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  • Ranger Oil F:/cotedivo/westafricaconf/paper99 1

    A SEQUENCE STRATIGRAPHIC APPROACH TO EXPLORATION AND

    RE-DEVELOPMENT IN THE ABIDJAN MARGIN, COTE DIVOIRE

    Justin Morrison

    Ranger Oil, Walnut Tree Close, Guildford, Surrey, GU1 4US, UK.

    Juliette Tea, Bleoue NZalasse and Victor Boblai

    PETROCI, Imm.Les Heveas 14, Bd. Carde, B.P.V 194, Abidjan, Cte dIvoire.

    With contributions from:

    Geomark Research, Robertson Research, TimeTrax Ltd, and Western Geophysical

    Offshore West Africa 99 Conference and Exhibition

    March 23-25, 1999 Abidjan, Cte dIvoire

    ABSTRACT

    The Abidjan Margin, Cte dIvoire, has been the subject of exploration activity for forty years

    and has generated reasonable hydrocarbon success. From 1974-1992 the Espoir and Belier

    fields were produced with 31 mmbo and 20 mmbo of cumulative production respectively. More

    recently, as a result of improved fiscal terms established by the Ivorian government, several

    independent oil companies have come to the area to develop existing discoveries (Lion,

    Panthere, Gazelle, and Foxtrot), re-develop old fields (Espoir with 93 mmbo and 190 bcf of

    remaining recoverable reserves) and explore for new hydrocarbon traps.

    A sequence stratigraphic model for the Upper Cretaceous to Palaeogene sediments has been

    created for the Abidjan Margin. It integrates high resolution biostratigraphy, sedimentological

    analysis on the Upper Albian Espoir sandstone and regional seismic data. The sequence

    stratigraphic model will be used to predict reservoir presence in the Espoir field re-development,

    as well as exploration targets in the shallow and deeper water areas of the Abidjan Margin.

    New technologies such as integrated sequence stratigraphic models, deep water drilling, and low

    cost shallow water development have given oil companies new opportunities in this region of

    West Africa.

    GENERALISED STRATIGRAPHY

    The generalised stratigraphy of the Abidjan Margin is shown in Figure 1 and includes the main

    hydrocarbon plays in the Albian and Upper Cretaceous identified offshore Cte dIvoire

    (Chierici 1996 and Tucker 1992). Further speculative hydrocarbon plays exist in the Tertiary,

    lower syn-rift Early Albian-Aptian and pre-rift section.

    Pre-rift stratigraphy may include Devonian sandstones productive in the Saltpond Basin, as well

    as Permian and Carboniferous sands penetrated on the Tano High offshore Ghana.

    Rifting was initiated in the early Aptian and sands of this age are preserved on the Tano High

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 2

    offshore Ghana (Tucker 1992).

    The oldest stratigraphy penetrated offshore Cte dIvoire are Lower Albian syn-rift sediments.

    During the Apto-Albian times the basin was enclosed with the deposition of lacustrine

    claystones as well as turbidite and delta sandstone reservoirs. The Middle Albian turbidites are

    the reservoir in the Foxtrot gas field and Upper Albian turbidite/delta sandstones are the

    reservoir in the Espoir and Lion oil fields.

    After continental break-up at the end of the Albian, a series of delta and submarine fan systems

    deposited Upper Cretaceous sands across the Abidjan Margin. These include Cenomanian

    SubmarineChannel Sands+ Turbidites

    PASSIVE MARGINDOWN WARPING

    ALBIAN

    APTIAN

    END OLIGOCENESEA LEVEL FALL

    BREAK-UP &ASSOCIATED

    -TRANSPRESSION

    CONTINENTALDRIFT

    PRE RIFT

    MAIN PHASE OFRIFTING BETWEEN

    COTE D'IVOIREAND BRAZIL

    ?

    Submarine Fan

    TE

    RT

    IAR

    YC

    RE

    TA

    CE

    OU

    S

    RECENTTO

    MIOCENE

    EOCENE

    PALAEOCENE

    MAASTRITCHTIAN

    CAMPANIAN

    LOWERSENONIAN

    +TURONIAN

    CENOMANIAN

    JURASSIC

    TRIASSIC

    PERMOCARBON-IFEROUS

    DEVONIAN

    PRE-CAMBIAN

    BASEMENT

    Shallow Marine Sands

    Marine Sands

    LacustrineTurbiditic Sandstones

    Unknown Quality

    Sands Present InAccra - Keta andVoltaian Basin

    Early Rift TerrestrialSands Passing UpInto Shallow Lacustrine

    Incised Channel FillLacustrine / Marine Delta/ Turbidite Sandstones

    Figure 1 : Generalised Stratigraphy of the Abidjan Margin, Cte d'Ivoire

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 3

    reservoirs (Panthere gas field), Lower Senonian reservoirs (Belier oil field), Campanian sands

    (B-3X gas/condensate discovery), and the Maastrichtian reservoirs (the Ibex and Lion fields).

