algerian margin sedimentation patterns

16 Pages·2011·4.69 MB·English

by  Robert Clarke

ALGERIAN MARGIN SEDIMENTATION PATTERNS 69
ALGERIAN MARGIN SEDIMENTATION PATTERNS (ALGIERS AREA,
SOUTHWESTERN MEDITERRANEAN)
GABRIELA DAN-UNTERSEH
IFREMER, Géosciences Marines, Laboratoire Environnements Sédimentaires, Plouzané, France
AND
Université de Bretagne Occidentale, IUEM-CNRS UMR6538, 29280 Plouzané, France
[email protected]
BRUNO SAVOYE (DECEASED)
VIRGINIE GAULLIER
LEGEM, Université de Perpignan, 66860 Perpignan, France
ANTONIO CATTANEO
IFREMER, Géosciences Marines, Laboratoire Environnements Sédimentaires, Plouzané, France
JACQUES DEVERCHERE
Université de Bretagne Occidentale, IUEM-CNRS UMR6538, 29280 Plouzané, France
KARIM YELLES
CRAAG, Centre de Recherche en Astronomie, Astrophysique et Géophysique, Bouzaréah, Alger, Algérie
AND
MARADJA 2003 TEAM
Abstract: The present study provides an overview of recent sedimentation patterns on the central Algerian continental margin. Recent
sedimentation patterns were assessed from morphological analysis, which is based on swath bathymetry and echo-facies mapping. It
appears that sedimentation along the Algerian margin is controlled by two processes: (1) gravity-induced processes, including both mass-
transport deposits and turbidity currents, and (2) hemipelagic sedimentation. Mass-transport deposits occur on the Algerian margin at the
canyon heads and flanks, in the interfluve areas between canyons, along the seafloor escarpments, and on the flanks of salt diapirs. Mass-
transport deposits (MTDs) sampled by coring consist of a variety of soft and hard mud-clast conglomerate and turbidite deposits. MTDs
are mostly localized at the toes of steep slopes, where thrust faults were previously identified and mapped. Analysis of the spatial
distribution of MTDs and their recurrence in time help reconstruct the main predisposing factors and triggering mechanisms, and evaluate
their impact on evolution of the Algerian margin.
KEY WORDS: Algerian margin, backscatter, Boumerdès earthquake, diapirs, echo facies, mass-transport deposits, submarine canyons,
sediment waves
INTRODUCTION seismic event, swath bathymetry, chirp subbottom profiles, and
sediment cores were acquired in the area affected by the
Occurrences of MTDs involving large volumes of sediment Boumerdès earthquake.
are known across continental slopes worldwide, especially along The present study describes geomorphological features and
passive margins and volcanic islands (e.g., Masson et al., 1998; characterizes sedimentary processes on the central Algerian
Bryn et al., 2003; Haflidason et al., 2004; Canals et al., 2004). margin (Fig. 1), located offshore the cities of Tipasa, Algiers, and
However, MTDs were also documented along active margins, Dellys. The main objectives of this study are to:
where tectonic activity may be one of the most relevant factors in
generating sediment instabilities (e.g., von Huene et al., 1989; von •Highlight the main geomorphological features existing along
Huene et al., 2000; Collot et al., 2001). A well-documented earth- the central Algiers margin, and provide a detailed description
quake-induced MTD is the 1929 Grand Banks event, which of the seafloor characterized by many MTDs.
occurred between Newfoundland and Nova Scotia off Atlantic
Canada (Rupke, 1978; Piper and Asku, 1987; Piper et al., 1999). •Describe the main subsurface features with high-resolution
Earthquakes are known to trigger MTDs and generate tsunamis, seismic data and document the most significant echo facies.
which can seriously damage coastal and offshore infrastructures.
This is the case of the Algerian margin, where several devastating •Integrate different data types to better understand regional
earthquakes occurred during the last century (Heezen and Ewing, sedimentary dynamics along the central Algerian margin.
