Geo 316 Geology of Nigeria for students.pptx

This is for students studying geology

1. DEPARTMENT OF APPLIED GEOLOGY FACULTY OF SCIENCE ABUBAKAR TAFAWA BALEWA UNIVERSITY, BAUCHI. GEO 316: REGIONAL GEOLOGY OF NIGERIA (2 UNITS) PART TWO (2)

2. GEO 316: REGIONAL GEOLOGY OF NIGERIA 2 + 0 + 0 (2 units) 1- Pre-Cambrian geology of Nigeria, comprising the Basement Complex: the Migmatite-Gneiss Complex, the Schist Belt and the Older Granite. The Jurassic-Younger Granites. Economic Geology of the Basement and the Younger Granite Complexes. 2- Stratigraphy, Paleogeography and economic geology/petroleum resources of sedimentary basins of Nigeria (Southern, Central and Northern Benue Trough, the Niger Delta, the Bornu Basin, the Sokoto Basin, the Bida /Nupe Basin and the Dahomey Embayment). The Cretaceous and later volcanics in Nigeria.

3. REFERENCES AND FURTHER READINGS Geology of Nigeria’s sedimentary Basins by C.S. Nwajide 2013 Geology and Mineral Resources of Nigeria by Nuhu George Obaje 2009 Tukur et al (2015); Two member subdivision of the Bima Sandstone, Upper Benue Trough, Nigeria: Based on sedimentological data Obianuju , U. P (2013); Southern and Central Benue Trough: A stratigraphic Revision Geology and Petroleum Potential of Nigerian Sedimentary Basins Boboye , O.A. and Omotosho , O.J. (2017) Petrological and Geochemical Evaluation of the Paleocene- Eocene Lithofacies in Dahomey Embayment, Southwestern Nigeria. Open Journal of Geology, 7, 690-719. https://doi.org/10.4236/ojg.2017.75047 Ejeh , O. (2016) Geochemical Discriminant for Provenance Characterization and Palaeogeography of Shales from Dahomey Embayment, Southwestern Nigeria. Journal of Geoscience and Environment Protection , 4 , 56-68. doi : 10.4236/gep.2016.46005 . Boboye , O.A. and Omotosho , O.J. (2017) Petrological and Geochemical Evaluation of the Paleocene- Eocene Lithofacies in Dahomey Embayment, Southwestern Nigeria. Open Journal of Geology, 7, 690-719. https://doi.org/10.4236/ojg.2017.75047 Ejeh , O. (2016) Geochemical Discriminant for Provenance Characterization and Palaeogeography of Shales from Dahomey Embayment, Southwestern Nigeria. Journal of Geoscience and Environment Protection , 4 , 56-68. doi : 10.4236/gep.2016.46005 .

4. COURSE CONTENT Stratigraphy Paleogeography Economic geology/petroleum resources OBJECTIVE Students should be able to discuss the Stratigraphy, Palaeogeography and Economic Geology of all the sedimentary basins in Nigeria.

5. INTRODUCTION Sedimentary basins are regions of prolonged subsidence of the Earth’s surface. The driving mechanism of subsidence are principally related to processes within the relatively rigid, cooled thermal boundary layer of the Earth known as the lithosphere (comprising of the crust and upper mantle). The lithosphere is composed of a number of plates which are in constant motion with respect to each other. Therefore, a sedimentary basin is, in general sense, any area of the Earth surface in which sediments accumulate or have accumulated to considerable thickness and have been or can be preserved for long geological time periods.

6. TERMINOLOGICAL DIFFERENCES Basin ; is a large low-lying area . It is often below sea lavel . Trough : a long narrow structural depression that extends laterally over a distance Embayment : from ‘bay’ which means a recessed , coastal body of water that directly connects to a larger main body of water , such as an ocean, a lake or another bay. A larger body is called a gulf, sea, sound, or bight.

7. Sedimentary Basins in Nigeria In Nigeria, we have seven (7) of such areas as outlined below; 1. Benue Trough Complex 2. Bida Basin (Mid Niger Basin) Iullemmeden Basin (Sokoto Basin) Chad Basin (Bornu Basin) Dahomey Basin (Benin Basin) Anambra Basin Niger Delta Basin These basins have been named differently by different workers Also, all these basins except the Anambra and the Bida Basins traverse international boundaries. Sedimentary Basins of Nigeria

8. 1- The Benue Trough: Introduction The Benue Trough is a fundamental tectono-sedimentological feature in the evolution of the Cretaceous and Tertiary geology of Nigeria. The Benue trough is a part of a mega-rift system termed “ West and Central Africa Rift System” (WCARS). WCARS is as a result of rifting following the breakup of Gondwana and the opening of the south Atlantic and Indian oceans in the lower/early Cretaceous. The WCARS was subsequently modified strongly by transcurrent (strike-slip) faulting at its central axis (E-W,CARS subsystem) while the ( NW-SE WARS subsystem) are majorly rift basins. Other Basins in the WCARS are Termit Basin (Niger and Western Chad), Bongo, Doba and Dosco Basins (Southern Chad), Salamat Basin of CAR, Muglad Basin (Sudan) Anza Basin of Kenya

9. The Benue Trough: Origin It may be assumed that prior to its inception, before the break up of Gondwana supercontinent, no part of the Nigerian landmass had any sedimentary cover. The entire surface of the pan African crystalline basement, at least within Nigeria, was exposed . The Benue Trough of Nigeria is a rift basin in central West Africa that extends NNE–SSW for about 800 km in length and 150 km in width. Other workers reported about 1,000 km long and up to about 250 km in its widest part. Though the precise bounds and dimensions of the Benue Trough are yet to be accurately demarcated. Taken from the Nigerian coastline, its limits are buried under younger basins-the Anambra and the Niger Delta Basins in the southwest, and the Chad Basin in the northeast. However, the southern limit is the northern boundary of the Niger Delta, while the northern limit is the southern boundary of the Chad Basin. The trough contains up to 6,000 m of Cretaceous – Tertiary sediments of which those predating the mid-Santonian have been compressionally folded, faulted, and uplifted in several places. Compressional folding during the mid-Santonian tectonic episode affected the whole of the Benue Trough and was quite intense, producing over 100 anticlines and synclines ( Benkhelil , 1989). Major such deformational structures include; the Abakaliki anticlinorium and the Afikpo syncline in the Southern Benue Trough, the Giza anticline and the Obi syncline in the Central Benue Trough, and the Lamurde anticline and the Dadiya syncline in the Northern Benue Trough.

10. The Benue Trough: Origin cont’d Studies have shown that the structure is a set of pull-apart basins or grabens generated by sinistral displacements along a pre-existing zone of northeast-southwest trending transcurrent faults. Following mid-Santonian tectonism and magmatism, depositional axis in the Benue Trough was displaced westward resulting in subsidence of the Anambra Basin. The Anambra Basin, therefore, is a part of the Lower Benue Trough containing post-deformational sediments of Campanian-Maastrichtian to Eocene ages. It is logical to include the Anambra Basin in the Benue Trough, being a related structure that developed after the compressional stage (Akande and Erdtmann , 1998).

