Seismic Geohistory and Differential Interformational Velocity Analysis in the Anambra Basin, Nigeria

p p p Composite 133 lpi at 45 degrees

EARTH SCIENCES RESEARCH JOURNAL

Earth Sci. Res. J. Vol. 14, No. 1 (June 2010): 88-99

SEISMIC GEOHISTORY AND DIFFERENTIAL INTERFORMATIONAL VELOCITY ANALYSIS IN THE ANAMBRA BASIN, NIGERIA

Ekine, A.S. 1 and Onuoha, K. M. 2 1 Department of Pure and Applied Physics, University of Port Harcourt, PortHarcourt 2 Department of Geology, University of Nigeria, Nsukka, Nigeria [email protected]

ABSTRACT The methods of seismic geohistory analysis and differential interformational velocity analysis have been applied using data from some interpreted seismic sections within the Anambra basin. These two techniques for basin analysis have been applied in the basin in an attempt to aid the identification of anomalous velocity zones. Results from the seismic geohistory analysis indicate that some faults arising probably from compressional stresses, due to the upliftment of the Abakaliki anticlinorium, were observed to be significant mostly in the northern and southeastern regions of the basin. These faults which originated in the Santonian are probably related to the first folding episode in the evolution of the Benue Trough. The Maestrichtian / Campanian faults observed towards the north of Anambra River-3 well may also have been influenced by these stresses or are directly related to the Post-Maestrichtian folding episode in the Benue Trough. The fault system KP identified on the seismic section is a Pre-Eocene event which cuts across from the south of Okpo-1 and Nzam-1 to the north of Iji-1 well. Sediments to the north of Nzam-1 well site have experienced more faulting during the Lower-Maestrichtian times. Fault systems that occurred after the Paleocene times are more prominent in the southern parts of Nzam-1 towards Iji-1 well sites. Generally most of the major faults occurred in the Paleocene. The major ‘DIVA’ anomaly observed southeast of Anambra River-1 well corre - lates with the zone of overpressures within which liquid hydrocarbon, water and gas have been discovered in the basin. The Maestrichtian to Paleocene sediments in the southern and mainly in the southwestern sector of the Anambra basin should be the major sedimentary strata with liquid hydrocarbon potentials, whereas the Lower Cretaceous and particularly the Santonian sediments exhibit the highest potentials for gaseous hydrocarbons.

Key words : seismic geohistory; seismic section; differential velocity; Anambra basin.

RESUMEN Los métodos de Análisis Sísmicos histórico y análisis de velocidad interformacional diferencial se han aplicado usando datos de algunas secciones sísmicas interpretadas de la cuenca Anambra. Estas técnicas se han aplicado en un intento de ayudar a la identificación de zonas de velocidad anómalas. Los resultados del Análisis Sísmico histórico indican que algunas fallas probablemente surgen de esfuerzos de compresión, debido a la elevación del Anticlinorio Abakaliki, importantes sobre todo en las regiones norte y el sureste de la cuenca. Estas fallas que tuvieron su origen en el Santoniano, están probablemente relacionados con el primer episodio de plegamiento en la evolución de la depresión de Benue. Las fallas maestrichtiense /

Manuscript received: 17/12/2009 Accepted for publication: 15/05/2010

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SEISMIC GEOHISTORY AND DIFFERENTIAL INTERFORMATIONAL VELOCITY ANALYSIS IN THE ANAMBRA BASIN, NIGERIA