1955; El-Robrini et al., 1985). The most violent instrumentally
recorded earthquake (7.1 Mw) occurred on 10 October 1980 in El TECTONIC AND GEOLOGIC CONTEXT
Asnam. More recently on 21 May 2003 an earthquake with a
magnitude of 6.8 (Mw) struck the city of Boumerdès, on the coast Since the early Cenozoic, the Algerian margin has been under
near Algiers, and generated significant turbidity currents, con- a compressional regime with a northwest–southeast conver-
firmed by numerous submarine-cable breaks. Following the 2003 gence (Stich et al., 2003). This active zone absorbs approximately
Mass-Transport Deposits in Deepwater Settings
SEPM Special Publication No. 96, Copyright © 2011
SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-287-9, p. 69–84.
70 G. DAN, B. SAVOYE, V. GAULLIER, A. CATTANEO, J. DEVERCHERE, K. YELLES, AND MARADJA 2003 TEAM
2.2°E 2.4°E 2.6°E 2.8°E 3.0°E 3.2°E 3.4°E 3.6°E 3.8°E 4.0°E
0 20 km
37.4°N Idnotmeranianl /beoxutenrdnaarl y Great Lesser Kabylia 37.4°N
Study area Kabylia
Algiers Annaba
Tenes
El Marsa KMDJ-04
37.2°N 2500 m MD04-2798 37.2°N
MD04-2799
2000 m
KMDJ-01
37.0°N MD04-2800 KMDJ-02 37.0°N
KMDJ-03
1500 m
Dellys
500 m
m
36.8°N 1000 Algiers Sebaou River 36.8°N
Boumerdès
Isser River
Mazafran River
36.6°N Rivers Tzeolnlieasn) units (External 36.6°N
Tipasa
Bathymetric contours Volcanism
Tracklines Kabylian basement
+ Dorsale Kabyle
Sediment core Kabylian Oligo-Miocene
Boumerdès epicenter Flyschs
2.2°E 2.4°E 2.6°E 2.8°E 3.0°E 3.2°E 3.4°E 3.6°E 3.8°E 4.0°E
FIG. 1.—Location of the study area on the Algerian margin and the 2003 Boumerdès earthquake epicenter (red star). Gray track line
are the seismic chirp profile; black diamonds are either sediment cores (KMDJ-01, -02, -03, and- 04) collected during the
MARADJA cruise (2003), or sediment cores (MD04-2798, -2799, and -2800) collected during PRISMA cruise (2004). Bathymetric
contour interval is 500 m. Onshore geology illustrates the main units of the Maghrebian chain (from Domzig et al., 2006).
5 mm/year of crustal shortening (Calais et al., 2003; Nocquet and zone and enjoys a mild Mediterranean climate. Rainfall is fairly
Calais, 2004), with the onshore part accommodating only 50% of abundant along the coastal area, ranging from 0.3 cm/month
the long-term convergence between the European and African during summertime to 10 to 12 cm/month during wintertime in
plates (Meghraoui and Doumaz, 1996). It appears that active the Algiers area. As a consequence, rivers have a seasonal regime
deformation offshore northern Algeria is expressed by 2 to 3 with significant flood periods.
