Marine Geology 228 (2006) 93 – 116
www.elsevier.com/locate/margeo
Miocene reversal of bottom water flow along the Pacific Margin of
the Antarctic Peninsula: Stratigraphic evidence from a contourite
sedimentary tail
F.J. Hernández-Molina a,⁎, R.D. Larter b , M. Rebesco c , A. Maldonado d
a
Dpto. de Geociencias Marinas, Universidad de Vigo, 36200 Vigo, Spain
British Antarctic Survey (BAS), High Cross, Madingley Road, Cambridge CB3 0ET, UK
c
Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Borgo Grotta Gigante 42/C, 34010 Sgonico, Trieste, Italy
d
Instituto Andaluz de Ciencias de la Tierra (IACT), CSIC/University of Granada, Campus Fuentenueva, s/n 18002 Granada, Spain
b
Received 4 March 2005; received in revised form 15 December 2005; accepted 22 December 2005
Abstract
A Fossil Mounded Sedimentary Body (MB) has been identified in the sedimentary record on the central continental rise west of
Adelaide Island, on the Antarctic Peninsula Pacific margin. The growth patterns of the MB are defined through a detailed regional
stratigraphic analysis using multichannel seismic reflection profiles. The MB has an elongated NE trend. It overlaps and continues
to the NE of an extensive cluster of seamounts, and it developed between two non-depositional troughs. Nine seismic units have
been identified: Unit 9 (the pre-MB stage), Unit 8 (MB growth stage), Units 7 and 6 (MB maintenance stage), Units 5 and 4
(transitional stage), and Units 3, 2 and 1 (inactive stage). We interpret the MB as a patch drift plastered against the NE, lee side of
an obstacle, as a long Contourite Sedimentary Tail (CST), within a deep current that flowed northeastward. This segment of the rise
is, however, affected at present by a SW-flowing branch of the Lower Circumpolar Deep Water (LCDW) from the Weddell Sea.
The depositional patterns of the MB growth and maintenance stages, which are attributed an early Miocene age on the basis of
regional correlation of MCS profiles with DSDP Site 325 and ODP Leg 178 drill sites, provide the first evidence that bottom
currents on the central continental rise flowed towards the NE at that time, probably as part of the Lower Circumpolar Deep Water
(LCDW) of the Antarctic Circumpolar Current (ACC). We suggest that significant palaeocirculation and palaeoceanographic
changes occurred in this area, and probably more widely, during the middle Miocene or at the Miocene/Pliocene boundary.
Although these results do not modify the regional stratigraphy of the major sediment drifts found on the continental rise of the
Antarctic Peninsula's Pacific margin, they do indicate that the bottom current regime controlling the development of contourite
deposits may have changed over time and also that more than one water mass has probably affected their distribution.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Antarctic Peninsula Pacific margin; contourite deposits; seamounts; palaeoceanography; seismic stratigraphy; Miocene; Pliocene;
Quaternary
1. Introduction
⁎ Corresponding author.
E-mail address: [email protected] (F.J. Hernández-Molina).
0025-3227/$ - see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.margeo.2005.12.010
Bottom contour currents in modern ocean basins
often generate large sedimentary bodies (contourite
deposits or drifts), comparable in size to turbidite fans
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F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
Fig. 1. (A) Regional setting of the study area. The sea surface position of the Antarctic Circumpolar Current (ACC) fronts and present circulation
pattern of bottom water masses is shown: (a) Circumpolar Deep Water (CDW) and (b) Lower Circumpolar Deep Water (LCDW) branch from the
Weddell Sea. The Southern Boundary of the ACC (SB) dips northwestward, and LCDW from the Weddell Sea flows southwestward beneath it (SM =
Seamount; HFZ = Hero Fracture Zone; bathymetric map from Rebesco et al., 1998). Grey-filled circles represent Ocean Drilling Program drill sites.
(B) Sketch with the positions of seismic reflection profiles used, and the MB position on the continental rise of the margin. The main morphological
provinces are also marked.
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
(Stow et al., 1986, 2002; Rebesco, 2005). Several drift
classification systems have recently been proposed,
based mainly on morphologic, sedimentologic and
seismic characteristics (McCave and Tucholke, 1986;
Faugères and Stow, 1993; Faugères et al., 1999;
Rebesco and Stow, 2001; Stow et al., 2002; Rebesco,
2005). All drifts are related to the regional oceanographic conditions and the physiographic domains
where they developed. Thus, it is possible to decode,
from their morphologic, stratigraphic and sedimentary
characteristics, the pathway and approximate flow
velocity of the water mass that was responsible for
their development. This is particularly relevant when
buried contourite drifts and erosional discontinuities are
found in the sedimentary record of a basin, because it is
then possible to reconstruct it palaeoceanographic
conditions.
We have recently completed a morphologic and
stratigraphic interpretation of the region between 68°
and 74°W and 65°–67°30′S (Fig. 1A), using multichannel seismic profiles and multibeam echo sounder
data collected by several projects and research groups.
In this area, on the central continental rise off Adelaide
Island, we found a large Fossil Mounded Sedimentary
Body (MB) (Hernández-Molina et al., 2004). In this
paper we give a more complete description of the
development of the MB, present new multibeam echo
sounder data that reveals additional seamounts within
the MB area, and discuss the palaeoceanographic
implications of these observations.
2. Geological and oceanographic setting
There was continuous subduction at the Pacific
margin of the Antarctic Peninsula at least from early
Cretaceous time until the early Tertiary (Storey et al.,
1996). During the Tertiary period, subduction stopped
along most of the margin, as ridge-crest segments of the
Antarctic–Phoenix spreading centre migrated into the
trench (Barker, 1982; Larter and Barker, 1991a). Ridgecrest segments arrived first at the southwestern part of
the margin during the Palaeocene or Eocene, then
progressively later towards the northeast. The study area
is located between the Tula and Biscoe Fracture Zones,
and is divided into two parts by the Adelaide Fracture
Zone (Fig. 1A). These fracture zones formed at offsets in
the Antarctic–Phoenix ridge as it migrated towards a
former trench at the Antarctic Peninsula margin. The
ridge segment between Tula and Adelaide Fracture
Zones reached the trench at 19 ± 0.8 Ma, and the
segment between Adelaide and Biscoe Fracture Zones
reached the trench at 16.7 ± 0.7 Ma (Larter et al., 1997).
95
As the ridge migrated towards the trench, ocean floor
formed on its NW flank was part of the Antarctic Plate,
so features on this flank of the ridge never moved
relative to the Antarctic Peninsula after they were
formed (Larter and Barker, 1991a).
The continental shelf and slope on the Pacific margin
of the Antarctic Peninsula have a thick Miocene to
Quaternary sedimentary cover with progradational and
aggradational stacking patterns. Since Late Miocene
times, prograding sequences formed as a consequence
of sediment transport and deposition beneath ice sheets
which were grounded to the continental shelf edge
during glacial maxima (Larter and Barker, 1989; Bart
and Anderson, 1995; Larter et al., 1997; Barker and
Camerlenghi, 2002). The continental rise is underlain by
a thick succession of clastic sediments which have been
the subject of many studies, using data from Deep Sea
Drilling Project (DSDP) Site 325 (Leg 35), multichannel
seismic reflection profiles, and more recently, from Leg
178 of the Ocean Drilling Program (ODP) (Fig. 1A). On
the upper continental rise there are several large
asymmetric sedimentary mounds (drifts) generally
having steep SW flanks, gently dipping, smoother NE
flanks, and long narrow crests, separated from the base
of the continental slope and from each other by turbidity
current channels (Rebesco et al., 1996, 1997, in press;
Pudsey and Camerlenghi, 1998; Pudsey, 2000; Rebesco
et al., 2002; Lucchi et al., 2002). Through seismic
stratigraphic analysis, Rebesco et al. (1996, 1997, 2002)
identified six depositional units on the continental rise
and summarised the history of sedimentation in three
main stages (Table 1): (1) a pre-drift stage (units M6 and
M5; 36–15 Ma) characterised mainly by subparallel
reflectors representing a dominantly turbiditic sequence;
(2) a drift-growth stage (units M4 and M3; 15–5 Ma),
showing substantial variations in thickness as a
consequence of increased bottom current activity and
rapid glacial sediment supply from the margin; and (3) a
drift-maintenance stage (units M2 and M1; 5–5.3 Ma to
the present), characterised by preservation of drift
morphology, with a fairly uniform drape of younger
sediments on the NE gentle side and more condensed
succession over the SW steeper side. The upper three
units were thought to be composed mainly of glacially
derived sediments of Late Miocene to Pleistocene age
(Rebesco et al., 1997).
Among the deep-water masses in the Southern
Ocean, two components can be distinguished (Orsi et
al., 1995, 1999; Naveira-Garabato et al., 2002a,b, 2003).
1) The voluminous Circumpolar Deep Water (CDW),
which is internally sub-divided into Upper Circumpolar
Deep Water and Lower Circumpolar Deep Water
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F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
(UCDW and LCDW) and flows continuously to the east
(Fig. 2B) within the Antarctic Circumpolar Current
(ACC). (2) The deepest water mass around the Antarctic
continent, although it lacks a circumpolar distribution
(Fig. 2A), is the Antarctic Bottom Water (AABW)
which is generated by a combination of brine rejection
on the continental shelf and by super-cooling of water
masses under floating ice shelves. The main source of
AABW is the Weddell Sea, which contributes approximately 60% of the total AABW production.
AABW in the Weddell Sea is composed of the
Weddell Sea Bottom Water (WSBW) and the Weddell
Sea Deep Water (WSDW) (Fig. 2B). Above the WSDW
flows the Warm Deep Water (WDW), which is a branch
of the LCDW (Naveira-Garabato et al., 2002a,b).
