Seismic stratigraphy and development of Avon canyon in Benin (Dahomey) basin, southwestern Nigeria

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Journal of African Earth Sciences 50 (2008) 286–304

Seismic stratigraphy and development of Avon canyon inBenin (Dahomey) basin, southwestern Nigeria

S.O. Olabode *, J.A. Adekoya

Department of Applied Geology, Federal University of Technology, P.M.B. 704, Ondo State, Nigeria

Received 21 February 2007; received in revised form 20 September 2007; accepted 1 October 2007Available online 6 October 2007

Abstract

Interpretation of a grid of high resolution seismic profiles from the offshore eastern part of the Benin (Dahomey) basin in southwest-ern Nigeria area permitted the identification of cyclic events of cut and fill associated with the Avon canyon. Seismic stratigraphic anal-ysis was carried out to evaluate the canyon morphology, origin and evolution. At least three generations of ancient submarine canyonsand a newly formed submarine canyon have been identified. Seismic reflection parameters of the ancient canyons are characterized bytransparent to slightly transparent, continuous to slightly discontinuous, high to moderate amplitude and parallel to sub-parallel reflec-tions. Locally, high amplitude and chaotic reflections were observed. The reflection configurations consist of regular oblique, chaoticoblique, progradational and parallel to sub-parallel types. These seismic reflection characteristics are probably due to variable sedimen-tation processes within the canyons, which were affected by mass wasting. Canyon morphological features include step-wise and spoon-shaped wall development, deep valley incision, a V-shaped valley, similar orientation in the southeast direction, and simple to complexerosion features in the axial floor. The canyons have a composite origin, caused partly by lowering of the sea level probably associatedwith the formation of the Antarctic Ice Sheet about 30 Ma ago and partly by complex sedimentary processes. Regional correlation withgeological ages using the reflectors show that the canyons cut through the Cretaceous and lower Tertiary sediments while the sedimentaryinfill of the canyon is predominantly Miocene and younger. Gravity-driven depositional processes, downward excavation by down slopesediment flows, mass wasting from the canyon walls and variation in terrigenous sediment supply have played significant roles in main-taining the canyons. These canyons were probably conduits for sediment transport to deep-waters in the Gulf of Guinea during theirperiod of formation.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Canyons; Seismic facies and evolution

1. Introduction

Submarine canyons are continental slope features thatare characterized by deep erosion. Their origins have beenlinked to river incision, subaerial erosion, turbidity currenterosion, faulting and activity of benthic fauna in marineenvironments (Shepard and Dill, 1966; Shepard, 1981; Bel-derson and Kenyon, 1976; Twichell and Roberts, 1982).May et al. (1983) emphasized that several factors played

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* Corresponding author. Tel.: +234 8033 783 498.E-mail addresses: [email protected] (S.O. Olabode), yinka-

[email protected] (J.A. Adekoya).

a part in originating, altering and maintaining the canyons.These factors include tectonics, eustacy and sedimentaryprocesses operating over a long period of time. Recentstudies have shown that submarine canyons are of compos-ite origin. Some are related to halokinesis (Lee et al., 1992),while others such as the large canyons in the north westernGulf of Mexico and Mauritania have been attributed tocomplex faulting, folding, active diapirism and coalescingof salt domes (Bouma et al., 1972; Kenyon et al., 1978;Antobreh and Krastel, 2006).

Submarine canyons have been recognized in both conver-gent and divergent continental margins to serve as pathwaysfor downslope mass sediment transport as in the case of

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S.O. Olabode, J.A. Adekoya / Journal of African Earth Sciences 50 (2008) 286–304 287

slides, slumps, debris flows and turbidity currents that trans-port sediments from shallow marine to deep marine environ-ments (Laursen and Normark, 2002; McHugh et al., 2002;Antobreh and Krastel, 2006). The study of submarine can-yons is important because they not only preserve the sedi-mentation history of an area but also serve as modernanalogues of deepwater hydrocarbon reservoirs with sandrich turbidities (Stow and Mayall, 2000; Posementier, 2003).

The development of submarine canyons along the off-shore continental margin of Nigeria and the role they haveplayed in the sediment deposition dynamics of the areaappear to have received very little attention. However,few studies have revealed that ancient and present-day can-yons occur in the Benin (Dahomey) basin and the neigh-bouring Niger Delta basin. Burke (1972) reported theexistence of the Avon, Mahin and present-day canyons inthe offshore part of the Benin basin in southwestern Nige-ria. Billman (1992) attributed the complications of strati-graphic relations in this part of the basin to submarinedeep channel cutting into the Paleogene and older rocks.Ancient submarine canyons of Oligocene–Miocene agehave been studied in the nearby Niger delta (Petters, 1984).

The area covered by the present study is located betweenlongitude 6�10 0 and 6�25 0N, and latitude 3�48 0 and 4�05 0Eoffshore of the Atlantic Ocean (Fig. 1A). The Avon canyonidentified by Burke (1972) falls within the present studyarea, which is about 82 km and 94 km from Lagos andOkitipupa, respectively. Bathymetrically, the study areacovers the continental shelf up to the upper part of the con-tinental slope (Fig. 1A). Water depth ranges from 10 m to570 m with the shallow water portion corresponding to theupper part of the canyon.

To the best of our knowledge there have been no studiesdirectly investigating the origin, evolution and geologicalsignificance of Avon submarine canyon. The aim of thispaper is to describe the seismic stratigraphy of differentgenerations of cut and fill episodes associated with theAvon canyon in the area within the limit of available data(Fig. 1B). The seismic characteristics will be related to thepossible origin and evolution of the canyon, as well as theinfluence of the depositional processes on the canyon.

2. General geology

The Benin (Dahomey) basin is a very extensive sedimen-tary basin that extends from southeastern Ghana in thewest to the western flank of Niger Delta in Nigeria. It isbounded to the west by the Ghana ridge, which is an exten-sion of the Romanche Fracture Zone; and on the east bythe Benin Hinge line, a basement escarpment which sepa-rates the Okitipupa Structure from the Niger Delta Basinand also marks the continental extension of the ChainFracture Zone (Wilson and Willians, 1979). The Nigeriaportion of the basin extends from the boundary betweenNigeria and Republic of Benin to the Benin Hinge Line.