mm/year of shortening, and is likely related to occurrence of
earthquakes. Numerous studies focused on tectonic activity or DATA SET AND METHODS
sedimentary processes in the marine domain were conducted
after the Boumerdès earthquake in 2003. As a consequence, the The MARADJA survey took place on the R/V Le Suroît
fault believed responsible for the Boumerdès earthquake was (IFREMER) in August through September 2003. In order to
identified between 6 and 16 km below the seafloor (Yelles et al., investigate the imprint of recent and past earthquakes, this sur-
2004; Meghraoui et al., 2004; Semmane et al., 2005). The fault vey focused on the part of the Algerian margin affected by the
imprint on the seafloor was mapped on the lower part of the Boumerdès earthquake (Fig. 1). Data gathered during the survey
continental slope offshore the city of Dellys (Déverchère et al., consist of swath bathymetry and backscatter data (Kongsberg
2005; Domzig et al., 2006) (see fault trace in Figure 2). Simrad EM-300 and EM 1000 echosounder), subbottom profiler
Northern Algeria is part of the Maghrebian mountain chain, (chirp), and Kullenberg cores (Fig. 1). A 50-m-resolution digital
which can be divided from south to north into three units: (1) the elevation model was created using the IFREMER CARAÏBES
external domain (Tellian units), composed of sedimentary units, software, and the backscatter data provided a mosaic with 12.5 m
mainly marls and limestones; (2) the flysch nappes thrusting the resolution. The chirp subbottom profiler of the R/V Le Suroît uses
external zones; and (3) the internal domain, composed of frequencies between 1.8 and 5.3 kHz, reaching a maximum
Hercynian basement sometimes associated with its sedimentary vertical penetration of 80–100 m in muddy sediment. More than
cover (e.g., Bracene et al., 2003). Thus, the study area covers the 2800 km of chirp profiles were acquired for the study area (Fig. 1).
internal domain (Fig. 1). The central Algiers slope is composed of Four gravity cores (designated with letters KMD) were collected
Oligo-Miocene sediments, consisting mostly of flysch and volca- in the study area during the MARADJA cruise in 2003, and have
nic deposits (Domzig et al., 2006). a maximum length of about 7 m (Table 1). In addition, three giant
There are three main rivers in the study area: from east to west, Calypso cores (designated with letters MD) were collected dur-
the Sebaou River, the Isser River, and the Mazafran River (Fig. 1), ing the PRISMA survey (May 2005) from the R/V Marion Dufresne
which supply sediment to the study area. The river regime is (Table 1). The sediment cores were analyzed in the Sedimentary
influenced by the Algerian climate, which is typically arid and Environments Laboratory at IFREMER. Unopened core sections
hot, although northern coastal Algeria is part of the temperate were analyzed using the GEOTEK core logger (MSCL, http://
ALGERIAN MARGIN SEDIMENTATION PATTERNS 71
2.2°E 2.4°E 2.6°E 2.8°E 3.0°E 3.2°E 3.4°E 3.6°E 3.8°E 4.0°E
37.4°N Canyons Sediment wave 37.4°N
Fig. 5a
Rivers Diapirs Sebaou Canyon
Slope break Mass-transport deposits
Thrust fault ADSF Algiers Deep-Sea Fan D2
37.2°N S2 Fig. 8B 37.2°N
Dellys Canyon
D4 D3 S1 D1 B1
Inset ADSF Fig. 8A
Fig. 7 B5
37.0°N F 37.0°N
Ci Fig. 4a
s B4 B3
B2
Dellys
Pockmarks area
Khayr al Din Bank
36.8°N Algiers Canyon 36.8°N
Algiers
Sebaou River
Boumerdès
Isser River
36.6°N 36.6°N
Tipasa
Mazafran River
0 20 km
36.4°N 36.4°N
2.2°E 2.4°E 2.6°E 2.8°E 3.0°E 3.2°E 3.4°E 3.6°E 3.8°E 4.0°E
FIG. 2.—Shaded relief map showing the main morphological features in the study area. Slope breaks delimiting the continental slope,
B1 to B5; slope breaks delimiting the deep curvilinear escarpments, S1 and S2; Deep basins, D1 to D4; Suspended basins, Ci
(circular) and F (flat); Smooth area on the continental slope, s. Location of thrust fault is from Déverchère et al. (2005).
www.geotek.co.uk). Sections of split cores were photographed to 8 km) in the eastern part (Fig. 2). Bathymetry on the continental
and then X-rayed using a SCOPIX X-ray device (University of shelf is not available for this study; only the shelf break, ranging
Bordeaux I). Grain-size analysis was performed by the laser between 100 and 150 m water depth, is locally imaged within the
technique (Coulter LS130). MARADJA data.
