The Orinoco turbidite system:
Tectonic controls on sea-floor
morphology and sedimentation
Yannick Callec, Eric Deville, Guy Desaubliaux, Roger
Griboulard, Pascale Huyghe, Alain Mascle, Georges
Mascle, Mark Noble, Crelia Padron de Carillo, and
Julien Schmitz
ABSTRACT
Because of its location in an active margin context, the sandrich Orinoco turbidite system is controlled morphologically
and tectonically by the compressional structures of the Barbados
prism, and as a consequence, the sedimentation system does
not exhibit a classic fan geometry. The sea-floor geometry between the slope of the front of the Barbados prism and the slope
of the Guyana margin induces the convergence of the turbidite
channels toward the abyssal plain at the front of the Barbados
accretionary prism. Also, whereas in most passive margins the
turbidite systems are commonly organized upstream to downstream as canyon, then channel levee, then lobes, here, because
of the control by active tectonics, the sedimentary system is organized as channel levee, then canyons, then channelized lobes.
In shallow water, landward of the prism, the system has multiple sources with several distributaries, and progressively downward, the channel courses are more complex with frequent
convergences or divergences that are emphasized by the effects
of the undulating sea-floor morphologies. Erosional processes
are almost absent in the upper part of the turbidite system shallower than 1500 m (4921 ft). Erosion along channels develops
mostly between 2000 and 4000 m (6562 and 13,123 ft) of
water depth, above the compressional structures of the Barbados prism. Incisions show irregular meandering and sinuous
courses in the low-relief segments and less sinuous courses
where channels incise the structures. Larger incisions (canyons)
are 3 km (1.9 mi) wide and 300 m (984 ft) deep. The occurrence of different phases of successive incisions is responsible
Copyright ©2010. The American Association of Petroleum Geologists. All rights reserved.
Manuscript received February 13, 2009; provisional acceptance April 2, 2009; revised manuscript
received May 30, 2009; 2nd revised manuscript received September 28, 2009; final acceptance
November 2, 2009.
DOI:10.1306/11020909021
AAPG Bulletin, v. 94, no. 6 (June 2010), pp. 869–887
869
AUTHORS
Yannick Callec Institut Français du Pétrole,
Direction Géologie-Géochimie-Géophysique,
1-4 avenue du Bois Préau, F-92852 RueilMalmaison Cedex, France; present address:
Bureau de Recherches Géologiques et Minières,
Service GEO/GSO, 3 av. Claude Guillemin,
45060 Orléans Cedex 2, France
Yannick Callec received an M.Sc. degree in geosciences from the University d’Orsay, Paris XI
in 1996 and a Ph.D. from the Paris School of Mines
in 2001. He joined the Institut Français du
Pétrole in 2002 doing research on the CARAMBA
project. Since 2003, he has worked as a sedimentologist in the Bureau de Recherche Géologique et Minière for mapping projects and petroleum exploration in west Africa.
Eric Deville Institut Français du Pétrole,
Direction Géologie-Géochimie-Géophysique,
1-4 avenue du Bois Préau, F-92852 RueilMalmaison Cedex, France; [email protected]
Eric Deville received an M.Sc. degree in geosciences from the Pierre and Marie Curie University, Paris VI in 1983 and a Ph.D. from the
University of Chambery, France, in 1987. He
joined Institut Français du Pétrole in 1990 doing
research on a wide range of sedimentary basins,
notably in the Alps. His main research interests
include deformation processes, thermicity, and
fluid dynamics in convergent orogens and mud
volcanism and shale mobilization processes.
Guy Desaubliaux Institut Français du Pétrole, Direction Géologie-Géochimie-Géophysique,
1-4 avenue du Bois Préau, F-92852 RueilMalmaison Cedex, France; present address: Gaz
de France-Suez, 361, avenue du President
Wilson, BP33, Saint Denis, France
Guy Desaubliaux worked for two decades at
the Institut Français du Pétrole as a sedimentologist. He joined Gaz de France in 2008 where
he is now in charge of the coordination of research programs.