Detailed geology, evolution, stratigraphy and hydrocar-bon occurrence of the basin are contained in the works of

Jones and Hockey (1964), Reyment (1965), Adegoke(1969), Omatsola and Adegoke (1981), Coker and Ejedawe(1987), Billman (1992), Okosun (1996), and Hack et al.(2000). Most of these authors have described the Benin(Dahomey) basin and the Okitipupa structure that partlycontrolled sedimentation in the basin. Coker and Ejedawe(1987) identified three geoblocks, namely, the onshore geo-block (Bodashe – Ileppa – Ojo geoblock), the Okitipupastructure (Union – Gbekebo geoblock) and offshore geo-block. They emphasized that these three geoblocks havegone through three main stages of basin evolution. Thesestages are initial graben (pre-drift) phase, prolonged transi-tional stage and open marine (drift) phase.

The stratigraphy of the sediments in the Nigerian sec-tor of the Benin basin is controversial. This is primarilybecause different stratigraphic names have been proposedfor the same formation in different localities in the basin.This situation can be partly blamed on the lack of goodborehole coverage and adequate outcrops for detailedstratigraphic studies. Billman (1992) divided the stratigra-phy of the entire basin into three chronostratigraphicpackages. They are pre-lower Cretaceous folded sedi-ments, Cretaceous sediments and Tertiary sediments(Fig. 2). In the Nigerian portion of the basin the Creta-ceous sequence, as compiled from outcrop and boreholerecords, consists of the Abeokuta Group sub-divided intothree formational units, namely, Ise, Afowo, and AraromiFormations (Omatsola and Adegoke, 1981). Ise Forma-tion overlies the basement complex unconformably andcomprises coarse conglomeratic sediments. Afowo Forma-tion is composed of transitional to marine sands andsandstone with variable but thick interbedded shales andsiltstone. Araromi is the uppermost formation and ismade up of shales and siltstone with interbeds of lime-stone and sands (Fig. 2).

The Tertiary sediments consist of Ewekoro, Akinbo,Oshosun, Ilaro and Benin (coastal plain sand) Formations.Ewekoro Formation is made up of fossiliferous well-bed-ded limestone while Akinbo and Oshosun Formations aremade up of flaggy grey and black shales. Glauconitic rockbands and phosphatic beds define the boundary betweenEwekoro and Akinbo Formations. Ilaro and Benin Forma-tions are predominantly coarse sandy estuarine, deltaic andcontinental beds (Kogbe, 1975).

The Benin Basin has a high hydrocarbon potential. Thisassertion is supported by the occurrence of large depositsof tar sand in the Nigerian sector of the basin. Also, therehave been reported cases of hydrocarbon production in theCretaceous and Tertiary sedimentary rocks in the SemeField offshore in the Benin Republic (Coker and Ejedawe,1987).

3. Materials and methods

The seismic data used in this study consist of 54migrated seismic reflection profiles covering an entire OilMining Lease (OML) located offshore of the Atlantic

Fig. 1. (A) Regional bathymetric map of Nigeria continental margin showing the locations of Avon, Mahin and Calabar canyons, and their correspondingfans (modified after Burke, 1972; Mascle, 1976 and Damuth, 1994). Avon canyon (study area) is located in Dahomey (Benin) basin the western part ofNiger Delta. B1 is the seismic lines covering the entire study area and well locations used for age determination on the seismic. Avon canyon is located inthe area shown with dotted lines. The expanded section and interpreted lines are shown in B2. Lines trending SE are located down canyon towards thedirection of sediment transport within the canyon, while lines trending SW are located perpendicular to the canyon.

288 S.O. Olabode, J.A. Adekoya / Journal of African Earth Sciences 50 (2008) 286–304

Ocean bordering southwestern Nigeria. (Fig. 1B1). Thereflection profiles that pass through the northeastern partof the OML where the canyons are located were selectedfor detailed analysis and interpretation (Fig. 1B2). Thedata sets were acquired from ChevronTexaco Nigeria.

The seismo-stratigraphic interpretation for this studyfollows the general procedure of Vail et al. (1977), Sangreeand Widmier (1979) and Mann et al. (1992). Special atten-

tion was paid to the seismic facies analysis and environ-mental interpretation. The parameters analysed includereflection configuration, amplitude, continuity and fre-quency. Each of the different generations of the canyonswas characterized by constant reflection discontinuity andchange in amplitude, frequency and configurations. Timevalues were digitized in relation to the shot points on theseismic data and related to geographic coordinates on the

Fig. 2. Simplified geological map of the Nigerian sector of Dahomey (Benin) Basin and the location of Avon canyon. The stratigraphy are composed ofboth the Cretaceous and Tertiary sediments as shown. The third well used for age determination and calibration on the seismic is named after the canyonas shown. Note the directions of longshore drift and the prevailing wind (compiled from Jones and Hockey, 1964; Ako et al., 1980; Burke, 1972;Whiteman, 1982).


location map. These values were loaded into computersoftware to generate various maps. Very few drilling datawere available for the area where the canyon was identified.However detailed biostratigraphic data of a well namedAvon-1 and located very close to the canyon were provided(Fig. 2). Biostratigraphic information from two other wells(Epiya-1 and Baba-1) drilled in the southeastern part of theOML was also available for study (Fig. 3). The biostrati-graphic information facilitated age determination on theseismic sections and regional correlation between the wells(Figs. 1–3).

4. Results and discussion

Four generations of submarine canyons were identifiedfrom the seismic data. Three ancient canyons have beenfilled with sediments, and the last is probably active at pres-ent. They are numbered I, II, III and IV in chronologicalorder. These canyons are all prominent on the seismic pro-files (profiles 01–07) that run both across the width andlongitudinal axes, except canyon I whose remnant couldonly be identified on the profiles. The various features ofthe canyons are shown on the seismic profiles. Similar ser-ies of old and modern canyons have been reported in theCenozoic strata of New Jersey continental slope (Pratsonet al., 2004).

4.1. Seismic facies analysis

4.1.1. Canyon I

This represents the first generation of ancient submarinecanyon in the area. Only the remnant (Martinsen, 2003) ofthis canyon could be identified on profiles 01, 03 and 04due to the effect of erosion caused by subsequent canyons.This remnant is characterized by very deep incision on allthe profiles where it was delineated. Because the canyonis preserved as small remnants in the seismic profiles, itwas not possible to give a detailed description of it seismicfacies. However, the seismic characteristics of the canyonremnant consist of moderate to high amplitude, variablefrequency and fairly chaotic reflections (Figs. 4a and b to7a and b). It is difficult to make the estimate of the two-way time (TWT) values with the contemporary seabed,because of the erosion occasioned by the formation ofyounger second generation canyon (canyon II). On profile04 the incision is up to 1.75 s TWT compared to the presentday seabed. The maximum measurable width of the canyonremnant from the seismic distance is 1.25 km (position ofFigs. 4a and b to 7a and b).