Campaniano observadas hacia el norte del pozo Anambra River -3, también pueden haber sido influenciadas por estos esfuerzos o están directamente relacionados con el episodio de plegamiento post-maestrichtiano de la depresión de Benue. El sistema de fallas KP identificado en la sección sísmica es un evento pre-Eoceno que atraviesa desde el sur de Okpo-1 y Nzam 1-al norte del pozo Iji-1. Los sedimentos al norte de la ubicación del pozo Nzam-1 han experimentado mayor fallamiento en el maestrichtiano temprano. El sistema de fallas producido después del Paleoceno es más prominente en las partes meridionales desde Nzam-1 hacia el pozo Iji-1. En general la mayoría de las principales fallas se produjeron en el Paleoceno. La gran anomalía ‘DIVA’ observada al sudeste del pozo Anambra River -1 se correlaciona bien con la zona de sobrepresiones en la que hidrocarburos líquidos, agua y gas han sido descubiertos. Los sedimentos que van del maestrichtiano al Paleoceno en el sur y principalmente en el sector suroccidental de la cuenca Anambra deberían ser los principales estratos sedimentarios con potencial de hidrocarburos líquidos, mientras que los del Cretácico Inferior y en particular los sedimentos Santonianos exhiben el más alto potencial de hidrocarburos gaseosos. Palabras clave : Geohistoria sísmica, sección sísmica; velocidad diferencial; cuenca Anambra.

Introduction between the Onitsha environs in Anambra State to the Loko area in Benue State of Nigeria. Its southwestern tip is about The Anambra Basin has been identified as one of the major 160 km wide, while the northeastern extreme is about 48 km in-land sedimentary basins in Nigeria. It is bounded on the wide (Whiteman, 1982) (Fig. 1). east by the Abakaliki anticlinorium and on a south-westerly direction by the Benin hinge-line, while the southern ex- The geologic history of the basin has been that of nearly treme is marked by the upper limits of the Eocene growth continuous subsidence and sedimentation, and had therefore faults of the Niger Delta (Merki, 1972). The basin is about remained largely unaffected by major tectonism. The strati- 300 km long in a northeast – southwest direction, extending graphic successions in the Anambra Basin and environs

Cratonic Stable or block foulted Basinal Orogenic Hinge line Site of shoal carbonate Oil, tar seapage

Transgressive Regregressive Phose Phose Imo Shale Ameki Fm. Nkporo Shale Mamu, Ajali Nsukka

Lower Campanian - Lower Eocene

Figure 1. Tectonic map of Southern Nigeria (adapted from Murat 1970).

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EKINE, A.S. AND ONUOHA, K. M.

have been discussed by several authors which include Again in recent times, the great advances in exploration (Reyment, 1965; Murat, 1972; Adeleye, 1975; Peters, 1978; tools, techniques and experiences have compelled and moti - Whiteman, 1982; Hoque and Nwajide, 1984; Agagu et al , vated many explorationists to shift their exploration empha - 1985). sis from the quest for simple structural to stratigraphic traps. The difference between structural and stratigraphic traps can The reconstruction and the analysis of the geologic his - either be quite clear or so subtle for differentiation where tory of a sedimentary basin are very significant for the analy - sis of the subsidence and thermal histories of such a basin. both traps play significant roles as trapping mechanisms. This method of reconstruction or geohistory analysis has The use of seismic techniques for the identification and defi - been applied by many authors using stratigraphic and other nition of stratigraphically trapped hydrocarbons has been geophysical data (Angevine and Turcotte, 1981; Middleton, made possible by the introduction of sophisticated packages 1982; Onuoha, 1985; Onuoha and Ekine, 1999; Ekine and and approaches in seismic data interpretation. The differen - Onuoha, 2008). However, in recent times, geohistory analy - tial interformational velocity analysis, originated by Neidel sis has been successfully applied to seismic data (Middleton and Beard (1984), attempts to delineate anomalous low ve - and Falvey, 1983; Middleton, 1984). Seismic geohistory locity zones by tracking laterally the interval velocity (stack - analysis is a technique whereby the geologic history of a ing velocity) along a seismic profile by using the travel times sedimentary basin is reconstructed in terms of two-way for the reflectors that have been identified. These two tech - travel times from observed seismic reflection data. This niques for basin analysis have been applied in the Anambra method provides a means of rapidly reconstructing the geo - basin using some interpreted seismic sections (see Fig. 2). logic history from an interpreted seismic section. This attempt is to aid in the identification of anomalous ve -

6°32’E 6°40’ 7°00’ 7°20’E

ALD-1 7°00’

ATU-1

OPL 447

129/128-776/77-18

ANR-3 ANR-1 ANR-2 ODR-1

447-84-216 6°30’ NZAM-1 ALO-1 OKP-1 AMA-1

44-84-259 IJI-1

AJR-1 447-84-248 ALO-1 447-84-217 AKU-1

OPL 447

0 20 km

6°00’N

Figure 2. Location of Seismic Sections.