Roger Griboulard Département de Géologie et Océanographie, URA CNRS 197, Université de Bordeaux-I, F-33000 Bordeaux Cedex,
France
Roger Griboulard is a researcher and teacher at
the Bordeaux 1 University. His field of investigation concerns sedimentology and morphotectonics.
He participated in several studies about the
south Barbados accretionary prism and the deep
Orinoco turbidite system. He was the initiator
of the CARAMBA project.
Pascale Huyghe Laboratoire de Géodynamique des Chaînes Alpines, UMR 5025,
Université Joseph Fourier, F-38041 Grenoble
Cedex, France
Pascale Huyghe is a researcher and teacher at
the Grenoble 1 University. Her field of investigation concerns tectonics and sedimentation
on either onshore or offshore. She participated
on several studies about the south Barbados
accretionary prism and its relationship with the
deep Orinoco turbidite system.
Alain Mascle Institut Français du Pétrole,
Direction Géologie-Géochimie-Géophysique,
1-4 avenue du Bois Préau, F-92852 RueilMalmaison Cedex, France
Alain Mascle received his M.Sc. degree in applied geophysics from the University of Paris VI
in 1973, and his “Habilitation à Diriger des
Recherches” from the University of ChamberySavoie in 1998. He joined the Institut Français
du Pétrole (IFP) in 1973 as a geologist in charge
of the exploration of continental margins in
collaboration with French oil companies. He moved
to IFP in 1996 where he has been in charge
of different M.Sc. programs in both petroleum
geoscience and reservoir geoscience and
engineering.
Georges Mascle Département de Géologie et Océanographie, URA CNRS 197, Université de Bordeaux-I, F-33000 Bordeaux Cedex,
France
George Mascle is a professor at Joseph Fourier
Grenoble I University. He worked in many parts
of the world, especially in Sicily and the Himalayas, and he participated in many marine
surveys, notably in the Mediterranean Sea.
Mark Noble Centre de Géosciences, UMR
7619 Sisyphe, Mines ParisTech, Fontainebleau,
France
Mark Noble received an M.Sc. degree in geophysics from the University of Paris Diderot
(Paris VII) in 1986 and a Ph.D. from the Institut
de Physique du Globe de Paris in 1992. He
joined the geophysics research team of Mines
ParisTech in 1992. His current research interests
include theoretical seismology, seismic wave
870
The Orinoco Turbidite System
for the development of morphologically correlative terraces in
both flanks of the canyons. This might be the consequence of
two mechanisms: the tectonic activity of the deformation front
characterized by progressive uplift and thrusting of recent sediments, and the superimposition of the cycles of the Orinoco
turbidite system. Piston-core surveys have demonstrated that
turbidite sediments moving through the channel and canyon
system and deposited in the abyssal plain are mostly coarse sandy
deposits covered by recent pelagic planktonic-rich sedimentation, which indicates that sand deposition slowed down during
the postglacial sea level rise.
INTRODUCTION
The Orinoco turbidite system develops from the east Venezuela and Trinidad continental slope down to the Atlantic
abyssal plain (Embley and Langseth, 1977; Belderson et al.,
1984; Ercilla et al., 1998). Most of the recent sediments of the
deep Orinoco delta and the southern Barbados ridge complex
originate from the South American continent and are sourced
by the Orinoco River (Herrera et al., 1981; Milliman et al.,
1982; Meade, 1990; Warne et al., 2002; Aslan et al., 2003), plus
some fine material from the rivers of the Guyana margin and the
Amazon transported northwestward by the Guyana current
along the South American shoreline. The Orinoco River contributed to turbidite sedimentation in the Atlantic abyssal
plain during the late Miocene and has possibly contributed
since the Eocene ( Wright, 1984; Beck et al., 1990; Diaz de
Gamero, 1996; Di Crocce et al., 1999). Early multibeam and
seismic acquisitions imaged canyon incisions along the deep
turbidite system where the channels cross cut the frontal structures of the southern Barbados accretionary prism (Biju-Duval
et al., 1982; Mascle et al., 1990). Coring surveys have evidenced
the sand-rich nature of this turbidite system, notably in the abyssal plain in front of the Barbados tectonic prism and in some
piggyback basins above the prism (Faugères et al., 1991, 1993).
