BIDA, NUPE, OR MIDDLE NIGER BASINSedimentology and depositional environments of the Maastrichtian

Patti Formation, southeastern Bida Basin, NigeriaOlusola J. Ojo , a, and Samuel O. Akandea

aDepartment of Geology and Mineral Sciences, University Of Ilorin, P. M. B. 1515, Ilorin, NigeriaReceived 12 December 2008; accepted 29 August 2009. Available online 9 September 2009.

AbstractThe Maastrichtian Patti Formation, which consists of shale - claystone and sandstone members, constitutes one of the three Upper Cretaceous lithostratigraphic units of the intracratonic southeastern Bida Basin, in central Nigeria. Well exposed outcrops of this formation were investigated at various locations around the confluence of the Niger and Benue Rivers. The lithostratigraphic sections were measured and their peculiar sedimentological features such as textures, physical and biogenic sedimentary structures, facies variations and associations were documented and used to interpret the depositional environments and develop a paleogeographic model. Some selected representative samples of the sedimentary depositional facies were also subjected to grain size analysis.Three shoreline sedimentary depositional facies composed of shoreface, tidal channel, and tidal marsh to coastal swamp facies were recognized in the study area. Continental sedimentary depositional facies such as fluvial channel, swamp, and overbank were also documented. The sandstones of the shoreface and tidal channel facies are medium- to coarse-grained, moderately sorted (standard deviation ranges from 0.45–1.28 averaging 0.72), and quartzarenitic. The fluvial channel sandstone facies are coarse- to very coarse-grained, mostly poorly sorted (standard deviation ranges from 0.6–1.56 averaging 1.17), and subarkosic. Typical sedimentary structures displayed by the shoreface and tidal channel facies include burrows, clay drapes, hummocky and herringbone cross stratifications, whereas the fluvial channel sandstone facies are dominated by massive and planar cross beddings. The tidal marsh to coastal swamp shales and ferruginised siltstone facies are fossiliferous and bioturbated, whereas the nonmarine swamp siltstones contain vegetal imprints and lignite interbeds. The overbank claystone facies are massive and kaolinitic.In the study area, a regressive to transgressive model is proposed for the Patti Formation. This model correlates with stratigraphically equivalent sediments of the Ajali and Mamu Formations in the adjacent Anambra Basin to a great extent.Keywords: Sedimentology; Sedimentary facies; Paleoenvironment; Patti Formation; Bida Basin; NigeriaArticle Outline1. Introduction 2. Regional stratigraphic setting 3. Methods and locations 4. Sedimentary facies and depositional environments 4.1. Shoreface facies association 4.2. Tidal channel facies 4.3. Tidal marsh to coastal swamp facies association 4.4. Fluvial channel facies association 4.5. Nonmarine swamp/overbank facies association5. Grain size distribution and paleoenvironmental implications 6. Paleogeography 7. Conclusions Acknowledgements References

SEDIMENTATION AND TECTONICS IN THE SOUTHERN BIDA BASIN, NIGERIA: DEPOSITIONAL RESPONSE TO VARYING

TECTONIC CONTEXTCreator/Author: Braide, S.P. (Federal Univ. of Technology, Minna (Nigeria)) Publication Date: 1990 May 01; OSTI Identifier: OSTI ID: 6796922; Report Number(s): CONF-900605--Other Number(s): Journal ID: ISSN 0149-1423; CODEN: AABUDResource Type: Conference Specific Type: Journal ArticleResource Relation Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA); Journal Volume: 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990Subject: 02 PETROLEUM; 58 GEOSCIENCES; NIGERIA; PETROLEUM GEOLOGY; SEDIMENTARY BASINS; SEDIMENTATION; TECTONICS; CRETACEOUS PERIOD; PRECAMBRIAN ERA; RIFT ZONES; SCHISTS; AFRICA; DEVELOPING COUNTRIES; GEOLOGIC AGES; GEOLOGIC STRUCTURES; GEOLOGY; MESOZOIC ERA; METAMORPHIC ROCKS; ROCKS

Abstract

The Upper Cretaceous Bida basin of central Nigeria is sandwiched between the Precambrian schist belts of the Northern Nigerian massif and the West African craton. Of interest is the southern part of the basin, which developed in continental settings, because the facies architecture of the sedimentary fill suggests a close relation between sedimentation dynamics and basin margin tectonics. This relationship is significant to an understanding of the basin's origin, which has been controversial. A simple sag and rift origin has been suggested, and consequently dominated the negative thinking on the hydrocarbon prospects of the basin which were considered poor. This detailed study of the facies indicates rapid basin-wide changes from various alluvial fan facies through flood-basin and deltaic facies to lacustrine facies. Paleogeographic reconstruction suggests lacustrine environments were widespread and elongate. Lacustrine environments occurred at the basin's axis and close to the margins. This suggests the depocenter must have migrated during the basin's depositional history and subsided rapidly to accommodate the 3.5-km-thick sedimentary fill. Although distinguishing pull-apart basins from rift basins, based solely on sedimentologic grounds, may be difficult, the temporal migration of the depocenter, as well as the basin architecture of upward coarsening cyclicity, show a strong tectonic and structural overprint that suggests a tectonic framework for the Southern Bida basin similar in origin to a pull-apart basin.

Fig. 1 (a) Map of Nigeria showing NW/SE trending Bida Basin (b) Geological map of study area after Agyingi (1991) showing locations of studied sections.