Chirp profiles were used to define echo facies in the study
area. The echo-facies methodology, first described by Damuth Continental Slope.—
(1975, 1980), and more recently refined by other workers (Gaullier
and Bellaiche, 1998; Loncke et al., 2002), was adapted for the The continental slope is steep, with an average angle of 11° (Fig.
present study. First, we listed and classified different echo facies, 3). The slope is defined by northeast–southwest abrupt slope
followed by the mapping of each echo facies along ship tracks and breaks (B1 to B5) and by intermediate breaks forming flat areas (F)
interpolation between the lines. This last step was facilitated by or circular suspended basins (Ci) (Fig. 2). Well-developed canyon
also considering bathymetric and backscatter maps. systems and numerous ravines incise the slope and have an
enhanced expression on the slope map. MTDs occur on the slope
RESULTS especially at canyon heads and flanks, in the interfluve areas
between canyons, and particularly on the lower part of the slope.
Physiography of the Algiers Area For instance, a large area west of the Algiers Canyon is affected by
submarine slides, which occur at various water depths: on the
The study area is along the central Algerian margin (an area upper slope at 500 m, on the middle slope between 1000 and 1200
measuring 200 km x 50 km), located between 2.2° E (west of m, and on the lower slope between 1600 and 1700 m. The lower part
Tipasa) and 4.1° E (east of Dellys). The following major physi- of the continental slope offshore Dellys is also affected by numer-
ographic domains were defined in the study area: (1) continental ous MTDs. A particular feature showing a head scarp of more than
shelf; (2) continental slope delimited by different slope breaks (B1 200 m in height and approximately 1.5 km in width is visible on the
to B5); (3) major canyons; (4) Khayr al Din Bank; (5) abyssal plain shaded relief map (Figs. 4A, B). Part of the failed sediment seems
(basins D1 to D4); and (6) deep curvilinear escarpments (S1 and deposited on the slope (Fig. 4B), ranging between steep lateral
S2). The following discussion examines each one of these do- walls of the failure (Fig. 4C). The MTD covers a significant surface
mains separately. of 4 km2, with an estimated volume of approximately 0.20 km3.
Continental Shelf.— Major Canyons.—
The continental shelf has a variable width. The shelf width Three well-developed canyon systems were identified on the
ranges from 11 to 30 km west of Algiers, and becomes narrow (1 continental slope: from east to west, Dellys Canyon, Sebaou Can-
72 G. DAN, B. SAVOYE, V. GAULLIER, A. CATTANEO, J. DEVERCHERE, K. YELLES, AND MARADJA 2003 TEAM
Frequency(# ofsequences/meter)3.455.715.383.314.534.169.86 37.2°N 37°N 36.8°N 36.6°N 30° 2.
28° re
u
rmation on turbidity sequences. Echo facies are describedstribution in the study area is shown in Figure 6. Number ofMaximumAverageEchoThickness ofTurbidityThicknessThicknessFaciesthe MTDs (m)Sequences(cm)(cm) T2219105.2L11.8621.5L1-14102.7T1-25457.7T1-1301107.3L2-8551.2T38-910751.5 3.2°E 3.4°E 3.6°E 3.8°E 4°E D2 S1S2 D1 D3ADSFB1 B2B3 Dellys Boumerdès Slope (degrees) 0°°2°4°68°°1012°14°16°18°20°22°24°°26 3.2°E 3.4°E 3.6°E 3.8°E 4°E caption of Figc designations and symbols on the map are defined in the
