Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria w sciencedirect com Journal of Palaeogeography, 2017, ▪(▪) 1e15 Available online at ww Scie[.]
Journal of Palaeogeography, 2017, ▪(▪): 1e15 Available online at www.sciencedirect.com ScienceDirect journal homepage: http://www.journals.elsevier.com/journal-of-palaeogeography/ Biopalaeogeography and palaeoecology Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria S.A Bankole a b a,* , A.O Ola-Buraimo b Department of Chemical and Geological Sciences, Al-Hikmah University, Ilorin, Nigeria Department of Geology, Federal University, Birnin Kebbi, Nigeria Abstract Biostratigraphy investigation of Nsukka Formation was carried out by subjecting well cutting samples obtained from Nzam-1 well to palynological studies with the view towards determining the relative geologic age and palaeoenvironment of deposition of the sediments Samples were treated in the laboratory through digestion with hydrofluoric acid, sieving with mm, oxidation with Nitric acid and mounting of the slides into sections with DPX mountant A fairly high abundance and diversity of miospores were recovered, while the interval (847e1372 m) contains distinctive and diagnostic palynomorphs which are stratigraphically important A Spinizonocolpites baculatus assemblage zone was established based on the basal occurrence of S baculatus, Spinizonocolpites echinatus, Constructipollenites ineffectus, Periretisyncolpites sp Periretisyncolpites giganteus, Monocolpites sp 1, Foveotriletes margaritae, Syncolporites marginatus, and Longapertites marginatus The upper part of the interval is marked by association of Anacolosidites luidonisis (at top), Mauritiidites crassibaculatus, Retistephanocolpites williamsi, Proteacidites dehaani, Echitriporites trianguliformis, Proxapertites cursus, Retidiporites magdalenensis, S baculatus, Retitricolpites gigeonetti, F margaritae and Araucariacites sp The Nsukka Formation is dated as Late Maastrichtian based on the cooccurrence of recovered index fossils Importantly, CretaceouseTertiary (K/T) boundary is marked by high fossil content in the Maastrichtian sediments compared to paucity in palynomorph that characterise the overlying Paleocene facies Palaeoenvironment of the analyzed section varies alternately from marginal marine to continental setting based on the presence of land-derived miospores and dinoflagellates Keywords Biostratigraphy, Palaeoenvironment, Assemblage, Gonyaulacacean/Peridinacean ratio, Index fossil, Anambra Basin © 2017 China University of Petroleum (Beijing) Production and hosting by Elsevier B.V on behalf of China University of Petroleum (Beijing) This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/) Received 24 October 2015; accepted November 2016; available online xxx * Corresponding author E-mail address: bayus4sure2@alhikmah.edu.ng (S.A Bankole) Peer review under responsibility of China University of Petroleum (Beijing) http://dx.doi.org/10.1016/j.jop.2016.11.001 2095-3836/© 2017 China University of Petroleum (Beijing) Production and hosting by Elsevier B.V on behalf of China University of Petroleum (Beijing) This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 S.A Bankole, A.O Ola-Buraimo Introduction The Anambra Basin is an inland intracratonic basin located adjacent to Niger Delta, Nigeria (Fig 1) Its study continues to attract attention of many geologists because of proven hydrocarbon reserves present The Anambra Basin ranks almost next to Niger Delta in terms of richness in hydrocarbon reserves Despite enormous amount of work done on the geology of the basin including the petroleum geology, biostratigraphy and sedimentology, there are no much details available on the biostratigraphy of Nsukka Formation Therefore, there is need to further understand the stratigraphic stacking pattern especially the biostratigraphy of Nsukka Formation in terms of age and palaeoenvironment of deposition which could serve as a correlation platform for regional stratigraphic study Such study would help to optimize hydrocarbon exploration and exploitation in the basin These parameters are the main focus of this research work Geologic setting The Anambra Basin is a major inland sedimentary basin in Nigeria (Fig 1) Its evolution was based on the theory of the separation of the African and South