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SEISMIC GEOHISTORY AND DIFFERENTIAL INTERFORMATIONAL VELOCITY ANALYSIS IN THE ANAMBRA BASIN, NIGERIA

’ ’ locity zones which in normal circumstances could be attrib - where z1 and z2 are the depths to the top sedimentary ’ uted to the occurrence of reefs, sand bars, geomorphic fea - units when z1= z 1 is at the surface. tures and other features commonly associated with Substituting equation (2) into equation (3) gives stratigraphic traps. Also the study will demonstrate the ap - plicability of these non conventional techniques in the 1 1æT- 2 b ö 1 = + kç ÷ n (6) search for the subtle traps. ç ÷ F(T ) F 0 è 2a ø

and equation 5(b) now becomes Methodology 1 æT’-2 b ö n 1 é æT ’ -2b öù P-waves travelling through sedimentary layers are found to ç 2 ÷ - + F ç 2 ÷ = ’ ç ÷ 1n ê 1 0 k ç ÷ú Fn( T1 , T 1 , T 2 ) (7) obey a power law equation given by Acheson (1981) as è 2aø k ëê è 2a øûú

t= azn + b (1) with

where t = the one-way travel time; z = depth to reflector; 1 1 1 æT’-2 b ö n æT ’ -2b ö næT -2b ö n ’ ç 1 ÷ ç 2 ÷ ç 1 ÷ a, b and n = constants. Fn( T1 , T 1 , T 2 ) = ç + ç - ç è 2a ø÷ è 2 a ø÷ è 2a ø÷ é æT ’ -2b ù (8) Consequently, the two-way travel time T can be ex - ç 2 ö 1 ê 1+F 0 k ÷ ú é ù 1 ç 2a ÷ 1 ê æT ’ -2b ö n ú pressed as - 1n ê è ø ú -1n 1 + F k ç 1 ÷ k ê æT ’ -2b ö ú k ê 0 ç 2a ÷ ú +F ç 2 ÷ ê è ø ú n ê 1 0 k ç ÷ ú ë û T = 2(a z + b) (2) ëê è 2a ø ûú

According to Falvey and Middleton (1981), and ’ ’ ’ T1 and T2 are the reflector times when T1= T 1 is at the Middleton, (1984), the behaviour of porosity Fz with depth z surface. can be sufficiently approximated by the expression ’ ’ (T2, T 1 and z 2 have been defined in the equations as re- 1 1 = + kz (3) quired) F(z ) F 0 Equation (8) is the basis for the seismic geohistory anal- ‘ ‘ ysis. This equation is solved numerically for T 2 , with T 1 = 0 where F0 = the depositional porosity and k = a constant. The above expression has been used in this study as the main at the surface for the first instance. Fig. 3 is a schematic rep- thrust of the study is not the evaluation of reservoirs as in resentation of the process of seismic history analysis. For Ehrenberg et al ., (2009). subsequent reflectors and cycles a similar procedure as em - ployed for the burial history reconstruction was used in this To decompact and reconstruct the geologic history of a study (Ekine and Onuoha, 2008). Using the two-way travel sedimentary basin from interpreted seismic section, a proce - time versus depth plots obtained at Anambra River-1, Oda dure similar to burial history reconstruction is applied. In River-1 and Nzam-1 well sites (Figs. 4a, b, and c), a this case depths are replaced with arrival times. According to time-depth relation was obtained for the basin. Sclater and Christie (1980), the height of sediment grain h sg This relation can be expressed as for a unit cross-sectional area between the intervals z 1 and z 2 is given by the expression t = 0.46 z 0.83 + 18.99 (9)

z 2 where t is in milliseconds and z is in feet. hsg=ò[1 - F ( z ) ] dz (4) z 1 Seismic geohistory analysis was carried out along three and interpreted seismic sections which were calibrated at Iji-1, Nzam-1 and Okpo-1 wells. The generalized porosity-depth