A relatively cold and fresh branch of the WSDW
spills over the South Scotia Ridge, spreads westward
through Drake Passage, and fills the bottom of the South
Shetland Trench (Fig 2B; Sievers and Nowlin, 1984).
After passing the Hero Fracture Zone it loses its identity
through mixing with the overlying LCDW (NaveiraGarabato et al., 2002a, 2003). A branch of LCDW
derived from water that has circulated in the Weddell
Gyre, also flows along the slope on the southern flank of
the South Shetland Trench above the WSDW. This
water mass continues southwestward along the Antarctic Peninsula Pacific margin (Nowlin and Zenk, 1988;
Orsi et al., 1999; Naveira-Garabato et al., 2002a), where
is active at around 3500 m depth and follows contours
around large drifts (Figs. 1A and 2) on the central and
upper rise (Rebesco et al., 2002; Giorgetti et al., 2003).
This LCDW branch was first inferred on the basis of
physical properties of the water mass, short-term current
measurements and migration patterns of sedimentary
waves (see summary in Tucholke and Houtz, 1976;
Tucholke, 1977). More recently its existence has been
verified by direct current-meter measurements, which
indicated mean current speeds of ∼6 cm/s and
maximum speeds of b 20 cm/s, with potential temperatures of 0.11–0.13 °C, between water depths of 3475
and 3338 m (Camerlenghi et al., 1997; Giorgetti et al.,
2003).
3. Methodology
The present study is based on the analysis of
multichannel seismic reflection (MCS) profiles collected by the British Antarctic Survey (BAS) and the Istituto
Nazionale di Oceanografía e di Geofisica Sperimentale
(OGS). However, this work is part of a more extensive
regional work (Hernández-Molina et al., in preparation)
which also utilises seismic reflection data from the
Brazilian Antarctic Program, Rice University of Texas,
and Spain (Project ANT99-0817), as well as multibeam
echo sounding data from various sources. Results of
ODP Leg 178 (Barker et al., 1999) and DSDP Site 325
(Hollister et al., 1976) were also incorporated into the
study. Correlation of seismic units and discontinuities
with these sites was essential in order to analyse the
timing of the processes responsible for the development
of depositional units and to establish the chronology of
growth patterns on the continental rise. The age of the
oceanic crust, based on interpretation of marine
magnetic anomalies (Larter and Barker, 1991a), was
used to constrain the age of the oldest sediments on the
rise. Magnetic anomaly ages were based on the
magnetic reversal timescale of Cande and Kent (1995).
MCS data collected by BAS on RRS Discovery
cruise 172 during the 1987/1988 austral summer were
acquired with an 800-m long, 32-channel streamer and a
Fig. 2. Summary of regional oceanographic framework and water mass dynamics. (A) Distribution of the flow pattern of Antarctic Bottom Water
(AABW) with different density values (from Orsi et al., 1999). (B) Schematic circulation patterns of the deep water masses in the Weddell Sea,
Bellingshausen Sea and Scotia Sea overlaid on regional bathymetry (Isobaths of 1500, 4000 and 6000 m). Also shown are Antarctic Circumpolar
Current (ACC) fronts (summary using data from the following authors: Hollister and Elder, 1969; Tucholke, 1977; Whitworth et al., 1982, 1994;
Whitworth and Nowlin, 1987; Foldvik and Gammelrsød, 1988; Nowlin and Zenk, 1988; Domack et al., 1992; Locarnini et al., 1993; Orsi et al., 1993,
1995, 1999; Fahrbach et al., 1995, 1998; Barber and Crane, 1995; Hoffmann et al., 1996; Camerlenghi et al., 1997; Pudsey and Howe, 1998; Arhan et
al., 1999; Gordon et al., 2001; Meredith et al., 2001; Naveira Garabato et al., 2002a,b, 2003; Hillenbrand et al., 2003). Legends of the ACC fronts:
SAF = Subantarctic Front; PF = Polar Front; SACCF = Southern ACC Front; SB = Southern Boundary of the ACC. Legend of the physiographic
reference points, in alphabetical order: AI = Adelaide Island; AlI = Alexander Island; BAP = Bellingshausen Abyssal Plain; BB = Burdwood Bank;
BP = Bruce Passage; BS = Bransfield Strait; BeS = Bellingshausen Sea; CT = Chile Trench; DP = Discovery Passage; FI = Falkland Island; FE =
Falkland Escarpment; FP = Falkland Passage; FPL = Falkland Plateau; FR = Falkland Ridge; GB = Georgia Basin; GP = Georgia Passage; HFZ =
Hero Fracture Zone; JB = Jane Basin; MEB = Maurice Ewing Bank; NGP = Northeast Georgia Passage; NGR = Northeast Georgia Ridge; NSR =
North Scotia Ridge; OP = Orkney Passage; OR = Orcadas Ridge; PB = Powell Basin; PCM = Pacific Continental Margin of Antarctic Peninsula;
PI = Peter Island; PhP = Philip Passage; SG = South Georgia; SFZ = Shackleton Fracture Zone; SOI = South Orkney Island; SPB = Southeastern
Pacific Basin; SRP = Shag Rocks Passage; SSFZ = South Sandwich Fracture Zone; SShI = South Shetland Island; SSI = South Sandwich Island; SSR
= South Scotia Ridge; SST = South Sandwich Ridge; WAP = Weddell Abyssal Plain; YT = Yaghan Basin. Legend of the water masses: ACC =
Antarctic Circumpolar Current; CDW = Circumpolar Deep Water; SPDW = Southeast Pacific Deep Water; LCDW = Lower Circumpolar Deep
Water; UCDW = Upper Circumpolar Deep Water; AABW = Antarctic Bottom Water; WSC = Weddell Scotia Confluence; WDW = Warm Deep
Water; WSBW = Weddell Sea Bottom Water; WSDW = Weddell Sea Deep Water.
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
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F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
4-airgun source with a total volume of 15.8 l. The
analogue signals from pairs of channels in the streamer
were summed before being digitized, so the recorded
data effectively represent 16 hydrophone groups, each
50 m long. MCS data collected by OGS on R/V OGSExplora during the austral summers of 1989/1990 and
1991/1992 were acquired with a 3000-m long, 120channel hydrophone streamer towed at a depth of 8 m.
During the 1989/1990 season, the source consisted of 36
airguns with a total volume of 45.2 l., whereas in the
1991/1992 season the source consisted of 40 airguns
with a total volume of 72 1. On all three cruises, shots
were fired every 50 m, giving 8-fold coverage on the
BAS data, and 30-fold coverage on the OGS data. The
data sampling interval on all three cruises was 4 ms. The
data were processed with a standard processing
sequence, but the data from line BAS878-19 shown in
Figs 3 and 4 have been f–k migrated.
For the purposes of the present paper, we have
focused on interpretation of lines BAS878-19 and
BAS878-20 from BAS (hereinafter referred to as lines
BAS19 and BAS20), and OGS lines IT89-048 and
IT92-110 (hereinafter referred to as lines IT48 and
IT110) (Fig. 1B). The 3D definition of the MB is based
on these seismic lines. These are the only presently
existing lines available to define the body. Although
there is no tie line along the length of the body,
reflections on all lines can be traced to DSDP Site 325
(via a tie to line IT89049, in the case of line IT48), and
so the stratigraphic interpretations are tied through
correlation to this site. In addition, we present new
multibeam echo sounding data over the central continental rise collected using the Kongsberg Simrad
EM120 system (12 kHz, 1° × 1° beams) on RRS
James Clark Ross during cruise JR104 (January–
February 2004). These data were processed using the
Simrad ‘Neptune’ software package.
4. The fossil mounded sedimentary body (MB):
morphosedimentary features and seismic
stratigraphic analysis
We have identified a MB on the central continental
rise offshore from Adelaide Island between 65°S and
65°30′S and 71°45′W–72°45′W (Fig. 1B). The MB
(Seismic Units 8 to 6 in Figs. 3 and 4) is buried 300 to
150 m below the sea floor, which is at a water depth of
3600 m, and at which it has no morphological
expression. It has a mounded, elongated shape, overlapping and continuing to the NE of an extensive cluster
of seamounts. Buried seamounts are identified on line
IT110 and line BAS20, suggesting a cluster with a
general E–W trend (Figs. 1B and 3). In addition, the
recently collected multibeam echo sounding data reveal
two seamounts that rise above the surrounding sea floor
within the northern and central part of the MB, between
lines BAS19 and IT48 (Fig. 5).
The seismic profiles show that during its development the MB was bounded by two marginal troughs.
Towards the northeast the MB becomes less pronounced
and has a more subdued external shape. The MB is at
least 48 km long and up to 25 km wide (Fig. 1B) where
it overlaps the seamount cluster (line BAS19), but it is
narrower to the northeast (≤ 20 km on line IT48). The
thickness is variable, both across and along the body.
Below we describe the development of the MB as it is
observed mainly on two MCS profiles: line BAS19 in
the area where the MB overlaps the seamount cluster,
and line IT48 to the NE of the seamounts. In the
overlapping area the MB is around 850 ms (twt) thick on
average, but it decreases in thickness NE of the
seamounts to around 400 ms (twt) on average (Fig. 3).
4.1. Oceanic crustal basement and seamounts
The reflection interpreted as the top of the oceanic
basement is located at around 6 s (twt) on average. A
feature of the top of the basement on line BAS19 is a
shallow depression below the MB and corresponding
closely to its extent (Figs. 3B and 4). The depression is
asymmetrical, with a deeper area in the SE, where the
top of the basement reaches a maximum two-way time
(twt) of 6240 ms (Figs. 3B and 4).