    Source rocks have been identified in the syn-rift Albian lacustrine shales and multiple Upper

    Cretaceous marine claystones.

    TECTONIC ELEMENTS AND STRUCTURAL HISTORY

    The Abidjan Margin shown in Figure 2 is predominantly an offshore basin running from the

    Cte dIvoire into Ghana. It is bounded to the east and west by major strike slip faults, the

    Romanche and St Pauls Fracture Zones respectively. To the north the basin is bounded by the

    Lagunes fault system made up of a series of east west normal faults down-thrown to the south.

    To the south the basin is bounded by the continental-oceanic crustal boundary recognised by

    Mascle et al (1996).

    The basin is believed to have begun rifting in the early Aptian (or Barremian) times. Although

    the oldest rocks penetrated offshore Cte dIvoire are of Lower Albian age, wells offshore

    Ghana have penetrated syn-rift Aptian stratigraphy as well as pre-rift Permian, Carboniferous

    and Devonian rocks.

    Continental break-up occurred at the end of the Albian, when a series of Albian highs were

    created which include the Foxtrot, Espoir and Quebec Highs. These highs are made up of

    numerous tilted fault blocks cut by faults trending westnorthwest-eastsoutheast. The highs are

    often bounded to the north by a series of en-echelon normal faults down-throwing into the

    Jacqueville Trough to the north. The highs are also bounded on their southern flank by a series

    Figure 2 : Tectonic Elements of the Abidjan Margin, Cte d'Ivoire

    PANTHERE

    LION

    FOXTROT

    Cote d'Ivoire

    GhanaGAZELLE

    KUDU

    ELAND

    IBEX

    NORTHTANO

    SOUTHTANO

    ABIDJAN

    GULF

    OF G

    UINE

    A

    ABYS

    SAL P

    LAIN

    MARG

    INAL R

    IDGE O

    F ROM

    ANCH

    E FRA

    CTUR

    E ZON

    ES O U T H T A N O

    S U B B A S I N

    SALTPONDPALAEOZOIC

    BASIN

    G R A N I T I C A N D M E T A M O R P H I CB A S E M E N T

    G R A N I T I C A N D M E T A M O R P H I CB A S E M E N T

    LAGU EN SA F ULT

    EAST TANOSUB BASIN

    G R A N D B A S S A M

    S U B B A S I N

    S T R E T C H E DC O N T I N E N T A L

    C R U S T

    3000

    2000

    1000

    100

    SHALLOWBASEMENT

    St. PAU

    L'S

    FZ

    WEST GRANDLAHOU

    DEPRESSION

    SOUTHGRANDLAHOU

    DEPRESSION

    H

    C O T E D ' I V O I R E

    A B Y S S A L P L A I N

    400'W

    400'W

    200'W

    200'W

    500'N

    400'N

    300'W

    300'W

    500'W

    500'W

    50 Kilometres

    OCEANIC-CONTINENTAL BOUNDARY (Mascle et al 96)

    ESPOIR

    QUEBECSOUTHBELIER

    JACQUEVILLETROUGH

    BELIER

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 4

    of en-echelon faults down-throwing to the south into the Grand Bassam Sub Basin.

    The en-echelon nature of the Top Albian Highs, their internal faults and the potential offsets

    seen on the Lagunes Fault, implies that transfer zones may be present trending northeast-

    southwest and related to the major strike slip faults bounding the basin to the east and west

    (Romanche and St Pauls Fault Zones).