Geophysical data acquired during the CARAMBA (Caribbean America Bathymetry) survey, with the French scientific
O/V Atalante (65,000 km2 [25,097 mi2] of multibeam data
and backscattering imagery, 5300 km [3293 mi] of 6-trace
two-dimensional seismic lines, and 3.5 kHz profiles), provided
a wide coverage of the Orinoco turbidite system with the exception of the very upper continental slope and the more distal
zones in the Atlantic abyssal plain (Figure 1). These data
coupled with the sampling of new Kullenberg piston cores
(Figure 2) allow a better understanding of the whole recent
depositional system and of the structure of the area. We present
here the main results illustrating how the tectonic activity of the
Barbados accretionary prism controlled the sea-floor morphology and hence the turbidite sedimentation. This example of a
recent deep-water tectonically controlled turbidite system
can be used as an analog for the study of ancient and buried
systems developed in active tectonic areas, including passive
margins with mobile substrata.
GEODYNAMIC CONTEXT
In the southeastern Caribbean area, the Caribbean plate currently has an eastward relative movement of about 2 cm/yr
(0.8 in./yr) with respect to the South American plate. This
movement is responsible for the frontal convergence between
the Atlantic oceanic lithosphere and dextral relative movement
between the Caribbean plate and the South American continent (DeMets et al., 2000; Jansma et al., 2000; Weber et al.,
2000; Calais et al., 2002; Mann et al., 2002). In Trinidad, recent Global Positioning System calculations and a historical
comparison of geodesic measurements onshore Trinidad have
shown that the present-day tectonic movements of the plate
boundary are concentrated mostly in the southern part of the
island (Saleh et al., 2004). The compressional deformation
front of the Barbados prism is transferred across the Orinoco
delta toward the west to the southern area of Trinidad, the Columbus Channel, and eastern Venezuela where marine Late
Cretaceous to Pliocene sediments are severely deformed within a south-verging fold and thrust belt facing the South American shield (Jacome et al., 2003).
The turbidite system of the Orinoco delta develops at the
southern edge of the Lesser Antilles active margin above the
southern part of the large Barbados accretionary prism and
downslope at the front of this prism within the Atlantic abyssal
plain (Biju-Duval et al., 1982; Brown and Westbrook, 1987;
Deville et al., 2003b; Deville and Mascle, in press) (Figure 1).
Downslope of the proximal turbidite system of the Orinoco delta, the deformation zone at the boundary between the
Caribbean plate and the South America plate is diffuse and
shows a high diversity of tectonic features (Deville et al., 2006).
In the shelfal area south and east of Trinidad, the recent deformation is mainly characterized by strike-slip faulting (Mann
and Wood, 2003), whereas shallow extension tectonics have
favored the development of large accommodation areas for
recent sediments in the Columbus Basin, southeast of Trinidad, and in the Orinoco platform (plataforma deltana) in the
propagation, and tomography to characterize the
near subsurface.
Crelia Padron de Carillo Institut Français du Pétrole, Direction Géologie-GéochimieGéophysique, 1-4 avenue du Bois Préau, F-92852
Rueil-Malmaison Cedex, France; Laboratoire
de Géodynamique des Chaînes Alpines, UMR
5025, Université Joseph Fourier, F-38041 Grenoble Cedex, France; present address: Departamento de Ciencias de la Tierra, Universidad
Simón Bolívar (USB), Apartado 89000, Valle de
Sartenejas, Baruta. Edo. Miranda, Venezuela
Crelia Padrón de Carrillo received her B.Sc.
degree in geophysics engineering from the Central University of Venezuela in 1997, an M.Sc.
degree in science of the Earth from the Central
University of Venezuela in 2002, and a Ph.D.
from Joseph Fourier Grenoble 1 University, France,
in 2007. She worked in PDVSA Exploration
from 1996 to 2002. Her experience is in seismic
interpretation focusing on exploration projects
for the oil and gas industry, and her main research interests include tectonics and sedimentation and integration geophysics data. Since
2006, she has been a professor of geophysics
and seismic interpretation for undergraduate and
graduate students at Simon Bolivar University.