11. Subdivision of the Benue Trough Based on the tectonic, geographic, and stratigraphic features, a subdivision of the Benue Trough into the northern, central and southern segments is adopted. However, other workers use the upper, middle and lower respectively. No concrete line of subdivision can be drawn to demarcate the individual portions but major localities (towns/settlements) that constitute the depocentres of the different portions have been well documented. For e.g the depocentres of the southern (Lower) Benue Trough comprise mainly the areas around Nkalagu and Abakalikii , while those of the Anambra Basin centre around Enugu, Awka and okigwe . The central (Middle) Benue Trough comprises the areas from Makurdi through Yandev , Lafia, obi, Jangwa to wukari . In the northern (Upper) Benue Trough the depocentres comprise Pindiga, Gombe, Nafada , Ashaka (in the Gongola Arm) and Bambam , Tula, Jessu , Lakun , and Numan in the (Yola Arm) However, The Gbako Line, which represents a wrench fault demarcates the southern Benue Trough from the central segment. The northern Benue Trough is not as clearly demarcated from the central segment; the boundary is therefore arbitrary. A minor distinguishing feature is the rugged topography due to the presence of Cretaceous sandstone salient and numerous tertiary volcanic plugs in the northern segment. The central and southern segments are more or less flat or only gently undulating, with a few low hills. The northern segment of the trough presents a highly complex tectonic character, being composed of several smaller units. E.g the kaltungo inlier.

12. Stratigraphic successions in the Benue Trough and the Nigerian sector of the Chad Basin

13. Lithostratigraphic succession of the Upper Benue Trough (adopted from Tukur et al . 2015) Lithostratigraphic section of the Benue Trough showing both the Gongola and Yola sub-basins

14. Lithostratigraphic section of the Benue Trough showing both the Gongola and Yola sub-basins

15. The Northern Benue Trough Northern Benue Trough is made up of two sub-basins : E–W trending Yola Sub-basin N–S trending Gongola Sub-basin A lthough some authors have sub-divided the Northern Benue Trough to include a third central Lau-Gombe sub-basin , eg. Akande et al., 1998 ). The Yola and the Gongola Sub-basins are separated by a structural high ( Wuyo-Kaltungo high member) dissected by four NE-SW trending sinistral strike-slip faults of the Gombe, Bima- Teli , Kaltungo-Wuyo and Shani faults collectively termed the “ Zambuk Ridge ” Carter et al (1963) or “ Wuyo-Kaltungo high” ( Zarborski 1998). Other Authors, (Bata et al 2015) reported an exposure of Zambuk ridge ( Dumbulwa-Bage high member ) as a boundary between the Gongola arm and the Chad basin . It is thus safe to think of the Zambuk ridge not as a local feature but as an extensive regional structure in the Upper Benue Trough. In both arms of the basin, the Albian Bima Sandstone lies nonconformably on the Precambian Basement . This formation was deposited under continental conditions (fluvial, deltaic, lacustrine) and is made up of coarse to medium grained sandstones, intercalated with carbonaceous clays, shales, and mudstones.

16. E-W trending Yola Sub basin and N-S trending Gongola Sub basin

17. Stratigraphic successions in the Northern/Upper Benue Trough (Gongola Arm) Stratigraphic Succession (Gongola Arm) Kerri-Kerri Formation Gombe Sandstone Pindiga/ Gongila Formation Yolde Formation Bima Formation Younging direction

18. Stratigraphic successions in the Northern/Upper Benue Trough (Yola Arm) Stratigraphic Succession (Yola Arm) Lamja Sandstone Numanha Shale Sekuliye Formation Jessu Formation Dukul Formation Yolde Formation Bima Sandstone Younging direction

19. Stratigraphy of Yola arm, Zambuk Ridge and Gongola arm (modified from Carter et al, 1963, Oti,1990 and Nwajide, 2003) Model Stratigraphy of Gongola arm, Zambuk Ridge and Chad Basin (Bata et al, 2015)

20. The Bima Sandstone The Bima Sandstone is evidently the most extensive unit of the northern Benue Trough and rests nonconformably on the on the Pan-African basement. The Bima Sandstone was subdivided by Carter et al . (1963) into; Lower Bima Middle Bima Upper Bima. The Lower Bima Member is bounded at the base by a nonconformity and at the top by an angular unconformity. It consists of large-scale trough cross-bedded gravels and coarse-grained sandstones characterized by well defined fining upward motif . The Middle Bima Member is shaley in most parts with some limestone intercalations and assumed to be deposited under a more aqueous anoxic condition (lacustrine, brief marine). An approximation to this description are the dark, carbonaceous shales within the Bima Sandstone in the section along the river channel to the south of the bridge, 200 mm (just) before the village of Bambam . Similar shales also occur within units of the Bima Sandstone that outcrop extensively on the Lamurde anticline (2 km to the town of Lafiya , on the Gombe – Numan road). Good exposures of the Bima Sandstone (however, without the so-called Middle Bima can be studied at Biliri , Filiya and Shani. The Upper Bima Member this consists of a homogenous succession of oblique planar cross-bedded sandstones. However , the work of Tukur et al (2015) has only recognised a two-member subdivision of the Bima Sandstone; the Lower and Upper Bima Sandstone Members.

21. The Yolde Formation The Yolde Formation lies conformably on the Bima Sandstone. This formation of Cenomanian age represents the beginning of marine incursion into this part of the Benue Trough. The Yolde Formation is taken as part of transition series , i.e. those units marking the gradual change from continental to marine sedimentation. Thus the base is marked by the first disappearance of sandstones and the introduction of limestone. The type locality is within the Dadiya Syncline and is exposed in a stream channel at Yolde , 50 km to Numan town as a 150 m section. Here, thinly bedded sandstones, succeeded by alternating sandy mudstones and fossiliferous limestones, overlie the Bima Sandstone. The base of the formation is best exposed in the Biriji River near Gombe. The Pindiga Formation In the Gongola Arm, the laterally equivalents Gongila and Pindiga Formations and the possibly younger Fika Shale lie conformably on the Yolde Formation. These formations represent full marine incursion into the Upper Benue during the Turonian – Santonian times. Lithologically, these formations are characterized by the dark/black carbonaceous shales and limestones , intercalating with pale colored limestones, shales and minor sandstones . The type locality of the Gongila Formation is at the Quarry of the Ashaka Cement Company at Ashaka , while that of Pindiga Formation is at Pindiga village. the Pindiga Formation is about 200 m thick, the lower 80 m being largely shale with thin (< 1 m) limestones. The upper part is 120 m of largely blue-black shales, parts of which contain a band of shelly limestone, a calcareous sandstone, and a bed of oolithic phosphatic ironstone. The Pindiga Formation is now believed to have five members; 1- Fika Shale (youngest) 2. Deba Fulani Member 3.Gulani Member 4. Dumbulwa Member 5. Kanawa Member (oldest)