American Plates during the Middle Mesozoic period (Burke et al., 1972; Nwachukwu, 1972) The theory ascertains that the Anambra Basin contains AlbianeSantonian sediments in the eastern half referred to as Abakaliki depression while the other half proto-Anambra was a platform consisting of post Santonian sediments (Benkhelil, 1982; Murat, 1972; Nwachukwu, 1972; Nwajide and Reijers, 1996, 1997; Obi, 2000) Past research works showed that the northern and western parts of the Anambra Basin mainly consist of post Santonian sediments However it has been proven otherwise that the northern and the western parts of the basin in Onitsha and Edo state respectively, contain Middle Cretaceous to Late Tertiary sediments (OlaBuraimo, 2013a, 2013b; Ola-Buraimo and Akaegbobi, 2012; Ola-Buraimo and Akaegbobi, 2013a) The Santonian period marked the stage when the basin experienced tectonic event that involved deformation, folding, faulting and uplifting of the pre-Santonian sediments in the Onitsha area which evolved as depression to the uplift (Benkhelil, 1987) However, this depression was limited in extent excluding the northern part of the Anambra Basin and southwestern part of the basin (Ola-Buraimo and Akaegbobi, 2013b) The oldest sediment in the Anambra Basin has been erroneously placed to be Nkporo Group (Nwajide, 1990) but recent study shows that apart from southern Onitsha area, the basin contains Asu-River Group sediments dated as Albian to Lower Cenomanian (Ola-Buraimo and Akaegbobi, 2013b) The stratigraphic sequence of the Anambra Basin has been discussed extensively by several workers including Agagu et al (1985); Dessauvagie (1975); Fig Geological map of the Anambra Basin showing location of study area (From Nton and Bankole, 2013) Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 Biostratigraphy and palaeoenvironment, southeastern Nigeria Ladipo (1986); Murat (1972); Nton and Bankole (2013); Ola-Buraimo and Akaegbobi (2013b); Reyment (1965); Though, sedimentation in the Anambra Basin was based on the long standing assumption that it started and ranged from late Santonian to Eocene but recent research work of Ola-Buraimo and Akaegbobi (2012) on OgwashieAsaba Formation has shown that the formation in actual fact is of Late Miocene to Pliocene age based on the presence of dinoflagellate cysts It has also been advanced that the oldest sediment in the basin like the other known parts is Asu-River Group, dated as Albian to early Cenomanian (Ola-Buraimo and Akaegbobi, 2013b) through the use of pollen and spores assemblages The Asu-River Group has varied lithologic unit, dark grey to black coloured shale, variously ferruginized, deposited in environment varying from continental through marginal marine to open marine systems (OlaBuraimo and Akaegbobi, 2013b) This is overlain by Eze-Aku Formation, composed of predominantly dark shale, dated late Cenomanian to Turonian (OlaBuraimo, 2013a) Awgu Shale dated Coniacian (OlaBuraimo, 2013b) overlies the Eze-Aku Formation and marked the end of the first phase of sedimentation in the Anambra Basin before the commencement of tectonic event in the Santonian The dislocation of the depocenter into the Anambra platform resulted into the deposition of the Nkporo Shale (Nwajide, 1990) The Nkporo Group comprises of Nkporo Shale, Owelli Sandstone, and Enugu Shale dated late Campanian (Obi, 2000; Reyment, 1965) However, study based on palynology has dated the Asata/Nkporo Shale to be Campanianeearliest Maastrichtian age (Ola-Buraimo and Akaegbobi, 2013b) The Nkporo Shale is overlain by Mamu Formation deposited during early Maastrichtian (Kogbe, 1989; Obi, 2000) It is composed of siltstone, shale, coal seams and sandstone (Kogbe, 1989; Nton and Bankole, 2013) The age dating Mamu Formation has been further refined and recently dated to range from early to middle Maastrichtian based on pollen and spores recovered (Ogala et al., 2009) The Ajali Sandstone broadly dated Maastrichtian age overlies the Mamu Formation (Nwajide, 1990; Reyment, 1965) The sandstone is unconsolidated, coarse to fine grained, poorly cemented, with little mudstone and siltstone (Kogbe, 1989) The Ajali Sandstone is overlain by Nsukka Formation dated MaastrichtianeDanian This is also known as Upper Coal Measures (Obi, 2000; Reyment, 1965) The Imo Shale (Paleocene) overlies