4.1.1.1. Interpretation. It is difficult to deduce the continu-ity of the seismic facies and the continuity of the sedimen-tary infill of the canyon. The seismic facies parameters

Fig. 3. Lithostratigraphic and age correlation of the three wells used to calibrate the seismic sections. The sedimentary section of Avon-1 shows theabsence of lower Tertiary sediments interpreted to have been eroded by Avon canyon. Unconformities represented by erosional features are identified inthe other two wells.

Fig. 4a. Un-interpreted seismic line 01.


suggest that the sedimentary infill is probably composed ofmoderately thick alternating beds of shales, sandstones andsiltstones. The reflections are truncated at the point of inci-sion of the canyon within the older rocks. This shows theeffect of deep channeling erosion during the formation ofcanyon I.

4.1.2. Canyon II

Canyon II was identified on all the seismic profiles inspite of being affected by later erosion. Significant amountsof canyon fill are preserved on both the SW and NE sidesof the canyon ( Figs. 4a and b to 8a and b). There are sharpdifferences in the seismic parameters of the sedimentary

Fig. 4b. Seismic profile 01 crossing the upper part of the canyons. Canyon I was identified using the remnants of preserved sediments. This is shown asdeep valley incision. Canyon II is shown as distinct discontinuous reflections between older and younger sediments as a result of erosion. Canyon III showsdiscordant reflections against canyon II. These reflections are chaotic on the NE and slightly parallel and gently dipping on the SW. Note the newlygenerated canyon IV with both V-shaped and U-shaped valleys.


Fig. 5b. Seismic profile 02. There is a change in the wall structure of canyon II from stepwise to spoon shaped. Note the different reflection characteristicsin the SW and SE parts of canyon III. The two valleys in canyon IV have almost merged completely causing width expansion and depth increase.



Fig. 6b. Seismic profiles 03 showing the continuity transparent facies in canyon II and the contrast between the wall morphology both on the SW and NEsides. Canyon IV has merged completely into a single channel. The reflection characteristics in canyon III shows that sediments are prograding into thecanyon from the two sides, suggesting that canyon III was essentially fed from the sides.


infill of canyon II and the pre-existing rocks in the area.They exhibit distinct reflection discontinuity, frequencyand configurations as well as change in reflectionamplitude.

Canyon II is better preserved than canyon I and iscomposed of transparent to semi-transparent and rarehigh amplitude reflections in the proximal part as shownon the majority of the dip lines (Figs. 4a and b to 8aand b). On profile 07 (Figs. 8a and b), which occurs atthe distal part, the reflections are of moderate to highamplitude and low to moderate frequency. Reflection con-tinuity is not uniform both across and along the canyon.Seismic profiles across the canyon show that the reflec-tions are fairly chaotic and discontinuous. Along the can-yon, they are fairly continuous and non-chaotic (Fig. 9).At the boundary of canyon II and III high amplitudereflections are easily observable. On profiles 01 and 03,the uneroded part of the canyon showed that its two wallsattained a horizontal width of approximately 5.4 km and3.2 km (Figs. 4a and b; 6a and b). Seismic evidence showsthat the total width of canyon II (before the subsequent

erosion attributable to canyon III) varies from 7.5 km to11 km.

4.1.2.1. Interpretation. Low amplitude and transparentreflections observed in canyon II could have been causedby the occurrence of any of the following: (i) beds too thinto be resolved in the seismic section; and (ii) a zone of onepredominant lithology, which could be sand prone or shaleprone (Mitchum et al., 1977; Sangree and Widmier, 1979).Although well information was not available to identify thecorrect lithology, the proximal transparent reflections areprobably a sand-prone facies. This facies grades impercep-tibly in the distal portion to siltstone and, possibly, shale.The chaotic facies observed across the canyon could havebeen caused by the sediments transported by mass-trans-port processes from the side of the canyon to its centre.

4.1.3. Canyon III

This is the last generation of ancient submarine canyonsrecognized in the seismic profiles 01, 02, 03 and 04 that cutthrough the entire width of the canyon. The effect of cut


Fig. 7b. Seismic profile 04 shows the prominence of canyon I valley incision, spoon shaped and stepwise wall morphology of canyon II and II. Note thedifference in the reflection characteristics of canyon III in the NE and SW. Infilling of sediments was probably uniform in the SW while in the NE it wasaffected by mass wasting.



Fig. 8b. Seismic profile 07 shows the SE side of canyons II and III. The seismic in canyon II shows a combination of transparent and few high amplitudereflections. Canyon III is characterized by regular oblique progradational and chaotic seismic patterns.


Fig. 9b. Seismic line 56 located in the down canyon direction displays the prominence of canyon II and III. The floor of canyon II as seen on the profile ismade up of irregular, curved and undulating surface. This was interpreted as complex floor development caused by differential erosion. The chaoticreflections in canyon III was interpreted as gravity induced sediments during canyon filling while the topmost regular reflections could be related to lateryounger sediments after the canyon has been filled.



and fill sedimentary process on the canyon is easily obser-vable on all the seismic profiles. The width of the canyonon profile 01 is about 10 km (Fig. 4a and b) and thisincreases offshore towards the southeast to about 15 kmon profile 04 (Fig. 7a and b) suggesting that this canyonis much wider in the offshore area. Profile 03 shows a por-tion of canyon III characterized by deep incision up to 1.2 sTWT. The seismic section across the canyon revealed bothoblique progradational and parallel to sub-parallel reflec-tion configurations. In all the seismic sections, the obliqueprogradational configurations show prominently on thesides of the canyon.

The southwestern side of canyon III is typically less cha-otic and shows parallel oblique configurations on some ofthe seismic lines (Figs. 4a and b; 5a and b). At a more distalpart as shown on profile 07 (Fig. 8a and b), the reflectionsare characterized by complex sigmoid to oblique configura-tions. Towards the boundary between canyon II and III thereflections are slightly chaotic and become continuous far-ther away from the boundary. The oblique progradationalfacies was separated from the facies on top by toplap termi-nations (Figs. 4a and b; 5a and b; 8a and b).

