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Table 1 Representative examples and short descriptions of seismic facies from Weddell Sea
Sediment
units
Tentative
age (Ma)
Seismic characteristics
Major events
Full glacial
15 Ma - now
ws_u5
Drift, channel and basin fill in,
finely laminated, high ampli-
tude reflections, unconformi-
ties, parts are chaotic
reflections with lower reflec-
tivity due to debris flows
Grounding cycles of EAIS and
WAIS on the continental WAIS
bring terrigenous sediments to
margin
Early expansions of APIS onto
the continental shelf in the
south
Transitional
34 - 15 Ma?
ws_u4
Medium reflectivity, discontin-
uous and horizontal reflections
higher amplitude close to bot-
tom of pre-glacial
Earliest glacial event on the
Antarctic Peninsula EAIS and
WAIS formation onset of the
Antarctic Circumpolar Current
Abrut Eocene-Oligocene
cooling
Pre-glacial
160
34
Lower amplitude sequence
with strong discontinuous
re
Drake passage open, ASM-
Antarctic Penisula separation
complete Antarctic bottom
water forms (AABW) Weddell
Sea spening
-
Ma?
ections in parts, horizontal,
spaced, transparent background
fl
Most of the seismic pro
les in the Weddell Sea show three clearly distinguishable
sedimentary units (Table 1 ) above the acoustic basement.
The bottom-most sedimentary unit I is characterized by sub-parallel wavy
re
ec-
tions and seismically transparent zones (Fig. 2 and 3 ). Early Cretaceous organic-
rich mudstones from this unit were drilled at ODP Site 693 off the southeastern
Weddell Sea margin (Barker et al. 1988 ). The unconformity WS-u4 (Huang and
Jokat 2014 ) is the upper boundary of unit I. Due to its Cretaceous minimum age, we
name unit I pre-glacial unit.
Unit II is characterized by medium acoustic response and laminated re
fl
ectors, low-amplitude sequences with occasional strong discontinuous re
fl
fl
ections.
Chaotic facies are separated by thin draping layers of medium re
ectivity, partly
spaced semi-transparent zones (Fig. 2 and 3 ). The Early Oligocene diatom silty,
clayey mud and sandy mudstone from this unit were drilled at the ODP site 693 and
the ODP site 696 (Barker et al. 1988 ). The unit II is overlaid on the unit I and
separated from the upper unit by an unconformity mapped as WS-u5. We name unit
II as transitional unit according to seismic characteristics and its age indication by
the drill cores recovery (Table 1 ).
Unit III is generally characterized by a regular and thin-bedded pattern of par-
allel, continuous re
fl
fl
ections with high amplitude. Parts of them are chaotic re
fl
ec-
tions with lower re
ectivity in the southern Weddell Sea (Fig. 2 , 3 and 4 ).
Abundant drifts and channel-levee systems are present on the southern continental
rise in this unit. The sediment drifts show semi-transparent, continuous, sub-parallel
or irregular, wavy to discontinuous as well as moderate to low amplitude re
fl
ectors
(Fig. 2 ). Within Unit III, glacial turbidities were drilled at ODP site 694 (Barker
fl
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