’1 ’1 ’ relations were obtained from each well along individual z2=+- hstg z 11n( 1 +F 01 k z )( +1n 1 + F 02 k z ) (5a) k k seismic line and not a generalized relation for the whole ba - sin. This approach significantly reduced the possible errors or associated with simple assumed basinal generalized func - 1 1 tions and thus enhances the representativeness of the poros - z’-1n() 1 +F kz ’’ =+- h z 1n () 1 + F k z ’ (5b) 2k 02stg 1k 01 ity-depth and the time-depth functions. The reconstructed

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EKINE, A.S. AND ONUOHA, K. M.

1 Reflector A T2 = 0 0 0

Reflector A 1.0 T2 1.0

Reflector B T2 2.0 2.0

Reflector B

T3 3.0 3.0

T3 Reflector C

4.0 4.0 Reflector C

5.0 5.0

Reconstructed Seismic Section Interpreted Seismic Section (Reflector A Time) (Present Day) Figure 3. Schematic Diagram of the Seismic Geohistory Analysis Method.

seismic sections as obtained from the solutions of equation and that obtained from seismic geohistory analysis by con- (7) are shown on Figs. 5(i), (ii) and (iii). verting travel-times to depths using the time-depth relation obtained for the basin. Similarly, some faults arising proba- Finally, the method of differential interformational ve- bly from compressional stresses, due to the upliftment of the locity analysis (DIVA) was applied to some interpreted seismic section within the basin. These velocity sections include Abakaliki anticlinorium (Ekine, 1989) were observed to be those calibrated at Anambra River-1, Anambra River-3, Iji-1 significant mostly in the northern and southeastern regions and Nzam-1 wells. The graphics of the analysis are dis - of the basin. These faults which originated in the Santonian played on Figs. 6a, b, c and d. are probably related to the first folding episode in the evolu - tion of the Benue Trough. The Maestrichtian / Campanian faults observed towards the north of Anambra River-3 well Discussions may also have been influenced by these stresses or are di - rectly related to the Post-Maestrichtian folding episode in The results of seismic geohistory analysis carried out along the Benue Trough. The fault system KP identified on the in - three interpreted seismic sections indicate that most of the major faults in the basin originated in the Post-Maestrichtian terpreted seismic section [see Figs. 5(i)(b) and 5(iii)(b)], is a times and mainly in the Paleocene. The observed major Pre-Eocene event which cuts across from the south of faults are found to commence mainly within the Nkporo Okpo-1 and Nzam-1 to the north of Iji-1 well. It is observed shales at Okpo-1 well site (Fig. 5(i) (d, e)); within the Lower that sediments to the north of Nzam-1 well site have experi - Coal Measure at Iji-1 (Fig. 5(ii)(d, e)) and Nzam-1 (5(iii)(c)) enced more faulting during the Lower-Maestrichtian times. well sites. These formations were deposited in the However, fault systems that occurred after the Paleocene Post-Maestrichtian times. This observation correlates with times are more prominent in the southern parts of Nzam-1 the renewed high rate of subsidence and sedimentation re - towards Iji-1 well sites. Generally, we observed that most of vealed by the reconstructed burial analysis (Ekine and the major faults occurred in the Paleocene. Some other Onuoha, 2008). A very good correlation also exist between faultings which occurred in the Santonian were mainly sig - sediments depths obtained from the decompaction method nificant in the northern and the southeastern parts, whereas

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One-Way Travel Time (sec) 0.2 0.4 0.6 0.8 1.0 0.2 0.4 0.6 0.8 1.0 0 0