Parallel to sub-parallel reflections occur at the topmostpart of canyon III. They occur on all the sections cuttingacross the canyon, but they are well displayed on the pro-files where the erosive activity of canyon IV is less pro-nounced (Figs. 4a and b; 5a and b). Reflections exhibitmoderate to high amplitude, moderate to high frequency,as well as fairly continuous and regular configurations.

4.1.3.1. Interpretation. Oblique progradational configura-tions have been suggested to denote deposits associatedwith high sediment supply and high energy sedimentaryregime (Mitchum et al., 1977; Sangree and Widmier,1979). Based on the occurrence of similar reflection config-urations, the canyon III sedimentary infill can be inter-preted to indicate a sediment supply in a high energyregime. The variation observed in the reflection configura-tions can be ascribed to variable depositional processes inthe canyon. The southwestern side of canyon III with obli-que parallel reflections suggests a regular outbuilding ofsediment into the centre of the canyon with less mass-trans-port influence. The sedimentation in the northeastern sidewas probably affected by sliding and slumping, which isreflected in the chaotic reflections. Sigmoid facies are usu-ally associated with rising sea level or subsiding land levelcreating accommodation space (Sangree and Widmier,1979). The complex sigmoid to oblique configurations onprofile 07 (Figs. 8a and b) are interpreted as alternatingupbuilding and depositional bypass within a high energydepositional regime as sediments were fed into the canyoncentre from the sides. This implies that the sediments weredeposited in the centre of the canyon from its sides as therelative sea level rose. As a result of the development ofsteep margins of the canyon, the sediments were probablytransported by sliding and slumping. The fairly chaotic sig-moid to oblique reflection configurations of canyon III sed-

imentary infill support this interpretation. Sub-parallel toparallel reflection configurations delineated at the topmostpart of canyon III implies uniform rates of deposition.Reflection amplitude, continuity and cycle breadth suggestalternating layers of sandstones, siltstones and shales thatare laterally continuous.

The toplap observed in the seismic sections represents atop discordant relation whereby reflections terminateagainst an overlying surface as a result of non-depositionand minor erosion (Mitchum et al., 1977). This implies thatthe toplap termination represents the period when canyonIII was completely filled and that period was followed byanother period of non-deposition or minor erosion. Thissurface probably represents upper surface of canyon IIIbefore later infill under uniform rates of deposition. Thetoplap termination that separates the two reflection config-urations delineated in canyon III suggests that at a partic-ular time the canyon infill was at the same level with thesurrounding sediments. Subsequent rise in sea level possi-bly created accommodation space (Myers and Milton,1998) both in the canyon and the surrounding areas. Theaccommodation space was later filled with sediments,which made canyon III and the surrounding areas to beat same level.

4.1.4. Canyon IV

Bathymetric contour and surface perspective maps fromFigs. 10a and b obtained from computer plots combinedwith seismic profiles show that another canyon is probablybeing formed in the area. On all the profiles where the newcanyon axis is visible, the depth of the water column to sea-bed increases towards the offshore area. The V-shape mor-phology of the canyon becomes more pronounced fromprofile 01 to 04 (Figs. 4b, 5b, 6b and 7b). The maps pre-sented in Figs. 10a and b show that the presently activeAvon canyon is characterized by a major valley branch thatgoes to the east and is possibly oriented towards the nearbyMahin canyon. This provides an initial indication thatthere is a link between the two canyons particularly inthe distal offshore part.

4.2. Well log correlation with seismic

The lithostratigraphy as derived from the three wellsdrilled in the study area (Baba-1, Epiya-1 and Avon-1),consists of shale, siltstone, sand and sandstone depositedin a variety of environments. Avon-1 shown in Fig. 2located very close to the canyon was drilled to a total depthof 1463 m where it bottomed on the basement. Baba-1 andEpiya-1 wells were drilled to depths of 3272 m and 2931 m,respectively. In two (Avon-1 and Epiya-1) of the three wellson which detailed biostratigraphic analysis was done, refer-ence microfossils such as foraminifera, ostracods and pal-ynomorphs were employed for the analysis. In Avon-1,unlike the other well (Epiya-1), the lithologic section pene-trated by the well was characterized by scarce and poorlypreserved fauna that probably led to crude estimations of

Fig. 10a. Bathymetric contour of the study area derived from water depth on the seismic. It shows the active canyon (IV) in the area. The orientation issimilar to the ancient canyons (II and III) towards the SE direction.

Fig. 10b. Bathymetric orthographic surface map for canyon IV. Canyon size and V-shape morphology become more pronounced towards the SEdirection.


chronostratigraphic age. However, the analysis showedthat Avon-1 penetrated 384 m of Maastrichtian and1099 m of Miocene to Recent sediments. In this well, lowerTertiary sediments of Paleocene, Eocene and Oligocene

were not recognized. The Cretaceous section observed inEpiya-1 consists of Cenomanian to Lower Maastrichtiansediments, which are approximately 869 m thick. TheTertiary sediments range in age from Paleocene to Early


Pliocene and are approximately 1966 m thick. The uppersection of the well could not be dated as a result of poorpreservation of fossils. The oldest sediments recognized inBaba-1 were dated Maastrichtian with an approximatethickness of 380 m. Sediments observed in the Paleogenesection are Paleocene in age and are approximately 482 min thickness. Eocene and Oligocene sediments were notobserved in the Paleogene section of this well. All the Neo-gene sections from Miocene to Pleistocene are present andtheir total thickness is approximately 1654 m. The uppersection of the well which represents Quaternary sedimentswas not analysed as a result of scarce and poorly preservedmicrofossils.

The gaps that were recognized in the age of the sequencepenetrated by the wells are interpreted as unconformities,which were caused by erosional activities. Although thereis insufficient information on the erosional processes in thearea, Billman (1992) pointed out that subsurface strati-graphic interpretation within the Benin (Dahomey) basinwas complicated by numerous cut-and-fill features whichmade interpretation difficult. The occurrence of unconfo-rmities at different levels in the three wells supports this fact.The absence of Lower Tertiary sediments from Paleocene toOligocene in Avon-1 can be linked with the erosional activ-ities caused by the canyon. It is most likely that the missingsection of the sequence as observed in the seismic sections,represents the eroded portion in the lithostratigraphic sec-tion of Avon-1 (Fig. 3). If this is true, the early erosionalactivity that occurred in the canyon probably predates Mio-cene while the initial infilling took place during Miocene.This is supported by the biostratigraphic information inAvon-1, which showed the oldest Tertiary sediment overly-ing the Cretaceous section to be Miocene.