Julien Schmitz Institut Français du Pétrole,
Direction Géologie-Géochimie-Géophysique,
1-4 avenue du Bois Préau, F-92852 RueilMalmaison Cedex, France
Julien Schmitz joined the Institut Français du
Pétrole in 1996. He participated in many marine surveys. His expertise during the CARAMBA
project was in multibeam data processing and
interpretation.
ACKNOWLEDGEMENTS
The AAPG editor thanks the following reviewers
for their work on this paper: John M. Armentrout,
Bradford E. Prather, and Gabor C. Tari.
Callec et al.
871
Figure 1. (A) Sketch map of the Orinoco drainage area (black lines are the main channels; dotted lines are the supposed location of
main channels). (B) Map of the Orinoco turbidite system (white represents the emergent structures of the Barbados accretionary prism)
with the location of the cores of Figure 2 and the location of Figures 3–10. ODFZ = Orinoco delta fault zone. White arrows are pointing
toward the upstream part of the main channels.
872
The Orinoco Turbidite System
offshore of Venezuela (Galbraith and Brown,
1999; Gersztenkorn et al., 1999; Heppard et al.,
1998; Gibson and Bentham, 2003).
In the area of the southern Barbados accretionary prism, the Orinoco turbidite sedimentation is
widely influenced by the sea-floor topography. Syntectonic sedimentation in the southern area of the
Barbados accretionary prism and in the deep Atlantic Plain contributes both to the growth of the
Barbados tectonic prism, respectively, by piggyback basin development above the prism and by
frontal accretion at the convergent front. Upslope
in the tectonic prism, the clastic sediment fluxes
are characterized by gravity flows (turbidites, grain
flows, debris flows,…). This area is also characterized by hemipelagic sedimentation and recycling of
the sediments within the prism by superficial flows
from mud volcanoes and gravity mass flows sliding
on topographic slopes and resedimentation in the
piggyback basins (in-situ source) (Faugères et al.,
1993).
Because of its location within an active margin
(east Caribbean or Lesser Antilles active margin),
the Orinoco turbidite system is not a passive-margin
delta-fed deep-sea fan. The transport and depositional system are controlled by the compressional
structures of the Barbados prism. One consequence
is that this turbidite system does not exhibit a classic
fan geometry. The sea floor low between the Barbados ridge and the continental slope of the Guyana margin induces the convergence of the turbidite
channels toward the abyssal plain at the front of the
accretionary prism (Figure 1). In the upper slope
(above 1500 m [4921 ft] of water depth), the system has multiple sources with several distributaries. Downward (between 1500 m [4921 ft] and
the front of the accretionary wedge), the channel
courses are more complex with frequent convergences or divergences, which are emphasized by
the effects of the undulating sea-floor morphologies.
The geometry of the sea floor of the southern
Barbados area highlights the complexity of the structures of the accretionary prism (Biju-Duval et al.,
1982; Mascle et al., 1990; Gonthier et al., 1994;
Huyghe et al., 1996, 1999) where tectonics and
mud volcanism force the sea floor morphology, generating local highs and confined piggyback basins,
which control the channels courses (Griboulard
et al., 1991, 1996; Faugères et al., 1993; Huyghe
et al., 1996, 1999, 2004). In some areas, the development of ramp anticlines has formed closed basins
disconnected from the turbidite sources. These
starved basins show relatively deep sea floor bathymetry compared to the surrounding basins partially filled by the recent turbidite sedimentation
(Figure 1).
CHANNEL PATTERN
Because of its active tectonic setting, the recent Orinoco turbidite system presents an atypical evolution
of the channel architecture from the upper slope to
the abyssal plain (Huyghe et al., 2004), and channels courses show a broad range of highly variable
sinuosity (Figures 1, 3–8) showing similarities with
equivalent systems (Saller et al., 2004).