    HIGH RESOLUTION BIOSTRATIGRAPHY

    Recent work by TimeTrax on behalf of Ranger Oil and Partners has concentrated on quantitative

    biostratigraphic analysis of palynoflora, microfossils and nannofossils from numerous wells in

    the Abidjan Margin. The analysis that TimeTrax have evolved (Janice Weston Pers. Com.) is

    similar to that published by Armentrout (1996) in the Gulf of Mexico, and is based on the

    analysis of the exact same size of sample at regular intervals down-hole. Each sample is

    measured for abundance and diversity of the individual species and histograms are then

    generated. Periods of maximum abundance and diversity are candidates for Maximum Flooding

    Surfaces. Where the abundance and diversity increases gradually up hole, a potential

    transgressive systems tract may be present often associated with significant changes in

    assemblages. Conversely, if the abundance and diversity dramatically decrease up hole, then a

    sequence boundary may be present.

    Using the abundance and diversity data in combination with diagnostic species allows Third

    Order Cyclicity to be recorded and tied to world wide sea level curves (Haq et al. 1987 & 1988).

    The biostratigraphic interpretation of a West Espoir well is shown in Figure 3, where the main

    Espoir sands are of Upper Albian age between the 98.25 Ma Maximum Flooding Surface and

    the 98 Ma Sequence Boundary.

    The recognition of sequence stratigraphic units can be particularly strong when two

    biostratigraphic disciplines are combined such as the use of microfossils and nannofossils. This

    has been especially useful in differentiating the Upper Cretaceous and Tertiary sequences.

    ESPOIR SANDSTONE RESERVOIR CORRELATION

    Correlation of West and East Espoir (Figure 4) indicates that the Espoir reservoir sandstones

    were predominantly deposited in the 98.25-98 Ma Highstand Systems Tract. It should be noted,

    however, that the upper sand reservoir unit XIII was deposited between the 98 Ma Sequence

    Boundary and the 97 Ma Maximum Flooding Surface and hence could be either a Lowstand or a

    Transgressive Systems Tract. The recognition of the different sequences will help to predict the

    changes in sandstone geometries across the Espoir field.

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 5

    Figure 3 : Quantitative Palynological Analysis of a West Espoir Well - Albian Section

    Figure 4 : Reservoir Correlation from West to East Espoir (Espoir Reservoir Zonation I-XIII)

    LITHOLOGYGR

    DE

    PT

    H

    SONICPALYNOMORPH

    ABUNDANCE

    PALYNOMORPH ABUNDANCE

    PALYNOMORPHDIVERSITY

    PALYNOMORPH DIVERSITY

    140

    100.5 SB99.5 MFS

    99 SB

    ? 101 MFS? 103 SB

    98.25 MFS

    98 SB

    0 00 40 700 50150

    DINOCYST

    DINOCYST

    PRASINOPHYTE ALGAE

    PRASINOPHYTE ALGAE

    FRESHWATER ALGAE

    FRESHWATER ALGAE

    MIOSPORE

    MIOSPORE

    1000

    ft

    West Espoir

    XIII

    XI

    X

    IX

    VIII

    VII

    VI

    V

    IV

    III

    II

    I

    XII

    East Espoir

    10

    0 f

    t

    00

    80

    GR GR

    80

    98 SB

    96.5 SB97 MFS

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 6

    ESPOIR SEDIMENTOLOGY

    In March 1998 the Espoir group performed a reservoir study on core from four wells in block

    CI-26 (wells C1-1X, C1-3X, A-1X, and A-3X). The study was directed at sedimentological

    logging, reservoir quality and petrological analysis.

    The sedimentary log from a West Espoir well which covers the 98 Ma Sequence Boundary is

    shown in Figure 5a, where the lithology changes from sandstone (commonly friable, micaceous,

    carbonaceous, with metamorphic fragments, siderite clasts and locally bioclastic debris) up-hole

    into mudstone (alternating laminations with differing colour, calcite content and swelling clays).

    A sedimentary core log from deeper in the West Espoir well (Figure 5b) shows sandstone beds,

    commonly structureless, with occasional dish and pipe structures indicating de-watering. The

    sands often exhibit scoured bases and include rip-up clasts.

    The Espoir sands have been interpreted as being deposited in a lacustrine delta front to shelf

    slope environment. The latter includes Bouma Sequences tbc and tab.