22. The Fika Shale is lithologically made up of bluish-greenish carbonaceous, sometime pale gypsiferous , highly fissile shales and occasional limestones in places. The formation is entirely marine and has its type locality at Nafada village on the Gombe – Ashaka road. In the Yola Arm, the Dukul , Jessu and Sekuliye Formations, the Numanha Shale, and the Lamja Sandstone are the Turonian – Santonian equivalents of the Gongila and Pindiga Formations. The Turonian – Santonian deposits in the Yola Arm are lithologically and palaeoenvironmentally similar to those in the Gongola Arm, except the Lamja Sandstone which has a dominating marine sandstone lithology. The recovery of diversed assemblages of arenaceous along side planktonic foraminifera from samples obtained from the Dukul , Jessu and Sekuliye formations indicate deposition in shallow marine – neritic – shelfal environments. The type locality of the Dukul Formation is in the village of Dukul with good exposures also at Bambam and Lakun on the Gombe – Yola road. All the other formations have their type localities in the villages named after them. The Santonian was a period of folding and deformation in the whole of the Benue Trough. Post-folding sediments are represented by the continental Gombe Sandstone of Maastrichtian age and the Keri–Keri Formation of Tertiary age. The Gombe Sandstone is lithologically similar to the Bima Sandstone, attesting to the reestablishment of the Albian palaeoenvironmental condition. The Gombe Sandstone Formation, however, contains coal, lignite, and coally shale intercalations which in places are very thick. The type locality of the Gombe Sandstone is along the bank of Pantami River in Gombe town. Good exposures are also encountered in many parts of Gombe town and Birin Fulani village. The Keri–Keri Formation is made up of whitish grey sandstones, siltstones, and claystones with the claystones dominating the lithology in most places, Typical sections are exposed in Gombe Aba, Duku (not Dukul ) and Alkaleri .

23. Paleogeography of the Northern Benue Trough Sedimentation in the Northern Benue Trough started in the Aptian up to Maastrichtian. Studies have suggested that the depositional environment of the sediment varied from continental to marine at different times. Bima was deposited in a continental condition . A long marine transgressive regime started the deposition of the transitive Yolde , then Dukul , Gongila and Pindiga. During this time, the Benue trough served as a connection between the Tethys and the Atlantic. A return to continental conditions (regression) started the deposition of Jessu Formation which bears transitional characteristics similar to Yolde . Sekuliye and Fika Formations marked a resumption of transgressive activities (marine) probably from the Atlantic. A last transgressive regime in the mid-Maastrichtian deposited the Numanha Shale followed by a final regression which deposited the Lamja and the coal- bearing Gombe Formation after a great erosive gap

24. Economic Geology of the northern Benue Trough The economically useful Earth materials of the Northern Benue trough falls under four classes; 1- Energy materials/fossil fuels, (coal) 2- Industrial minerals and rocks (e.g. limestone, gypsum, laterite and salt) 3- Chemical minerals, and 4- Metalliferous minerals (Pb-Zn mineralization) By far the greatest interest is in the prospects of petroleum . The petroleum prospects of the northern Benue trough are in no doubt, following the discovery of commercial reserves in both Niger and Chad Republics.

25. The central/middle Benue Trough The Central Benue trough is an integral part of the Benue Trough. Therefore the origin of the Benue trough discussed earlier applies to it also. Its northern boundary arbitrarily fixed at the Lau-Muri- Zurak-Bashar line while the southern boundary is marked at a line running south of Gboko westward towards Otukpo and then northward to east of Lafia.

26. Stratigraphy of the central Benue Trough In the central Benue Trough , around the Obi/Lafia area, six Upper Cretaceous lithogenic formations comprise the stratigraphic succession. This succession is made up of Albian Arufu , Uomba and Gboko Formations, generally referred to as the Asu River Group ( Offodile , 1976; Nwajide, 1990). These are overlain by the Cenomanian – Turonian Keana and Awe Formations and the Cenomanian – Turonian Ezeaku Formation . The Ezeaku Formation is coterminous with the Konshisha River Group and the Wadata Limestone in the Makurdi area. The Late Turonian – Early Santonian coal-bearing Awgu Formation lies conformably on the Ezeaku Formation. In the Makurdi area, the Makurdi Sandstone interfingers with the Awgu Formation. The mid-Santonian was a period of folding throughout the Benue Trough. The post-folding Campano-Maastrichtian Lafia Formation/Sandstone ended the sedimentation in the central Benue Trough, after which widespread volcanic activities took over in the Tertiary.

27. Stratigraphy of the central Benue Trough con’d However, Several workers on the stratigraphy of the Benue Trough have given differing subdivisions of the Asu River Group . Using a simplified scheme, the Asu River Group in the central Benue Trough consists of four units; the Arufu Limestone, the Uomba Formation, the Gboko Limestone, and the Awe Formation.

28. Stratigraphic succession in the central Benue Trough Stratigraphic succession in the central Benue Trough Stratigraphic Succession Lafia Formation Makurdi Sandstone ? Awgu Formation Ezeaku / Konshisha / Wadata Formations Keana /Awe Formation Arufu / Uomba / Gboko Formations ( Asu River Group) Younging direction

29. The Asu River Group A. The Uomba Formation; Type locality is the Uomba River, Taraba State. It consists of sandstones, sandy shales and shales Also consists of oxytropidoceratids and diploceratid ammonites (awaiting detailed characterization) B. The Arufu Limestone Some 70 km east of Makurdi on the left bank of the Benue River, though not studied in detail Associated with Pb-Zn minerlization Occurenece of ammonite Elobeceras sp recorded Whiteman (1982) considered it as probably not worth more than a member of a Formation without stating the Formation, but logical reasoning can place it to be the basal member of Uomba Formation. C. The Gboko Limestone Type locality is in Yandev in Benue State. Limestone occurrences were first recorded around the village in 1950 by the prospectors of the Amalgamated tin Mines of Nigeria. Biofacies and microfacies recorded Reserve estimate of about 70 million tones of limestone with 88% CaCO 3 content, informed the establishment of Benue Cement Company. Siltstones intercalated with sandstones , as well as fissile and carbonaceous shales have been found with the limestone D. Awe Formation Considered the southernmost component of the Asu River Group Composed of flaggy, medium to coarse sandstone interbedded with carbonaceous shales from which brines issue copiously Probably deposited under transitional marine to fluviatile conditions

30. The Eze Aku Group The units of the Eze Aku group found in the central Benue Trough include the Keana , the Zurak, the Makurdi and the Wukari Formations. These units are not really strictly superimposed in order, rather they are more of southward younging lateral equivalents, with the Keana Formation as the oldest. A . The Keana Formation It succeeds the Awe Formation across a hiatus Consists of poorly sorted feldsparthic , micaceous, planar cross-bedded sandstone with subordinate siltstone and shale B. The Zurak Formation Directly overlies the Muri Formation Stratigraphically equivalent to both the Yolde and Pindiga Formations. Resulted from the extensive marine transgression C. The Makurdi Formation Sandstones showing fining upward succession Analysis shows a deposition from high-sinuosity rivers Planar cross-bedding as sedimentary structure. D. The Wukari Formation 1. The formation did not receive much attention from geologists and has only been broadly characterized as comprising mainly of continental and marine shales, sandstones and limestones . The shales are barren of fossils and belong to the deposits of an initial transgressive stage.