Upslope, close to the Trinidad-Venezuelan continental platform, the sea floor is generally regular
and is only locally disturbed by the edifices of isolated mud volcanoes (Brami et al., 2000; Rutledge
and Leonard, 2001; Deville et al., 2003a, b, c; 2004,
2006; Sullivan et al., 2004; Moscardelli et al., 2006;
Deville and Mascle, in press). In the upslope area,
sedimentation processes show a multiple-source
system with highly sinuous and meandering subparallel channel-levee systems. Courses of the channels become irregularly sinuous where folds and
mud volcanoes of the tectonic prism influence the
topography of the sea floor. In several locations,
avulsion processes can be observed (see example
in Figure 8), probably because of changes of the
channel course related to the progressive deformation of the sea floor associated with tectonic movements below.
Downslope, channels develop in the piggyback
basins above the accretionary prism (Figure 9) and
are characterized by well-developed aggrading
channel-levee complexes with highly sinuous and
meandering geometries (Figures 5, 7). As illustrated
on the seismic data, the channels are filling the syntectonic piggyback basins of the prism, and in some
locations, they are covering early deformation (fold
and thrust structures, Figure 9). The general course
Callec et al.
873
Figure 2. Example of cores
collected during the CARAMBA
cruise of the O/V Atalante in
the Orinoco turbidite system. The
correlation line is the base of
the uppermost hemipelagic
sediments.
of the channels is controlled by the orientation of the
elongated piggyback basins. Severe inflections toward the east or the southeast are observed when the
channels incise the northeast-southwest–trending
ramp anticlines of the tectonic prism, notably in the
frontal part of the accretionary wedge (Figures 5, 7).
In the proximal downslope area above the compressional structure of the Barbados prism, the drainage network shows a complex architecture with
874
The Orinoco Turbidite System
convergence and divergence of the channel courses
related to the tectonic control of the morphology of
the sea floor (Figure 1B). Local tectonic and mud
volcanism processes induce frequent and massive
gravity deposits and control the morphology of the
channels from narrow channel levees with locally
confined levees in the piggyback basins to erosional
channels and canyon geometries where they cut
through the structures (Figures 5, 7).
Figure 2. Continued.
Callec et al.
875
Figure 3. Block diagram from the EM12
multibeam acquisition showing the geometry of the canyons within the tectonic
front of the Barbados prism. The channels
are converging at the front of the prism
within the abyssal plain.
Active thrust structures, as well as mud volcano
edifices control channel courses. Levee deposits are
locally pinched out toward the folds and the mud
volcano edifices. Also, tectonics and mud volcanism
processes induce frequent massive gravity-flow deposits, which also contribute to control the morphology of the channels from narrow channel-levee
complexes with locally confined levees in the piggyback basins to erosional channels and canyon geometries where they cut through the growing structures
(Figures 5, 7).
In the frontal zone of the tectonic prism, channel courses are mostly controlled by the complex
morphology of the sea floor, and their geometries
evolve systematically to deep incisions (canyons).
Notably, four recent canyons with several terraces
deeply incise the frontal anticlines related to active
thrusting. Even the more erosive canyons have meandering courses (Figure 3). In the abyssal plain, the
876
The Orinoco Turbidite System
course of the channels is much straighter. Northward, an older canyon is deformed by thrust tectonics (folded channel 1 in Figure 3). In front of
the tectonic wedge, V-shaped erosional channels
with numerous terraces characterize the transition
zone toward the abyssal plain where several smaller,
commonly unleveed channels are dominant. Old
minor braided channels run along the front of the
wedge, and a major meandering channel runs toward the abyssal plain where sandy distal lobes are
observed (Figure 6).