Fig. 2 Regional stratigraphic successions in the Bida Basin and restored NW-SE-S stratigraphic relationships from the Bida basin to the Anambra Basin (Modified after Akande et al. 2005)

Fig. 3 Lithologic section and distribution of pollen and spore and dinoflagelates in the Patti Formation exposed at Ahoko, along Lokoja – Abuja highway.

Fig. 4 Lithologic sections and distribution of pollen and spores and dinoflagellates in the Patti formation exposed at Ahoko quarry.

Fig. 5 Frequency chart of the dinoflagellate groups in the study area (a) Pie chart (b) Bar chart.

Plate 1 Fig. 1 Andalusiella polymorpha; Fig. 2 Senegalinium bicavatum; Fig. 3 S. bicavatum; Fig. 4 Senegalinium psilatum; Fig. 5 Deflandrea sp.; Fig. 6 Dinogymnium euclaensis; Fig. 7 Dinogymnium acuminatum; Fig. 8 Dinogymnium digitus; Fig. 9 Paleocystodinium australinium; Fig. 10 Microforaminifera lining; Fig. 11 Isabelidium cooksoni; Fig. 12 Florentinia sp.; Fig. 13 Aeroligera senonensis; Fig. 14 Spiniferites ramosus; Fig. 15 Pediastrum; Fig. 16 Cristaeturites cristatus, Fig. 17 Buttinia andreevi; Fig. 18 Retidiporites magdalenensis [Magnifications; Figs 1,3,4,5,9,10,16 x 800, others x 1000.]

Mid-Niger/Bida BasinAlthough TOC values (Table 1) and liptinite contents are relatively high in the Mid-Niger Basin samples, the Tmax values, Ts/Tm and moretane/hopane ratios are indicative that hydrocarbons of mainly gaseous composition (Fig. 5) are probably just being generated in the basin and may not yet have been expelled nor migrated in large quantities. However, it is important to note at this stage that some hydrocarbon seepages have been reported along the bank of River Niger around Pategi and Mokwa in the Niger State of Nigeria (Philip Shekwolo, 2003, personal communications).

TABLE : IRON ORE DEPOSITS IN THE BIDA [NUPE OR MIDDLE NIGER] BASIN

Deposit or Occurrence Agbaja PattiGeological origin Sedimentary OolitcOre type Geothite and HydrothiteTotal Fe (%) 47.8Fe in concentrate 52.1Estimated Resource (million tonnes)

370-5,000

SOURCE: NGSA [2010]

PETROGRAPHIC-MICROCHEMICAL STUDIES AND ORIGIN OF THE AGBAJA PHANEROZOIC IRONSTONE FORMATION, NUPE BASIN, NIGERIA: A PRODUCT OF A FERRUGINIZED OOIDAL KAOLIN PRECURSOR NOT IDENTICAL TO THE MINETTE-TYPE

A. Mücke1, T. A. Badejoko2 and S. O. Akande3

(1) Mineralogisch-Petrologisches Institut, Georg-August-Universität, Goldschmidtstrasse 1, D-37077 Göttingen, Germany, DE

(2)  Department of Geology, University of Ibadan, Ibadan, Nigeria, NG(3)  Department of Geology, University of Ilorin, Ilorin, Nigeria, NG

Abstract   The Campanian-Maastrichtian Agbaja Ironstone Formation of the Nupe basin, Nigeria, forms a major part of the about 2 billion tons of iron ore reserves of the Middle Niger Embayment. The ironstone deposits were previously reported to be similar to the Minette-type ironstones because of their depositional patterns, composition and inferred origin. Four rock-types are recognized within the Agbaja Ironstone Formation: ooidal pack-ironstone, pisoidal pack-ironstone, mud-ironstone and bog iron ore. In the ironstones, kaolinite of both the groundmass and the ooids/pisoids is of lateritic origin, whereas the associated quartz, mica and heavy minerals are of detrital origin. Ooids and pisoids were formed by mechanical accretion of platy kaolinite crystals by rolling on the sea floor in a near-shore environment, and were subsequently transported and deposited together with a fine-grained kaolinitic groundmass. Pyrite (mainly framboidal) and siderite (both exclusively occurring as pseudomorphs of goethite and/or hematite) are diagenetic whereas goethite is post-diagenetic in origin, resulting from the ferruginization of the kaolinitic precursor. Crandallite-gorxeicite-goyazite, bolivarite and boehmite are also post-diagenetic in origin. Hematite was formed from the dehydration of goethite, whereas gibbsite (restricted to the upper part of the deposit) is of recent and in situ lateritic origin. The presence of

newly formed authigenic pyrite and siderite (now replaced by hematite and goethite) are indicators of a reducing environment during diagenesis. The absence of diagenetic chamositic clay minerals, evidently caused by a low Mg concentration, suggests that fully marine conditions were not established during sedimentation. This is supported by the lack of fossils, brecciated shell materials and bioturbation features in the deposit. Reworking and redeposition of the primary constituents are inferred from broken pisoids, nuclei of pisoidal/ooidal fragments in pisoids and high iron concentrations present in the pisoids and ooids compared to that of the groundmass. These observations indicate that the Agbaja ironstone deposits of the Lokoja study area exhibit some environmental and mineralogical characteristics that are markedly different from other known deposits of Minette-type, where primary chamositic clay minerals generally form the protore for the ironstones. The recognition of kaolinite as the precursor constituent and the occurrence of similar deposits of the same age (Late Cretaceous) in Nigeria, Sudan and Egypt have implications for the paleoenvironmental interpretations of Phanerozoic ironstone deposits. Received: 16 February 1998 / Accepted: 8 July 1998