31. The Awgu Formation 1. The deposition of Awgu Formation marks the end of marine deposition in this part of the Benue Trough. 2. The formation is made up of bluish-grey to dark-black carbonaceous shales, calcareous shales, shaley limestones , limestones, sandstones, siltstones, and coal seams. The Lafia Sandstone The Lafia Formation is the youngest formation in this area. The formation was deposited under continental condition (fluviatile) in the Maastrichtian and lies unconformably on the Awgu Formation. It is lithologically characterized by ferruginized sandstones , red, loose sands, flaggy mudstones, clays and claystones . Outcrops and sections of the Lafia Formation occur in and around the town of Lafia, and along the bank of River Amba on the Lafia – Doma road

32. Paleogeography of the Central Benue Trough The central Benue Trough is a mass of lithofacies resulting from depositional environment ranging from continental to marine . The area witnessed the first marine occupation depositing Gboko and Arufu Limestones during the late Aptian to Cenomanian. Brackish and shallow marine conditions prevailed reducing the population of fauna as seen from the limestones. Awe formation was deposited during the Cenomanian regression. Lagoonal pools and stranded shorelines prevailed in this area during this time. Ezeaku group of sediments were deposited following the Turonian transgression so also is Wadata limestones. Awgu Formation represents another major transgressive deposit from Turonian through Coniacian to Santonian. The shales were deposited in shallow restricted, anoxic marine settings. Makurdi Formation and Keana Sandstone are fully continental . The Campanian to Maastrichtian Lafia formation is also continental .

33. Economic Geology of the central Benue Trough The economically useful Earth materials of the Northern Benue trough falls under four classes; 1- Metalliferous minerals ( Pb-Zn mineralization locally associated with sliver and copper ) 2- Energy materials ( coal around Lafia-Obi area) 3- Industrial Earth materials (e.g. stone aggregates, sand, clay, laterite, and limestone ) 4- Chemical minerals ( barytes and salt ) Hydrocarbon potential : 32 coal samples from two outcrops and 4 boreholes drilled into the Awgu Formation in the Lafia-Obi area showed that formation fell within the hydrocarbon generation window that will mainly favour gas generation Obaje et al (1998) using

34. THE SOUTHERN/LOWER BENUE TROUGH The southern Benue Trough is also an integral part of the Benue Trough. Therefore, the origin of the Benue trough as discussed earlier applies to it also. The southern Benue Trough is the area from the Gboko-Oturkpo line southwards up to the area where the Anambra basin commences . It could also be taken as the area underlain by sedimentary units of Santonian and older sediments southward from the Gboko-Oturkpo line. This part of the Benue trough is sometimes referred to as the “ Abakaliki Basin” or “ Abakaliki - Benue Trough” This is to demarcate it from the NW block which latter formed the Anambra and Afikpo Basins . Note that the larger southern Benue Trough formed as part of the pulled apart basin was longitudinally faulted, splitting the block into two- NW and SE blocks. While the SE block subsided forming a depocentre that became the Abakaliki sub-Basin or Southern Benue Trough, the NW counterpart remained a stable platform up until the Santonian.

35. Stratigraphy of the southern Benue Trough Sedimentation in the southern Benue Trough commenced with the marine Albian Asu River Group, although some pyroclastics of Aptian – Early Albian ages have been sparingly reported ( Ojoh , 1992). The Asu River Group in the Lower Benue Trough comprises the shales, limestones and sandstone lenses of the Abakaliki Formation in the Abakaliki area and the Mfamosing Limestone in the Calabar Flank (Petters, 1982). The marine Cenomanian – Turonian Nkalagu Formation (black shales, limestones and siltsones ) and the interfingering regressive sandstones of the Agala and Agbani Formations rest on the Asu River Group. Mid-Santonian deformation in the Benue Trough displaced the major depositional axis westward which led to the formation of the Anambra Basin.

36. Stratigraphy of the Southern Benue Trough Agbani Sandstone Nkalagu Limestone Agala Formation Odukpani Formation Mfamosing-Abakaliki Formation Younging direction

37. Paleogeography of the Southern Benue Trough The pile of sediments in the southern Benue Trough were deposited under a range of both marine and continental conditions. Agbani sands are continental in origin given that they were deposited as fluivial clastic influx that terminated the Turonian-Santonian marine sedimentation. Nkalagu Formation is marine followed by continental Agala Formation . The older sediments, Odukpani and Mfamosing - Abakaliki Formations that make up the lower units of the southern Benue Trough are essentially marine by origin .

38. Economic Geology of the southern Benue Trough The classification of the Earth material resources is into; Metalliferous minerals; (Pb-Zn mineralization) associated with copper (chalcopyrite) also found here Industrial minerals; stone aggregates, clay and limestone Chemical minerals; salt water Hydrocarbons Water is given a special consideration here because some of the fractured shales of the Asu River Group produce saline water

39. THE ANAMBRA BASIN The Anambra basin refers to areas covered by the Campanian to early Paleocene lithofacies that corresponds to the Nkporo group and coal measures. It is the sediment pile that directly overlies the facies of the southern Benue Trough up to the point of Paleocene sedimentation commenced. Note that the popular “ Afikpo Basin” is a part of Anambra Basin . This is because they were both formed from the same Santonian thermotectonic event, the sediment packages are common and continuous and there is really no physical separation between the two areas neither is there any tectonic setup of the area into a separate basin. Post-deformational sedimentation in the southern Benue Trough , therefore, constitutes the Anambra Basin . Sedimentation in the Anambra Basin thus commenced with the Campanian-Maastrichtian marine and paralic shales of the Enugu and Nkporo Formations, overlain by the coal measures of the Mamu Formation . The fluviodeltaic sandstones of the Ajali and Owelli Formations lie on the Mamu Formation and constitute its lateral equivalents in most places. In the Paleocene , the marine shales of the Imo and Nsukka Formations were deposited, overlain by the tidal Nanka Sandstone of Eocene age. Downdip, towards the Niger Delta, the Akata Shale and the Agbada Formation constitute the Paleogene equivalents of the Anambra Basin.