T 1.—Synthesis of sediment cores and infoABLEin the text and in Table 2, and their di WaterLengthDepthSediment Core Setting(m)(m) 24007.83Foot of the continental slope16196.36Foot of the slope, eastward Algiers canyon23413.73Foot of the slope, west of Algiers canyon27117.56Abyssal plain, downslope S1 escarpment270728.68Abyssal plain, downslope S1 escarpment224825.30Upper part of the S1 escarpment275627.27Abyssal plain, downslope Khayr al Din Bank 2.4°E 2.6°E 2.8°E 3°E 0 20 km D4 B5 B4 Algiers Tipasa 2.4°E 2.6°E 2.8°E 3°E adient map showing seafloor slope in degrees. Alphanumeri
r
dimentCore MDJ-01MDJ-02MDJ-03MDJ-0404-279804-279904-2800 2.2°E N N N N 2.2°E —Slope-g
Se KKKKMDMDMD 37.2° 37° 36.8° 36.6° . 3.G
FI
ALGERIAN MARGIN SEDIMENTATION PATTERNS 73
A
3°44'E 3°45'E 3°46'E 3°47'E 3°48'E
B
37°3'N (B) 2400 37°3'N SE NW
1700 Max. head-wall
height
1900 Initial slope
m)
37°2'N 2400 37°2'N Depth ( 2100 MTD i
2300
Slip surface
2300 i 2000 2500 V.E. = 2.6x
2200 0 1000 2000 3000 4000 5000 6000
Down dip distance(m)
(C)
37°1'N 37°1'N C
W i E
1900 1700 Depth (m) 22118600 Side-wall MTD VS.iEde. -=w 7a.l3lx
37°N Headscarp Thrust fault 37°N 0 400 800 1200 1600 2000 2400
Lateral scarp i Intersection 1500 Along strike distance(m)
between profiles
MTD-1600 0 1 km
1400
3°44'E 3°45'E 3°46'E 3°47'E 3°48'E
FIG. 4.—A) Shaded relief map showing mass-wasting deposits on the lower part of the continental slope. Thin black lines mark
prominent scarps associated with mass-wasting deposits. Location of map area is indicated in Figure 2. B) Dip bathymetric profile
through the slide area. C) Strike bathymetric profile through the slide area. Location of both profiles is indicated in Part A.
yon, and Algiers Canyon. The Dellys Canyon drainage area con- Khayr al Din Bank.—
sists of two main branches, which collect several tributaries (Fig.
5A). This canyon incises the slope at 100 m deep on the upper slope A major change in orientation of the Algerian margin (striking
and at 350 m deep on the middle slope. Canyon flanks are steep, west-southwest to east-northeast) is observed west of the city of
with slope angles of 15 to 25° (Fig. 3). In its lower part, three Algiers (Fig. 2). Khayr al Din Bank is an elongated area of high
escarpments as high as 70, 120, and 200 m from the canyon floor are relief (500 m water depth), facing towards a deep basin (2700 m
observed, together with a plateau probably of tectonic origin (Fig. deep; Domzig et al., 2006). A first slope break occurs at 600 to 650
5B). Beyond the plateau, Dellys Canyon is no longer visible on the m of water depth, followed by change of orientation towards the
seafloor. west and change in slope angle from 2° to 5° (Fig. 3). Superficial
Sebaou Canyon is characterized by a rectilinear morphology, MTDs affect the western and northern part of Khayr al Din Bank,
and is fed by several tributaries, probably connected with the and an alignment of pockmarks occurs in its northern part (Fig.
Sebaou River (Fig. 5A). Slope gradient ranges between 15 and 25° 2). The pockmarks are 300 m to 450 m in diameter and up to 17 m
for the canyon head and flank (Fig. 3). Seaward of the B1 slope in depth. The eastern slope exhibits gullies and small MTDs. In
break, Sebaou Canyon becomes wider (approximately 3 km) with contrast, the western slope is much gentler, probably affected by
moderately high flanks. Two asymmetric branches exist more a significant erosive process (see s on the western end of Figure 2).
than 26 km from the canyon head (Fig. 5A). The primary branch
follows a northward course, while the secondary branch, consist- Abyssal Plain.—
ing of a smaller canyon incision of approximately 30 to 50 m
depth, follows a northwestward direction. Large depressions/ There are four sedimentary basins in the study area (Fig. 2).