    Figure 5a: Sedimentary Log - West Espoir Well -

    Top Espoir Reservoir

    Figure 5b: Sedimentary Log - West Espoir Well -

    Lower Espoir Reservoir

    S

    S

    S

    S S

    S

    S

    S

    S

    S S S

    S

    S S

    S

    S

    S

    S

    S

    S

    M

    M

    M

    S

    S

    M

    M

    M

    M

    M

    M

    M

    Py

    Py

    M

    M

    LITH

    SAND

    SIL

    TY

    CL

    AY

    AN

    D/

    CO

    AL

    GRAIN SIZE

    Thick beds are commonlystructureless or displaydewatering dish structuresand pipes

    Possible Bouma sequences

    Bases are commonly sharp,scoured and locally grooved

    Thin beds are commonlyplanar or current rippled

    Abundant plant debris, micaand claystone rip-up clasts

    VV Red

    PyM

    M

    M

    M

    M

    M

    M

    M

    M

    M

    M

    M

    M

    M

    M

    S

    S

    S

    S

    S

    S

    SS

    S

    S

    Fe

    MUDSTONE :

    CLAY :

    Alternating laminations withdiffering :-colour, calcite content andswelling clays

    Local slumps andsynsedimentary fractures

    MINOR LIMESTONES & SANDSTONES : Common current ripples, rarewave ripples and common loadstructures

    SANDSTONE : Commonly friable, micaceous,carbonaceous,metamorphic fragments,siderite clasts and locallybioclastic

    Locally cross-bedded, planarlaminated, current and waveripples or slumped, dishstructures, scouredbases and locally loaded

    10ft

    10f

    t

    98 SB

    LITH

    SAND

    SIL

    TY

    CL

    AY

    AN

    D/

    CO

    AL

    GRAIN SIZE

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 7

    REGIONAL RESERVOIRS

    Regional reservoirs have been identified in the Middle Albian, Upper Albian, Cenomanian,

    Lower Senonian and Maastrichtian (examples of the regional reservoirs are shown in Figure 6).

    The Middle Albian sandstone reservoir can be seen in Figure 6a, with a gross interval of 4381 ft,

    net sandstone reservoir of 2989ft and average porosity of 15%.

    The Upper Albian sandstone reservoir can be seen in Figure 6b with 935ft of gross section, net

    sand of 409 ft and average porosity of 21%. This well also has net pay of 278ft with average

    porosity of 22.5% and average water saturation of 28%.

    Cenomanian reservoirs have been identified on the Quebec High (Figure 6c), with gross section

    of 447ft, net sandstone reservoir of 259ft and average porosity of 20%. A Lower Senonian

    sandstone reservoir from the Belier Field is shown in Figure 6d, with 160ft of gross section, 72ft

    of net sandstone reservoir and average porosity of 21%. This well had 59ft of net pay, with

    average porosity of 21% and average water saturation of 39%.

    The Maastrichtian reservoir section shown in a south Belier High well (Figure 6e) has good

    reservoir potential with 653ft of gross section, 329ft of net sandstone reservoir and average

    porosity of 21%. It should be noted that a 32ft hydrocarbon column was identified in this well.

    Further potential sandstone reservoirs have been noted in the Aptian, Palaeocene, Eocene and

    Oligocene.

    SEISMIC SEQUENCE STRATIGRAPHY

    Regional seismic lines running north-south through the Central Abidjan Margin can be seen in

    Figures 7a &7b. The West Espoir Field (Figure 7a) is located in the first tilted fault block at the

    shelf break (Grillot et al. 1991), with a fault block on trend with the Foxtrot Field to the south

    and the Jacqueville Trough to the north. The Top Albian Unconformity (96.5 Ma Sequence

    Boundary) can be observed eroding the Espoir sandstone reservoir both to the north and south of

    the Espoir field.

    The Western seismic line in Figure 7b runs north-south into deeper water. It can be observed

    from this line that Apto-Albian syn-rift reflections are present at the southern end of this line,

    considerably further offshore than previously recognised. Secondly, there is a clear Cenomanian

    basin, here named the Grand Bassam Sub Basin, which is present to the south of the shelf break

    created during continental break up at the end of the Albian. Deepwater hydrocarbon plays

    present in the Grand Bassam Sub Basin include Apto-Albian syn-rift sandstones in the intra-

    basinal highs, Cenomanian and younger sand drapes over intra-basinal highs, Albian sands in

    tilted fault blocks and multiple sandstone pinch-outs on the southern side of the shelf break (in

    the Cenomanian, Lower Senonian and Maastrichtian).

