Biological Journal of the Linnean Society, 2011, 103, 346–362. With 5 figures
Geological aspects and evolution of the Patagonian
continental margin
JOSÉ LUIS CAVALLOTTO1*, ROBERTO ANTONIO VIOLANTE1 and
FRANCISCO JAVIER HERNÁNDEZ-MOLINA2
1
Servicio de Hidrografía Naval, División Geología y Geofísica Marina, Sección Geología Marina
‘Dr Gerardo Parker’. Avenue. Montes de Oca 2124, Buenos Aires C1270ABV, Argentina
2
Facultad de Ciencias del Mar, Universidad de Vigo, 36200 Vigo, Spain
Received 9 March 2011; accepted for publication 9 March 2011
bij_1683
346..362
The Patagonian continental margin records some of the tectonic, sedimentary, climatic, and oceanographic events
that participated in the evolution of the Patagonian and south-western Atlantic regions. Those records are essential
for fully understanding the geology and biodiversity of Patagonia. Regional geotectonic and morphosedimentary
features are characterized by different types of continental margins (passive, transcurrent, and transpressive). In
each of them the constituent features (shelf, slope, and rise) acquire particular morphological and sedimentary
configurations. Characteristics of the sedimentary sequences and the limiting discontinuities document the
different evolutive stages of the margin and intervening major processes. The regional tectonic, palaeoclimatic, and
palaeoceanographic events that occurred after the break-up of Gondwana until the Quaternary, which conditioned
the morphosedimentary characteristics, are analysed and described here. It is concluded that the region evolved
in three major stages, according to the predominance of different factors: (1) a stage dominated by endogene factors,
which occurred in Mesozoic times, when the major processes at work were plate tectonics and oceanic opening; (2)
a transitional stage, which occurred in the lower Tertiary, when the proto-Atlantic Ocean evolved towards an open
sea, and climatic and oceanographic factors became at least as important as tectonic factors; and (3) a stage
dominated by exogene factors, which occurred in post-Oligocene times, when the Atlantic Ocean was definitively
installed and the circulation of oceanic currents influenced the characteristics of the sedimentary environments –
this stage ended in the Quaternary when glacioeustatic fluctuations imprinted the present morphosedimentary
configuration. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103,
346–362.
ADDITIONAL KEYWORDS: Argentina – margin evolution – palaeoceanography – Patagonia – shelf – slope.
El Margen Continental Patagónico guarda gran parte de los registros de eventos tectónicos, sedimentarios,
climáticos y oceanográficos que participaron en la evolución de la región Patagónica y del Atlántico Suroccidental.
Su conocimiento es esencial para comprender cabalmente la geología y biodiversidad de Patagonia. Los rasgos
geotectónicos y morfosedimentarios regionales se caracterizan por diferentes tipos de márgenes continentales
(pasivo, transcurrente y transpresivo), en cada uno los cuales sus elementos constituyentes, la plataforma, el talud
y la emersión, adquieren configuraciones morfológicas y sedimentarias particulares. Las características de las
secuencias estratigráficas y sus discontinuidades documentan las distintas etapas de evolución del margen y los
procesos mayores intervinientes. Se analizan y describen los eventos tectónicos, palaeoclimáticos y palaeoceanográficos de extensión regional que caracterizaron a la región desde la apertura de Gondwana hasta el Cuaternario
y condicionaron sus aspectos morfosedimentarios. Se concluye que la región evolucionó en tres etapas mayores de
acuerdo al predominio de diferentes factores: 1) etapa dominada por factores endógenos, ocurrida en tiempos
Mesozoicos, cuando los procesos mayores fueron la tectónica de placas y la apertura oceánica; 2) etapa transicional,
en el Terciario bajo, cuando el proto-Océano Atlántico ya comenzaba a evolucionar hacia un mar abierto y los
*Corresponding author. E-mail: [email protected]
346
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PATAGONIA CONTINENTAL MARGIN
347
factores condicionantes climático-oceanográficos se hicieron al menos tan importantes como los tectónicos; 3)
etapa dominada por factores exógenos, ocurrida en tiempos post-Oligocenos, cuando el Océano Atlántico ya
estaba definitivamente instalado y la circulación de las corrientes oceánicas influenció las características de los
ambientes sedimentarios; esta etapa culminó en el Cuaternario cuando las fluctuaciones glacioeustáticas le
dieron a la región su configuración actual.
PALABRAS CLAVE: Margen Continental Patagónico– plataforma – talud – palaeoceanografía – evolución del
margen.
INTRODUCTION
Patagonia, the southernmost region of South
America, is the only land mass in the world (except
Antarctica) that extends south of ~40°S. It is a narrow
wedge of land penetrating into the Southern Ocean
completely surrounded by sea, in a context of an
‘ocean-dominated’ Southern Hemisphere. Oceanographic and oceanic-induced climatic factors have
therefore greatly influenced the evolution of the
region, and the land–sea interrelationship that characterizes the evolution of any coastal region in the
world plays a more significant role here. This influence was particularly significant in the Quaternary.
During the glacioeustatic sea-level falls that accompanied the glacial (cold) periods, large extensions of
the present Argentine continental shelf were exposed
to subaerial conditions. Given the similarity between
the extension of the Patagonian shelf south of the
Colorado River mouth (39°50′S) and continental
Patagonia (~730 000 and 800 000 km2, respectively),
the region experienced an alternating near duplication or reduction to half of the area during glacial/
interglacial times. Undoubtedly, these changes are
likely to have conditioned much of the geological,
climatic, and biological evolution of Patagonia.
The Atlantic marine regions adjacent to Patagonia
thus contain the stratigraphical, sedimentological,
and biological records of the regional evolution, which
are useful for interregional correlations and comparisons, and in turn can help solve some questions
arising from ‘continental Patagonia’ geology. Essentially, in many places the records of the Quaternary
transgressions and regressions are better preserved
on the shelf than on the coasts. On the other hand,
sedimentary sequences preserved on the slope contain
nearly continuous records of palaeoceanographic and
palaeoclimatic changes.
This contribution synthesizes our current knowledge of the Patagonian continental margin (PCM).
Two main objectives are pursued: (1) to describe
the morphosedimentary and stratigraphic aspects
of the shelf, slope and rise; and (2) to present a
new synthesis of the regional evolution, considering
the different tectonic, climatic, oceanographic, and
sedimentary conditioning factors involved.