We infer the general distribution of the cluster of
seamounts based on lines BAS20 and IT110, together
with the new multibeam echo sounding data (Figs. 1B,
3A and 5), but in detail the three-dimensional
morphology of the cluster is not well defined. On
line IT110, close to the MB, two buried seamounts can
be seen (Fig. 3B). The peak of the largest one is 900
ms (twt) above the average level of the oceanic
basement, and this seamount is at least 12 km wide at
its base. A smaller seamount is located further
northwestward along the same seismic line. Its peak
is 200 ms (twt) above the nearby oceanic basement,
and it is about 5 km wide at its base. It is likely that
this profile does not cross their true summits, and
represents a partial view of larger seamount structures.
If we consider the total area occupied by these two
buried seamounts at their base, it is at least 20 km
wide, a dimension comparable with the width of the
MB (up to 25 km).
The seamounts observed in the multibeam data
that emerge above the sea floor are located within the
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
99
4.2.1. Seismic unit 9 (the pre-MB stage)
SU9 lies directly above the basement, and is
identified within the area of the seamount cluster on
lines IT110 and BAS19 (Fig. 3A and B). Within the
depression in the top of the basement below the MB on
line BAS19, this unit is well developed (Fig. 3B), and
here it reaches a thickness of up to 150 ms (twt).
Reflectors within this unit have high amplitudes, good
lateral continuity, an aggradational configuration, and
onlap onto the basement. This unit cannot be resolved
unambiguously on line IT48, which is outside the
seamount area (Fig. 3C).
4.2.3. Seismic Units 7 and 6 (MB maintenance stage)
Both SU7 and SU6 have similar mounded morphology to SU8, with marginal troughs on both sides of the
MB. Once again, the marginal trough on the SE side is
slightly more developed than the one to the NW, and its
seismic facies are characterised by a high acoustic
response, which laterally changes to a weaker acoustic
response (Fig. 4C). This particular facies is observed on
both sides of the MB; however, it is more developed on
the SE side than on the NW side. A small furrow can be
detected in the central part of the MB, particularly in the
upper discontinuities of these two units (Figs 3 and 4B).
SU7 has an average thickness of 100 ms (twt) within
the seamount area, but gradually thickens from NW to
SE over the MB (line BAS19, Fig. 3B). The unit is
approximately 50–60 ms (twt) thick to the NE of the
seamounts (line IT48). Seismic facies of this unit are
characterised by a weak acoustic response with an
aggradational configuration.
SU6 has an asymmetric cross-section on line BAS19
(Fig. 3B) with a lesser thickness on the southeastern side
(350 ms, twt) and a greater thickness on the northwestern side (400–450 ms twt). The thickness of this unit
decreases to approximately 100–150 ms (twt) to the NE
of the seamounts (line IT48). It has a draping shape with
an aggradational stacking pattern and a weak-totransparent acoustic response.
4.2.2. Seismic unit 8 (MB growth stage)
This unit characterises the formation and growth
stage of the MB, with marginal troughs present on both
sides of it on line BAS19, which crosses the MB
between the buried seamounts on line IT110 and the
emergent seamounts observed in the multibeam data. In
the MB, SU8 is about 400 ms (twt) thick, on average,
within the seamount area (line BAS19, Fig. 3B) and
approximately 150–200 ms (twt) thick to the NE of the
seamounts (line IT48). The unit has a slightly
asymmetric cross-section on line BAS19 being a little
thinner on the southeastern side of the MB (350 ms,
twt) than on its northwestern side (400–450 ms, twt).
The unit has a mounded external shape and an
aggradational stacking pattern in the central part of
the mound. Within this unit, seismic facies in the MB
change from a high acoustic response with reflectors
having high lateral continuity at the base to slightly
weaker acoustic response with less continuous reflectors at the top. In general, a more reflective acoustic
response is presented on the southeast side of the
deposits. The marginal trough on the SE side of the
MB is slightly more developed than the one to the NW
(Figs. 3B and 4).
4.2.4. SU5 and SU4 (transitional stage)
SU5 is observed regionally over the continental rise,
and at Site 325 has an average thickness of ∼100 ms
(twt). However, in the MB area, this unit is not present
on line BAS19 because it is truncated by the
discontinuity at the base of SU4 (Fig. 4A). The unit is
present over part of the MB to the NE of the seamounts
(line IT48, Fig. 3), with a thickness between 50 and 150
ms (twt). Data in that area are inadequate to determine
the morphology and seismic facies of this unit.
However, SU5 has an aggradational stacking pattern
with a weak-to-high acoustic response in other areas
away from the MB.
SU4 represents an important change in the depositional style on the margin. Interpretation of seismic
reflection data over the wider region shows that its lower
boundary represents the most prominent unconformity
in the entire study area. Associated with this surface, the
development of the marginal troughs is enhanced. At
this stage, the trough to the NW of the MB was clearly
larger than the one to its SE (Figs. 3B and 4). The
thickness of the unit decreases from ∼300 ms (twt) on
the SE margin to ∼200 ms (twt) on the NW margin of
the MB (line BAS19, Fig. 3B) within the seamount area,
northern and central part of the MB (Fig. 5). The peaks
of these seamounts are at around 2800 m water depth,
800 m above the average depth of the surrounding sea
floor. The total area occupied by these seamounts on the
sea floor is about 5 km wide and 8.9 km long, but they
undoubtedly cover a greater area at the top of oceanic
basement (Fig. 5).
4.2. Seismic units
Nine seismic units (SU), characterizing five evolutionary stages of the MB stratigraphic evolution, have
been identified in the sedimentary succession above
oceanic basement (Figs. 3, 4 and Table 1).
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Fig. 3. Multichannel seismic profiles across the MB: (A) Seamounts area (IT110); (B) proximal area of the Sedimentary Tail (BAS19, f–k migrated
data) and (C) distal area of the Sedimentary Tail (IT48). See position of the lines in Fig. 1B.
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
pp. 101–104
Fig. 4. (A) and (B) F–k migrated multichannel seismic profile (BAS19) with a detailed stratigraphic interpretation of the MB and adjacent areas and its correlation with DSDP Site 325. Note the mounded morphology and the related marginal troughs on both sides, and the small drift deposits that developed either side of
the MB in Seismic Unit 4. Also, note a small troughs in the upper discontinuities of Seismic Units 7 and 6 in the middle of the MB (explanation on the text). Unit 5 is in shaded dark grey to emphasize how it is truncated by the basal discontinuity of Unit 4. See position of the line in Fig. 1B. (C) Detail of the seismic facies
of the marginal trough on the SE side of the MB. High-amplitude reflections are interpreted as representing coarse lags in the marginal troughs. Location of data panel shown in A.
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
105
Fig. 5. Swath bathymetry data showing seamounts that rise 800 m above the surrounding sea floor located within the northern and central part of
the MB, between the positions of the seismic lines BAS19 and IT48. Multibeam data are displayed with shaded-relief illumination from the
north.
and from ∼250 ms (twt) on the SE margin to ∼200 ms
(twt) on the NW margin to the NE of the seamounts (line
IT48). Seismic Unit 4 exhibits high-to-very high
acoustic response with reflections with high amplitude
and good lateral continuity. This unit has an aggradational stacking pattern over the MB, but farther NW, a
mounded and elongated sedimentary deposit prograding
towards the SE is observed on lines BAS19, IT110 and
IT48, separated from the MB by the marginal trough
(Fig. 4A).
4.2.5. Seismic Units 3, 2 and 1 (inactive stage)
The lower boundary of SU3 represents an important
unconformity with marginal troughs on both sides of the
MB developed on top of SU4, although the trough on
the NW margin is largest. Within the seamount area, this
unit is absent on top of the MB within the proximal areas
(line BAS19), being restricted to its flanks with an
aggradational, onlapping stacking pattern (Figs. 3B
and 4). On the NW flank of the MB, this unit reaches a
maximum thickness of 260 ms (twt), and has a
maximum thickness of 300 ms (twt) on the SE margin
(Fig. 4). To the NE of the seamounts, this unit is present
over the MB with an aggradational stacking pattern and
an average thickness of 100–150 ms (twt). SU3
exhibits high acoustic response and contains reflections
with high lateral continuity. A mounded elongated drift
deposit is present to the SE of the MB, i.e. on its
opposite side with respect to the sedimentary mound
developed within SU4 (Fig. 4). This mound, which is
separated from the MB by a marginal trough, progrades
northwestward and evolves laterally southeastward to a
sheeted drift with an aggradational stacking pattern
(Fig. 4), and closely spaced small troughs can be
observed in the transition area between the two kinds of
deposit. In contrast, no depositional mounds are present
within SU3 on the NW margin of the MB, where the
seismic succession shows a more regular aggradational
stacking pattern (Fig. 4).
Both SU2 and SU1 contain the uppermost deposits of
the sedimentary record. The upper boundary of SU1 is
the present seafloor and they are bounded by an
unconformity at the base of SU2. The average combined
thickness of SU1 and SU2 is approximately 150–200 ms
(twt) within the seamount area (line BAS19), and
approximately 150 ms (twt) to the NE of the seamounts
(line IT48) (Fig. 3B and C). Detailed description of these
units is outside of the scope of the present paper.
5. Chronostratigraphic constraints
The age of the seismic units can be assessed by
correlation with DSDP Site 325 (Hollister et al., 1976),
through which lines BAS19 and IT110 both pass
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F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
approximately 60 km NW of the MB (Figs. 1B and 4A).
Reflections on line 48 can also be traced to Site 325, via
intersecting line IT89049 (Fig. 1B). In addition, a
regional stratigraphic study of the continental margin
off Adelaide Island has been carried out (HernándezMolina et al., in preparation), taking into consideration
chronostratigraphic constraints from other drill sites in
the region (ODP sites 1095–1097) (Barker et al., 1999),
combined regional seismic datasets, and the stratigraphic
interpretations proposed by previous authors (Larter and
Barker, 1991b; Larter and Cunningham, 1993; McGinnis and Hayes, 1995; Rebesco et al., 1996, 1997;
McGinnis et al., 1997; Barker et al., 1999; Rebesco et al.,
2002; Barker and Camerlenghi, 2002). Table 1 summarizes the age constraints on the seismic units
constituting the MB.