the Nsukka Formation (Nwajide, 1990) while it is successively overlain by Ameki Group, dated Eocene (Obi, 2000); Ogwasi-Asaba Formation consists of dark grey shale and sandy shale, characterized by evidence of sediment reworking and dated Late MioceneePliocene (Ola-Buraimo and Akaegbobi, 2012) The most recent sediment in the basin is the Benin Formation deposited by fluvial processes and is suggested to belong to Pliocene to recent in age based on stratigraphic position The detailed stratigraphy of the basin is given below in Table Methodology Twenty two ditch cutting samples of Nzam-1 well situated in the Anambra Basin ranging in depth from 847 m to 1372 m were used for the preparation of the palynological slides The samples were taken for preparation at 24 m interval except where samples are not available The sample preparation was carried out in the laboratory following the common practice (Green, 2001; Wood et al., 1996) Indurated samples were crushed with mortar and pestle in order to enhance maximum recovery of pollen and spores The crushed samples along with the friable ones of about 20 g weight (20 gm) were poured into labelled plastic beakers which were initially treated with dilute hydrochloric acid (HCl, 10%) in order to eliminate carbonate substance present in them They were later soaked in 60% hydrofluoric acid (HF) overnight for about 20 h and stirred intermittently in order to achieve near complete digestion of silica and silicates The samples were not oxidized in order to avoid corrosion, but were sieved with mm mesh in order to maximize concentration of miospore grains and in Table Correlation chart for Early Cretaceous strata in southeastern Nigeria (After Nwajide, 1990) Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 S.A Bankole, A.O Ola-Buraimo Table Palynological distribution chart of Nsukka Formation (847e1372 m) Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 Biostratigraphy and palaeoenvironment, southeastern Nigeria Fig All magnification at ×400 1eMonosulcites sp.; 2eIndeterminate dinocyst; 3eE trianguliformis Van-Hoeken Klinkenberg, 1964; 4,6,11ePeriretisyncolpites sp Lawal, 1982; 5ePhelodinium bolonienae Riegel, 1974; 7eInaperturopollenites sp.; 8e C ineffectus Van Hoeken-Klinkenberg, 1964; 9eCrassoretitriletes vanraadshooveni Germeraad et al., 1968; 10eCtenolophonidites costatus; 12eP giganteus Kieser and Jan du Chehe, 1979 order to achieve clean slides for easy petrographic analysis Other stages of preparation include heavy liquid separation of the macerals before they were finally mounted on glass slides with Deepex (DPX) mountant Result and interpretation Twenty two samples were prepared and analyzed petrographically for palynomorph content Palynological result reveals that the samples were rich in pollen, spore and dinoflagellates The lower part of the interval is moderately to highly rich in miospores, the middle part is rare to barren, while the upper part is increasingly highly rich in pollen, spore and dinoflagelates (Table 2) The forms encountered are quite rich in abundance and diversity and they are well preserved as indicated in the Figs 2e9 Lithofacies sequence of the interval is mainly dark grey fissile shale but interval 1109e1116 m is composed of dark grey sandy shale with sand/shale ratio of 30.70%, fine to medium in grain size, angular to subangular in shape, and rarely ferruginized in nature The assemblages of the pollen forms in the interval 847e1372 m are characterized mainly by Maastrichtian forms The assemblage belongs to S baculatus assemblage zone compared with the works of Lawal (1982), Lawal and Moullade (1986) for the Lower Benue Trough, Nigeria, Jardine and Magloire (1965) for Senegal and Cote D' Ivoire sedimentary deposits Palynozone: S baculatus Assemblage Zone Interval: 847e1372 m Age: late Maastrichtian Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 S.A Bankole, A.O Ola-Buraimo Fig All magnification at ×400 1eR magdalenensis Van der Hammen and Garcia, 1965; 2eBatiacasphaera sp Lawal, 1982; 3eL marginatus Van Hoeken-Klinkenberg, 1964; 4eOligosphaeridium sp Lawal, 1982; 5eFlorentinia sp Lawal, 1982; 7e Cyathidites sp.; 8eP operculatus Van der Hammen, 1956b; 9eOligosphaeridium pulcherrimun (Deflandre and Cookson) Davey and Williams, 1966; 10eP bolonienae Riegel, 1974; 11,15eCyathidites