True t-z curve True t-z curve 0.83 Computed t = 0.46 Z + 68.98

0.83 t = 0.46 Z0.83 + 18.99 t = 0.46 Z + 18.99

1.0 1.0

)

(km

Depth

2.0 2.0

3.0 3.0 (a) Anambra River - I Well (b) Oda River - I Well

One-Way Time (sec)

0.2 0.4 0.6 0.8 1.0 1.2 1.4 0

True t-z curve Computed 1.0

)

(km 2.0

Depth

1 = 0.46 Z0.83 + 18.99

3.0

4.0

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610 650 690 730 770 810 610 650 690 710 770 810 OKPO 0.0 0.0 Base of KN Eocene KP 1.0 Top 1.0 UCM Top 2.0 NKP 2.0 (c) Top UCM of Surface

3.0 0.0 (a) Present Day

0.0 1.0

1.0 2.0 (d) Top Nkporo Shale at Surface

2.0 0.0

3.0 1.0 (b) Top Imo Shale at Surface

2.0 (e) End if Santonian UCM = Upper Coal Measure RP = Major Faults as identified on Seismic Sections

Figure 5(i) . Reconstructed Line 447-84-216 at OKPO-1.

80 120 160 200 240 280 320 360 90 120 160 200 240 280 320 360

IJI 0.0 0.0 FTB Base of Eocene GL 1.0 HF Top 1.0 ICM Horizon within 2.0 Imo Top 2.0 HK VB LCM (c) Lower Imo Shale at Surface FT Top UCM 3.0 KR 0.0

4.0 1.0 (a) Present Day

0.0 2.0 (d) Top UCM at Surface Top LCM 1.0 0.0

2.0 1.0

3.0 2.0 (b) Top Imo Shale at Surface (e) Top LCM at Surface

UCM = Upper Coat Measure LCM = Lower Coat Measure FTB = Major Faults As Indentified on Seismic Sections Figure 5(ii) . Reconstructed Line 447-84-259 at IJI-1.

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SEISMIC GEOHISTORY AND DIFFERENTIAL INTERFORMATIONAL VELOCITY ANALYSIS IN THE ANAMBRA BASIN, NIGERIA

140 200 260 320 380 440 500 560 620 680 740 800 860 920 980 1040 1100 1160

NZAM 0.0 VB LB GA HK KR KP 1.0 HA Base of Eocene GL LE Too KH 2.0 GL UCM MP KN LA 3.0 Top LCM

4.0 (a) Present Time

0.0

1.0

2.0

3.0 (b) Top Imo Shale at Surface

UCM = Upper Coat Measure LCM = Lower Coat Measure GA = Major Faults As Indentified on Seismic Sections

Figure 5(iii) . Reconstructed Line 447-84-217 at NZAM-1.

CDP 1331 1033 735 437 138

1.5 H1

3.5 H2

1.5 H1

3.5 H3

-1 1.5 H1

-S)

H4 3.5

Velocity (km 2.5

H3 4.5

1.5

3.5 H2 2.5 H4

H3 4.5

H1 = Top Nsukka Fm. H2 = Top Mamu Fm.

H3 = Top Nkporo Shale. H4 = Top Awgu Shale. Figure 6(a) . “ DIVA ” Display for Line 129/128-76/77-78.

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SP IJI-I 0 50 100 200 350

2.3 H1 H2 3.3

2.3 H1

H3 3.3

2.3 H1

H 4.3 4

-1

-S)

(km

2.3 H2

Velocity 3.3

2.3 H3

H4 4.3

2.3 H4

H3 4.3

H1 = Top Imo Shale. H2 = Top Nsukka Fm.