SU9 (pre-MB stage) thins seaward and is too thin to
be resolved on line BAS19 where it passes through Site
325 (Fig. 4). At the drill site, the age of the oceanic
basement is late Oligocene (anomaly 6Cn.3n: Larter and
Barker, 1991a), 24 Ma on the magnetic reversal time
scale of Cande and Kent (1995). The MB lies parallel to
the trend of the magnetic anomalies, between anomaly
6AAn (21.8 Ma) and the young edge of anomaly 6Bn
(22.6 Ma). Therefore, we can be certain that the
sediments in SU9 above the igneous basement are
younger than 22.6 Ma. Excluding variations in thickness
across the MB, SU8 gradually increases in thickness
towards the margin, which suggests that most of it was
deposited after the Antarctic−Phoenix ridge segment in
this spreading corridor reached the margin, i.e. no earlier
than 17.4 Ma. Consequently, most of SU8 must have
been deposited during the latter part of the Early
Miocene. Therefore, the thin sediments in SU9 represent
very slow accumulation over an interval of several
million years after the volcanic basement was formed,
during which time sediment supply from the margin was
blocked by the intervening spreading ridge.
Biostratigraphic constraints on sedimentation rates at
Site 325 indicate that it contains a hiatus or condensed
sequence spanning most of the Middle Miocene (b6 m/
Ma between 15 and 8 Ma; Hollister et al., 1976).
Correlation along line BAS19 to Site 325 indicates that
most of SU6 in the region of the MB must be older than
the Mid-Miocene condensed sequence at Site 325 (Fig.
4), i.e. N 15 Ma. Therefore, SU8, SU7 and SU6 (MB
maintenance stage) were deposited rapidly during an
interval of b2.4 Ma in the latter part of the early
Miocene (Fig. 4, Table 1). The lower boundary of SU5
correlates with a reflection located 460 ms (twt) below
sea floor (bsf) on line BAS19 where it passes through
Site 325 (Fig. 4; Larter and Barker, 1991b). There is
little doubt that this reflection is from the same boundary
as the reflection picked at 475 ms (twt) bsf on the
original single-channel site survey data for Site 325
(Hollister et al., 1976). The 15 ms difference in the
picked two-way times represents only about half of the
dominant wavelength of the data on line BAS19, and
probably results from a combination of differences in
seismic wave shape between the two datasets and
interpreters picking different phases of the waveform.
This reflection was originally interpreted as corresponding to a level below the Middle Miocene hiatus or
condensed sequence (Tucholke and Houtz, 1976:
Hollister et al., 1976), even though this implied a rather
high average interval velocity below the sea floor of
2.25 km/s. However, it is associated with an unconformity that can be traced all across the continental rise on
line BAS19, and on this basis Larter and Barker (1991b)
re-interpreted it as corresponding to the Middle
Miocene hiatus or condensed interval at Site 325. The
hiatus or condensed interval has been attributed to a
reduction in terrigenous supply as a result of margin
uplift following interaction of the ridge-crest with the
margin (Larter and Barker, 1991b). Therefore, SU5 is
Middle–Late Miocene in age (Table 1). However,
beneath the MB this unit is either represented by a
very condensed sequence or it is missing, with S4
directly overlying S6.
We correlate the prominent erosional discontinuity at
the base of SU4 (transitional stage) to a seismic
reflection identified at 0.370 s (twt) below the seafloor
(bsf) at Site 325 (Fig. 4A). We consider the upper
discontinuity of SU4 to correlate to Horizon R, defined
previously by Tucholke and Houtz (1976), which we
have traced to 0.225 s (twt) at Site 325. This correlation
implies that SU4 has an Early Pliocene age (Table 1).
The youngest units are SU3, SU2 and SU1 (inactive
stage); SU3 developed from the Early Pliocene to the
Late Pliocene, and SU2 and SU1 from the Late Pliocene
to the Recent (Table 1).
Seismic profile intersections allow us (Table 1) to
correlate our SU with the units defined by previous
authors on the continental rise (Larter and Barker,
1991b; Rebesco et al., 1997, 2002), and with the results
of the Ocean Drilling Program Leg 178 (Barker et al.,
1999; Volpi et al., 2001; Barker and Camerlenghi,
2002). SU9, SU8, SU7 and SU6 correlate with the predrift stage of the upper rise drifts of Rebesco et al.
(1997, 2002). This implies that growth and maintenance
stages of MB developed before the upper rise drifts. SU
5 correlates with M3 sequence of these authors, coeval
with the drift-growth stage of the upper rise drifts. We
interpret the lower boundary of S4 as correlating with
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
the base of the prograding shelf sequences, previously
referred to as the “base of glacial margin sequences”
(Larter et al., 1997). SU4 represents most of the MB
transitional stage and the period when the most
significant change in the depositional style of the
margin occurred, after its transformation from an active
to a passive margin in the Early Miocene (HernándezMolina et al., 2003, in press), and it correlates with the
base of the M2 sequence of Rebesco et al. (1997, 2002).
This change in the depositional style at the end of the
Miocene–Early Pliocene has been associated with the
development of the “glacial margin sequences” on the
shelf by Larter et al. (1997), which they interpreted as
marking the onset of frequent advances of grounded ice
to the shelf break. At this time there was a change to
greater influence of down-slope sedimentary processes
which interacted with the along-slope sedimentary
processes within a palaeoceanographic setting similar
to the present day (Hernández-Molina et al., 2003, in
press). Our correlation implies that the MB transitional
stage is synchronous with the onset of development of
glacial margin sequences on the shelf. SU3, SU2 and
SU1 correlate with the upper part of the M2 and M1
Sequences of the sediment drifts of the upper rise
(Rebesco et al., 1997, 2002), representing the driftmaintenance stage of the upper rise drifts.
6. Genesis of the MB and palaeoceanographic
implications
6.1. Effect of seamounts on an impinging flow
Knowledge of how seamounts and seamount chains
interact with ocean circulation is important from a
geological point of view. Akin to island mass effects
(Heywood et al., 1990), seamounts generate seamount
effects, with important effects on oceanographic processes (Roden, 1987), marine biota (Rogers, 1994),
sedimentation and erosion rates (Davies and Laughton,
1972; Roberts et al., 1974), and hence palaeoceanographic interpretations (Roden, 1987). The streamline
distortion around obstacles is relevant to sediment
distribution around seamounts (Fig. 6).
The hydrodynamic processes resulting from interaction between ocean currents and a seamount are
complex, but two end members may be considered in
which either advection processes or vorticity interaction
dominate (Fig. 6A and B):
1. If vorticity interaction processes are dominant, the
impinging flow generates a pair of oppositely rotating
eddies (double vortex generation) on the flanks of the
seamount, with flow intensification of the left-hand side
107
of the obstacle when looking downstream (in the
northern hemisphere). Both eddies interact with each
other (in time and space) and with the mean flow in a
complicated manner to produce many transient and
trapped features (Roden, 1987, 1991; Zhang and Boyer,
1991). Seamounts also condition the generation of
internal waves downcurrent (Roden, 1987, 1991).
2. If the mean velocity of the flow is lower, advection
processes may dominate. In this case, flow local to the
seamount is clockwise around it (in the northern
hemisphere), and an anticyclonic eddy-column-like
upwelling cone (Taylor column) appears near its top
(Taylor, 1917; Gould et al., 1981; Eriksen, 1991; Roden,
1991; Ou, 1991; Zhang and Boyer, 1991; Bograd et al.,
1997), although when the flow rate oscillates over time,
eddies are periodically shed from the seamount (Roden,
1991). Water mass stratification, in general, inhibits
vertical motion and the vertical extent of topographically generated disturbances. Eddies atop seamounts
then become bottom trapped, and if the stratification is
very strong, a surface cyclonic eddy may appear above
the deep anticyclonic eddy (Roden, 1991).
Where a bottom current encounters major solid
obstacles, such as seamounts, its flow is constricted and
accelerated, and thereby its competence is increased,
which may result in erosion in front of the obstacles
(Fig. 6C).
Many seamounts have marginal troughs (scours or
moats), which develop preferentially one side of the
seamount relative to the flow direction depending on
which hemisphere the seamount is in (Fig. 6A and
C), with accelerated flow to the left of the seamount
(looking downstream) in the northern hemisphere and
decelerated flow to the right (Roberts et al., 1974;
Gould et al., 1981), resulting in both locally faster
and slower accumulation than in areas distant from
obstacles.
Downstream from an obstacle, the two separate flows
decelerate and develop small turbulent eddies, which
tend to return back towards the obstacle. The positive
relief of obstacles also causes upwelling and downwelling eddies, internal waves, and transverse turbulent
rolls of the shear layer in the flow over them (Fig. 6A
and B), and many of these processes could occur in a
deep water mass (Roden, 1987). The net result of these
processes can be the generation of a shadow zone
downstream of large obstacles or groups of obstacles,
where turbulence intensity slowly diminishes and the
currents are slower relative to the marginal troughs, as
proposed by Allen (1982, 1994) and Zhang and Boyer
(1991). In this shadow zone behind an obstacle a
depositional tail may develop (Davies and Laughton,
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F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
1972; Masson et al., 2003), with a mounded and
elongated external morphology (Fig. 6A and C).
formed the marginal troughs remained so widely
separated for such a long distance downstream of the
buried seamounts.
6.2. MB depositional model
The morphology and seismic characteristics of the
MB enable us to infer the depositional processes that
were responsible for the development of these deposits. We interpret the MB as a mounded, elongated
sedimentary body produced by the redistribution of
sediments by bottom currents that were diverted
around and disturbed by the extensive cluster of
seamounts.