australis; 12eP giganteus Kieser and Jan du Chene, 1979; 13eTriporites sp.; 14eOdontochitina sp.; 16eMicroforaminiferal wall lining Characteristic: The base of the interval is marked by the co-occurrence of S baculatus and S echinatus in association with C ineffectus, Periretisyncolpites sp, P giganteus, Monocolpites sp (Fig 10), reduced abundance of L marginatus, P cursus, and Verrucatosporites sp The top of the zone is defined by the co-occurrence of A luidonisis and M crassibaculatus (Fig 2) At the level (847 m) Periretisyncolpites spp shows first disappearance Other forms still present at the top of the interval are increased angiosperm pollen, Retimonocolpites sp, stephanoporate pollen, and Monosulcites sp The top of the zone is also placed where there is high abundance and diversity of recovered sporomorphs end; this conforms to the observations of Lawal and Moullade (1986), Ola-Buraimo (2012) in marking the boundary between late Maastrichtian and Paleocene (K/T boundary) (Table 2) Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 Biostratigraphy and palaeoenvironment, southeastern Nigeria Fig All magnification at ×400 1eProteacidites sp.; 2eC australis 3e Tricolpites gigantoreticulatus Jardine and Magloire, 1965; 4eL marginatus Lawal, 1982; 5eAuriculiidites sp.; 6eOligosphaeridium sp.; 7ePhelodinium sp.; 8eSenegalinium bicavatum Jain and Millepied, 1975; 9eSubtilisphaera sp.; 10eIndeterminate pollen; 11eP giganteus (corroded); 12eInaperturopollenites sp Lawal, 1982; 13eFungal spore; 14eCupanieidites reticularis Cookson and Pike, 1954; 15eA polymorpha Malloy, 1972; 16e Florentinia sp Assemblages of miospores recovered in this zone is equivalent in part to those of sequences III, II, I for the Maastrichtian sediments in Senegal and Cote d’ Ivoire by Jardine and Magloire (1965) The interval is characterized by increased angiosperms and decreased gymnosperms The lower part of the zone is marked by relatively moderate abundance and diversity of miospore, the middle part is poor to barren while the upper part is most fossiliferous and diverse in nature (Figs 11 and 12) The forms that characterize the upper section of the interval include R williamsi, P dehani, E trianguliformis, C ineffectus, L marginatus, P cursus, R magdalenensis, S baciulatus, Anacolosidites sp, R gigeonetti, F margaritae, and Araucariacites sp This portion of the interval is suggested to belong to late Maastrichtian to Early Paleocene The presence of Anacolocidites sp suggests the Early Paleocene deposit (Germeraad et al., 1968) The lower part (924e1372 m) is less fossiliferous, sparse of miospores and rarely barren The Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 S.A Bankole, A.O Ola-Buraimo Fig All magnification at ×400 1eSubtilisphaera sp.; 2eTriporate pollen 3e Stephanocolpites 4e R magdalenensis Van der Hammen and Garcia, 1965; 5eL microfoveolatus Jan du Chene and Adegoke, 1978; 6eLongapertites verneendenburgi Germeraad et al., 1968; 7eOligosphaeridium sp.; 8eRetitriporites sp.; 9eSubtilisphaera sp Lawal, 1982; 10eCyathidites sp.; 11,16eL marginatus Van HoekenKlinkenberg, 1964; 12eCaningia sp Lawal, 1982; 13eBotryococcus braunii; 14e Oligosphaeridium sp Lawal, 1982; 15eInaperturopollenites sp microfloral present include P cursus, Longapertites sp, E trianguliformis, F margaritae, Tetradites sp, Mauritiidites crasibaculatus, S marginatus, Lycopodium sp, and Longapertites microfoveolatus This part is suggested to belong to late Maastrichtian age The S baculatus assemblage zone established in this well is similar to palynological content of S baculatus Assemblage Zone erected by Lawal and Moullade (1986) However, Trichotomosulcites sp 1, and Milfordia jardinei, described by Lawal and Moullade (1986) for this zone for the Lower Benue Trough sediments are restricted to older sediments (OlaBuraimo and Akaegbobi, 2013a) Those forms may be contaminants in the sediment analyzed by Lawal and Moullade (1986) The assemblages of miospores present in this zone are similar to the forms described in late Maastrichtian or younger age sediments of other places This was observed by Germeraad et al (1968), Jan Du Chene (1977), Jan Du Chene et al (1978), Jardine and Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 Biostratigraphy and palaeoenvironment, southeastern Nigeria Fig