H3 = Horizon in Imo Shale. H4 = Top Mamu Fm. Figure 6(b) . “ DIVA ” Display for Line 447-84-259.

the Post-Eocene faults were predominantly in the southwest - River-3 well. This anomaly is within the same levels with ern portions of the basin. beds dipping southwest, or shows the trend of migrating flu - ids and hydrocarbons. The top of Agwu Shales contains the The differential interformational velocity analysis, column of water and liquid hydrocarbons observed at the ‘DIVA’ , carried out along four seismic sections indicated Anambra River-1 well. The major ‘DIVA’ anomaly observed mainly minor ‘DIVA’ anomalies. However, the ‘DIVA’ dis - southeast of Anambra River-1 well correlates with the zone play for line 129/128 – 76/77 – 78, calibrated at Anambra of overpressures within which liquid hydrocarbon, water Rivers-1 and -3 wells, show major anomaly beyond CDP 437 and gas have been discovered in the basin. The absence of and to the end of the seismic line southeast of Anambra any other well defined anomaly along this section implies River-1 [see Fig. 6(a)]. This anomaly is within the tops of that the overpressured condition and the hydrocarbon de - Mamu Formation and the Agwu Shales. A similar anomaly, posit do not extend in that direction or that the section ana - not clearly defined, is indicated northwest of Anambra lyzed is not long enough to clearly show this trend.

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SEISMIC GEOHISTORY AND DIFFERENTIAL INTERFORMATIONAL VELOCITY ANALYSIS IN THE ANAMBRA BASIN, NIGERIA

SP IJI-1 0 100 200 350 400

2.5 H1 H 3.5 2

2.5 H1

3.5 H3

2.5 H1

4.5 H4

2.5 H2

3.5 H3

2.5

4.5 H4

2.5

45 H4

H1 = Top Imo Shale. H2 = Top Nsukka Fm.

H3 = Horizon in Imo. H4 = Top Mamu Fm. Figure 6(c) . “ DIVA ” Display for Line 447-84-248.

Conclusions Results of the differential interformational velocity analysis have further confirmed the existence of velocity The method of seismic geohistory analysis has shown that anomalies resulting from changes in rock type and or fluid the timing of faulting in a basin is very important for the un - content, which substantially enhances the magnitude of the derstanding of the problem of hydrocarbon migration and anomaly when the presence of gas is indicated. The DIVA re - accumulation. The lack of adequate stratigraphic or struc - sults indicate that the Maestrichtian to Paleocene sediments tural trappings may lead to vertical or lateral migration of in the southern and mainly in the southwestern sector of the liquid hydrocarbon and their possible dissemination. When Anambra basin should be the major sedimentary strata with the time of hydrocarbon maturation (Ekine, 1989), is related liquid hydrocarbon potentials, whereas the Lower Creta - to the timing of the observed fault systems, the absence of ceous and particularly the Santonian sediments exhibit the accumulated liquid hydrocarbons in the north-central parts highest potentials for gaseous hydrocarbons. The above of the Anambra basin can be explained. geophysical tools employed in this study for basin analysis,

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SP NZAM-1 0 138 338 538 738 938 1138

2.0 H1 H2

4.0

-1 2.0 H1

(km - S ) 4.0 H3

Velocity

2.0 H2

4.0 H3

H1 = Top Imo Shale.

H2 = Top Nsukka Fm.

H3 = Top Mamu Fm.

Figure 6(d) . “ DIVA ” Display for Line 447-84-2178.