We interpret the marginal troughs flanking the MB as
having been produced by separate, turbulent, faster
cores on both sides of the seamounts (Fig. 6A),
generating a pair of oppositely rotating eddies, as
reported previously around seamounts (Roden, 1987),
influencing deposits as described by Allen (1982, 1994).
Marginal troughs are expected on the right side of
seamounts in the southern hemisphere (McCave and
Carter, 1997), so that during the deposition of Seismic
Units 8, 7 and 6, the greater development of the
marginal trough on the SE margin of the MB suggests
northeastward-directed main flow on this margin. The
development of a down-flow shadow zone, as discussed
above explains the northeastward continuation of the
MB to line IT48. Gaps between seamounts might also
have accelerated flow, resulting in the scouring of
sediments and their redeposition downstream as the
flow decelerated: this might explain some details of the
stratigraphic patterns we observe, such as small troughs
in the central part of the MB, in the upper discontinuities
of SU8, SU7 and SU6 (Figs. 3 and 4). Therefore, we
interpret the MB, as a patch drift, plastered between and
against the NE (lee) side of the extensive cluster of
seamounts, as a large Contourite Sedimentary Tail
(CST) deposited in the shadow zone of the seamounts
by the action of a deep current flowing northeastward
(Fig. 6A).
The MB depositional model was developed by
considering the likely effect of the extensive cluster of
buried seamounts on an impinging northeastward flow.
More recently, new multibeam echo sounding data have
revealed additional, larger seamounts within the central
part of the MB, northeast of where it is most developed
(on line BAS19). We consider the interpretation that the
MB developed in a shadow zone is still correct, but it is
now clear that this zone was partly within the wider
cluster or seamounts rather than entirely downstream of
it. The position of the newly discovered seamounts
probably explains why the two main current cores that
6.3. Stratigraphic considerations and palaeoceanographic implications
SU9 is resolved only in the depressions of the
basement close to the seamounts (Figs. 3 and 4). This
unit is thin and sheeted, filling the irregularities of the
basement and without a mounded morphology. We refer
to this unit, developed during the Early Miocene, as the
pre-MB stage, and interpret it as being composed mainly
of distal turbidites that accumulated slowly before the
segment of the Antarctic–Phoenix Ridge between the
Adelaide and Biscoe fracture zones reached the margin.
SU8 (MB growth stage), and SU7 and SU6 (MB
maintenance stage) were deposited during the latter part
of the Early Miocene. The observation that the marginal
trough on the SE side of the MB was slightly more
developed than the one on its NW side during the
deposition of these units suggests that there was
interaction of a northeast-flowing contour current with
the extensive cluster of seamounts on the central
continental rise at this time. The position and orientation
of the MB in relation to the seamount cluster is also
consistent with flow in that direction having concentrated deposition in shadow zones between and
downstream of seamounts. Correlations with Site 325
indicate that SU8, SU7, and SU6 are older than the main
phase of development of sediment drifts on the nearby
upper continental rise (M4 and M3 Units), the drift
growth stage of Rebesco et al. (1997, 2002). The growth
of the MB during deposition of SU 8 suggests a
vigorous bottom current regime on the central continental rise in the latter part of the Early Miocene.
Previously, the earliest indications of strong bottom
current activity on the continental rise west of the
Antarctic Peninsula have been observed at a stratigraphic level equivalent to SU5, corresponding to the start of
the Middle Miocene. The characteristics of SU7 and
SU6 suggest a similar pattern of bottom current flow
was also active during their deposition. However, in
contrast to SU8, these units show less of an increase in
thickness over the MB and few internal variations in
seismic facies, suggesting more sluggish currents. The
seismic facies of these units suggest fine- to very finegrained sediments (silts and clays) similar to those cored
in the nearby Middle Miocene–Recent sediment drifts
(Barker et al., 1999; Pudsey, 2000; Lucchi et al., 2002).
We envisage that the fine-grained components of
sediments supplied by gravity flows from the adjacent
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
109
Fig. 6. (A) Sketch with the main hydrodynamic features related to an incoming flow with a seamount (summary using data from the following
authors: Taylor, 1917; Davies and Laughton, 1972; Roberts et al., 1974; Owens and Hogg, 1980; Gould et al., 1981; Roden, 1987, 1991; Saunders,
1988; Eriksen, 1991; Ou, 1991; Zhang and Boyer, 1991; Rogers, 1994; Bograd et al., 1997; McCave and Carter, 1997; Wright, 2001; Masson et al.,
2003). (B) Sketches of streamlines for vortex shedding regime in oscillatory free stream impinging on two obstacles such as seamounts (from Zhang
and Boyer, 1991): 1.—Relatively smooth streamline field with wave-like undulations in the near wake, 2.—quite three-dimensional motion in the
near wake with relatively stagnant region extending far downstream; and 3.—in the absence of a strong advective current, interaction of Coriolis
Force with obstacles produces a chain of closed vortices. (C) Formation of marginal troughs (moats) and sedimentary tails when bottom currents
encounter major obstacles, such as a seamount (from Davies and Laughton, 1972).
110
Table 1
Chronostratigraphic framework for the seismic units of the MB
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
The units and discontinuities have been laterally correlated with the results from DSDP Site 325. A correlation with the regional units of other authors and ODP sites is also presented.
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
continental margin were entrained and transported
northeastward in a nepheloid layer by a persistent
ambient contour current. Presently, however, LCDW
from the Weddell Sea flows over this area in the
opposite direction, and consequently we suggest that a
major palaeoceanographic change has occurred in the
area at some time since the Early Miocene.
SU5 is not present in the MB area because it is
truncated by the basal discontinuity of SU4. Consequently, the palaeoceanographic change could have
taken place during deposition of SU5. However, on the
continental rise west of the Antarctic Peninsula, the base
of SU4 (transitional stage) may hold the key to
understanding the palaeoceanographic change that we
infer, because it represents an important change in the
depositional style on the continental rise. The prominent
erosion surface at the base of SU4 is indicative of more
energetic bottom current flow in comparison with the
earlier SU5, and the more developed marginal trough to
the NW of the MB at this time suggests it was formed by
a strong core of a current flowing southwestwards, i.e. in
the opposite direction to the current inferred to have
been associated with the growth and maintenance stages
(SU8–SU6) of the MB. In this new oceanographic
scenario the seamounts located within the northern and
central part of the MB would have affected the current
flowing southwestwards in the opposite sense to the way
the seamount cluster to the SW affected the northeastward flowing current during the deposition of SU8, SU7
and SU6. Hence a new aggrading, mounded unit
developed over the central part of the MB, to the SW
or the large seamounts observed on the multibeam echo
sounding data. Based on the chronology of the seismic
units, the change in bottom current regime took place
during the interval represented by the SU5 or SU5/SU4
boundary over the MB, but presently available age
constraints leave a large degree of uncertainty regarding
the precise time at which the change in bottom current
flow occurred. The change could have taken place at any
time between the beginning of the Middle Miocene and
the end of the Miocene (i.e. 15–5 Ma). The prominent
erosional surface at the base of SU4, the high-to-very
high acoustic response, and the high lateral continuity of
reflections within SU4 indicate a more energetic deep
water regime, compared with the previous units SU7–
SU5.
This segment of the Pacific margin continental rise is
presently affected by a LCDW branch flowing southwestward from the Weddell Sea. Farther north lies the
axis of the east-flowing ACC (Nowlin and Zenk, 1988;
Camerlenghi et al., 1997: Giorgetti et al., 2003; Naveira
Garabato et al., 2003). Stronger bottom currents
111
following similar paths to the modern ones have been
interpreted to have generated the major sediment drifts
along the upper continental rise during the Middle and
Late Miocene (Rebesco et al., 1996, 1997; Barker et al.,
1999; Rebesco et al., 2002; Barker and Camerlenghi,
2002). The development of the MB during the early
Miocene indicates the predominance of northeastward
contour current flow on the central continental rise at
that time. During the Early and Middle Miocene, there
was certainly a deep water pathway through Drake
Passage for Circumpolar Deep Water (CDW) (Barker
and Burrell, 1977), but, there may not have been a route
for WSDW and LCDW from the Weddell Sea to reach
the continental rise west of the Antarctic Peninsula
through the southern Scotia Sea. The first incursion of
WSDW into the central Scotia Sea has been interpreted
as having occurred during the Middle Miocene, when
plate movements had produced sufficient gaps in the
South Scotia Ridge to allow deep water inflow from the
northern Weddell Sea (Maldonado et al., 2003; Bohoyo,
2004; Maldonado et al., 2005). At the same time LCDW
from the Weddell Sea probably started to flow into the
Scotia Sea and move towards the southwest. Therefore,
a vigorous northeastward flowing contour current
related to one of the frontal zones of the ACC might
have operated closer to the Margin in the Early Miocene
and generated the MB on the central rise (Fig. 7A).
On the basis of the chronostratigraphic constraints on
the data presented here, oceanographic change could
have begun in the Middle Miocene, at the same time as
the drift-growth stage defined by Rebesco et al. (1997,
2002). However, we suggest that the prominent erosive
surface at the SU5/SU4 boundary could represent the
onset of a stage of more intense bottom water circulation
and a major reorganization of deep water flows towards
a regional oceanographic pattern more similar to the
present one (Billups, 2002). As a result, LCDW from the
Weddell Sea may have extended over the central rise
along the Antarctica Peninsula, displacing CDW and
forcing it to move to a more distal position (Fig. 7B).
SU3, SU2 and SU1 buried the MB (inactive stage)
and, consequently, indicate that a new bottom current
regime was established. Therefore, bottom flows similar
in pattern and strength to those found presently have
probably been established during the Pliocene and
Quaternary. SU3, SU2 and SU1 record two main stages
of the glacially dominated margin during which downslope processes were dominant over along-slope
processes (Hernández-Molina et al., 2003, in press),
favouring MB buried on the rise.