THE ARGENTINE AND THE PATAGONIAN
CONTINENTAL MARGINS
The Argentine continental margin (ACM) (Fig. 1) is
one of the most extensive margins worldwide, and it
is the largest in South America, covering an area of
around 2 ¥ 106 km2. The margin exhibits a regional
orientation from NNE to SSW, and an extension of
2400 km from the Río de la Plata (35°S) to Cape Horn
(55°S). Its width is variable: 550 km at the latitude of
the Río de la Plata, 1000 km in front of San Jorge
Gulf, 100 km south of Tierra del Fuego, and at the
latitude of the Santa Cruz River in the direction
of the eastern extreme of the Malvinas Plateau, it
reaches a maximum width of ~2000 km. The boundaries of the ACM are: to the west, the coastal regions
of the Pampean and Patagonian plains, as well as the
Figure 1. Location map. The dotted line of NNW–SE
orientation marks the northern boundary of the Patagonian continental margin.
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J. L. CAVALLOTTO ET AL.
southernmost extreme of the Andes in Tierra del
Fuego; to the east the Argentine Basin; to the north
the Uruguayan continental margin; and to the south
the Scotia Sea.
The PCM (Fig. 1) extends south of the Colorado
River outlet into the Atlantic Ocean, and its offshore
continuation along the Colorado fracture zone, as
a prolongation of the Huincul High. This definition is
based on the conclusions of Ghidella et al. (1995),
Ramos (1999), Ramos, Riccardi & Rolleri (2004),
Franke et al. (2007, 2010), Rabassa (2008), and
Coronato et al. (2008).
The southern boundary of the PCM at sea is the
line of 200 nautical miles from the coastal baseline,
south of Cape Horn. Therefore, the PCM extends
between 43° and 58°S and includes the marine
regions adjacent to continental Patagonia, Tierra del
Fuego, Malvinas (Falkland) Islands and the Northern
Scotia Ridge. From an oceanographic viewpoint,
Matano, Palma & Piola (2010) defined the Patagonian
shelf as the sector of the Argentine continental shelf
extended from the Brazil–Malvinas Confluence
(~38°S) to the southern tip of South America (55°S).
(Fig. 2), a complex transference fracture zone represented by a strike-displacement fault, along which the
southern margin of the South America Plate was
displaced to the west during continental separation.
The major feature characterizing this margin is the
Malvinas Escarpment, located at 48–49°S, which constitutes the northern boundary of the Malvinas
Plateau (and includes the Malvinas/Falkland Islands
and the Maurice Ewing Bank) (Fig. 3), a complex
feature that resulted from the interaction between
the South America and Scotia plates that shares
morphostructural characteristics of the three types of
margins.
According to Turic, Nevistic & Rebay (1996), north
of 55°S (comprising both types of margins mentioned
above) the shelf region was affected by down-warping
processes conditioned by isostatic equilibrium and
sediment overloading: thick sedimentary deposits
were accumulated there, favoured by the increasing
tilting of the continent towards the east as a result of
the Andean uplifting in the Miocene.
TYPES OF MARGINS IN THE ACM
The transpressive margin corresponds to the Scotia
Arc, a complex tectonic element comprising ancient
blocks of continental crust and volcanic arcs, displaced to the east from the southern extreme of the
Andes Cordillera. This block was inserted between
the South America and Antarctica plates, and constitutes an arc joining Tierra del Fuego with the Antarctic Peninsula. The northern part of the arc (which
is part of the PCM) is the North Scotia Ridge that
extends through Isla de los Estados, Burdwood Bank,
and Georgia Islands to the east, and ends at the
South Sandwich volcanic arc. The Malvinas Trough
represents the boundary between the transcurrent
and the transpressive margins, i.e. the boundary
between the South America and Scotia plates (Fig. 2).
The ACM comprises three types of margins (Ramos,
1996; Hinz et al., 1999; Franke et al., 2007) resulting
from the interaction among three major processes
affecting different latitudes (Fig. 2): the westward
motion of the South America Plate; translational
movements relative to the Malvinas–Agulhas fracture
zone; and the interaction with the Scotia Plate.
The volcanic-rifted continental margin corresponds
to a typical lower-plate passive margin, with rift
basins (Ramos, 1996) associated with sea-floor
spreading. It is characterized by a young and thin
crust with pre-rift associations and longitudinal rifts,
and was strongly affected by volcanism. This margin
extends from eastern Brazil to ~48–49°S. The Argentine part of this margin extends between the Rio de la
Plata and the northern PCM (north of central Santa
Cruz province) (Fig. 1). The margin is structured
(Franke et al., 2007) in four segments (I, II, III, and
IV, from south to north), delimited at its southern
boundaries by transference fracture zones (Malvinas,
Colorado, Ventana, and Salado, respectively; Fig. 3).
The Colorado transference zone, identified by magnetic (Ghidella et al., 1995) and seismic (Franke et al.,
2007) data, is considered to be the northern limit of
the ‘Patagonian shelf domain’ (Max et al., 1999;
Ramos et al., 2004).
THE
TRANSCURRENT MARGIN
The transcurrent margin is the part of the margin associated with the Malvinas–Agulhas fracture
THE
TRANSPRESSIVE MARGIN
REGIONAL OCEANOGRAPHIC SETTING
The ACM is located in a key region of the world ocean
because surface and deep Antarctic-sourced water
masses penetrate deeply in mid latitudes and interact
with North Atlantic-sourced water masses (Piola &
Rivas, 1997; Wefer, Mulitza & Ratmeyer, 2004). The
oceanographic factors that dominate are different in
nearshore and offshore regions.
The nearshore regions comprise two sectors according to the dominant oceanographic shallow processes:
waves and tides. The boundary between them is not
precise because of the gradual change of the conditions prevailing north and south. In a general sense,
regions north of ~42°S are wave dominated and
microtidal (< 2 m amplitude), whereas regions south
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PATAGONIA CONTINENTAL MARGIN
349
Figure 2. Geotectonic lineaments of the Argentine continental margin (compiled from Ramos, 1996: figs 8, 10 and 11;
Ramos, 1996: fig. 44).
© 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 346–362
350
J. L. CAVALLOTTO ET AL.
Figure 3. Tectonic and palaeoceanographic events that conditioned the evolution of the Argentine continental margin
(modified after Ortiz-Jaureguizar & Cladera, 2006). References: sea level after Haq et al. (1987); mean global deep-sea
oxygen, temperatures, and climatic events after Zachos et al. (2001); tectonic events after Yrigoyen (1979, 1999), Zachos
et al. (2001), and Rabassa (1999); major seismic horizon after Ewing & Lonardi, 1971, Hinz et al. 1999, and Parker et al.