scours, 1 km in width and more than 40 m in depth, exist on the They are delimited by continental slope breaks and deep escarp-
seafloor along the Sebaou Canyon, and are considered as strong ments. In the eastern part of the study area, the D1 basin is 30 km
evidence for significant erosion (Fig. 5C). long and 15 km wide in 2300 to 2400 m water depth. The D2 basin
Algiers Canyon consists of two main meandering tributaries, is located seawards of the curvilinear escarpment (S1). The D3
with their heads located on the shelf break (Fig. 2). The Algiers basin corresponds to an elevated area downslope of the Algiers
western tributary is sinuous, highly incised (200 to 300 m deep), Canyon. The D3 basin is interpreted as the Algiers deepsea fan
and collects three other branches, each one with small tributaries. (ADSF), which is confined on its northern part by salt diapirs and
In contrast, the Algiers eastern tributary has a rectilinear mor- a curvilinear escarpment (S2 in Figure 2). Sediment across the
phology and consists of only two tributaries. ADSF may be sourced by turbidity currents or bottom currents,
West of Algiers Canyon, the continental slope is incised by since sediment waves occur across the ADSF. A large MTD of
well-developed canyons, with numerous gully-like tributaries. approximately 2 km width exits on the northern part of the ADSF.
These tributaries connect in the middle part of the slope, creating Salt diapirs form elongated walls or rounded ridges with variable
a large canyon with an average width between 1.5 and 3 km (Fig. length (1 to 7 km), and a maximum height of 100 m above the
2). These canyons have steep flanks, with an average slope of 18° seafloor. Small (0.2 km x 0.5 km across) subcircular diapirs also
(Fig. 3). The morphological path of these canyons is difficult to exist at the foot of the ADSF. Several MTDs are identified on the
follow beyond slope breaks B3 and B4 (Fig. 2). diapir flanks. A convex-upward area occurs on the abyssal plain
74 G. DAN, B. SAVOYE, V. GAULLIER, A. CATTANEO, J. DEVERCHERE, K. YELLES, AND MARADJA 2003 TEAM
A B Dellys Canyon
3.8°E 3.9°E 4°E 4.1°E
37.4°N 37.4°N
5 km 2100 S N
2200
Sebaou Canyon
(C) m) 2300 Escarpments
h (
Secondary pt 2400
e
branch D
2500
Scours
37.2°N 37.2°N 2600 V.E. = 8.5x
Dellys Canyon
(B) 0 2000 4000 6000 8000 10000 12000 14000
Distance (m)
Escarpments
C Sebaou Canyon
S N
37°N 37°N 2300
m) 2400
h ( Scours
pt 2500
Dellys De
2600
Canyon
Isser River 2700 V.E. = 18.5x
Thrust fault
0 5000 10000 15000 20000 25000
36.8°N 36.8°N
3.8°E 3.9°E 4°E 4.1°E Distance (m)
FIG. 5.—A) Shaded relief map in Dellys and Sebaou canyons. Location of map area is indicated in Figure 2. B) Bathymetric profile
throughout Dellys Canyon showing three escarpments on the distal part (thin blue line B in Panel A). C) Bathymetric profile
throughout Sebaou Canyon showing scours on the canyon floor (thin blue line C in Panel A).
downslope of the Khayr al Din Bank (D4 basin). This morphologi- chaotic (C), and transparent (T). All echo facies are illustrated in
cal feature probably corresponds to a significant MTD accumu- Table 2, displayed on the echo-facies distribution map (Fig. 6),
lated at the foot of the slope (Fig. 2). and discussed in detail below. Due to the very high slope gradi-
ents and considerable change in the seafloor morphology, the
Deep Curvilinear Escarpments.— continental slope has not been well imaged on chirp profiles in
the study area (white area in Figure 6).