5. Canyon morphological features

Although it was difficult to identify the general featuresof canyons I and II due to erosion caused by canyon III,the following features were recognized based on the seismicfacies analysis and maps generated from the available data:(a) canyons plan view (b) deep channeling/valley incision,(c) step-wise and spoon-shaped canyon wall development(d) similar canyon orientations.

5.1. Plan view shape

Contour and perspective orthographic maps generatedfor the basal erosional surfaces of canyons II and III (Figs.11a and b; 12a and b), and bathymetric maps generated forcanyon IV (Figs. 10a and b) were examined to determinethe plan view of these canyons. Contour maps could notbe generated for canyon I because of the intense erosioncaused by canyon II.

The main course of all the submarine canyons extends inthe same southeast direction. Available seismic sections didnot cover the head segment of canyons II and III. Featuresthat mark the heads of the canyons such as V-shaped

notches and small linear troughs (Chuang and Yu, 2002;Yu and Chang, 2002) with steep walls have not been iden-tified. The head segments of canyon II and III may be pres-ent in the proximal landward direction outside the oil-mining lease (OML) being studied at present. Broadtroughs with varying widths and irregular walls areobserved in the seismic reflections for canyons II and III.These features are interpreted to be signatures of the mid-dle segments and mouth of the two canyons.

Two distinct parts were identified in canyon IV (activecanyon at present): the head and the middle segments.Available data did not cover the canyon mouth, which isin deeper offshore waters. The main canyon is V-shaped;it is flanked by small gullies on both sides. The gullies areflat bottomed and U-shaped as shown on seismic profiles01 and 02 (Figs. 4a and b; 5a and b). The shape of thesegullies contrasts with the main canyon shape; the gulliesprobably serve as feeder channels to the main canyon inthis head region. The head segment consists of a V-shapednotch, and small linear troughs, steep walls and relativelyshallow water depths. Further down towards the middlesegment the feeder gullies have disappeared merging withthe bigger main canyon as shown on the seismic profiles03 and 04 as the canyon loses its topographic expression(Figs. 6a and b; 7a and b). Such changes in canyon profiledown slope have been reported for a number of modernday canyons. These changes can be explained by two pro-cesses; these are small-scale processes such as bioerosionand large-scale processes such as slumping or turbidity cur-rent (Stanley and Kelling, 1978; Malahoff et al., 1982;Chow et al., 2001).

5.2. Valley incision

The morphology of canyons I and II is very difficult todetermine, because they have been intensely eroded duringthe formation of canyon III. Nevertheless, seismic evidenceshows that canyon I and III were characterized by verydeep channel cutting. Although the channel cutting is pres-ent on profiles 01, 02 and 03, it is conspicuous and moreeasily identified in profile 04 (Fig. 7a and b). The only traceof canyon I is the channel cutting, which has preservedremnants of the sediments which originally filled canyonI before the commencement of canyon II erosional activi-ties. On the same axis, canyon III shows channel shallowcutting. From the profiles, there is not enough evidenceto identify similar features in canyon II, except on profiles03, where a minor deep channel cutting occurs in the SSWof the canyon. Time value contour and surface ortho-graphic perspective maps for canyons II and III relativeto the contemporary sea beds generally show that canyonIII experienced deep channel incision when compared withcanyon II, but the width of the eroded area is larger in can-yon II (Figs. 11a and b). Seismic lines that run through thecanyons showed the form of the canyon floors. Theyrevealed a combination of simple and complex axial floorplans for canyon II, while the initial shape of canyon II

Fig. 11a. Time contour from seismic sections for canyon II relative to the contemporary sea bed. Contour values are in seconds. Negative time values areused to reflect the true morphology of the canyon.

Fig. 11b. Time orthographic surface map of canyon II with the contemporary sea bed. High time values at the canyon axis represent area where thesediments of the canyon have been completely eroded. The degree of incision is lower but the canyon width is higher when compared with canyon III.


determines the floor of canyon III. Canyon I floor couldnot be discerned because of erosion. The simple floor shapeof canyon II is composed of flat uniform floor as observedon one of the cross profiles sited near the centre of the can-yon. Profile 56 located towards the southern wall of thecanyon reveals a complex floor pattern (Figs. 9a and b).The floor of the canyon varies from slightly flat to curvedand undulating shape. The depth of erosion increases fromthe NW to the SE part that is from the proximal to the dis-tal offshore parts. Therefore, the truncated reflectionsobserved on the seismic sections and the occurrence ofcut-and-fill features are evidence of erosion of both consol-

idated and less indurated material of older rocks during thedevelopment of the canyon. Similar features are present inthe canyons identified in the USA Atlantic ContinentalSlope (Mitchell, 2005).

5.3. Canyon wall development

The walls of canyon II show a complex morphology asobserved from the various seismic profiles. Generally, theboundary on the SW side shows a relatively steep step-wisewall. Three different levels have been identified when thecanyon is viewed from the SW direction on profile 01.

Fig. 12a. This figure shows the time contour of canyon III relative to the contemporary sea bed.

Fig. 12b. Time orthographic surface map of canyon III relative to the contemporary sea bed. Degree of incision is higher and width is smaller whencompared with canyon II.


However, similar but less distinct feature is present on theopposite side, i.e. the NE direction of the canyon (Figs. 4aand b). The inclination of the steps decreases towards thecanyon axis, while the canyon wall terrace, formed as aresult of erosion, increases in width downwards; the widthof the topmost terrace is approximately 1 km, the middle2 km and the lowest 9 km. On profile 02 the wall morphol-ogy has changed slightly with the preservation of the lowestplatform on the SW, while the step-wise feature on the NEis irregular. Profiles 03 and 04 show that, although the step-wise wall has been completely changed to a spoon-shaped

wall on the SW flank, the step-wise feature is still preservedon the NE side wall with reduced number of steps (Figs. 6aand b).