2005. Abbreviations: AABW, Antarctic bottom water; AAIW, Antarctic intermediate water; ACC, Antarctic Circumpolar
Current; CDW, circumpolar deep water; LCDW, lower circumpolar deep water; NADW, North Atlantic deep water.
of 42°S are tide dominated, although waves here are
very high (up to 8 m), mainly because of wind activity.
Most of the Patagonian coasts correspond to the
second sector.
The deep regions located offshore, represented by
the shelf, slope, and rise, are current dominated,
where surface and subsurface currents are driven by
geostrophic and thermohaline circulation. This circulation determines a vertical stratification of water
masses (Piola & Matano, 2001; Matano et al., 2010;
Piola et al., 2010; Fig. 4), which conditions most of the
sedimentary processes and morphology of the margin.
The PCM is dominated in its surface water masses
by northwards-flowing Antarctic-sourced cold and lowsalinity currents corresponding to the Malvinas
Current (MC). This water mass is a rapid and barotropic branch of the Antarctic Circumpolar Current
(ACC), transporting between 40–70 Sverdrup (Sv;
1Sv = 106 m3 s-1 of water), and includes less salty
Antarctic Intermediate Water (AAIW) at depths below
700–1000 m. MC meets the southwards-flowing Brazil
Current (BC) in the Brazil–Malvinas confluence zone
(BMCZ) centred around 38°S. The north and south
shifting of the BMCZ as a result of climatic influences
can affect regions located, even at 40°S. Matano et al.
(2010) consider the Patagonian continental shelf (PCS)
as the shelf sector located south of the BMCZ.
Below the MC flows the North Atlantic deep water
(NADW), which flows polewards, and is characterized
by high temperature and salinity.
The circumpolar deep water (CDW), which corresponds to the deeper fraction of the ACC, affects the
ACM at depths below 800–1000 m. It flows northwards and is divided into two fractions: the upper
(UCDW) and the lower (LCDW) circumpolar deep
water. The UCDW flows northwards through the
Drake Passage into the Argentine Basin along the
1000–1500-m isobath. The LCDW enters the Argentine Basin as a dense water mass over the Malvinas
Plateau and east of the Ewing Bank, and follows the
slope at a depth of 3000–3500 m.
The deepest water masses are represented by the
very cold and dense Antarctic bottom water (AABW),
which originates in the Weddell Sea. It is introduced
in the Argentine Basin at different depths (> 3500 m)
and is deflected to the west against the Malvinas
Scarp, producing both a circulation parallel with the
South Atlantic Ridge and an anticyclonic gyre on the
Argentine Basin, where it remains trapped as a result
of the complex sea-floor morphology.
The MC is the main component of the oceanic
circulation in the PCS (Matano et al., 2010; Piola
et al., 2010), which is influenced by strong westerly
winds, large tidal amplitudes, and low-salinity water
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PATAGONIA CONTINENTAL MARGIN
351
Figure 4. Oceanographic context (modified after Frenz et al., 2004, compiled from Piola & Matano, 2001). Abbreviations:
BB, Brazil; FP, Falkland Plateau; RGR, Rio Grande Ridge; VC, Vema Channel; VTV, Victoria Trinidad Ridge. Arrows show
the generalised main flow paths of water masses along the western boundary (AABW, Antartic bottom water; AAIW,
Antartic intermediate water; BC, Brazil Current; MC, Malvinas Current; NADW, North Atlantic Deep Water; SAW,
sub-Antartic water; TW, thermocline water; (U/L)CDW, (upper/lower) circumpolar deep water). BMC indicates the Brazil
Malvinas confluence, and its extension. The line A–B shows the positions of the projections plain presented in panel below.
The dotted arrows indicate the projection path for two exemplary locations: Rio de Janeiro and a sample position from
the abyssal Brazil Basin.
discharges. The MC conditions most of the crossshelf processes and shelf-break dynamics. A jet
derived from the MC in the inner shelf south of 49°S
originates the Patagonian Current (Matano et al.,
2010).
The circulation of the water masses on the PCS
has a significant importance at a global scale as it
influences the global carbon budget, as large volumes
of CO2 are absorbed there from the atmosphere
(Bianchi et al., 2005). Biological implications are significant because deep-water masses move onshore
and generate coastal upwelling off the shore of southern Patagonia (Matano et al., 2010), which transports
nutrient-rich waters to the surface and produces a
persistent zone of high chlorophyll content at the
shelf–slope transition. It impacts coastal ecosystems
and defines the region as one with the highest
primary productivity (Lopez Gappa, 2000; Matano
et al., 2010).
MORPHOSEDIMENTARY FEATURES
Morphosedimentary features are landforms on the
earth surface (including both continents and oceans)
with particular morphologies shaped by erosive and
depositional sedimentary processes. Major features
described herein (of different orders depending on the
regional development and scale of processes involved)
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352
J. L. CAVALLOTTO ET AL.
are continental margins, shelf, slope, rise, terraces,
scarps, ridges, submarine canyons, channels, and plateaus. In most of the cases they are different depending upon which type of margin they develop on, except
the continental shelf that shows relatively homogeneous and continuous characteristics overlapping the
different margins.
MORPHOSEDIMENTARY FEATURES IN THE
VOLCANIC-RIFTED CONTINENTAL MARGIN
Continental shelf
The continental shelf is described as a whole independently of the types of margins upon which it
develops. Parker et al. (1996, 1997 and 2008).
described most of the morphological and sedimentological aspects of the shelf, which were later synthesized by Cavallotto (2008). The shelf extends from the
shoreline to the shelf break in transition to the slope,
where the sea-floor slope drastically increases. The
regional shelf average gradient is around 1 : 1000.
The shelf break is at depths between 110 and 165 m,
and is located at distances from the coast of 350 km in
front of Puerto Deseado, 850 km in front of Bahía
Grande – including the Malvinas (Falkland) Islands
shelf – and only 10 km south of Isla de los Estados.
The sedimentary cover is terrigenous and siliciclastic,
mostly (> 65%) composed of relictic and palimpsestic
sands reworked during transgression after the last
glacial maximum (LGM). They have a mineralogical
composition showing a pampean–patagonian affinity
(volcanic–pyroclastic association). Subordinate fractions are shelly deposits representing former, presently submerged shorelines. Gravels are particularly
important in the PCS where they constitute ~25%
of the surface sediments. They are associated with
glacial–fluvial activity during Quaternary low-stand
periods, particularly at LGM times.