have demonstrated their effectiveness for obtaining infor- Ehrenberg, S. N., P. H. Nadeau and Ø. Steen, 2009. Petro- mation about the tectonism, hydrodynamics, hydrocarbon leum reservoir porosity versus depth: Influence of geo- and geothermal resource potentials of basin. Consequently, logical age. A. A. P. G. Bull., 93(# 10): 1281 – 1296. we suggest that the methods of seismic geohistory analysis Ekine, A. S., 1989. Empirical heat flow studies, geohistory and DIVA be further pursued using high fidelity seismic sec - analysis and hydrocarbon maturation modelling in the tions with greater coverage. Anambra Basin, Nigeria. Unpublished Ph. D. thesis, University of Nigeria, Nsukka. References Ekine, A. S. and K. M. Onuoha, 2008. Burial history analy - Acheson, C. H., 1981. Time-depth and velocity-depth rela - sis and subsidence in the Anambra basin, Nigeria. Nig. tions in sedimentary basins: A study based on current in - Journ. Phys., 20 (#1): 145 – 154. vestigations in the Arctic Islands and an interpretation Falvey, D. A. and M. F. Middleton, 1981. Passive continen - of experience elsewhere. Geophysics, 46: 707 – 716. tal margins: Evidence for break-up deep crustal meta - Adeleye, D. R., 1975. Nigerian late Cretaceous stratigraphy morphic subsidence mechanism. Oceanologica Acta, and paleogeography. A. A. P. G. Bull., 59: 2302 – 2313. suppl., 103 – 110.

Agagu, O. K., E. A. Fayose and S. W. Peters, 1985. Stratig - Hoque, M. and C. S. Nwajide, 1984. Tectono-sedimentological raphy and sedimentation in the Senonian Anambra ba - evolution of an elongate intracratonic basin (Aulacogen): sin of Eastern Nigeria. Nig. Journ. Min. Geol., 22: 25 – The case of the Benue Trough of Nigeria. Nig. Journ. Min. 36. Geol., 21: 19 – 26.

Angevine, C. L. and D. L. Turcotte, 1981. Thermal subsi - Merki, P., 1972. Structural geology of the Cenozoic Niger dence and compaction in sedimentary basins: Applica - delta. In African Geology, ed. T. J. F. Dessauvigie and tion to Baltimore Canyon trough. A. A. P. G. Bull., 65: A. J. Whiteman. University of Ibadan Press, pp. 251 – 219 – 225. 268.

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SEISMIC GEOHISTORY AND DIFFERENTIAL INTERFORMATIONAL VELOCITY ANALYSIS IN THE ANAMBRA BASIN, NIGERIA

Middleton, M. F., 1982. The subsidence and thermal history Applicability to the Anambra basin. N. A. P. E. Proc., 2: of the Bass basin, Southeastern Australia. 6 – 17. Tectonophysics, 87: 383 – 397. Onuoha, K. M. and A. S. Ekine, 1999. Subsurface tempera - Middleton, M. F. and Falvey, D. A. 1983. Maturation mod - ture variations and heat flow in the Anambra basin, Ni - elling in Otway Basin, Australia. A. A. P. G. Bull., geria. Journ. African Earth Sc., 28(#3): 641 – 652. 67(#2): 271 – 274. Peters, S. W., 1978. Stratigraphic evolution of the Benue Middleton, M. F., 1984. Seismic geohistory analysis – A Trough and its implication for the Upper Cretaceous case history from the Canning Basin, Western Australia. paleogeography of West Africa. Journ. Geol., 86; 311 – Geophysics, 49: 333 – 343. 322. Murat, R. C, 1972. Stratigraphy and paleogeography of the Reyment, R. A., 1965. Aspects of the geology of Nigeria: Cretaceous and Lower Tertiary in Southern Nigeria. In The stratigraphy of the Cretaceous and Cenozoic depos - African Geology. ed. T. J. F. Dessauvigie and A. J. its. University of Ibadan Press. Whiteman, University of Ibadan Press, pp. 635 – 648. Sclater, J. G. and P. A. F. Christie, 1980. Continental stretch- Neidel, N. S., and J. H. Beard, 1984. Progress in strati - ing: An explanation of the Post-Mid-Cretaceous subsi - graphic seismic exploration and the definition of reser - dence of the Central North Sea basin. Journ. voirs. Distinguished Author Series, Journ. Pet. Tech. Geophysical Research, 85: 3711 – 3739. pp. 709 – 726. Whiteman, A. J., 1982. Nigeria: Its petroleum geology, re - Onuoha, K. M., 1985. Basin subsidence, sediment sources and potential. Vols. I and II, Graham and decompaction and burial history modelling techniques: Trotham, London.

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