The seismic profiles did not pass through the head andthe mouth of canyon III, so that their precise location can-not be defined. However, there is evidence that profile 01 iscloser to the head, while profile 04 is closer to the mouthbased on the widening of the canyon observed on the pro-file. The seismic expression shows two subtle canyon mor-phological features as follows: (a) a relatively U-shapedvalley with flat bottom; and (b) a gradual change to a gen-


tle step-wise wall. The first feature is present on profiles 01and 02 and is characterized by a gentle slope wall (Figs. 4aand b; 5a and b). On profile 02, the step-wise wall of thecanyon has started developing, although it is not distinct.Profiles 03 and 04 show clearly the full development ofthe canyon wall morphology. Two steps can be recognizedabove the valley incision at the base of the canyon (Figs. 6aand b; 7a and b). Here, the slope angle reduces downwardjust as the platform length increases in the same direction.

Four profiles show the wall development of canyon IVat its proximal end. The distal section of the canyon wasnot covered by the lines. On profile 01 two relatively shal-low valleys were identified. Their water depths vary from176 m to 353 m. The two valleys gradually merge asobserved in profiles 02–04 with the valley depth increasingto about 485 m. The initial two valleys are U and V shaped.Their walls are simple and almost uniform, with very steepwall in the V-valley when compared with the U-valley. Onprofiles 03 and 04 where the valleys have completelymerged (Figs. 6a and b; 7a and b), the canyon has changedfrom a combination of U and V valleys to a single V valleywith fairly deep incision. The walls of the single V-shapedvalley are equally simple and uniform with almost similarangles.

Different wall morphologies are common canyon fea-tures for which different genetic models have also been pro-posed in the literature. The formation of walls and terracesin submarine canyons documents the history of canyonincisions and evolution (Hagen et al., 1994; Deptucket al., 2003). Antobreh and Krastel (2006) described thewall of Cap Timiris Canyon, offshore Mauritania, and pos-tulated that it developed through a combination of pro-cesses including those involved in the formation of slideand slump structures, ‘point bar’ through meanders, ‘inner’or ‘confined’ levees and deep seated faults.

In canyon II of the present study area, which has welldeveloped walls with terraces, we propose that these ter-races, which may be appropriately described as ‘slide’ or‘slump’ terraces, probably formed during the following 3-stage event: (i) the process of down-cutting, incision andsubsequent erosion that prompted instability in the vicinityof the canyon walls as the sea level lowstand commenced,(ii) failure of the canyon walls both in the NE and SW endswhich followed the instability in stage (i); and (iii) a secondphase of intense erosion, which modified the failed canyonwalls. It has been shown that canyon terraces, formed bythe slide and slump mechanisms, are characterized by dis-turbed seismic facies (Friedman, 2000; Deptuck et al.,2003). However, this type of disturbed facies is not presentin the seismic profile of canyon II. The absence of suchfacies along the walls of canyon II is probably related tothe effect of subsequent erosion, which had eroded the dis-turbed sediments from the canyon walls.

The variation in the canyon wall morphology asobserved along the seismic profiles is attributable to theeffect of cycles of erosion that shaped the canyon walls overtime. Erosional activities were probably more intense in the

proximal end of the canyon in the SW as revealed by arapid change in the canyon II morphology in the area.

5.4. Orientation of the canyons

The contour and perspective maps generated for thecanyons show that two generations (II and III) of the can-yons are oriented in the southeast direction (Figs. 11 and12). Canyon IV (newly formed) is oriented towards thesame direction. To illustrate further the canyon morphol-ogy, the computer bathymetric perspective plot shows arelative uniform seabed except for the canyon axis. Thecanyon axis reveals that the proximal end increases inwidth progressively towards the southeast offshore. Thisnewly formed canyon is characterized by deep channel giv-ing rise to a V-shaped valley (Fig. 7a and b).

6. Canyon evolution and development

The seismic reflection profiles taken across the canyonsand along the canyon axis were examined to decipher theevolution and development of the canyons. The factorsthat were likely to be responsible for initiation and mainte-nance of these canyons include changes in relative sea level,mass-flow depositional processes, downward excavation bydown slope sediment flows and variation in sediment inputfrom land. These depositional controls influence the initia-tion and maintenance of the canyons and there was no evi-dence of structural control on the evolution of the canyonsobserved on the seismic lines.

6.1. Sea level change control

This section addresses the possible role of the sea levelchange on the evolution and development of the differentgenerations of submarine canyons that have been observedin the area of study. As stated by Vail et al. (1977, 1991),relative sea level change is the major factor responsiblefor the formation of sequence boundaries along continentalmargins, especially passive ones. A major fall in sea levelwill result in the exposure of the continental shelf and itssubsequent erosion. Intensive erosion on the shelf andupper slope leads to incision of submarine canyons anddevelopment of regional unconformities, resulting in theformation of sequence boundaries (Yu and Hong, 2006).During the lowering of the sea level, canyon channels aregenerally active causing significant erosion and deepdown-cutting into the sediment below. Rising sea level willlead to a reversal of such depositional phenomena, causingactive canyon channel down-cutting to shift to the land-ward part. Relative changes in the sea level cause variationsin the quantity and types of terrigenous materials to betransported to the basin.

If this model is applied to the area of study, the older sed-iments truncated by younger sediments were probablyeroded as a result of lowering of the relative sea level. Sealevel lowering subsequently led to active canyon channels,


which eventually culminated in erosion and deep sedimentcutting. Mann et al. (1992) proposed a similar model forthe Northern Green Canyon area in the Gulf of Mexico.

Regional correlation (Fig. 3) shows that the Avon can-yon cut through Cretaceous and lower Tertiary sediments.Significant erosion of canyon II and III started during theMiocene as shown on the regional age correlation of thereflectors (Figs. 4–8). It is difficult to compare canyon Iwith the contemporary seabed because it was the first can-yon formed in the area. Previous studies have shown that ahigh increase in submarine canyon development off thecoast of Africa took place about 30 Ma. This was the per-iod when the sea level was lowered in response to AntarcticIce sheet formation and about the time the present swelltopography of Africa began to develop (Burke, 1996;Burke et al., 2003). The combination of both sea level low-ering and uplift of the African continent at this time musthave contributed substantially to the formation of canyonsalong the African coast. Other well studied canyon alongthe African coast is the Congo canyon which cuts throughevaporites of Cretaceous age (Shepard and Emery, 1973).Since significant erosion and infilling of canyon II probablystarted in Miocene, one can infer that the development ofcanyon I commenced earlier than Miocene. This periodcould have coincided with the 30 Ma Oligocene age sug-gested by various workers.