40. The Anambra Basin cont’d The Enugu and the Nkporo Shales represent the brackish marsh and fossiliferous pro-delta facies of the Late Campanian-Early Maastrichtian depositional cycle (ReijersandNwajide,1998).Deposition of the sediments of the Nkporo/Enugu Formations reflects a funnel-shaped shallow marine setting that graded into channeled low-energy marshes. The coal-bearing Mamu Formation and the Ajali Sandstone accumulated during this epoch of over all regression of the Nkporo cycle. The Mamu Formation occurs as a narrow strip trending north–south from the Calabar Flank, swinging west around the Ankpa plateau and terminating at Idah near the River Niger (Fig. 4.5). The Ajali Sandstone marks the height of the regression at a time when the coastline was still concave. The converging littoral drift cells governed the sedimentation and are reflected in the tidal sand waves which are characteristic for the Ajali Sandstone. The best exposure of the Nkporo Shale is at the village of Leru ( Lopauku ), 72 km south of Enugu on the Enugu – Portharcourt express road, while that of Enugu Shale is at Enugu, near the Onitsha-Road Flyover. The Mamu Formation is best exposed at the Miliken Hills in Enugu, with well-preserved secions along the road cuts from the King Petrol Station up the Miliken Hills and at the left bank of River Ekulu near the bridge to Onyeama mine. The Nsukka Formation and the Imo Shale mark the onset of another transgression in the Anambra Basin during the Paleocene . The shales contain significant amount of organic matter and may be a potential source for the hydrocarbons in the northern part of the Niger Delta ( Reijers and Nwajide, 1998). In the Anambra Basin, they are only locally expected to reach maturity levels for hydrocarbon expulsion

41. Stratigraphy of the Anambra Basin Nanka Formation ? Imo Formation Nsukka Shale Ajali Sandstone Mamu Formation Nkporo Group Younging direction

42. Paleogeography of the Anambra Basin The Nkporo group represents a major transgressive movement in the Campanian. The shales facies of the Nkporo group have been inferred to be pro-delta front environments based on their mixed arenaceous and planktonic foramineral suites. The Enugu shale is a product of Delta flood plain processes. Mamu Formation represents a delta strand plain and thickly vegetated tidal mud flats which resulted in coals. The overlying Ajali Formation is attributed to fluvial deposition and shallow marine subtidal sand bars. Thus depending on the location, Ajali shows variability of deposition of environment (fluviatile and marginal marine sedimentation). The deposition of coal was terminated by Ajali Formation perhaps due to epeirogenic movement of adjoining uplands generating large volume of sands deposited at a rapid rate that prevented growth of vegetation. Nsukka Formation was deposited under marine conditions as indicated by the presence of limestones with a return to coal forming conditions. Imo Formation which marked the end of sedimentation in the Anambra basin was deposited by extensive transgressive activity.

43. Economic importance

44. THE BIDA BASIN The Bida Basin is also known as Nupe Basin, Mid-Niger Basin, Niger Embayment, Middle Niger Embayment among others. It is one of the few sedimentary basins of Nigeria located exclusively within the country It lies largely within Niger State with minimal extensions in Kogi , Kwara and Nasarawa States, and Federal Capital Territory . It stretches 400 km NE-SW from Kontagora in Niger State to Dekina in Kogi State and is 160 km wide , covering an area of approximately 60,000 km 2 . In most parts, it is surrounded by basement complex rocks. However, it merges into the Sokoto Basin in the North and Anambra Basin in the South . Sometimes, it is considered as the Northwestern extension of the Anambra Basin as the boundary is not defined.

45. ORIGIN OF THE BIDA BASIN It doesn’t appear to be important in the tectonic evolution of Nigeria. Its origin has been a subject of much speculation. Its somewhat similar to the Benue Trough in its cross sectional geometry, the Bida Basin has an irregular floor. There is also an axial positive gravity anomaly flanked by negative ones. This is consistent with an underlying rift structures. One explanation given for the origin of Bida Basin suggests that it was formed by rifting . This idea is supported by the positive gravity anomaly flanked by negative anomalies. However, the width of the basin as well as the fact that there are no volcanic intrusions and no evidence of uplift retards this model. Still, shallow structural effects that should support rifting may have been obliterated. The rifting theory holds that the initial rifting between the African and South American plates and the failed extension into Africa resulted in both the Benue Trough and the Bida Basin producing a system of NW-SE trending faults in the Bida Basin area. However, the Bida Basin only contains unfolded upper Cretaceous Campanian-Maastrichtian strata. Another attempt to explain the origin of Bida Basin reasons that the Basin is a result of the Isostatic readjustment (Thinning and subsidence) that followed tectonic activity related to the emplacement of the Younger Granites in the Jurassic. Another school of thought proposed that the genesis of the Basin may be linked to the Santonian orogenic activity that affected south East Nigeria and the Benue valley. This may be because sediment deposition in this basin started only during the Campanian time .

46. STRATIGRAPHY OF BIDA BASIN The stratigraphy of Bida basin is in two distinct packages of the Northwestern Bida area and the Southeastern Lokoja area . Stratigraphy of Bida Basin Lokoja Area (SE) Agbaja Ironstone Patti Formation Lokoja Sandstone Bida Area (NW) Batati Ironstone Enagi Siltstone Sakpe Ironstone Bida Sandstone Fig 10: Stratigraphic Succession in the Bida Basin After Akande,2005: Obaje,2009) Younging direction

47. Restored SE-NW Stratigraphic relationship from the Anambra Basin to Bida Basin (Obaje et al. , 2011) STRATIGRAPHY OF BIDA BASIN SHOWING ITS STRATIGRAPHIC RELATIONSHIP WITH ANAMBRA BASIN

48. Stratigraphic Description The Lokoja Formation The type section is located in a stream channel south of the Agbaja Plateau (confluence of the Niger and Benue Rivers) The formation is composed of coarse , pebbly, and clayey cross-bedded sandstone and a few thin oolitic ironstones. There is poorly exposed basal conglomerates. Braide (1992b) recognised the following distinct facies as the components of the Lokoja Formation: alluvial fans, flood basin and lacustrine facies, and deltaic facies. Bida Sandstone Braide (1992d) recognised the following the typical alluvial fan subfacies comprising; A- base of slope breccia B- proximal fan (massive conglomerate) C- midfan (cross-bedded pebbly sand ), D- distal fan (poorly laminated cross-laminated fine sandstone) E- lacustrine mudrocks Adeleye (1972) recognised two members; Doko and Jima Members Sakpe Ironstone Formation Occurs in an extensive area west of Bida town Two laterally equivalent members comprising this formation are the Wuyo Ironstone Member and the Baro Ironstone Member Patti Formation This formation consists of fine to medium, grey to white sandtostones , carbonaceous silts and shales and oolitic ironstones. There are thin coal seems and massive, white sandy clays are common

49. Stratigraphic Description cont’d The Enagi Siltstone This formation consists of siltstones and surbodinate sandstones, claystones and siltstones/sandstone intermix The Agbaja Ironstone Formation The oolitic ironstones of the Agbaja Plateau occur as a capping on the mesas around Lokoja. The oolites are probably of lateritic origin in view of their massive nature and the resrtictionof their occurrence to high-lying plateaus. The Batati Ironstone Formation Also consists of two members; the Edozhigi and the Kutugi Ironstone Members. Where they occur together the former unconformably overlies the latter

50. PALEOGEOGRAPHY OF BIDA BASIN Generally, Continental (alluvial) environments dominates the facies of Bida Basin. This is so because all around the area, depositional facies range from fanglomerates, fluvial, lacustrine to floodplain . However in the early Maastrichtian (lower Patti Formation), there was marine deposition as evidenced by the recovery of Dynocysts .