We interpret the occurrence of the MB in the
sedimentary succession of the central continental rise
112
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
Fig. 7. Sketches with (A) the inferred past circulation pattern of bottom water masses for the MB growth and maintenance stages and (B) present
circulation pattern of bottom water masses. (a) Circumpolar Deep Water (CDW) and (b) LCDW branch from the Weddell Sea.
as evidence that this area was affected by CDW flowing
northeastward as a contour current within the ACC
during the latter part of the Early Miocene (Fig. 7A).
However, since at least the Late Miocene–Early Pliocene the area has been affected by LCDW from the
Weddell Sea flowing southwestward (Fig. 7B), as
described above. These palaeoceanographic changes
could be explained by three possible hypotheses:
1. Migration and coexistence hypothesis. During most
of the Miocene, the influence of WSDW along the
South Scotia Ridge, and LCDW from the Weddell
Sea along the Pacific margin of the Antarctic
Peninsula, was less extensive than it has been during
the Late Miocene, Pliocene and Quaternary, and as a
result it was restricted to the upper rise. Consequently, CDW within the ACC circulated closer to the
margin and its northeastward flow generated the MB
on the central rise. Later, a more intense bottom water
circulation and reorganization of bottom currents
during the Late Miocene or Early Pliocene could
have been associated with increased LCDW outflow
from the Weddell Sea. As a result, LCDW from the
Weddell Sea may have extended over the central rise,
and CDW was displaced to a more distal position.
Such a palaeoceanographic change over the central
rise could have produced the ‘inactive’ stage of the
MB. According to this hypothesis, the CDW from
the ACC on the central rise and the LCDW from
the Weddell Sea on the upper rise coexisted during
the Middle to Late Miocene.
2. All change hypothesis. The MB was developed by
northeastward-flowing CDW, which was the only
water mass flowing over the entire margin during the
Early Miocene. Later, an oceanographic regime
similar to the modern one, but with more energetic
bottom currents, was established as a result of
increased outflow of LCDW from the Weddell Sea
and reorganization of bottom currents between
Middle Miocene and Early Pliocene times. The MB
was fossilised during the Pliocene and Pleistocene as
weaker southwestward-flowing LCDW from the
Weddell Sea allowed down-slope sedimentary processes to dominate. According to this hypothesis,
there was a widespread change in thermohaline
circulation, either near the beginning of the Middle
Miocene (start of the drift-growth stage on the upper
rise described by Rebesco et al. (1997, 2002) or
during Late Miocene/earliest Pliocene times (cf.
Billups, 2002).
3. Diversion of ACC fronts hypothesis. A study of
satellite-derived sea surface temperature data reveals
that the mean path of the Polar Front is strongly
steered by the topographic features of the Southern
Ocean (Moore et al., 1999). At present the mean
path of the Polar Front in Drake Passage lies just to
the north of a prominent ridge along the southern
part of the Shackleton Fracture Zone (SFZ).
Livermore et al. (2004) have recently suggested
that this ridge was only uplifted since spreading
stopped on the West Scotia Ridge in Drake Passage
during the Late Miocene. In this case, the path of the
Polar Front, and probably also the SACCF and SB,
may have been farther south in Drake Passage and
on the Antarctic Peninsula continental rise before
the latest Miocene. Uplift of the ridge might have
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
caused northward migration of the Polar Front,
allowing the other fronts to migrate northward as
well, and this could explain some of the changes
observed around the Late Miocene to Miocene–
Pliocene boundary. According to this hypothesis,
there would not necessarily have been any change in
LCDW outflow from the Weddell Sea in the
Middle–Late Miocene. When the Polar Front and
other ACC fronts were displaced northwards, as a
result of the uplift of the ridge at the Shackleton
Fracture Zone, the WSDW and LCDW from the
Weddell Sea would have been able to spread across
the rise. In this hypothesis the two flows coexist but
the ‘driving’ mechanism was the northward displacement of the ACC fronts.
7. Conclusions
The analysis and interpretation of three parallel MCS
profiles and multibeam echo sounding data collected
over the continental rise on the Pacific margin of the
Antarctic Peninsula can be summarised with the
following conclusions:
a) A Fossil Mounded Sedimentary Body (MB) has been
identified in the Early Miocene sedimentary record
over the oceanic crust on the central continental rise
offshore from Adelaide Island.
b) The MB has an elongated NE trend, overlapping and
continuing to the NE of an extensive cluster of
seamounts, and it developed bounded by two
marginal troughs. It is over 48 km long and ranges
from nearly 25 km wide where it overlaps the
seamount cluster to about 20 km wide NE of the
seamounts. Its thickness is variable, across and along
the body. In the area where it overlaps the seamount
cluster it measures ∼850 ms (twt), but thickness
decreases towards the NE (∼400 ms twt).
c) Nine seismic units have been identified in the
sedimentary record: Unit 9 (pre-MB stage); Unit
8 (MB growth stage); Units 7 and 6 (MB maintenance stage); Units 5 and 4 (transitional stage); and
Units 3, 2 and 1 (inactive stage).
d) We interpret the MB as a patch drift plastered
between and against the NE (lee) side of the
extensive cluster of seamounts, as a large Contourite
Sedimentary Tail. It was deposited in a “shadow
zone” between and behind the seamounts that was
generated by the action of a deep current flowing
northeastward.
e) The central and upper continental rise are presently
affected by a southwestward-flowing branch of
113
LCDW from the Weddell Sea. The occurrence of
the MB in the Miocene sedimentary record provides
evidence that during the Early Miocene, the contour
current flow on the central rise was towards the NE,
probably involving CDW within the ACC. Therefore
a palaeoceanographic change occurred in the area at
some time between the start of the Middle Miocene
and the end of the Miocene.
f) Our stratigraphic interpretations are consistent with
previous work in the region, which mainly focussed
on sediment drifts along the upper continental rise
(Rebesco et al., 1996, 1997, 2002; Barker et al.,
1999; Barker and Camerlenghi, 2002). However, our
observations do indicate that Miocene contourite
deposits in the region were not all produced by the
same water masses.
g) Our results are an example of how contourite
deposits, moats, and marginal troughs present in
the deep marine environment can provide evidence
for the reconstruction of palaeoceanographic
changes.
Acknowledgements
This research has been partially supported by
Spain's Inter-ministerial Science and Technology
Committee (CYCIT), through Project ANT99-0817
We thank the officers, crew, technical support staff
and scientists who sailed on RRS Discovery cruise
172 (1988) and R/V OGS-Explora cruises in 1989
and 1992. On the OGS-Explora cruises, seismic data
were collected as part of Italy's PNRA (Programma
Nazionale di Ricerche in Antartide). PNRA supported Michele Rebesco's contributions through the
SEDANO (Sediment Drifts of the Antarctic Offshore
project).
This work has been carried out during research stages
at BAS funded by the Secretaría de Estado de Educación
y Universidades (PR2002-0271 and PR2003-0421), and
within the scientific Spanish–British agreement on the
study of the continental margin offshore from Adelaide
Island.
Dr. Alberto C. Naveira Garabato (National Oceanographic Centre, Southampton, NOCS) is thanked for his
full and constructive reviews of the Oceanographic
Setting chapter and the Fig. 2 of this paper. We are
grateful to Dr. Carol Pudsey for processing the multibeam echo sounding data in Fig. 6 and commenting on
an earlier version of the manuscript. Finally, we thank the
positive comments and suggestions of David J.W. Piper,
Paul C. Knutz and one anonymous reviewer who helped
us to improve the present paper.
114
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
References
Allen, J.R.L., 1982. Sedimentary structures, their character and
physical basis. Developments in Sedimentology, vol. 2. Elsevier,
Amsterdam. 30 (vol. A and B). 663 pp.
Allen, J.R.L., 1994. Fundamental properties of fluids and their relation
to sediment transport processes. In: Kenneth, P. (Ed.), Sediment
Transport and Depositional Processes. Blackwell Scientific
Publications, Oxford, pp. 25–60.
Arhan, M., Heywood, K.J., King, B.A., 1999. The deep waters from
the Southern Ocean at the entry to the Argentine Basin. Deep-Sea
Res. II 46, 475–499.
Barber, M., Crane, D., 1995. Current flow in the north-west Weddell
Sea. Antarct. Sci. 7 (1), 39–50.
Bart, P.J., Anderson, J.B., 1995. Seismic record of glacial events
affecting the Pacific Margin of the Northwestern Antarctic
Peninsula. In: Cooper, A.K., Barker, P.F., Brancolini, G. (Eds.),
Geology and Seismic Stratigraphy of the Antarctic Margin, AGU.
Antarct. Res. Ser., vol. 68, pp. 74–95.
Barker, P.F., 1982. The Cenozoic subduction history of the Pacific
margin of the Antarctic Peninsula: ridge crest–trench collisions.
J. Geol. Soc. Lond. 139, 787–801.
Barker, P.F., Burrell, J., 1977. The opening of Drake Passage. Mar.
Geol. 25, 15–34.
Barker, P.F., Camerlenghi, A., 2002. Glacial history of the Antarctic
Peninsula from Pacific margin sediments. In: Barker, P.F.,
Camerlenghi, A., Acton, G.D., Ramsay, A.T.S. (Eds.), Proc.
ODP, Sci. Results, vol. 178, pp. 1–40.
Barker, P.F., Camerlenghi, A., and the Leg 178 Scientific Party, 1999.
Proc. ODP, Init. Repts. 178: Ocean Drilling Program, Texas A&M
University College Station, Texas.
Billups, K., 2002. Late Miocene through early Pliocene deep water
circulation and climate change viewed from the sub-Antarctic
South Atlantic. Palaeogeogr. Palaeoclimatol. Palaeoecol. 185,
287–307.