Detailed biostratigraphic information obtained fromEpiya-1 and Avon-1 assisted in the determination of paleo-bathymetry and geologic ages of the sediments recognizedin the two wells. Avon-1 well (Fig. 3), which is very closeto the canyon shows that the Cretaceous sediments weredeposited in the neritic environments before the formationof the canyon. Subsequently, the deposition of other sedi-ments took place in the marginal marine to estuarine envi-ronments. This signifies a period of regression, whichprobably led to the sea level lowstand mentioned earlier.The absence of Paleogene sediments in the well probablyas a result of erosion in the canyon, made correlation diffi-cult. However, the age inference of 30 Ma deduced from acombination of this and previous studies show a period offalling relative sea level based on the correlation with theGlobal Cycle Chart of Haq et al. (1988). Lowstand periodsin the geologic history of sea level movement are usuallycharacterized by erosion and non-deposition on theshelves, as well as deposition of deep marine fans in thebasins (Vail et al., 1977). Therefore, the earlier develop-ment of Avon canyon possibly coincided with a period inthe global sea level history, when the sea level was at a low-stand. This probably facilitated erosion activities along theshelf that led to the formation of the canyon.

6.2. Sedimentary processes

In the earliest studies of submarine canyons, they wereinterpreted as submerged river beds during rising sea levelat the end of glaciations (Spencer, 1903; Shepard, 1934). Asnew techniques became available the origin of canyons was

fundamentally re-evaluated (detailed review is contained inthe work of Pratson et al., 1994). Popescu et al. (2006) pos-tulated two ideas as being responsible for the formation ofcanyons. These are: (i) sediment flow driven retrogressivefailure usually related to a sediment source on land; and/or (ii) retrogressive slide caused by slope destabilizationassociated with a variety of processes.

The complex morphology exhibited by the canyon walls,deep channeling, valley incision and the complex pattern ofthe canyon fill reflectors were used to interpret the influenceof sedimentary processes on the development of the can-yons. The steep and curved morphology of the wallsobserved on canyons II and III could have resulted fromslumping or sliding. The asymmetrical V-shaped small val-ley observed in canyon IV on profile 02 could have resultedfrom sliding on the SW part of the wall. Slumping and slid-ing of canyon walls and sediment spill-over are volumetri-cally important erosive agents for canyon formation (Mayet al., 1983; Chuang and Yu, 2002). This feature observedon profile 02, which is in the proximal landward directionprobably enhanced the effect of downslope erosion andresulted in widening the canyon on profiles 03 and 04 inthe distal direction.

Canyons II and III show cut and fill features in the flatlayers at the bottom of the canyon walls. The flat stepwiselayers of the canyon walls are interpreted as eroded layersthat were later infilled by sediments transported from theupper segments or by collapsed materials from the uppercanyon walls. Similar cut and fill features have been recog-nized in modern and ancient canyons. Yu and Chiang(1996) identified cut and fill features in Kaohsiung canyonand McGregor (1981) recognized the same features in theMiocene Wilmington Canyon in the England Shelf.

In Canyons I and II, deep channeling shows as U-shaped troughs. This reveals the lower segment of thetwo canyons where intense erosion had completely obliter-ated the V-shape of the upper segment. The U-shapedtroughs were formed on sediments derived from collapsedcanyon walls. Canyon IV displays V-shaped and U-shapedtroughs in several cross-sections that also show gentle can-yon walls (profiles 01–05). The presence of V-shaped andU-shaped troughs suggests significant down-cutting of theupper slopes immediately below the shelf edge that resultedin the initiation of canyon IV. It has been pointed out thatover-steeping of the upper slope near shelf edge results insediment failure, which is a common process in the initia-tion and development of submarine canyons (Fare et al.,1983; May et al., 1983; Chuang and Yu, 2002).

The complex fills in canyon III are well shown on theseismic profiles and this enhances good interpretation. Itwas difficult to delineate the fill pattern in canyon I,because only a remnant is preserved. Canyon II displays fillpatterns on profiles 01, 02, 03 and 04 at lesser degree as aresult of erosion that produced canyon III. Canyon IV isstill active and has no sediment infill. High to moderateamplitude, chaotic and hummocky seismic facies in canyonI are possibly indicative of mass movement deposits in the


form of slumps, slides, and debris flow that are derivedfrom both the sediment failure of the canyons walls andthe transported sediment from the upper canyon segment.Seismic facies of the sediments in canyon II are generallyuniform and continuous on the profiles. Reflections aretransparent to semitransparent with rare high amplitudesand are also barren of chaotic and hummocky seismicfacies. This suggests sedimentation under uniform condi-tions, possibly from terrigenous sources in the absence ofgravity-driven deposits.

Three types of sedimentation process can be interpretedfrom the complex pattern of the canyon fill reflectors incanyon III. These reflectors exhibit moderate to highamplitude and thick frequency top lap facies with a gentlydipping reflection configuration on the SSW part of profiles02, 03, 04 and NNE part of 07. This suggests a stable can-yon wall with progressive continuous building of sedimentsinto the canyon axis. The canyon wall on the NNE part ofprofiles 01, 02 03 and 04 is of high to moderate amplitudewith semi-continuous, chaotic and distorted seismic reflec-tions. This was interpreted as representing unstable canyonwall that experienced a sediment failure. The sedimentswere transported by a down-slope mass movement andthey accumulated rapidly. Mass-transport processes suchas slumping, sliding and debris flow could also have con-tributed significantly to the deposits. The third categoryof sedimentation pattern occurs in the topmost portion ofcanyon III. The reflections are parallel continuous andslightly even. They are highly discordant with the underly-ing dipping reflection facies. The boundary between themexhibits toplap terminations that developed on the canyonwalls (Figs. 6a and b; 7a and b; 8a and b). This facies sug-gests uniform deposits formed after the canyon had beenfilled. They probably represent pelagic to hemipelagicdeposits formed during a rise in the relative sea level.

The present day active canyon (canyon IV) exhibitsintense erosion. The erosive activity increases in the off-shore direction. The head of the canyon shows fairly U-shaped troughs (Figs. 4a and d; 5a and b) but in the distaloffshore area; these U-shaped troughs have been modifiedto slightly V-shaped troughs (Figs. 6–8). This gradual mod-ification in the trough shape suggests that a significantdown cutting has taken place as the intensity increasestowards the offshore area.