The abyssal plain exhibits two curvilinear escarpments that
are probably the seafloor expression of deformation repre- Layered Echo Facies (L).—Three subclasses are distinguished:
sented by buried thrust folds (Déverchère et al., 2005; Domzig et (1) parallel, continuous reflectors (L1 and L2); (2) discontinuous
al., 2006) (S1 and S2 in Figure 2). The S1 escarpment is steep (10° reflectors or undulations (L3, L4); and (3) parallel reflectors
to 15°) and is approximately 30 km in length and 350 to 450 m in overlying the rough acoustic basement (L5) (Table 2). At the same
height. Numerous small MTDs, approximately 0.5 to 3 km wide, time, two variants with a subclass exist in the first and second
occur on the S1 escarpment (Dan et al., 2009). The majority of subclasses: high-energy reflections (L1 and L3), and low-energy
these MTDs exist on the mid slope, although two corridors, reflections, corresponding to a transparent superficial layer (L2
formed by several MTDs, occur on the upper part of the escarp- and L4) (Table 2). Based on previous work, layered echo facies
ment in approximately 2300 m water depth. A second deep usually correspond to alternating hemipelagic intervals and tur-
curvilinear escarpment, delimited by the S2 slope break, occurs bidites (Damuth, 1980). However, the same echo facies could be
north of the ADSF between several salt diapirs (Fig. 2). Just like attributed to hemipelagic intervals (Pratson and Laine, 1989).
the previous one, the S2 escarpment is affected by MTDs less Discontinuous or undulated reflections are probably shaped by
than 0.5 km in width. contour currents or turbidity currents and are associated with
sediment waves (Heezen et al., 1966).
Echo-Facies Analysis The L1 echo facies occurs in the D1 and D4 basins, whereas the
L2 echo facies is observed mostly in the shallow part of the study
Echo-Facies Classification and Mapping.— area and on Khayr al Din Bank (Fig. 2). The field of sediment
waves on ADSF corresponds to the L4 echo facies. Another area
Definition of echo facies relies on acoustic properties and on characterized by the same echo facies (L4) exists at the foot of the
continuity of the bottom and sub-bottom seismic reflections. continental slope west of Algiers deep-sea fan. The L3 echo facies
Eleven distinctive echo facies exist in the study area, grouped into occurs only in two narrow areas north of ADSF. The L5 echo facies
four major categories: layered (L), non-penetrative, or rough (R), occurs on the continental shelf.
ALGERIAN MARGIN SEDIMENTATION PATTERNS 75
°N °N N vN uron
37.3 37.1 36.9° 36.7 ontoapti
4°E 2500 B1 Dellys T1L5 T2C RT3 no dataT4on shelf or slope 4°E d backscatter data. Cap are defined in the c
3.8°E D2 D1 1500 3.8°E anetric n the m
mo
1 L1 L2 L3 L4 hyols
3.6°E B8 .giF S A8 .giF 0 B2 005 3.6°E with the batns and symb
200 ned atio
bign
msi
3.4°E 3.4°E sis, coeric de
ym
alu
nn
aa
3.2°E S2 D3ADSF B3 2000 3.2°E p-profile e 2. Alph
hirabl
cT
e n
3°E Algiers 3°E sed on thdefined i
bad
2.8°E D4 B4 2500 2.8°E Algiers area, sed in text an
s
r u
oc
fs
p di
mare
2.6°E B5 005 2.6°E ution asses a
tribs cl
Inset Fig. 7 Tipasa s disfacie
2.2°E2.4°E 3°N 0 20 km 1°N 2500 9°N 7°N 2.2°E2.4°E . 6.—Seismic echo-facieGinterval is 100 m. Echo of Figure 2.