Parker et al. (1996) described different physiographic features defined by morphology and sedimentology: deltaic front of the Colorado and Negro
rivers, Patagonian gulfs, Patagonian inner shelf, Patagonian outer shelf, Tierra del Fuego shelf, and
Malvinas (Falkland) Islands shelf. On the other hand,
Parker et al. (1997) described four levels of terraces,
the top surfaces of which are at 25–35, 85–95, 110–
120, and 130–150 m, with all of them separated from
each other by terrace scarps or ‘steps’ of steeper
gradient. The origin of these terraces has been related
to wave action during short interruptions in the
velocity of the post-LGM sea-level rise (Perillo &
Kostadinoff, 2005; Violante, 2005; Ponce et al., 2011);
however, a combination of different factors such as
isostasy, tectonism, and sea-level fluctuations could
have influenced the modelling of the terraces (Ponce
et al., 2011).
The shelf contains evidence of the subaerial exposure during LGM times, like relicts of former fluvial
valleys and buried palaeosoils included in pretransgressive sequences (Violante, Osterrieth & Borrelli, 2007; Osterrieth, Violante & Borrelli, 2008). The
Tierra del Fuego shelf shows evidence of submerged
moraines, thus indicating glacial activity (Isla &
Schnack, 1995; Mouzo, 2005).
The characteristics and distribution of shelf sediments are mainly a function of sedimentary processes that took place during the Quaternary sealevel fluctuations (particularly the postglacial
transgression), as well as the dynamics and sediment supply of coastal waters. During the last sealevel low-stand, around 18 thousand years ago, the
shelf was a continental region probably very similar
to Patagonia. As sea levels rose during the postglacial transgression, erosive coastal retreat provoked sediment transference offshore. Isla & Cortizo
(2005) estimated that a total volume of 243.8 ¥ 106
tons per year of sediment is presently eroded from
the Patagonian cliffs into the sea. If this volume is
extrapolated to every stage of the transgression, a
broad estimation can be obtained about the enormous volume of sediments produced at the coastline
and deposited on the shelf surface during the last
18 thousand years. Ponce et al. (2011) modelled
several evolutive stages of the PCM during the last
transgression, and concluded that the coastline
recession occurred at a mean rate of 22–38 m per
year, depending on the region considered.
Pierce & Siegel (1979) and Gaiero et al. (2003)
estimated a total volume of 70 ¥ 106 tons per year of
terrigenous sediments transferred to the sea bypassing the Patagonian coasts: 56% (39 ¥ 106 tons per
year) corresponds to coastal erosion; 41% (29 ¥ 106
tons per year) corresponds to atmospheric processes
(dust transport); and 3% (2 ¥ 106 tons per year) corresponds to fluvial activity (Cavallotto, 2008). The
Patagonian fluvial network introduces relatively
reduced sedimentary volumes, as the smaller rivers
carry low volumes of sediments, whereas the bigger
rivers usually have estuarine environments that
retain most of the sedimentary load. However,
streams were more significant in pre-Holocene times,
as evidenced by today’s oversized fluvial valleys with
respect to the present fluvial dynamic, as well as by
the large volumes of gravel on the southern shelf
surface that cannot be transported by present
streams. Kokot (2004) estimated that the Santa Cruz
river presently has a discharge of one-tenth of the
discharge in the Pleistocene. Iantanos, Estrada & Isla
(2002) stressed the significant diminishing in the
discharge of the Deseado River since the last glaciation. Isla & Cortizo (2005) considered that Chubut
and Chico rivers experienced a reduction of 21–24% in
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PATAGONIA CONTINENTAL MARGIN
353
the area of their watersheds, and 32–34% in their
annual discharges, with respect to upper Pleistocene
times.
Based on the processes intervening in the sedimentary regime of the ACS, Violante (2004) classified the
shelf as passive and autochthonous.
carried towards the deepest ocean by the Antarcticsourced water masses that recirculate into the Argentine Basin after being detached from the continental
margin.
Continental slope
The slope in the volcanic-rifted continental margin
has an average gradient of 1 : 50 (> 1.5°), its width
varies from 140 to 270 km between 35 and 49°S,
reaching less than 50 km wide further south, and
its foot reaches average depths of around 3200 m. The
slope is dominated by gravitational (down-slope)
and along-slope processes that give rise to a varied
morphosedimentary configuration, characterized by
depositional and erosive features. The main features
are represented by the impressive countouritic depositional system (Hernández-Molina et al., 2009), one
of the largest contouritic systems worldwide, which is
genetically associated with the circulation of the
Antarctic-sourced currents along the slope and its
interaction with the sea floor. Countouritic deposition
associated with erosive processes at the interphases
between the different water masses gave rise to
several terraces: north of 43°S extends the Ewing
terrace, averaging a water depth of 1000 m, whereas
between 43 and 48°S extend the terraces Nágera (at
a water depth of 500 m), Perito Moreno (at a water
depth of 1000 m), Piedrabuena (at a water depth
of 2100–2500 m), and Valentin Feilberg (at a water
depth of 3500–4000 m). Fully erosive features are
represented by submarine canyon systems, the most
important named Ameghino (43°–44°30′S) and Almirante Brown (44°30′–46°S), which are deflected to
the north in their down-slope portions through the
influence of the contouritic processes.
TRANSCURRENT MARGIN
Continental rise
The continental rise extends offshore from the foot
of the slope north of 44°S, and its outer boundary
approaches the abyssal plains at depths deeper than
5000 m. The average gradient is around 1 : 100. Depositional features are principally coalescent submarine
fans at the base of submarine canyons. South of
44°S the rise disappears and the lower terrace slope
connects directly with the abyssal plain.
Argentine Basin
Although it does not belong to the ACM, as it corresponds to the abyssal plains, it is important to
mention that very large sedimentary drifts develop in
this region. These drifts are formed by huge mudwave fields (Zapiola, Argyro, and Ewing drifts; Flood
& Shor, 1988; von Lom-Keil, Spieb & Hopfauf, 2002)
containing most of the finest terrigeous sediments
MORPHOSEDIMENTARY
FEATURES IN THE
This margin is represented by the continental mass
that extends eastwards of the Malvinas/Falkland
Islands, constituting the Malvinas Plateau; as stated
above it contains geomorphic features that share different characteristics of the three types of margins.
Its nearly flat surface reaches a water depth of
2000 m on average, and is delimited by the 3000-m
contour line. Further east there is another flat, shallower surface that constitutes the M. Ewing Bank.