51. Economic Geology and Petroleum Potential of Bida Basin Petroleum Resources Metalliferous Mineral ( Iron Ore)

52. BORNU BASIN It is the Nigerian sector of the Chad Basin. Many authors used the terms; Chad Basin, Bornu Basin and even Kerri-Kerri Basin . It is one of the derivative basins , i.e. those basins whose origin and lithic fills depended on precursor structures . Here, the precursor structure is the Northern Benue Trough The Chad Basin is one of the several active intracontinental basins of the African continent. The Chad Basin territory has a roughly elliptical catchment area covering up to 4 million km 2 bounded by uneven topographic highs. The Nigerian sector underlies about 30,000 km 2 of territory (Adegoke et al., 1986; Dike 1993), most of which lies within Bauchi, Borno, Yobe , and Gombe States. This means over 75% of the present-day lake shoreline lies outside Nigeria . The Bornu Basin is the southwestern sector of the Chad Basin and is the Nigerian sector of the Chad basin. Its lithic fill in Nigeria consists of only two lithological units-the Kerri-Kerri and the Chad Formations . Additionally, taking the basin fill succession as spanning from the Cretaceous Bima Formation , through the Paleocene Kerri-Kerri to Pleistocene Chad formation. The Bima Sandstone is the lateral equivalent of the regional Nubian Sandstone which is the target aquifer unit in Niger, Chad, Sudan, Libya and Algeria.

53. ORIGIN OF THE BORNU BASIN This is related to the several basin-and-swell structures in Africa . It is believed that most of the swell structures are connected to volcanic rocks emplaced by underlying mantle processes. This confirms the observation that the Chad basin has been an active basin for the past 25my . This activity is due to the fact that the African plate became relatively stationary compared to the underlying mantle. Following the hypothesis of Burke (1976a) the processes leading to the formation of Chad basin can be summarized into four phases viz: Phase 1 : The African plate became stationary relative to the mantle . This happened around the Oligocene/Miocene times. Phase 2 : Thermal irregularities (mantle plume activities) due to the stationary position of the plate resulted in hotter areas becoming elevated relative to the rest of the plate . Also the continent became elevated relative to other continents. Phase 3 : Volcanic eruptions developed largely, though not entirely, on the elevated area . Erosion of the uplifted areas gave rise to increased sedimentation on African coasts and led to the accelerated progradation of the Niger Delta (Burke 1972). This probably deposited the Kerri-Kerri Formation within the Chad Basin. Phase 4: Continued elevation of areas overlying the hot upper mantle led to continued volcanism and elevation along the basin watershed. Erosion from the watershed into the basin during the later part of this time of episodic and sporadic uplift and volcanism deposited the Chad Formation .

54. STRATIGRAPHY OF THE BORNU BASIN Data gathered from the adjacent basins and boreholes indicate that the Bornu Basin is made up of five stratigraphic units that include: The Chad Formation The Kerri-Kerri Formation The Fika Shale The Gongila Formation The Bima Sandstone Gombe Sandstone and Kerri-Kerri Formations have not been penetrated by wells drilled in the past. So the occurrence of Gombe Formation in any significant proportion in the basin is doubtful . Whereas drilling concentrated north of Maiduguri towards Lake Chad , the Kerri-Kerri Formation occurs in the south of the basin along the boundary with the Benue Trough . In most cases the Chad Formation lies directly unconformably on the Fika Shale Stratigraphic successions in the Nigerian Sector of the Chad Basin

55. Stratigraphic succession of the Bornu Basin, NE Nigeria ( After Okosun 1995, Avbovbo et al 1986 and Carter et al 1963) Stratigraphy of The Bornu Basin Chad Formation Kerri-Kerri Formation Gombe Sandstone ? Fika Shale Gongila Formation Bima Formation Younging direction

56. STRATIGRAPHIC DESCRIPTION The Kerri-Kerri Formation The formation is an extensive clastic unit outcropping over an area more than 3,000 km2. Its essentially flat-lying and is the lithic material of the Kerri-Kerri Plateau. Dike 1993 established its diversity of facies and depositional environments, including alluvial fans, fan deltas, braided river and marginal marine setting. The Chad Formation This is the uppermost Pliocene–Pleistocene formation consisting of fluviatile and lacustrine thick bodies of clay, separating three major sand bodies, with lenses of diatomite up to a few meters thick (Wright, 1985). The sand is uncemented with angular and subangular quartz grains. The clay is massive and locally gritty in texture. Both the sand and the clay are of variable colors ranging from brown, yellow, and white to grey. The three sand bodies correspond to the upper, middle and lower aquifers defined by Barber and Jones (1965). The lower member is made of sands and sandy clays while the middle and the upper consist of sandy clays with diatomite and clays and sands, respectively. Based on exploratory wells studied by Moumouni et al. (2007), the Fika / Chad Formations boundary is fixed at about 1,500 m depth except in Kasade – 1 where it is estimated to be at about 700 m.

57. PALEOGEOGRAPHY OF THE BORNU BASIN The formations age-equivalent to the sediments in the Benue Trough have same paleogeography. The Paleocene Kerri-Kerri Formation though deposited under varied conditions is exclusively continental (fluvial and deltaic). An oolitic laterite layer unconformity separates the kerri-kerri Formation from the Chad Formation . The Chad Formation is extensive and covers up to 90% of the area. it is also largely continenta l in origin and mostly lacustrine .

58. Economic Geology Chemical mineral resources Diatomite used asa refractory material, filler and filter materials, absorbent, clarifier, insulator, and manufacture of insecticides Salt (potash) Groundwater (Chad Formation very promising, Kerri-Kerri unpredictable) Petroleum resources

59. lULLEMMEDEN BASIN (SOKOTO BASIN) The Nigerian sector of the lullemmeden basin is the Sokoto Basin . It is located in the North-western part of Nigeria. Various names; Iullemmeden Basin, Sokoto Basin and Sokoto Embayment have been used for the basin; however Iullemmeden Basin is considered most appropriate as only a small portion of the mega basin occurs within Nigeria . The name Iullemmeden refers to a federation of Toureg people occupying the central region of Niger Republic . The lullemmenden basin is a roughly circular sedimentary cover extending from Mali through Niger and Benin republics, Algeria and Northwest Nigeria. The basin covers over 700,000 km 2 but presently less than it was originally.