7. Sediment transport

Although it is difficult to estimate the quantity of sedi-ments that would have been eroded and transported to dee-per water in this area, it is clear that a very large volume ofsediments must have been removed and deposited some-where in the southeast offshore deeper waters. These sedi-ments were probably derived from two main sources,namely, (a) localized clastics derived from where the can-yons were formed; and (b) terrigenous sediments from thecontinental areas. The different stages and morphologyidentified in the wall development, canyon incisions and ter-

race formation (Figs. 4a and b; 5a and b; 6a and b) can beattributed to major surges in flow discharges. This suggeststhat the evolution of Avon canyon has been characterizedby large episodic sediment input. We associate such largeintermittent sediment supply to the canyon with periods ofsea level lowstands. In addition, the canyon could have beencoupled to the river systems during the sea level lowstands,and were thus likely kept very active (Antobreh and Krastel,2006). A fall in the sea level would have given rise to anincrease in river gradient (Babonneanu et al., 2002), thusrejuvenating the river systems to transport large quantitiesof sediments to the canyon head for onward transfer tothe deep sea. Burke (1972) suggested that four (Ogun, Osun,Ona, and Shasha) rivers may have fed the Avon canyon withsediments during the Pleistocene sea level lowering. Thestages of development of the Avon canyon walls and ter-races must have, therefore, been strongly influenced by theflow characteristics of these rivers.

The eastern and western re-entrants of the modern deltaare areas where opposing longshore drifts converge and gen-erate turbidity currents which produce submarine canyons(Burke, 1972; Petters, 1984). Both Burke (1972) and Petters(1984) suggested that the absence of beach sand ridges alongthe shore of Avon and Mahin canyons (Fig. 1) indicates thatthe two canyons are located in appropriate positions tochannel the sand down to the fans at the delta complex foot.The valley branch recognized in the bathymetric maps inFig. 10 supports the fact that sand materials carried fromthe northward longshore drift on the Niger Delta shore(Burke, 1972) through Mahin canyon are merged with thatof eastward longshore drift of Avon canyon where they areprobably channeled to deep offshore waters.

Seismic facies analysis has substantiated the removal ofsediments from canyons I, II and canyon III. Since the longaxes of all the four generations of the canyons (I–IV) areoriented towards the same southeast direction, most ofthese sediments would have been transported and depos-ited in this direction. In addition, canyons have beenknown to be conduits for sediment transport into deeperwaters (Lee et al., 1996; Poulsen et al., 1998; Pratsonet al., 2004). Therefore, these canyons would have servedas channel ways for transporting continental clastics duringtheir different developmental stages to the deep waters ofthe Atlantic Ocean.

8. Summary and conclusions

Seismic facies analysis in this part of the Benin (Daho-mey) Basin in southwestern Nigeria has revealed the exis-tence of three generations of ancient submarine canyons(I, II and III), the last (canyon IV) being currently devel-oped. These generations of canyon show that Avon canyonhas undergone several episodes of cut and fill. Canyon I iscomposed of moderate to thick amplitude, low to high fre-quency, and fairly chaotic seismic facies. Canyon II is dom-inated by transparent to semi-transparent seismic facieswith rare high amplitude reflections. The seismic facies


parameters recognized in canyon III are the most variable.Their configurations are oblique to progradational andparallel to sub-parallel. These two facies of canyon IIIare separated by toplap terminations, suggesting a periodof non-deposition. Generally, these reflections are of mod-erate to high amplitude, moderate to thick frequency, fairlycontinuous and regular. Interpretation of the seismic faciessuggests that the infills of the canyons are composed essen-tially of terrigenous sediments, which include uniformlythick or alternating beds of shales, sandstones and silt-stones. In addition, sediment outbuilding into the centreof the canyons has occurred especially in canyon III withsimultaneous rise in the sea level. This probably causedthe formation of sigmoid oblique configurations. Subse-quent modifications by gravity-driven processes as a resultof sediment failure along the canyon walls explain the cha-otic sigmoid configurations of the seismic facies. The direc-tion of progradation of sediments suggests that asubstantial sediment outbuilding occurred from the sides(NE and SW direction) of the canyon into the centre.

These canyons probably had developed as result ofvariation in the sea level and were maintained by: (i) grav-ity-driven depositional processes and/or (ii) downwardexcavation by down slope sediment flows. The wideningof the canyons was probably caused by mass wasting ofthe walls both at the NE and SW parts. Seismic reflectioncharacteristics reveal that canyon III experienced periodsof mass wasting (chaotic reflections) and other periodswhen mass wasting was insignificant (regular reflections).Bathymetric contours, surface maps and seismic profilesshow the morphological features of the canyons includingdeep channel/valley incision, V-shaped valleys, step-wiseand spoon-shaped wall development, and canyon orienta-tion in a persistent direction. The axial floor of the canyondisplays both simple and complex erosional surfaces. Agesof the reflectors from regional correlation show that trun-cated sediments include both Cretaceous and lower Ter-tiary rocks. It was difficult to determine the age ofcommencement of canyon I (the first generation canyon)as a result of intense erosion, but significant erosion andinfilling of canyon II started during the Miocene. Hence,the sedimentary infill of canyon II and III is probably Mio-cene and represents the younger sediments.

Although it was almost an impossibility to infer the sed-imentary infilling pattern for canyons I and II because oferosion, the seismic facies expression in canyon III hasrevealed complex sedimentary infill in the canyon. Grav-ity-driven deposits have occurred as a result of sedimentfailure on the walls of the canyons. Generally, the SWand NE walls of canyon III have experienced slight varia-tion in their development. The SW wall was not seriouslyaffected by gravity-driven processes and maintained aslightly stable wall, while the NE was affected, resultingin collapsed walls. The orientation of all the canyons istowards the southeastern offshore part of the basin andthese canyons were most probably conduits for sedimentsupply to deepwater areas of the Gulf of Guinea.

Acknowledgements

We thank ChevronTexaco Nigeria Limited and NigeriaDepartment of Petroleum Resources for releasing the dataand for permission to publish the research work. Specialthanks go to Mr. A.O. Akinpelu and Ms. Louise Lindenfor their full support and useful suggestions. The contribu-tions of Professors Kevin Burke and Pat Eriksson, as wellas another anonymous reviewer are greatly appreciated.Their suggestions have tremendously improved the qualityof the paper.

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Seismic stratigraphy and development of Avon canyon in Benin (Dahomey) basin, southwestern Nigeria

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