The entire surface including the Malvinas Plateau
and the M. Ewing Bank is about 1800 km long and
300 km wide. The northern boundary of the plateau is
the Malvinas Escarpment, which represents the
eastern extension of the lower slope in the southern
part of the passive margin, north of 48°S. The escarpment is very steep between water depths of 2200 and
5100 m, with a gradient of 1 : 5 and even 1 : 1 (slope
of 45°). The escarpment extends towards the east
outside the plateau in what is known as the Malvinas
fracture zone. The Malvinas Channel, extended at the
foot of the Malvinas fracture zone, reaching depths of
5800 m, marks the transition to the abyssal plain. On
the other hand, the southern part of the Malvinas
Plateau shows a gentle gradient reaching depths of
3500 m in the Malvinas Trough, with depths grading
from 300 to 3500 m from west to east. It is a long
submarine valley extended for more than 1500 km
from the west part of Malvinas/Falkland Islands to
the Abyssal Plain north of Georgia Islands. The
Malvinas Trough separates the Malvinas Plateau
from the North Scotia Ridge. As a result of the topographical characteristics, represented by a relatively
shallow, transverse-to-the-continent feature, the
Malvinas Plateau constitutes a topographic barrier to
the deep Antarctic-sourced water masses, so interfering in the oceanic circulation, and conditioning most
of the oceanographic and sedimentary characteristics
of the passive continental margin located to the north
(Arhan, Heywood & King, 1999).
MORPHOSEDIMENTARY
FEATURES IN THE
TRANSPRESSIVE MARGIN
This margin comprises different morphostructural
features associated with the Scotia Arc. However, as
only the northern part of this arc (Northern Scotia
Ridge) is considered as a part of the PCM, the present
description is restricted to this area. It represents the
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J. L. CAVALLOTTO ET AL.
submarine extension of the Southern Andes, which
reaches its more significant features in Isla de los
Estados, Burdwood Bank, Cormorán, and Negra
Rocks, and the insular shelf around Georgia Islands.
All these islands are composed of rocks similar to
those of the Andes cordillera (Dalziel & Elliot, 1971;
Ramos, 1996). In particular, the Burdwood Bank is an
isolated piece of continental shelf, 360 km long and
115 km wide, at depths averaging 180 m.
REGIONAL STRATIGRAPHY
Synthesizing the stratigraphy of the PCM is complex given the existence of several sedimentary basins
in the subsurface of the margin, each with its own
geological and sedimentological characteristics. It
can, however, be broadly described as comprising two
major units.
PRE-CRETACEOUS
BASEMENT
The pre-Cretaceous basement corresponds to the deep
geological substratum of the basins and interbasinal
regions. Its characteristics were defined by lithological aspects recorded in offshore drillings as well as
in seismic records, in which the differential seismic
velocity (the speed at which a seismic wave propagates into the rocks depending on lithology, consolidation, hardness, and other physical properties)
enable the identification of different rock layers.
According to Zambrano & Urien (1974) and Ramos
(1999), in the northern part of the PCM (between
39 and 43°S) there is an igneous basement covered
by metamorphized palaeozoic continental–marine
sedimentites, with seismic velocities between 5 and
5.5 km s-1. South of 44°S, above a precambrian
metamorphic basement, there are upper palaeozoic–
lower mesozoic metamorphic and acid intrusive rocks,
with seismic velocities of up to 6 km s-1, followed
by silurian–jurasic pyroclastic and acidic mesosilicic extrusive rocks interbedded with continental
sediments, with seismic velocities between 4.2 and
5.1 km s-1.
POST-CRETACEOUS
SEDIMENTARY FILLING
OF THE BASINS
Post-cretaceous
sequences
are
composed
of
continental–marine shales, filites, lutites, limestones,
sandstones and conglomerates with thicknesses of
6–8 km. The upper part of the sequences represents
the Neogene, which is not restricted to the basins but
overpass their limits and extend homogeneously onto
most of the margin. Two sequences are recognized:
the lower sequence (Miocene–lower Pliocene) is integrated by marine deposits formed during the Miocene
transgression, which covered most of South America
(Aceñolaza, 2000; Hernández et al., 2005), as well as
by regionally extended lower Pliocene continental
(mostly fluvial) deposits; the upper sequence (middle
Pliocene–Quaternary) south of 43°S is mainly represented by marine (interglacial)–continental (glacial)
sequences, which became progressively fully marine
offshore of the outer shelf. The discontinuous distribution of Quaternary deposits on the PCM can be
attributed to post-glacial isostatic rebound (which
was more significant in that region, closer to the
glaciated areas of Patagonia) and the consequent
increment in erosive processes. Malumián (1999) correlated the stratigraphy of several Patagonian basins
and related them to the global eustatic curve. Malumián & Nañez (1996) and Nañez & Malumián (2008)
studied and correlated geological units in the shelf on
the basis of the micro- and nanofossil content.
SEISMIC STRATIGRAPHY OF THE PCM
Seismic stratigraphy is an invaluable tool for synthesizing submarine sedimentary successions as it
enables us to record them at a regional scale. The
seismic method consists of the release of a shock wave
from a seismic source on the surface, which penetrates the sea floor and is reflected and/or refracted
at the boundary between structurally or texturally
contrasting geological units. The boundary is visually
manifested in the seismic records as a ‘seismic
horizon’. In the marine environment, most of the
seismic horizons constitute regional stratigraphic
unconformities of strong erosive character, resulting
from the occurrence of significant and often abrupt
climatic, oceanographic, and tectonic events. The
geological units separated by seismic reflectors
are seismic sequences (interpreted as ‘depositional
sequences’) representing particular environments
developed during the successive evolutionary stages
of the continental margin.
Major seismic horizons characterizing the Cenozoic
sequences of the ACM are synthesized in Table 1.
They were compiled from the work of Ewing &
Lonardi (1971), Urien & Zambrano (1996), Hinz et al.
(1999), Franke et al. (2007), Hernández-Molina et al.
(2009), and Violante et al. (2010). The present description begins with seismic reflector AR3 (Hinz et al.,
1999), which nearly represents the beginning of the
Cenozoic sedimentary successions in the PCM. Older
reflectors (AR1–AR2) defined by Hinz et al. (1999)
mainly correspond to volcanic rocks, as well as to
sedimentary sequences that represent the change
from ancient euxinic to open oceanic conditions associated with the initial stages of the Atlantic Ocean
opening.