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 8

    Gross 160ftNet Sand 72ftAv. Porosity 21%

    Net Pay 59ftAv. Porosity 21%Av. Sw 39%

    DST#1 6502-6563ft

    4045BOPD(33API)+ 1.7 mscf

    GR

    Porosity x Sw

    Porosity0 0

    0

    150 0.3

    0.3

    GR Porosity0 0150 0.3

    Gross 447ftNet Sand 259ftAv. Porosity 20%

    93 SB

    GR

    Porosity x Sw

    Porosity0 0

    0

    150 0.3

    0.3

    Gross 935ftNet Sand 409ft

    Av. Porosity 21%

    Net Pay 278ftAv. Porosity 22.5%Av. Sw 28%

    Seven DSTs run between 6530-7040ftWith Flow rates up to

    4959BOPD

    GR

    Porosity x Sw

    Porosity0 0

    0

    150 0.3

    0.3

    Gross 4381ftNet Sand 2989ftAv. Porosity 15%

    GR

    Porosity x Sw

    Porosity0 0

    0

    150 0.3

    0.3

    Gross 653ftNet Sand 329ft

    Av. Porosity 21%

    FIT #2 at 5743ftGas & Oil, (41API)

    Net Pay 32ftAv. Porosity 21%Av. Sw 47%

    100

    ft

    100

    ft 100f

    t

    100f

    t10

    00ft

    Figure 6b : Upper Albian Sandstone

    Figure 6c : Cenomanian Sandstone Figure 6d : Lower Senonian Sandstone

    Figure 6e : Maastrichtian Sandstone

    Figure 6 : Regional Reservoirs of the Abidjan Margin, Cte, dIvoire

    Figure 6a : Middle Albian Sandstone

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 9

    Figure 7a : Reprocessed 1980 Seismic through the Central Abidjan Margin & Espoir Field

    Figure 7b : Western 1997 Seismic Line across the Grand Bassam Sub Basin

    6146m

    1 s

    ec

    on

    d

    S N

    WEST ESPOIRJACQUE VILLE

    TROUGHFOXTROT FAULT BLOCK

    Base Miocene67 SB68 SB79 SB83 SB93 SB96.5 SB99 SB

    1

    se

    co

    nd

    S N

    Base Miocene67 SB68 SB79 SB83 SB93 SB96.5 SB

    1

    se

    co

    nd

    1 s

    ec

    on

    d

    INTRA BASINAL HIGHGRAND BASSAM

    MARGIN

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 10

    CRETACEOUS CHRONOSTRATIGRAPHY

    An outline of the Cretaceous Chronostratigraphy of the Abidjan Margin is shown in Figure 8.

    The chronostratigraphy has been based on quantitative biostratigraphic analysis of shallow water

    wells, tied to seismic in shallow and deep water areas of the basin.

    Numerous sequence boundaries have been identified which are related to erosion at the basin

    margin, shelf break and occasionally at the intra-basinal highs. The 96.5 Ma sequence boundary

    (taken as the end of the Albian by TimeTrax) is a major unconformity which marks the

    continental break-up and the change from an isolated basin to more open marine conditions. A

    second significant unconformity is the 83 Ma sequence boundary which marks a dramatic

    deepening of the Abidjan Margin.

    In the Central Abidjan Margin, potential sandstone reservoirs exist in two Middle Albian third

    order cycles (103-99 Ma), Upper Albian (98.25-98 Ma Highstand Systems Tract), three

    Cenomanian third order cycles (96.5-95.5, 95.5-94 and 94-93 Ma), Campanian third order cycle

    (83-80 Ma) and three Maastrichtian / Upper Campanian third order cycles (75-71, 71-68 and 68-

    67 Ma).

    ALBIAN

    CENOMANIAN

    TURONIAN

    CONIACIAN

    SANTONIAN

    CAMPANIAN

    MAASTRICH-TIAN

    STANDARDSTRATIGRAPHY

    SEQUENCECHRONOSTRATIGRAPHY

    (Haq et al)GRAND BASSAM SUB BASIN GRAND BASSAM

    SHELF MARGINESPOIR HIGH JACQUEVILLE

    TROUGH

    INTRABASINHIGH

    FOXTROTFAULTBLOCK

    ESPOIRFIELD

    RELATIVE CHANGE OFCOASTAL ONLAP

    Landward Basinward

    1.0 0.5 0

    ST

    AG

    ES

    EX

    TEN

    T O

    FS

    TA

    GE

    STR

    AT

    OTY

    PE

    SE

    QU

    EN

    CE

    BO

    UN

    DA

    RY

    AG

    E

    U

    U

    U

    U

    U

    74

    84

    88

    89

    92

    96

    U68 68

    LagunesFault

    71 71

    75 75

    77.5 77.5

    79 79

    80 80

    83 83

    85 85

    87.5 87.5

    88.5 88.5

    90 90

    91 91

    93 9394 94

    95.5 95.5

    96.5 96.5

    9899 99

    103 103

    106 106

    107.5 107.5

    U

    M

    M

    M

    L

    L

    L

    L

    L

    L

    L

    Marine Claystone

    Sandstone

    Lacustrine / Paralic Claystone

    Limestone

    Onlap

    Erosional truncation

    Fault

    Figure 8 : Outline of the Cretaceous Chronostratigraphy of the Abidjan Margin, Cte d'Ivoire