In the upper abyssal plain, east of the front of
the tectonic wedge, channels are V shaped with several terraces. Northward, in the abyssal plain, a large
ultradeep sand-rich braided deep-sea fan developed (Belderson et al., 1984; Ercilla et al., 1998)
with a main low-sinuosity channel, which presents
a broad geometry with low-relief aggrading channellevee architecture. Northward, the channel-to-lobe
Figure 4. Dip map deduced from the EM12 multibeam acquisition. Note the high values in the flanks of the canyon when they crosscut
the fold and thrust system of the Barbados prism.
transition is observed with plane-convex elementary bodies, which are characteristic of sandy turbidite lobes. The main channel extends mostly northeastward and probably joins the Vidal mid-ocean
channel (Baraza et al., 1997; Ercilla et al., 1998).
DEEP-WATER EROSION
The peculiarity of the Orinoco system is that no significant recent canyon developed on the GuyanaOrinoco margin shelf. This is confirmed by intensive
oil and gas exploration in the offshore of Trinidad
and in the Orinoco platform (plataforma deltana)
in the offshore of eastern Venezuela (Erlich, 1992;
Di Crocce et al., 1999; Brami et al., 2000; Wood,
2000; Moscardelli et al., 2006). Also, no significant
erosion along the present shelf break and in the upper slope is observed as noticed by Mascle et al.
(1990) and Brami et al. (2000). Whereas erosional
processes are mostly absent in the upper part of
the turbiditic system, they develop in the deepwater area between 2000 and 4000 m (6562 and
13,123 ft) of water depth above the compressional
structures of the Barbados prism as evidenced by
multibeam data (Mascle et al., 1990; Deville et al.,
2003d; Huyghe et al., 2004) (Figures 3, 5). In the
erosional area, ramp anticlines and abundant sedimentary mobilization (mud volcanoes) control the
channel courses by confining the turbidite flows.
Incised channels show irregular meandering and
highly sinuous courses in the low-relief segments.
Where channels cut high-relief structures, they are
more confined without levee or with asymmetrical
levee deposits and are deeply incised with a characteristic U shape (Figures 5–7). Downslope, channel
courses are controlled by the successive anticlines
and evolve systematically to canyon-scale geometries with a progressively increasing depth of incision. In the thrust front zone, low-sinuosity meandering canyons cut the anticlinal ridges (Figure 3).
To clearly illustrate the geometry of the incisions, we present depth-migrated 3.5-kHz profiles
(Figures 5–7). Larger canyons show a maximum
width of 3 km (1.9 mi) and depth of 300 m. Mean
dips of slope of canyon walls are steep, locally
higher than 15° (Figure 4). In the frontal folds of
the accretionary prism, the channel course probably
preexisted the development of the final structure
of the fold (syntectonic erosion). Immediately east
of the tectonic front, the main channel is also characterized by sinuous anatomy and also presents
canyon geometry with asymmetric levee deposits.
A progressive downward transition from U-shaped
to V-shaped incision is observed, and several internal terraces appear in both flanks of the main channel. The occurrence of similar terraces in both
flanks highlights obviously that erosion occurred in
Callec et al.
877
Figure 5. (A) Sun-shaded
bathymetric map (EM12 multibeam data; location on Figure 1B)
and (B) depth-migrated 3.5-kHz
profiles located on the bathymetric map showing different
features of the erosion processes
along the main deep canyon.
In the upper part (profiles 1 to 7)
and in the abyssal plain (profiles 12 to 14), the incision occurred within channel-levee
systems. In the front of the
Barbados fold and thrust system (profiles 8 to 11), canyon
erosion occurred deeply within
ramp anticlines. Note the terrace geometry within the canyon
and in the incised channel-levee
system of the abyssal plain.
different phases of successive incisions, leading to
the development of several terraces (Figures 10,
11). Defining the precise cause of the development
of these terraces is very difficult. They can be due
to the superposition of two mechanisms: (1) the
tectonic activity of the deformation front characterized by progressive uplift and thrusting of recent sediments and (2) the superimposition of
the fluctuations of the Orinoco turbidite system
activity. This second hypothesis is considered as
the most probable, and probably, the successive
878
The Orinoco Turbidite System
erosion phases occurred during cyclic phases of a
relative lowstand of sea level when the transit of
the sand-rich turbidites toward the abyssal plain
was the strongest. During these relative lowstand
events, a sediment bypass with transit of sand-rich
coarse-grained sandy sediments responsible for the
erosion in the canyons is observed. Muddy turbidity currents being more erosive than sandy ones, it
is also possible that the flows that erode the canyons are not the same flows from which the sands
are deposited (Deptuck et al., 2007).