© 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 346–362
PATAGONIA CONTINENTAL MARGIN
Table 1. Seismic horizons in the Argentine continental
margin
Seismic
reflector
Equivalent
reflectors
N
H1
b
L
H2
AR5
AR4
ARI
AR3
ARII
Period
Age
base of the Quaternary
lower–mid-Pliocene
boundary
Miocene–Pliocene
boundary
mid-Miocene
Eocene–Oligocene
boundary
Maastrichtian
2.6 Ma
16 Ma
81 Ma
AR3
The seismic reflector AR3 (Hinz et al., 1999) is found
at water depths of 1700–2500 m, deepening to the
east, and separates units with seismic velocities
higher than 3 km s–1 (below) and lower (above).
According to Hinz et al. (1999), AR3 is of Maastrichtian (lower Campanian) age (~81 Ma), and constitutes
the erosional surface of a complex drift sequence
developed offshore of the outer shelf. This horizon is
correlated with reflector ARII (Urien & Zambrano,
1996), which these authors (based on correlations
with offshore oil drillings) assigned to the Maastrichtian marine transgression.
AR4
The seismic reflector AR4 (Hinz et al., 1999) is relatively subhorizontal at water depths of 1000–1300 m,
separating seismic units with seismic velocities
higher than 2.4 km s-1 (below) and lower (above);
therefore, it separates consolidated from semiconsolidated beds, following the terminology used by
Ewing & Lonardi (1971). The reflector is considered to
be equivalent to reflector ARI of Urien & Zambrano
(1996), which represents the Eocene–Oligocene
boundary. Hinz et al. (1999) associate AR4 with
erosion produced by a strong expansion of Antarctic
ice masses in the late Eocene, which was responsible
of the thermohaline circulation that highly influenced
the depositional regimes. Sedimentary sequences
below and above this horizon are represented by
complex giant sedimentary drifts. Sequences above
correspond to the lower unit of the contourite depositional system defined by Hernández-Molina et al.
(2009, 2010).
AR5
The seismic reflector AR5 (Hinz et al., 1999) is a
strong reflector separating units with seismic velo-
355
cities higher (below) and lower (above) than
2.15 km s-1. This horizon lies very close to seismic
reflector H3 defined by Ewing & Lonardi (1971), at
water depths around 1500–1700 m, which was originally considered as being of Eocene age, although the
new seismic stratigraphic information undoubtedly
relates it to younger – Miocene – units. Therefore,
both horizons can be considered as equivalent at least
in the middle slope, although in deeper regions they
progressively separate from each other. According to
Hinz et al. (1999), AR5 represents a renewed cooling
with another extensive expansion of Antarctic ice
masses that took place in the mid-Miocene, approximately 15 Ma. This period has a global significance as
it was also recorded in other parts of the Southern
Hemisphere, such as in Antarctica (HernándezMolina et al., 2004, 2006), South Africa (Wildeboer
Schut, Uenzelmann-Neben & Gersonde, 2002; Wigley
& Compton, 2006), India, and in the South Pacific
Ocean (Hernández-Molina, Maldonado & Stow, 2008).
Above AR5 the intermediate and the upper units
of the contourite depositional system develop
(Hernández-Molina et al., 2009, 2010).
H2
The seismic reflector H2 (Ewing & Lonardi, 1971) was
well defined in the upper slope at water depths
around 1200 m, separating the underlying semiconsolidated from the overlying nonconsolidated layers
(in the sense of Ewing & Lonardi, 1971), with seismic
velocities higher and lower (respectively) than
2 km s-1. As they did with seismic reflector H3
(equivalent to AR5), these authors originally considered it as being Eocene in age, but following reinterpretation it is now considered as representing
the Miocene–Pliocene boundary. In regions offshore
of the province of Buenos Aires, a seismic reflector
also separating layers of seismic velocities higher and
lower than 2 km s-1 – and hence correlated with
H2 – was recognized in the outer shelf (Violante et al.,
2010). H2 marks the top of the upper unit of the
contourite depositional system defined by HernándezMolina et al. (2009, 2010).
H1
H1 was described for the upper slope by Ewing &
Lonardi (1971) at water depths averaging 800–
1000 m: it is continuous along most of the margin, gently deepening in the seaward direction. In
the bonaerensian outer shelf, Parker et al. (2005)
described reflector L at around water depths of 200 m,
and assigned it to the lower–mid Pliocene boundary.
This reflector L was correlated with H1 on the basis
of stratigraphic position and seismic-facies analysis.
© 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 346–362
356
J. L. CAVALLOTTO ET AL.
N
N was described by Parker et al. (2005) for the bonarensian shelf as representing the beginning of the
transgressive–regressive events associated with the
alternating interglacial and glacial periods, hence it
corresponds to the base of the Quaternary (in the
sense of Gibbard et al., 2009, i.e. 2.6 Ma). It was
correlated (Parker et al., 2008) with horizon ‘b’
defined by Ewing & Lonardi (1971), who considered
that this reflector is continuous along the outer shelf
at least up to the latitude of San Jorge Gulf (46°S),
therefore appearing in the northern PCM but probably not in southern PCM. Although more research is
still needed on the Quaternary deposits in the Patagonian shelf, the possibility of the occurrence of
transgressive sedimentary sequences associated with
the high-stand sequences preserved on the coast
cannot be disregarded. The well-known records of
sea-level transgressions in the coasts of Patagonia
correspond to OIS 9 (240–342 kyr), OIS 7 (158–
239 kyr), and OIS 5 (104–143 kyr) (Rostami, Peltier &
Manzini, 2000) (OIS: Oxygen Isotopic Stage). The
absence – or at least discontinuous distribution – of
the Quaternary transgressive sequences in the southern PCM could have resulted from erosion associated
with the isostatic uplift that affected Patagonia at an
average speed of 0.9 m per kyr (Rostami et al., 2000).
GEOTECTONIC AND
PALAEOCEANOGRAPHIC EVOLUTIVE
CONTEXT OF THE PCM
The ACM, as a part of the South America Plate, is
genetically associated with the cortical extension and
sea-floor spreading caused by the break-up of Gondwana. However, the margin was also indirectly
affected by processes taking place on the western part
of the plate, like the intense tectonism and complex
subduction regimes that were important during
Mesozoic and Cenozoic times (Uliana & Biddle, 1988).