60. ORIGIN OF LULLEMMEDEN BASIN It is a young, broad, shallow synclinal depression. It may be defined more appropriately as a broad regional structure (synclise) formed by slow crustal downwarp over several geological periods. Their origin involved a combination of basin forming process such as continental extension, thermal subsidence and isostatic readjustments over a large area. As an intracratonic basin , it occurs within continental interiors away from plate margins . They are oval and saucer shaped in plan and cross section respectively. Their floor is covered by continental crust. Major intracratonic basins were initiated during the breakup of supercontinents . Sediments occupying the intracratonic basins in different parts of the world show similar ages for interregional unconformities, similar thickness and volume . This observation suggest a global explanation and the similarity of ages implies large scale process that caused rifting and thermal subsidence.

61. STRATIGRAPHY OF SOKOTO BASIN Three (3) major subdivisions are recognized in the Sokoto Basin: (1) The lower, continental beds (Continental Intercalaire) of Late Jurassic to Early Cretaceous age, (2) Intermediate marine and brackish water deposits and (3) Continental Terminal of upper Eocene-Miocene age The sediments of the Iullemmeden Basin were accumulated during four (4) main phases of deposition , and this represents unconformity bounded lithostatigraphic packages listed from the oldest: 1- The Non-marine Continental Intercalaire – the Illo and Gundumi Formations unconformably overlying the Pre-Cambrian Basement 2.The mixed Rima Group : Taloka, Dukamaje and Wurno Formations unconformably overlying the Continental Intercalaire 3. The marine Sokoto Group : Dange , Kalambaina and Gamba Formations. 4. The Non-marine Continental Terminal : The overlying continental Gwandu Formation forms the Post- Paleocene Continental Terminal.

62. STRATIGRAPHIC DESCRIPTION The continental intercalaire This consists of mainly cross-bedded fluviatile and lacustrine sands and gravels, with clay intercalation In the Nigerian sector, the group consists of all pre-Maastrichtian sediments and is subdivided into the Gundumi and the Illo Formations, which are considered lateral equivalents Gundumi Formation It nonconformably overlies the crystalline Basement Complex, although this contact is not exposed at the type section at Dutsen Dambo . Its obviously continental in origin and may encompass environments ranging from alluvial fan to lacustrine. Illo Formation This is also another pre-Maastrichtian unit also nonconformably overlying the Basement. The formation is characterized by Jones (1948) as consisting of three subunits; Upper cross-bedded, coarse grained sandstone with subordinate clay content Middle, massive, white, chalky, highly aluminous clay Lower, white unconsolidated, cross-bedded, coarse to medium

63. STRATIGRAPHIC DESCRIPTION CONT’D The Rima Group The Maastrichtian Rima Group, consisting of mudstones and friable sandstones (Taloka and Wurno Formations), separated by the fossiliferous, shelly Dukamaje Formation. Wurno Formation Dukamaje Formation Taloka Formation The Sokoto Group The Dange and Gamba Formations (mainly shales) separated by the calcareous Kalambaina Formation constitute thePleocene Sokoto Group Gamba Formation Kalambaina Formation Gange Formation

64. IULLEMMEDEN BASIN (SOKOTO BASIN) Stratigraphy of Sokoto Basin Stratigraphy of Sokoto Basin

65. IULLEMMENDEN BASIN (SOKOTO BASIN) Stratigraphy of Sokoto Basin Gwandu Formation Gamba Formation Kalambaina Formation Dange Formation Wurno Formation Dukameje Formation Taloka Formation Gundumi Formation Illo Formation Younging direction

66. PALEOGEOGRAPHY OF IULLEMMENDEN BASIN Marginal marine conditions were prevalent in the Maastrichtian. Gypsiferous conditions were very common during the Dukameje times and reptilian and fauna flourished . Scanty arenaceous calcerous and pelagic foraminifera were present. All these indicate shallow marine conditions . Marine conditions prevailed during the deposition of Denge up to Gamba Formations . Continental condition was prevalent during the deposition of Gwandu Formation so also was late Jurassic to early Cretaceous Illo and Gundumi Formations.

67. ECONOMIC GEOLOGY OF IULLEMMENDEN BASIN Industrial rocks and Minerals such as: Clay Laterite Limestone Gypsum Gravel Ironstone Phosphate

68. DAHOMEY BASIN Dahomey Basin also called Benin Basin The Dahomey Basin is a combination of inland/coastal/offshore basin that stretches from southeastern Ghana through Togo and the Republic of Benin to southwestern Nigeria , a total latitudinal stretch of about 500 km . It is separated from the Niger Delta by a subsurface (faulted) basement high referred to as the Okitipupa Ridge The basin is described by Whiteman (1982) as miogeocline , i.e. a basin in which volcanism has not been associated with sedimentation . The basin is regarded as active , since its subaerial parts are eroding while deposition is taking place in its distal , submarine portions. It is described by an extensive wedge of Cretaceous to Recent sediments which lies unconformably on the basement. A faulted basement high, the Okitipupa basement ridge separated the Dahomey Embayment from the Benue Trough until the late Cretaceous subsidence and marine transgression united both basins. ??????

69. DAHOMEY BASIN Simplified Geological map of Nigerian section of Dahomey embayment( Redrawn from Petters and Olsson, 1979)

70. ORIGIN OF DAHOMEY BASIN The Dahomey basin is one of the many marginal basins formed along the coast of Africa and Brazil following the opening of the south Atlantic. The basin belongs to the sheared margin basin types specifically the fracture ridge dammed basins. The ridge serves as a passive sediment dam halting oceanward progradation of sediments. The dominant feature is the occurrence of marginal fractures produced by shearing between adjacent pieces of continental crust along marginal offsets.

71. STRATIGRAPHY OF DAHOMEY BASIN The Dahomey basin sedimentary fill is broadly packaged into two (2): The Cretaceous Abeokuta Group comprising the Araromi Formation Afowo Formation Ise Formation The Cenozoic Units comprising the Benin Formation (formerly coastal plain sands) Ogwasi-Asaba Formation Ilaro Formation Oshosun Formation Akinbo Formation Ewekoro Formation Younging direction NB: the Cretaceous sequence are older, one may be right to say that the Ise Formation is the oldest while the Benin Formation is the youngest.