Figure 6. (A) Sun-shaded
bathymetric map (EM12 multibeam data; location on Figure 1B),
(B) backscattering EM12 multibeam data, and (C) depth-migrated
3.5-kHz profiles located on the
bathymetric map showing the architecture of the channels in the
abyssal plain. Note the terrace geometry of the incised V channellevee system close to the tectonic
front (profiles 15 to 17) and
the U shape of the channel in
the distal area (profiles 18 and 19).
Sandy lobes develop north of
the abyssal plain (profiles 20 to 23).
FACIES DISTRIBUTION
We have seen that the channel pattern is different
from passive-margin delta-fed deep-sea fans, but the
Orinoco turbidite system is also different regarding
the spatial distribution of the sedimentary facies.
The different facies that have been distinguished in
the study area are shown on the map of Figure 1.
This mapping results from the compilation of piston
coring conducted in this area and from the interpre-
tation of multibeam data (bathymetric and backscattering) and seismic and 3.5-kHz profiles. Available
coring results from previous surveys were published
by Faugères et al. (1991, 1993) and Gonthier et al.
(1994). These authors showed that turbidite sediments transiting within the channels and canyon
system and deposited in the abyssal plain are mostly
sand rich. During the CARAMBA cruise, 25 new
piston cores were collected in this area, the most
characteristic being presented in Figure 2.
Callec et al.
879
Figure 7. (A) Sun-shaded
bathymetric map (EM12 multibeam data; location on Figure 1B)
and (B) depth-migrated 3.5-kHz
profiles located on the bathymetric map showing the lateral
evolution along channel 3.
Cores taken in the upslope area away from the
turbidite channels show mostly hemipelagic sediments with some clay-silt intercalations and very
thin turbidites, and gravity mass wasting (slump)
occurrences (C-12, C-13, Figure 2). This reflects
slope destabilization processes and significant detrital flux associated with proximity to the Orinoco
platform and influences of the Orinoco deltaic
plume. The highs on top of the folds of the accretionary prism are characterized by homogeneous
hemipelagic sedimentation (C-25, Figure 2).
Cores taken from the downslope area close to
the channel systems have found levee deposits corresponding to thin and fine-grained turbidites
made up of centimetric laminations (parallel or
cross-bedded) of silt and fine sands. These deposits
developed on the sides of the channels, but they
are also found on top of massive uplift structures
(Deville et al., 2006) (see example of core C-10,
Figure 2). These cores taken on the sides of the
880
The Orinoco Turbidite System
turbidite channels in the area of the accretionary
prism show episodic or continuous successions of
thin sandy turbidites with sequences of Bouma type
characterized by terms Tb, Tbc, Tce, and Tde,
which relate to low-density turbulent flows (Lowe,
1976). These sequences are occasionally interbedded with slump deposits due to the destabilization of the flanks of the channels associated with
the development of small normal faults.
In the channel axis, massive heterolithic mass
flows have been found (core C-20, Figure 2). In the
closed (starved) piggyback basins above the accretionary prism, away from the present-day turbidite
channels, low-density sandy turbidites have also
been found (C-4, Figure 2). They most likely correspond to deposits in ancient turbidite channels,
which are now abandoned.
Levee deposits cored within the piggyback basins above the accretionary prism correspond mostly
to fine-grained silty turbidites. A good example of
Figure 8. Avulsion example in the eastern offshore of Trinidad.
this type of deposit is given by core C-17 in Figure 2.
Coring inside the channel course was very difficult
because of very hard grounds, and the only sediments recovered correspond to heterolithic mass
flows resulting from levee collapse within the
channel (see example of core C-20, Figure 2).