Ortiz-Jaureguizar & Cladera (2006) considered that
this tectonic development, together with other major
external forcing factors such as sea-level fluctuations,
changes in sea temperatures, and glaciations, were
responsible for modifications in the palaeogeography
of the southern part of South America, and hence in
the biomes. Figure 2 shows the major geotectonic
features and lineaments that resulted from the development of the margin, whereas Figure 5 synthesizes
the tectonic, palaeoclimatic, and palaeoceanographic
events participating in the regional evolution.
According to Urien & Zambrano (1996), Ramos
(1996, 1999), and Turic et al. (1996), rift and wrench
processes characterized the initial tectonic stages of
the sea-floor spreading in middle Jurassic times.
After that, voluminous volcanic effusions took place
in late Jurassic–early Cretaceous times (Hinz et al.,
1999; Franke et al., 2007, 2010). The separation
between South America and Africa was completed
with the reactivation of the Malvinas–Agulhas fracture in the Aptian (~115 Ma), when the sea invaded
former euxinic environments (with very restricted
water circulation and stagnant conditions), and a
proto-Atlantic ocean (with more open-water circulation and increasing oxygenation) was installed (Hinz
et al., 1999). In the early Campanian (~81 Ma) deep
waters played an important role in shaping the sea
floor, as evidenced by complex sedimentary drifts in
the south-western Atlantic (Hinz et al., 1999). The
Maastrichtian (70–65 Ma) was characterized by a
global marine transgression. This event covered very
large areas of Patagonia from San Jorge Gulf and the
Austral Basin to Neuquén Basin, thus representing
the first Atlantic transgression reaching the Andean
basins (Malumián, 1999; Nañez & Malumián, 2008).
According to the same authors, this transgression
gave rise to the ‘first’ Argentine continental shelf,
characterized by a very extensive shallow sea with
widely distributed marginal environments. Sea levels
remained high in the Palaeocene (65.5–55 Ma), and
the resulting Atlantic transgression is known as
Salamanca Sea. A regressive marine event took place
at the end of this period, at the time that the
Laramica tectonic phase occurred as a significant
stage of cortical deformation associated with the
beginning of the Andes uplift.
At the beginning of the Eocene (55–50 Ma), when
the proto-Atlantic ocean was well developed, sea
levels were globally high in a climatic context of
high temperatures; surface and bottom ocean temperatures at low latitudes were typical of subtropical
seas. Marine waters reached some sectors of the present Patagonian lands according to microfaunistic evidence (Malumián & Nañez, 2009). As this
ocean progressively evolved into a fully open ocean,
thermohaline circulation developed, which in the first
stages was mainly controlled by salinity rather than
by temperature (Oberhansli & Hsü, 1986).
At the end of the Eocene (40–35 Ma) a new cooling
of the deep-water masses was accompanied by a
marine regression and the displacement of the zones
of formation of deep waters from low to high latitudes. At 34 Ma, the first evidence of formation of ice
masses appeared in East Antarctica (Einsele, 2000),
which occurred together with a global decrease in
temperature (stage Oi-1; Zachos et al., 2001). Global
tectonic deformations were documented at this time,
which had their largest effects on western South
America where the Inca tectonic phase – a new
reactivation of the Andean uplift – took place.
In the early Oligocene (around 32–30 Ma) the
opening of the Drake Passage took place (Lawver &
© 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 346–362
PATAGONIA CONTINENTAL MARGIN
357
Figure 5. Morphosedimentary features (compiled from Parker et al., 1996, 1997 for the continental shelf, and
Hernández-Molina et al., 2009 for the slope).
Gahagan, 2003; Livermore et al., 2004). This event,
together with the opening of the Tasmania Passage
(which started earlier, around 38 Ma) produced the
initiation of the circulation of the ACC, with the
consequent isolation of Antarctica (Einsele, 2000;
Zachos et al., 2001). The resulting interruption in
heat transference from low to high latitudes produced
the definitive cooling of Antarctica, where large
ice masses accumulated in its eastern regions and a
regressive event took place. These processes progressively gave rise to the present model of thermohaline
circulation in the world ocean, which in the PCM was
responsible for the progressive shaping of the margin
towards its present configuration, including the formation of the Contourite depositional system. The
Pehuenche tectonic phase, a major process involved
in the Andean uplift, developed simultaneously with
the final stages of the opening of the Drake Passage
(~29 Ma).
Nearly simultaneously with these events, in the
southern tip of South America the occurrence of the
first stages of the north-west–south-east sea-floor
spreading and transtensional motions associated with
the Scotia plate allowed it to penetrate beneath the
Drake Passage, with the consequent formation of the
Scotia Arc. This event lasted for a long time, between
30 and 6 Ma (Dalziel, 1982; Livermore et al., 2004). In
the intermediate times, in the late Oligocene (25 Ma),
a global warming with sea-level rise and associated
marine transgressions occurred: some parts of Patagonia were affected by this event, which is recorded
by very shallow and limited extended seas (Malumián
& Nañez, 2009). Soon after, in the lower Miocene
(23 Ma), a new global cooling with low sea levels led
to a new glaciation (Mi-1; Zachos et al., 2001).
The Miocene continued, between 17 and 14.5 Ma,
with another increase in temperature, a reduction in
the Antarctic ice masses, and the occurrence of a new
© 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 346–362
358
J. L. CAVALLOTTO ET AL.
sea-level rise on a global scale (Haq, Hardenbol &
Vail, 1987). Zachos et al. (2001) describe a regional
warm phase prevailing at those times, characterized
by global low ice volumes and slightly high bottom
water temperatures, with the exception of several
brief periods of glaciations. These processes, along
with a significant regional subsidence (van Andel
et al., 1977; Kennett, 1982), gave rise to Atlantic
marine transgressions, which in the Pampean regions
correspond to the Paranense Sea, and in Patagonia to
the marine facies described by Malumián & Nañez
(2009). According to Berggren et al. (in Malumián &
Nañez, 1996), the climatic optimum of the Neogene
occurred in the middle Miocene, between 15.6 and
13.6 Ma. Hernández et al. (2005) dated the Paranense
transgression to between 15 and 13 Ma.
The expansion of Antarctic ice masses and consequent regressive events represented by seismic
horizon AR5 – considered by Hinz et al. (1999) as
having occurred at ~15Ma – is included in the time
span of the warmer and transgressive mid-Miocene.
This apparent inconsistency deserves more attention
and further research. However, it can be preliminarily
considered that some of the ‘several brief periods
of glaciations’ mentioned by Zachos et al. (2001) as
having taken place in a warmer period, may have
been highly significant – at least around Antarctica –
and are evidenced by horizon AR5. In this case, AR5
should be slightly older (around 16 Ma) than it is
presently considered to be.