Bograd, S.J., Rabinovich, A.B., LeBlond, P.H., Shore, J.A., 1997.
Observations of seamount-attached eddies in the North Pacific.
J. Geophys. Res. 102 (C6), 12 441–12 456.
Bohoyo, F., 2004. Fragmentación continental y desarrollo de cuencas
oceánicas en el sector meridional del Arco de Scotia, Antártida,
Thesis. Universidad de Granada, Spain. 252 pp.
Camerlenghi, A., Crise, A., Pudsey, C.J., Accerboni, E., Laterza, R.,
Revesco, M., 1997. Ten-month observation of the bottom current
regime across a sediment drift of the Pacific margin of the
Antarctic Peninsula. Antarct. Sci. 9, 426–433.
Cande, S., Kent, D.V., 1995. Revised calibration of the geomagnetic polarity timescale for the late Cretaceous and Cenozoic.
J. Geophys. Res. 100, 6093–6095.
Davies, T.A., Laughton, A.S., 1972. Sedimentary processes in the
North Atlantic. In: Laughton, A.S., Berggren, W.A., et al. (Eds.),
Initial Reports of Deep Sea Drilling Project, vol. 12. U.S.
Government Printing Office, Washington, D.C., pp. 905–934.
Domack, E.W., Schere, E., McClennen, C., Anderson, J., 1992.
Intrusion of circumpolar deep water along the Bellinshausen Sea
continental shelf. Ocean Sci. 71.
Eriksen, C.C., 1991. Observations of amplified flows atop a large
seamount. J. Geophys. Res. 96 (C8), 15227–15236.
Fahrbach, E., Rohardt, G., Scheele, N., Schoder, M., Strass, V.,
Wisotzki, A., 1995. Formation and discharge of deep and bottom
water in the northwestern Weddell Sea. J. Mar. Res. 53, 515–538.
Fahrbach, E., Schoder, M.L., Klepikov, A., 1998. Circulation and
water masses in the Weddell Sea. In: Lepparanta, M. (Ed.), Physics
of Ice-Covered Seas. Lecture Notes from Helsinki University
Summer School, Savonlinna, Finland, pp. 569–603.
Faugères, J.C., Stow, D.A.V., 1993. Bottom current controlled
sedimentation: a synthesis of the contourite problem. Sediment.
Geol. 82, 287–297.
Faugères, J.C., Stow, D.A.V., Imbert, P., Viana, A., 1999. Seismic
features diagnostic of contourite drifts. Marine Geology 162 (1),
1–38.
Foldvik, A., Gammelrsød, T., 1988. Notes on Southern Ocean
hydrography, sea-ice and bottom water formation. Palaeogeogr.
Palaeoclimatol. Palaeoecol. 67, 3–17.
Giorgetti, A., Crise, A., Laterza, R., Perini, L., Rebesco, M.,
Camerlenghi, A., 2003. Water masses and bottom boundary
layer dynamics above a sediment drift of the Antarctic Peninsula
Pacific Margin. Antarct. Sci. 15 (4), 537–546.
Gordon, A.L., Visbeck, M., Huber, B., 2001. Export of Weddell Sea
Deep and Bottom Water. J. Geophys. Res. 106, 9005–9017.
Gould, W.J., Hendry, R., Huppert, H.E., 1981. An abyssal topographic
experiment. Deep-Sea Res. 28A (5), 409–440.
Hernández-Molina, F.J., Larter, R.D., Maldonado, A., RodríguezFernández, J., 2003. Pliocene and Quaternary stratigraphic
evolution of the Pacific margin offshore of the Antarctic Peninsula
offshore from Adelaide Island. 9th International Symposium on
Antarctic Earth Science. Potsdam (Germany). 8–12, September,
Abstracts Volume, pp. 153–154.
Hernández-Molina, F.J., Larter, R.D., Rebesco, M., Maldonado, A.,
2004. Miocene changes in bottom current regime recorded in
continental rise sediments on the Pacific margin of the Antarctic
Peninsula. Geophys. Res. Lett. 31, L22606. doi:10.1029/
2004GL020298.
Hernández-Molina, F.J., Larter, R.D., Maldonado, A., RodríguezFernández, J., in press. Pacific margin evolution since the late
Miocene evolution in the Antarctic Peninsula offshore the
Adelaida Island: An example of a glacial passive margin. Terra
Antarct. Reports.
Hernández-Molina, F.J., Larter, R.D., Maldonado, A., in preparation.
Neogene and Quaternary stratigraphic evolution of the Antarctic
Peninsula Pacific margin offshore from Adelaide Island.
Heywood, K.J., Barton, E.D., Simpson, J.H., 1990. The effects of flow
disturbance by an oceanic island. J. Mar. Res. 48, 55–73.
Hillenbrand, C.D., Grobe, H., Diekmann, B., Kuhn, G., Fütterer, D.K.,
2003. Distribution of clay minerals and proxies for productivity in
surface sediments of the Bellingshausen and Amundsen seas (West
Antarctica)—relation to modern environmental conditions. Mar.
Geol. 193, 253–271.
Hoffmann, E.E., Klinck, J.M., Lascara, C.M., Smith, D.A., 1996.
Water mass distribution and circulation west of the Antarctic
Peninsula and Bransfield Strait. Antarct. Res. Ser. 70, 61–80.
Hollister, C.D., Elder, R.B., 1969. Contour currents in the Weddell
Sea. Dee-Sea Res. 16, 99–101.
Hollister, C.D., Craddock, C., et al., 1976. Initial Reports of the Deep
Sea Drilling Project, vol. 35. U.S. Government Printing Office,
Washington, D.C. 930 pp.
Locarnini, R.A., Whitworth III, T., Nowlin Jr., W.D., 1993. The
importance of the Scotia Sea on the outflow of Weddell Sea Deep
Water. J. Mar. Res. 51, 135–153.
Larter, R.D., Barker, P.F., 1989. Seismic stratigraphy of the Antarctic
Peninsula Pacific margin: a record of Pliocene–Pleistocene ice
volume and paleoclimate. Geology 17, 731–734.
Larter, R.D., Barker, P.F., 1991a. Effects of ridge crest–trench
interaction on Antarctic–Phoenix spreading: forces on a young
subducting plate. J. Geophys. Res. 96 (19), 583–607.
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
Larter, R.D., Barker, P.F., 1991b. Neogene interaction of tectonic and
glacial processes at the Pacific margin of the Antarctic Peninsula.
Spec. Publs. Int. Ass. Sediment. 12, 165–186.
Larter, R.D., Cunningham, A.P., 1993. The depositional pattern
and distribution of glacial-interglacial sequences on the
Antarctic Peninsula Pacific margin. Mar. Geol. 109,
203–219.
Larter, R.D., Rebesco, M., Vanneste, L.E., Gamboa, L.A.P., Barker, P.
F., 1997. Cenozoic tectonic sedimentary and glacial history of the
continental shelf west of Graham land, Antarctic Peninsula.
Antarct. Res. Ser. 71, 1–27.
Livermore, R., Eagles, G., Morris, P., Maldonado, A., 2004.
Shackleton Fracture Zone: no barrier to early circumpolar ocean
circulation. Geology 32, 797–800.
Lucchi, R., Rebesco, M., Camerlenghi, A., Busetti, M., Tomadin, L.,
Villa, G., Persico, D., Morigi, C., Bonci, M.C., Giorgetti, G., 2002.
Glaciomarine sedimentary processes of a high-latitude. Deep-sea
sediment drift (Antarctic Peninsula Pacific margin). Mar. Geol.
189, 343–370.
Maldonado, A., Barnolas, A., Bohoyo, F., Galindo-Zaldivar, J.,
Hernandez-Molina, F.J., Lobo, F., Rodriguez-Fernandez, J.,
Somoza, L., Vazquez, J.T., 2003. Bottom deposits in the Central
Scotia Sea: the importance of the Antarctic Circumpolar Current
and the Weddell Gyre flows. Palaeogeogr. Palaeoclimatol.
Palaeoecol. 198, 187–221.
Maldonado, A., Barnolas, A., Bohoyo, F., Escutia, C., GalindoZaldívar, J., Hernández-Molina, F.J., Jabaloy, A., Lobo, F., Nelson,
C.H., Rodríguez-Fernández, J., Somoza, L., Vázquez, J.T., 2005.
Miocene to recent contourite drifts development in the northern
Weddell Sea (Antarctica). In: Florindo, F., Harwood, D.M.,
Wilson, G.S. (Eds.), Long-Term Changes in Southern HighLatitude Ice Sheets and Climate: The Cenozoic History. Global
Planet. Change, vol. 45, (1–3), pp. 99–129.
Masson, D.G., Bett, B.T., Billett, D.S.M., Jacobs, C.L., Wheeler, A.J.,
Wynn, R.B., 2003. The origin of deep-water, coral-topped mounds
in the northern Rockall trough, Northeast Atlantic. Mar. Geol. 194,
159–180.
McCave, I.N., Carter, L., 1997. Recent sedimentation beneath the deep
Western Boundary Current off northern New Zealand. Deep-Sea
Res. I 44 (7), 1203–1237.
McCave, I.N., Tucholke, B.E., 1986. Deep current controlled
sedimentation in the western North Atlantic. In: Vogt, P.R.,
Tucholke, B.E. (Eds.), The Geology of North America, Vol. M,
The Western North Atlantic Region. Geological Society of
America, Boulder, Colorado, pp. 451–468.
McGinnis, J.P., Hayes, D.E., 1995. The roles of down-slope and
along-slope depositional processes: southern Antarctic Peninsula
margin. In: Cooper, A.K., Barker, P.F., Brancolini, G. (Eds.),
Geology and Seismic Stratigraphy of the Antarctic MarginAmerican Geophysical Union, Antarct. Res. Ser., vol. 68, pp.