72. DAHOMEY BASIN Paleogeography of Dahomey Basin Fig 14: Stratigraphy of Nigerian Sector of Dahomey Basin (modified after Omatsola and Adegoke)

73. DAHOMEY BASIN Paleogeography of Dahomey Basin Fig 15: Stratigraphy of Nigerian Sector of Dahomey Basin (modified after Omatsola and Adegoke)

74. The Ise Formation succession of conglomerates, sands, and mudrocks and kaolinitic clays overlying the Basement Complex. The formation has a no nonmarine origin, probably alluvial fan deposit. The Afowo Formation Composed of mostly medium to coarse sandstones, with thin to thick interbeds of shales, siltstones and claystones . It shows shaling upward trend It has two bitumen-soaked fine-grained sand horizons, each about 15 m thick, separated by a thick organic-rich black shale The Araromi Formation Rayments (1965) informal Araromi Shale is the unit now formalized into the Araromi Formation by Omatsola and Adegoke (1981) Consists of fine to medium sands at the base, overlain by a seaward thickening shale and siltstone with thin limestones and marls, and also lignitic bands The formation is very richly fossiliferous. The Ewekoro Formation The formation is traceable over a distance of 320 km continuously from east of Accra, eastward through the whole of the Dahomey Basin. At the type section, the formation consists of limestone, shale, claystone/mudstone The formation is thinly bedded, and has intercalation of marls, shales, silts, minor sands and sandy limestone. Abundance of Gastropods and lamellibranch shell fragments, evidently marine. The Akinbo Formation The base of the formation is marked by a glauconitic rock band on the top of Ewekoro Limestone. A grey clayey sand marks its top. Richly fossiliferous, though poorly preserved. Evidently marine too.

75. The Oshosun Formation Composed of green to greenish grey clays and glauconitic shales interbedded with lose sand. The basal parts are arenaceous. Thin limestones and marls are locally or sporadically present. Fossiliferous (foraminifera), mostly benthics and subordinate planktics . Deep marine environment suggested, others suggest a marine dominated transitional environment. The Ilaro Formation Comprises of about 80 m of sands and shales The sands are characteristically medium to coasre grain, clayey and poorly sorted with subangular grains and often intercalated with clays and shales. Pebble beds are common Has abundant fish remains, corals, gastropods, foraminifera, ostracods. These marine fauna directly shows a marine depositional environment. The Benin Formation Formerly called Coastal Plain Sands Alternation of sands and clays, with only a 30 cm thick lignite interval Poor sorting, clayey and texturally immature, but the sands are mineralogically matured as feldspars are absent. Planar and trough-cross bedding as sedimentary structures Completely continental, specifically fluvial.

76. PALEOGEOGRAPHY OF DAHOMEY BASIN Ise Formation which lie unconformably on the basement is continental and deltaic in origin. The overlying Afowo Formation has transitional marine origin. All other overlying sediments are deep to shallow marine.

77. ECONOMIC GEOLOGY OF DAHOMEY BASIN Rich in three out of the four classes of economic earth materials, especially outside the Nigerian sector Industrial materials (sands, stones, gravels, clays, limestone) Chemical minerals (Phosphate rock, especially in Togo) Petroleum resources and Energy deposits The only one ruled out is the Metalliferous minerals

78. THE NIGER DELTA BASIN It lies in the south-westernmost part of the Benue Trough up to the Nigerian coastlines. Niger Delta refers to all the areas underlain by Cenozoic strata in Southern Nigeria. The Niger Delta Basin to date is the most prolific and economic sedimentary basin in Nigeria by the virtue of the impact size petroleum accumulations , discovered and produced as well as the spatial distribution of the petroleum resources to the onshore , continental shelf through deepwater terrains. The geophysicists and geologists have shown that the Niger Delta Basin has maintained a thick sedimentary apron and geological features favorable for petroleum generation, migration, and entrapment.

79. ORIGIN OF THE NIGER DELTA BASIN The Niger Delta Basin is an extensional basin whose origin is related to the Benue Trough. The basin was formed as a result of continued subsidence of area further south of the Benue Trough. The subsidence of this rifted Atlantic type continental margin resulted from thermal contraction of the lithosphere . It was the subsidence that induced the major marine transgression of the early Paleocene that began the filling of the new basin. Note: most continental margins created during the rifting of a lithospheric plate evolved into deep sedimentary basins occupying the transition zone between ocean and continent. This is so because there is thinning of the crust and sub-crustal lithosphere and filling of hot aesthenospheric material. This leads to crustal extension accompanied by Isostatic elevation changes and density change, heating and thermal expansion. Longer term subsidence occurred in the extended region as the margin cools by conduction and undergoes thermal contraction after extension stopped.

80. THE NIGER DELTA BASIN Stratigraphy of the Niger Delta Basin Fig 8: Average cross-section through the Niger Delta (Thomas, 1995) (See also Figs 3 and 4 for more details on stratigraphy of the ND Basin)

81. STRATIGRAPHY OF THE NIGER DELTA BASIN Benin Formation Agbada Formation Akata Formation Younging direction

82. Description of the Various Stratigraphic units of the Niger Delta The Akata Formation consists of clays and shales with minor sand intercalations. The sand percentage here is generally less than 30%. Rich in planktic foraminifera The sediments were deposited in shallow marine environments. The Agbada Formation consists of alternating sand and shales representing sediments of the transitional environment comprising the lower delta plain (mangrove swamps, floodplain, marsh) and the coastal barrier and fluviomarine realms. The sand percentage within the Agbada Formation varies from 30 to 70%, which results from the large number of depositional offlap cycles. A complete cycle generally consists of thin fossilferous transgressive marine sand, followed by an offlap sequence which commences with marine shale and continues with laminated fluviomarine sediments followed by barriers and/or fluviatile sediments terminated by another transgression (Weber, 1972; Ejedawe , 1989). The Benin Formation Formerly called the Benin Sands Series and later Coastal Plains Sands forms the top layer of the Niger Delta depositional sequence. characterized by high sand percentage (70–80%), few shale breaks (which increase in frequency towards the base) and the general absence of brackish water and marine faunas. The massive sands were deposited in continental environment comprising the fluvial realms (braided and meandering systems) of the upper and lower delta plain. Also involved are deltaic, estuarine, lagoonal and fluviolacustrine subenvironments .

83. PALEOGEOGRAPHY OF THE NIGER DELTA BASIN The pre-Akata facies are deposited in a transgressive environment . The Akata Formation was also installed by transgressive activity . It is mainly a marine mud facies with turbiditic sands and continental slope channel fills . The Benin sands were deposited under a prevailing continental conditions (fluvial, lagoonal and fluvio-lacustrine sub environments). Based on paleo-bathymetric evidence , the trace fossils identified in cores of Agbada Formation indicate series of depositional sub environments ranging from tide-influenced transitional marginal marine environment to wave dominated, tide influenced shoreface .

84. ECONOMIC GEOLOGY AND PETROLEUM POTENTIAL OF THE NIGER DELTA BASIN Petroleum Resources Energy Deposits Industrial rocks and Mineral