Following the regional warm periods of the midMiocene, a gradual cooling and re-establishment of a
major ice sheet on Antarctica occurred between 14
and 10 Ma (Zachos et al., 2001). As a result, the whole
Antarctic continent was affected by the cold climate, a
new marine regression occurred, and the circulation
of the AABW began to be very active (Einsele, 2000).
At the same time, the orogenic Quechua phase contributed to the uplifting of the Cordilleras Patagónica
and Principal, which nearly reached their present
configuration (Yrigoyen, 1979, 1999). This new geomorphological scenario led to changes in the climatic
conditions as a result of the ‘barrier effect’ of the
recently raised mountains that interfered with the
wind pattern and the circulation of moist air masses,
resulting in an increase in aridity in Patagonia.
Besides, a substantial increase in sediment supply
from west to east was favoured as a result of the
increasing slope gradients between the new highrelief mountains and the sea. At the same time, as a
consequence of the combination of all the aforementioned tectonic, geomorphological, and climatic
changes, the south-western Atlantic Ocean experienced the circulation of the NADW and the AAIW.
The interaction between the two currents gave rise
to most of the morphosedimentary changes that
allowed the PCM to evolve towards its present
configuration.
During the time span between approximately 16 and
5 Ma (seismic horizons AR5 and H2, respectively), very
significant morphosedimentary changes took place in
the slope. The contourite depositional system, which
developed from the early Oligocene through different
stages represented by the lower, intermediate, and
upper units, reached its most significant expression,
and finally – coincident with the deposition of the
upper unit – began to evolve towards its present
configuration (Hernández-Molina et al., 2009, 2010).
The new oceanographic and climatic conditions
imposed at the end of the Miocene by the interaction
between NADW and AAIW resulted in a decrease
in oceanic temperatures and the permanent installation of the Antarctic ice masses. The climate in the
Patagonian–Pampean region became cold and glaciers
made their first appearance, with evidence of glacier
advances recorded at 7 Ma (Rabassa et al., 2005).
Global cooling was interrupted at around 5–4 Ma, and
temperatures increased again at 4–3 Ma. During the
late Pliocene a new Andean diastrophic phase (Diaguita) took place. This phase was responsible for the
final uplift of the central Andes of Argentina and Chile,
the Puna, the Pampean Mountain Range, and the
Mesopotamia region. Soon after that another event of
global consequence occurred, at around 3–2.6 Ma,
when the definitive closing of the Panamá Isthmus led
to an increase in activity of the Gulf Stream that
resulted in a transport of warm and saline waters to
the North Atlantic, inducing the intensification of the
NADW, the formation of the ice masses in the Northern
Hemisphere, and the beginning of the Northern Hemisphere glaciations. Consequently, the increase in temperature gradients influenced the circulation of the
NADW towards the south-western Atlantic (Einsele,
2000). By now, glacial conditions were definitively
settled in Antarctica and Patagonia. The AABW was
definitely reactivated at the beginning of the Quaternary, and the deep-water circulation reached its
present configuration with an increase of the AABW
during glacial periods and of the NADW during interglacial periods (Duplessy et al., 1988; Sarnthein et al.,
1994). The final stages of the evolution of the ACM
were dominated by the Quaternary sea-level fluctuations associated with the alternating glacial–
interglacial periods, particularly with the post-LGM
transgression (Guilderson et al., 2000; Violante &
Parker, 2004; Parker et al., 2008). Rignot, Rivera &
Casassa (2003) consider that the melting of Patagonian glaciers – essentially resulting from climate
change – significantly contributes to sea-level rise
in a proportion 1.5 times greater than the melting
of Alaskan glaciers. If this relation is considered for past glacial times, it can be concluded that
© 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 346–362
PATAGONIA CONTINENTAL MARGIN
Patagonia had a strong impact in Quaternary eustatic
fluctuations.
EVOLUTION OF THE PCM
Three major stages of evolution can be synthesized.
1.A stage dominated by internal (endogene) factors,
corresponding to pre-Maastrichtian times, when
tectonic conditioning factors prevailed over oceanographic and climatic factors. Major processes
were related to plate tectonics, sea-floor spreading, and the separation of South America and
Africa, with predominant continental-dominated
sedimentation.
2. A transitional stage, corresponding to early Tertiary times (pre-Eocene–Oligocene), when the first
shallow marine environments settled in the region
(initial stages of the Atlantic Ocean evolution), and
oceanographic and climatic conditioning factors
became at least as important as tectonic factors in
the shaping of the margin.
3. A stage dominated by external (exogene) factors,
corresponding to post-Oligocene times, when the
Atlantic Ocean was definitively installed and
the climatic and oceanographic conditions evolved
towards its present configuration. The stratification of the oceanic water masses ensued, thus
inducing an ocean circulation pattern that became
a major forcing factor in the morphosedimentary
evolution of the margin. Climatic and oceanographic conditions were thus more important in
the short term than tectonism (mainly characterized by long-term factors such as the Andean uplift
and subsidence in the marine basins). The Quaternary glacio-eustatic sea-level fluctuations, and
the resulting effects experienced by the coast and
offshore (particularly the shelf) regions, gave the
PCM its final (present) configuration.
CONCLUSIONS
The PCM offers enormous possibilities for a better
understanding of the evolution of the adjacent
continent. The records of the regional palaeoclimatic, palaeooceanographic, and geotectonic processes are preserved there, and are thus available for
an integrated and multidisciplinary geological correlation between sea and land. Different types
of margins are present, each showing particular
features that are the result of a complex interaction among tectonic, sedimentological, dynamic,
morphological, climatic, oceanographic, and evolutive
conditioning factors.
In this contribution attempts were made to synthesize our current knowledge of the different processes
359
participating in the development of the Patagonian
continental shelf (PCS). Many questions are still
unsolved and more research is needed. In doing so it
is shown that an integration of marine and continental geology can provide insights that probably neither
discipline can address satisfactorily in isolation.
ACKNOWLEDGEMENTS
This contribution is based on our presentation at the
symposium entitled ‘Paleogeography and Paleoclimatology of Patagonia: Effects on Biodiversity’, held at
the La Plata Museum in Argentina in May 2009 and
organized by Jorge Rabassa, Eduardo Tonni, Alfredo
Carlini, and Daniel Ruzzante. The authors thank
Daniel Ruzzante and Jorge Rabassa for reviews and
comments on the article.
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