In the abyssal plain, immediately east of the
thrust front, the levee deposits correspond to fineto medium-grained sandy turbidites (see core C-5,
Figure 2). Downstream, all the recovered cores in
the abyssal plain were made of massive sandy turbidites with debrite intercalations (see example of
core C-2, Figure 2). The new piston cores taken
during the CARAMBA cruise confirmed the previous results that well-developed massive sandy
turbidites are found on the abyssal plain east of
the Barbados accretionary front (Faugères et al.,
1991, 1993). Sediments found in the abyssal plain
correspond to high-density massive sandy turbidites characterized by sand-clay mixing intervals
(slurry bed), reflecting abrasion processes of the
sea floor (C-02, Figure 2). Finally, note that all the
available piston-core surveys have demonstrated
that turbidite sediments moving through the
channel and canyon system and that are deposited
in the abyssal plain are indeed mostly coarse-grained
sandy deposits (Faugères et al., 1993) (Figure 2).
Also note that fine-grained sandy deposits are
stored on the outer shelf (Van Andel, 1967; Alfonso
et al., 2006), and in the slope close to the shelf edge,
the channels are currently overlapped by recent deposits, mostly by mass flows on the upper continental slope (Brami et al., 2000; Moscardelli et al.,
2006) (Figure 1). As such, the traces of the channels in the upper slope are commonly draped by
recent sediments. The relative absence or thinness
of this drape facies in channels farther downslope
supports low sedimentation rates in the turbidite
channel system related to the rise of sea level since
the last glacial lowstand. Also, the sand-rich sediments deposited in the tectonic prism area and in
the abyssal plain are systematically covered by a few
tens of centimeters of recent pelagic planktonicrich sedimentation, which indicates that sand deposition has stopped since the last glacial event
(Figure 2).
Callec et al.
881
882
The Orinoco Turbidite System
Figure 9. Seismic lines and depth-migrated 3.5-kHz profiles showing the subsurface structure of transported syntectonic basins. Note the diachronism of the deformations. Some of the
folds developed recently and are probably still active as illustrated by the pinch-out geometry of the syntectonic deposits, whereas some are clearly sealed by the recent turbidite
deposits. TWT = two-way traveltime.
Callec et al.
Figure 10. Location of the main terraces (in red) associated with the canyon system of the front of the Barbados accretionary prism (location on Figure 1B).
883
Figure 11. Synthesis of evolution of the architecture of the
turbidite channels along the Orinoco turbidite system.
CONCLUSION
Whereas in most of the passive margin the turbidite
system is classically organized upstream to downstream as canyon, then channel levee, then lobes,
due to the control by active tectonics, the Orinoco
turbidite system is organized as channel levee, then
canyons, then channelized lobes. Upslope, the sediment input is a mutiple-source sand-rich system. It
shows a relatively complex geometry with channel
divergences in flat-floor syntectonic piggyback basins and convergences in front of the prism. Sinuosity of the channels is highly variable because of the
884
The Orinoco Turbidite System
tectonic control of the morphology of the sea floor.
The architecture of the channels shows high variability from channel levee to canyon, controlled by
the morphology of the basement. The main erosion
is not located close to the present-day shelf edge, but
it is spectacular in the deep-water areas (between
2000 and 4000 m [6562 and 13,123 ft] of water
depth). A wide zone of predominantly sediment
transport (bypass) leaving only channel-levee deposits develops from above the 1000-m (3281-ft)
isobath down to the abyssal plain. In the abyssal
plain, the sedimentation is dominantly sandy. A
major recent straight channel is observed trending
northeastward toward the deep Atlantic plain.
Stacked sinuous channels are found trending north–
south, parallel to the front of the accretionary prism.
Detached sand-rich depositional lobes have been
found in the flattest areas of the abyssal plain where
the lowest sea-floor gradient results in deposition
of the remaining sand.
This system is currently in a low phase of activity since the recent Holocene rise of sea level. Nowadays, the sedimentation is mostly located on the
Orinoco delta platform and on the upper slope, although some hyperpycnal events have probably
been active recently and would be responsible
for sedimentation in deep-water areas. The turbidite system was most active during the last glacial
lowstand.
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