37. 37. 36. 36. FI
76 G. DAN, B. SAVOYE, V. GAULLIER, A. CATTANEO, J. DEVERCHERE, K. YELLES, AND MARADJA 2003 TEAM
s.
e
sn
cestioe 9.
oar
ary prCorreln Figu
mente 6. ed i
preted in term of sediarea is shown in Figurf backscatter is indicat
nterudy on o
s is ihe stocati
o facieon in ttext. L
tion. Each echheir distributiscribed in the
ate
cies classifiche text, and kscatter is d
atc
ho-fd in d ba
cen
p seismic eare describho facies a
2.—ChirBLEEcho facies between ec
A
T
ALGERIAN MARGIN SEDIMENTATION PATTERNS 77
Interpretation Mass-transport deposits Hemipelagic intervalsnd turbidite sequences Mass-transport deposits Mass-transport deposits Deposits formed bycurrents andhemipelagicsedimentation on thecontinental shelf
a
r
e
t
t
a
sc -
k
c
a
B
y
h
p
— X-raydiograImage - -
d). Ra
e
u
ntin mple 04 798 01 800
2 (coLE ore sa - KMDJ- MD04-2 KMDJ- MD04-2 -
B C
A
T
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x
E
Description C: Chaoticinternalseismic facies T1: Alternatingtransparent andlayeredreflections T2: Transparent,without internalseismic facies T3: Transparentlens. Present onseafloor orburied T4: Transparentoverlying roughacousticbasement
es nt
ho-faciClasses ChaoticC anspareT
c r
E T
78 G. DAN, B. SAVOYE, V. GAULLIER, A. CATTANEO, J. DEVERCHERE, K. YELLES, AND MARADJA 2003 TEAM
Non-Penetrative Echo Facies (Rough, R).—Non-penetrative echo Transparent Echo Facies (T).—Four transparent echo facies (T)
facies characterize areas where the seismic reflection signal does are distinguished on the chirp profiles. The first type consists of a
not penetrate below the seafloor. Generally, the R echo facies exists transparent acoustic body, with an irregular base on layered echo
in the axes of canyons, where the eroded seafloor is mostly covered facies (T1). The second type corresponds to alternating transparent
by coarse-grained deposits (Damuth, 1975). As an example, Sebaou and layered echo facies (T2). The third type consists of a transpar-
Canyon consists of the R echo facies, covering an area of approxi- ent lens, observed at the surface or buried (T3). The fourth type, the
mately 22.5 km long and greater than 10 km wide (Fig. 6). The R T4 echo facies, consists of transparent echo facies overlying rough
echo facies also occurs along the curvilinear escarpments and the echo facies. This echo facies exists only on the continental shelf
smooth area described on the north slope of Khayr al Din Bank, where a rough paleotopography is covered by younger sediment.
which seem associated with MTDs along the slopes (Fig. 6). Based on previous work, transparent echo facies are attrib-
uted to MTDs (e.g., Damuth et al., 1983). The T1 echo facies is
Chaotic Echo Facies (C).—The chaotic echo facies (C) represent identified at the foot of the S1 escarpment, characterizing the
highly disorganized sediments induced by gravity-driven pro- entire D2 basin (Fig. 6). Small areas characterized by the T2 echo
cesses (Pratson and Laine, 1989, Damuth, 1994). C echo facies facies were mapped at the edge of the eastern slope, while an
exist in various locations along the Algerian margin: at the foot of extended area characterized by the T3 echo facies was observed
the circular area (Ci in Figure 2), downslope of the S1 escarpment, a the foot of the Khayr al Din Bank. A fence diagram of intersect-
and in several limited areas in the D4 deep basin north of ADSF ing seismic lines shows several MTDs. The maximum estimated
(Fig. 6). Scattered areas corresponding to the C echo facies are thickness of the MTD sampled in core MD04-2800 is approxi-
observed on the Khayr al Din Bank and the western slope of the mately 11 m (Fig. 7). Successive appearances of MTD throughout
study area. the subsurface interval suggest a recurrent process.
MDJ 03
MDJ 04
MDJ 30
15 m
1 km
V.E. = 34x
T3
10 km CHIRP profile - MDJ 04
MD04-2800
T3
T3
T3
N CHIRP profile - MDJ 03 CHIRP profile - MDJ 30
FIG. 7.—Fence diagram of the chirp seismic profiles showing the extent of T3 echo facies and the location of the sediment core MD04-
2800. See Table 2 for further description of the T3 echo facies. Also see Figure 2 for location of inset map on this figure.