23X
24X
25X
26X
27X
28X
29X
30X
31X
32X
33X
34X
35X
36X
37X
38X
39X
40X
41X
0
50
100
150
200
250
300
350
400
024 6 8101214
Lith. unit
I
IIA
IIB
Total depth = 386.31 mbsf
WL-U8
WL-U7
Seismic
reector
WL-U6
Core
recovery
Diatom (t)
Diatom (b)
Radiolarian (t)
Rad iola rian (b)
Magnetostratigraphy
Foraminifer (o)
Foraminifer (y)
Clay/Silt enotsemiL ezoo lissofonnaN
Lithology
Diatom ooze
Change in sedimentation
rate
Figure 9. Age model for Hole U1361A.
0
200
400
600
800
1000
020 30 40 60
Hiatus
(9.5–4.74 Ma)
Hiatus/
condensed interval
(23.12–17.5 Ma)
47R-CC
46R-CC
1R-2,140 cm
Hiatus
(47.9–33.6 Ma)
95R-1
94R-CC
Hiatus
(≥51.90 Ma to ≤51.06 Ma)
101R-1,100
100R-1,100
~37 m m.y.-1
~67 m m.y.-1
~30 m m.y.-1
~24 m m.y.-1
Miocene Oligocene Eocene
lmelme
Plio.-
Pleist. Paleoc.
le
53.8 Ma
~100 m m.y.-1
Hole U1356A
Age
(Ma)
Diatom (t)
Diatom (b)
Radiolarian (t)
Radiolarian (b)
Palynomorph (t)
Palynomorph (b)
Magnetostratigraphy
Foraminifera (o)
Foraminifera (y)
Nannofossil (o)
Nannofossil (y)
0301
Palynomorph (y)
50
Depth (mbsf)
Core
recovery
1R
2R
3R
4R
5R
6R
7R
8R
9R
10R
11R
12R
13R
14R
15R
16R
17R
18R
19R
20R
21R
22R
23R
24R
25R
26R
27R
28R
29R
30R
31R
32R
33R
34R
35R
36R
37R
38R
39R
40R
41R
42R
43R
44R
45R
46R
47R
48R
49R
50R
51R
52R
53R
54R
55R
56R
57R
58R
59R
60R
61R
62R
63R
64R
65R
66R
67R
68R
69R
70R
71R
72R
73R
74R
75R
76R
77R
78R
79R
80R
81R
82R
83R
84R
85R
86R
87R
88R
89R
90R
91R
92R
93R
94R
95R
96R
97R
98R
99R
100R
101R
102R
103R
104R
105R
106R
Total depth = 1000.08 mbsf
I
VI
V
IV
III
II
VII
VIII
IX
X
WL-U5
WL-U4
WL-U3
Lith. unit
Seismic
reector
XI
Lithology
Clay/Silt Sand
Nannofossil ooze
Sandy mud Diamict
Limestone
Lithology
Figure 8. Age model for Hole U1356A.

22 Scientific Drilling, No. 12, September 2011
6FLHQFH5HSRUWV
The IODP Expedition 318 Scientists
C. Esc utia (Chief Sci entist), H. Brink huis (Chief Scie ntist),
A. K laus (Staff Scientist), J.A.P. Bendle, P.K. Bijl, S.M.
Bohaty, S.A. Carr, R.B. Dunbar, J.J. Gonzàlez, A. Fehr, T.G.
Hayden, M. Iwai, F.J. Jimemez-Espejo, K. K atsuki, G.S.
Kong, R.M. McKay, M. Nakai, M.P. Olney, S. Passchier, S.F.
Pekar, J. Pross, C. Riesselman, U. Röhl, T. Sakai, P.K.
Shrivastava, C.E. Stickley, S. Sugisaki, L. Tauxe, S. Tuo, T.
van de Flierdt, K. Welsh, T. Williams, M. Yamane .
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Acknowledgements
We thank the captain and crew of the JOIDES Resolution,
the IODP 318 operation superintendent, ice pilot, weather-
man, all technicians, and videographer who were instrumen-
tal in the success of Expedition 318. They allowed and as-
sisted us in drilling, documenting, sampling, and onboard
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Astrolabe for his support.
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MAD = moisture and density, IDPH = deep induction phasor-processed resistivity, IMPH =
medium induction phasor-processed resistivity, PWS-X = x-direction caliper.
Depth (mbsf)
Depth (mbsf)
0
50
100
150
200
250
300
350
400
0
50
100
150
200
250
300
350
400
0.5 1.2(Ωm)
IMPH
0.5 1.2(Ωm)
IDPH
(m s-1)
Pass 1
(m s-1)
Lab, PWS-X
1500 2000
1500 2000
Gamma ray (HSGR)
0 100(gAPI)
Hole diameter
10 30(inch)
Bulk density (MAD)
(g cm
-3
)
1.2 2
Density
1.3 2(g cm-3)
Porosity
90 30(%) (m s-1)
Pass 2
1500 2000
Core
recovery
1H
2H
3H
4H
5H
6H
7H
8H
9H
10H
11H
12H
13H
14H
15H
16H
17X
18X
19X
20X
21X
22X
23X
24X
25X
26X
27X
28X
29X
30X
31X
32X
33X
34X
35X
36X
37X
38X
39X
40X
41X
Resistivity
Velocity

Scientific Drilling, No. 12, September 2011 23
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Authors
Carlota Escutia, Instituto Andaluz de Ciencias de la Tierra,
CSIC-Universidad de Granada, Campus de Fuentenueva s/n,
18002 Granada, Spain, e-mail: cescutia@ugr.es.
Henk Brinkhuis, Biomarine Sciences, Institute of
Environmental Biology, Laboratory of Palaeobotany and
Palynology, Utrecht University, Budapestlaan 4, 358 4 CD
Utrecht, The Netherlands, e-mail: h.brinkhuis@uu.nl.
Adam Klaus, Staff Scientist/Expedition Project Manager,
United States Implementing Organization, Integrated Ocean
Drilling Program, Texas A&M Universit y, 1000 Discovery
Drive, College Station, TX 77845-9547, U.S.A ., e-mail:
aklaus@iodp.tamu.edu.
and the IODP Expedition 318 Scientists
Related Web Link
http://publications.iodp.org/preliminary_report/318/
http://www.stratigraphy.org/