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 11

    CONCLUSIONS

    The Abidjan Margin, Cte dIvoire is a proven hydrocarbon basin with small to medium sized oil

    and gas fields discovered to date. There are numerous proven reservoirs including the Albian,

    Cenomanian, Lower Senonian and Maastrichtian sandstones. Further potential sandstone

    reservoirs exist in the Aptian, Palaeocene, Eocene and Oligocene.

    Future hydrocarbon activity will be directed at developing existing reserves and exploration for

    new oil and gas reserves. The development activity will include the Espoir Field re-development

    in block CI-26 with estimated remaining recoverable reserves of 80 mmbo and 175 bcf. Other

    ongoing and future developments include the Foxtrot, Gazelle, Ibex, Eland and Kudu oil and gas

    fields.

    The future exploration will be directed at small to medium sized hydrocarbon prospects in

    shallow water (30-100 mmbo recoverable) and large prospects in the deep water (200-1000

    mmbo recoverable).

    It is noted that a greater understanding of the Cretaceous sequence stratigraphy of the Abidjan

    Margin will improve reservoir prediction for both development and exploration projects in the

    Cte dIvoire.

    ACKNOWLEDGEMENTS

    The authors of this paper would like to thank the management of Ranger Oil and PETROCI for

    allowing publication of this data. This paper was reviewed by Dave Pratt and David Ellis at

    Ranger Oil and Janice Weston at TimeTrax. We are indebted to Steve Hedley and Roy Rees

    Williams who produced the diagrams for this paper. We would also like to thank the support of

    our partners: Addax Petroleum Cte dIvoire Limited, Gentry International (Cte dIvoire) Inc.,

    Clyde Expro plc, Pan Canadian, Societe Nationale dOperations Petrolieres de la Cte dIvoire,

    Svenska Petroleum Exploration AB, T.C. Petroleum Inc., and Tullow Cte dIvoire Limited.

    REFERENCES

    Armentrout J.M. (1996), High resolution sequence biostratigraphy: examples from the Gulf of

    Mexico Plio-Pleistocene, Eds: Howell, J.A and Aitken J.F., High Resolution Sequence

    Stratigraphy: Innovations and Applications, Geological Society Special Publication No. 104,

    pages 65-86.

    Chierci M.A. (1996) Stratigraphy, palaeoenvironments and geological evolution of the Ivory

    Coast-Ghana Basin. Elf Memoir 16 pages 293-303.

    Grillot. L.R., Anderton P.W, Haselton T.M. and Dermargne J.F. (1991), Three-Dimensional

    Seismic Interpretation: Espoir Field Area, Offshore Ivory Coast AAPG Memoir 42, Ed: A.

    Brown, pages 214-217.

  • Ranger Oil F:/cotedivo/westafricaconf/paper99 12

    Haq, B.U., Hardenbol, J. & Vail, P.R. (1987) Chronology of fluctuating sea-levels since the

    Triassic. Science, Vol.235, pages 1153-1165.

    Haq, B.U., Hardenbol, J. & Vail, P.R. (1988) Mesozoic and Cenozoic chronostratigraphy and

    cycles of sea-level change. In: Sea-level changes: an Integrated Approach. Special Publication,

    Society of Economic Paleontologists and Mineralogists, Tulsa, Vol.42, pages 40-45.

    Mascle J., Lohmann, G.P., & Clift, P.D. (1996) Introduction. In: Proceedings of the Oceanic

    Drilling Program, Vol.159, pages 5-16.

    Tucker J.W. (1992) Aspects of the Tano Basin Stratigraphy Revealed by Recent Drilling in

    Ghana. Geologie Africaine, Ler Colloque de Stratigraphie et de Paleogeographie des Bassins

    Sedimentaires Quest-Africains, Libreville-Gabon 6-8 Mai 1991, Memoire 13, Ed: Curnelle,

    pages 153-159.