141–156.
McGinnis, J.P., Hayes, D.E., Driscoll, N.W., 1997. Sedimentary
processes across the continental rise of the southern Antarctic
Peninsula. Mar. Geol. 141, 91–109.
Meredith, M.P., Naveira Garabato, A.C., Stevens, D.P., Heywood, K.
J., Sanders, R.J., 2001. Deep and bottom waters in the eastern
Scotia Sea: rapid changes in properties and circulation. J. Phys.
Oceanogr. 31, 2157–2168.
Moore, P., Ehlers, S., Murphy, C.M., Reynolds, M.D., 1999.
Investigation of the stability of the ERS 1 range bias through
tide gauge augmented altimetry. J. Geophys. Res. 104 C12 (30),
21–38.
115
Naveira Garabato, A.C., Heywood, K.J., Stevens, D.P., 2002a.
Modification and pathways of Southern Ocean Deep Waters in
the Scotia Sea. Deep-Sea Res. I 49, 681–705.
Naveira Garabato, A.C., McDonagh, E.L., Stevens, D.P., Heywood, K.J., Sanders, R.J., 2002b. On the export of Antarctic
Bottom Water from the Weddell Sea. Deep-Sea Res. II 49,
4715–4742.
Naveira Garabato, A.C., Stevens, D.P., Heywood, K.J., 2003. Water
mass conversion, fluxes and mixing in the Scotia Sea diagnosed by
an inverse model. J. Phys. Oceanogr. 33, 2565–2587.
Nowlin Jr., W.D., Zenk, W., 1988. Westward bottom currents along the
margin of the South Shetland Island Arc. Deep-Sea Res. 35,
269–301.
Orsi, A.H., Nowlin Jr., W.D., Whitworth III, T., 1993. On the
circulation and stratification of the Weddell Gyre. Deep-Sea Res. I
40, 169–203.
Orsi, A.H., Johnson, G.C., Bullister, J.L., 1995. On the meridional
extent and fronts of the Antarctic Circumpolar Current. Deep-Sea
Res. I 42 (5), 641–673.
Orsi, A.H., Johnson, G.C., Bullister, J.L., 1999. Circulation, mixing
and production of Antarctic Bottom Water. Progr. Oceanogr. 43,
55–109.
Ou, H.W., 1991. Some effects of a seamount on oceanic flows. J. Phys.
Oceanogr. 21, 1835–1845.
Owens, W.B., Hogg, N.G., 1980. Oceanic observations of stratified
Taylor columns near a bump. Deep-Sea Res. 27A, 1029–1045.
Pudsey, C.J., 2000. Sedimentation on the continental rise west of the
Antarctic Peninsula over the last three glacial cycles. Mar. Geol.
167, 313–338.
Pudsey, C.J., Camerlenghi, A., 1998. Glacial–interglacial deposition
on a sediment drift on the Pacific margin of the Antarctic
Peninsula. Antarct. Sci. 10, 286–308.
Pudsey, C.J., Howe, J.A., 1998. Quaternary history of the Antarctic
Circumpolar Current: evidence from the Scotia Sea. Mar. Geol.
148, 83–112.
Rebesco, M., 2005. Contourites. In: Richard, C., Selley, R.C., Cocks,
L.R.M., Plimer, I.R. (Eds.), Encyclopedia of Geology, vol. 4.
Elsevier, London, pp. 513–527.
Rebesco, M., Stow, D., 2001. Seismic expression of contourites and
related deposits: a preface. Mar. Geophys. Res. 22, 303–308.
Rebesco, M., Larter, R.D., Camerlenghi, A., Barker, P.F., 1996. Giant
sediment drifts on the continental rise west of the Antarctic
Peninsula. Geo. Mar. Lett. 16, 65–75.
Rebesco, M., Larter, R.D., Barker, P.F., Camerlenghi, A., Vanneste, L.
E., 1997. The history of sedimentation on the continental rise west
of the Antarctic Peninsula. In: Barker, P.F., Cooper, A. (Eds.),
Geology and Seismic Stratigraphy of the Antarctic Margin: Part
2AGU, Antarct. Res. Ser., vol. 71, pp. 29–49.
Rebesco, M., Camerlenghi, A., Zanolla, C., 1998. Bathymetry and
morphogenesis of the Continental Margin West of the Antarctic
Peninsula. Terra Antart. 5 (4), 715–725.
Rebesco, M., Pudsey, C., Canals, M., Camerlenghi, A., Barker, P.,
Estrada, F., Giorgetti, A., 2002. Sediment drift and deep-sea
channel systems, Antarctic Peninsula Pacific Margin. In: Stow, D.
A.V., Pudsey, C.J., Howe, J.A., Faugeres, J.C., Viana, A.R. (Eds.),
Deep-Water Contourite Systems: Modern Drifts and Ancient
Series, Seismic and Sedimentary Characteristics. Geol. Soc.
London, Memoirs, vol. 22, pp. 353–371.
Rebesco, M., Camerlenghi, A., Volpi, V., Neagu, C., Accettella, D.,
Lindberg, B., Cova, A., Zgur, F., and the MAGICO party, in press.
Interaction of processes and importance of contourites: insights
from the detailed morphology of sediment drift 7, Antarctica. In:
116
F.J. Hernández-Molina et al. / Marine Geology 228 (2006) 93–116
Viana A., Rebesco M. (Eds.), Economic and Palaeoceanographic
Importance of Contourites. Geol. Soc. London. Special Volume
Geological Society of London.
Roberts, D.G., Hogg, N.G., Derek, G., Bishop, G., Flewellen, C.G.,
1974. Sediment distribution around moated seamounts in the
Rockall Trough. Deep-Sea Res. 21, 175–184.
Roden, G.I., 1987. Effects of seamount chains on ocean circulation
and thermohaline structure. In: Keating, B.H., et al. (Ed.), Seamounts, Islands and AtollsAGU Geophys. Monograph, vol. 96,
pp. 335–354.
Roden, G.I., 1991. Mesoscale flow and thermohaline structure around
Fieberling Seamount. J. Geophys. Res. 96 (C9), 653–672.
Rogers, A.D., 1994. The biology of seamounts. Adv. Mar. Biol. 30,
305–340.
Saunders, P.M., 1988. Bottom currents near a small hill on the Madeira
Abyssal Plain. J. Phys. Oceanogr. 18, 868–879.
Sievers, H.A., Nowlin Jr., W.D., 1984. The stratification and water
masses at Drake Passage. J. Geophys. Res. 89, 10489–10514.
Storey, B.C., Vaughan, A.P.M., Millar, I.L., 1996. Geodynamic
evolution of the Antarctic Peninsula during Mesozoic times and
its bearing on Weddell Sea history. In: Storey, B.C., King, E.C.,
Livermore, R.A. (Eds.), Weddell Sea Tectonics and Gondwana
BreakupGeol. Soc. London, Spec. Publ., vol. 108, pp. 87–103.
Stow, D.A.V., Faugères, J.C., Gonthier, E., 1986. Facies distribution
and textural variations in Faro drifts contourites: velocity
fluctuation and drift growth. Mar. Geol. 72, 71–100.
Stow, D.A.V., Faugeres, J.C., Howe, J.A., Pudsey, C.J., Viana, A.R.,
2002. Bottom currents, contourites and deep-sea sediment drifts:
current state-of-the-art. In: Stow, D.A.V., Pudsey, C.J., Howe, J.A.,
Faugeres, J.C., Viana, A.R. (Eds.), Deep-Water Contourite
Systems: Modern Drifts and Ancient Series, Seismic and
Sedimentary Characteristics. Geol. Soc. London, Memoirs, vol.
22, pp. 7–20.
Taylor, G.I., 1917. Motions of solids in fluids when the flow is not
irrotational. Proc. R. Soc., A 93, 99–113.
Tucholke, B.E., 1977. Sedimentation processes and acoustic stratigraphy in the Bellingshausen basin. Mar. Geol. 25, 209–230.
Tucholke, B.E., Houtz, R.E., 1976. Sedimentary framework of the
Bellingshausen Basin from seismic profiler data. In: Hollister, C.
D., Craddock, C., et al. (Eds.), Initial Reports of the Deep Sea
Drilling Project, vol. 35. U.S. Government Printing Office,
Washington, D.C., pp. 197–228.
Volpi, V., Camerlenghi, A., Moerz, T., Corubolo, P., Rebesco, M.,
Tinivella, U., 2001. Data report: physical properties relevant to
seismic stratigraphic studies, continental rise sites 1095, 1096, and
1101, ODP Leg 178, Antarctic Peninsula. In: Barker, P.F.,
Camerlenghi, A., Acton, G.D., Ramsay, A.T.S. (Eds.), Proc.
ODP, Sci. Results, vol. 178, pp. 1–36.
Whitworth III, T., Nowlin Jr., W.D., 1987. Water masses and currents
of the Southern Ocean at the Greenwhich Meridian. J. Geophys.
Res. 92, 6462–6476.
Whitworth III, T., Nowlin, W.D., Worley, S.J., 1982. The net
transport of the Antarctic Circumpolar current through Drake
Passage. J. Phys. Oceanogr. 12, 960–971.
Whitworth III, T, Nowlin Jr., W.D., Orsi, A.H., Locarnini, R.A., Smith,
S.G., 1994. Weddell sea shelf water in the Bransfield Strait and
Weddell–Scotia Confluence. Deep-Sea Res. I 41, 629–641.
Wright, I.C., 2001. In situ modification of modern submarine
hyaloclastic/pyroclastic deposits by oceanic currents: an example
from the Southern Kermadec arc (SW Pacific). Mar. Geol. 172,
287–307.
Zhang, X., Boyer, D., 1991. Current deflection in the vicinity of
multiple seamounts. J. Phys. Oceanogr. 21, 1122–1138.