All magnification at ×400 1eO pulcherrimun (Deflandre and Cookson) Davey and Williams, 1966; 2eMonocolpopollenites sphaeroidites Jardine and Magloire, 1965; 3eCf Subtilisphaera sp.; 4eForma; 5,6eBatiacasphaera sp.; 7,8eProteacidites longispinosus Jardine and Magloire, 1965; 9eCf Distaverrusporites sp.; 10,11ePeridinacae sp (Forma T1); 12eMonocolpites sp.; 13,14eA laevigata Malloy, 1972; 15eR magdalenensis Van der Hammen and Garcia, 1965; 16eInaperturopollenites sp Magloire (1965), Kieser and Jan du Chene (1979), Lawal and Moullade (1986), Muller (1968), OlaBuraimo (2012), Salard Cheboldaeff (1979, 1981, 1990), Sole de Porta (1972), Van der Hammen (1954), Van der Hammen and Wijmstra (1964) and Van HoekenKlinkenberg (1964) The analyzed interval is equivalent to the upper part of Gombe Formation characterized by decrease in gymnosperms and by development of angiosperms such as sulcate, triporate, tricolpates (SalardCheboldaeff, 1990) This zone is also equivalent to P dehaani zone established by Germeraad et al (1968) for the pantropical regions The sediment of the zone is equivalent to Nsukka Formation in this well which shares the same sporomorphs with those found in the Iullummeden Basin in the North-West, Nigeria (Boudouresque, 1980); upper part of Fika Formation in Bornu Basin, Nigeria (Ola-Buraimo, 2012) It is noted in this zone that some of the floral observed such as Proxapertites operculatus, M crassibaculatus, S echinatus, tricolpate grains, R williamsi were also reported in Kerrikerri Formation in the Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 10 S.A Bankole, A.O Ola-Buraimo Fig All magnification at ×400 1eL marginatus Van Hoeken-Klinkenberg, 1964; 2eMonosulcites sp.; 3eMonocolpites sp.? 4eTricolpites sp.; 5e F margaritae (Van der Hammen) Germeraad et al., 1968; 6eLaevigatosporites sp.; 7eL marginatus Van Hoeken-Klinkenberg, 1964; 8eR magdalenensis Van der Hammen and Garcia, 1966; 9,10,11eMonocolpites sp.; 12eMicroforaminiferal wall lining; 13eVerrucatosporites sp.; 14,15eMonocolpites marginatus Van der Hammen, 1954; 16eMonosulcites sp Jardine and Magloire, 1965 northeast The Gombe Formation in the northwest (Iullemmeden Basin), Ewekoro Formation in the southwest (Dahomey Embayment) and Ebenebe Formation in the southeast were assigned Paleocene age However, the assemblages of miospores described for the Mamu Formation Coal Seam Measure (Ogala et al., 2009) seem to be similar in part with those observed in this interval, but well correlated with established forms for the Lower Benue Trough, Nigeria which belong to the S baculatus assemblage zone (Lawal and Moullade, 1986) Therefore, the interval is dated late Maastrichtian age and lithologically equivalent to the Nsukka Formation of the Anambra Basin, southeastern Nigeria Palaeoenvironment of deposition Palaeoenvironment deduction of the analyzed interval was based on the presence of environmentally Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 Biostratigraphy and palaeoenvironment, southeastern Nigeria 11 Fig All magnification at ×400 1eMonosulcites sp.; 2eC ineffectus Van Hoeken-Klinkenberg, 1964; 3eR magdalenensis Van der Hammen and Garcia, 1966; 4,5ePeriretisyncolpites sp Lawal, 1982; 6,7eS marginatus Van Hoeken-Klinkenberg, 1964; 8eInaperturopollenites sp.; 9eMonosulcites sp.; 10eRetimonocolpites sp.; 11eTetradites sp Kotova, 1984; 12eE trianguliformis Van Hoeken-Klinkenberg, 1964; 13eTricolpites punctus Jan Du Chene, 1977; 14eTricolpites sp.; 15eTricolporopollenites sp Jardine and Magloire, 1965 significant forms The presence of marine derived forms such as dinoflagellate and microforaminifera wall lining would suggest marine environment while preponderance of terrestrially derived miospores without recovery of dinoflagellate forms in the assemblage is suggestive of continental deposit Therefore, interval 847e896 m is characterized by substantially high abundance of dinoflagellates such as Batiacasphaera sp, Polysphaeridium sp, Caningia capilata, Trichdiniumsp, Andalusiella laevigata, Andalusiella sp, Andalusiella polymorpha, Subtilisphaera sp and Thalassiphora sp Others are Trichodinium delicatum, Histrichodinium pulchrum, Oligosphaeridium complex, Cyclonephedinium distictum, Cribroperidinium edwardii, senegalidiniu sp and microforaminiferal wall lining The interval (847e896 m) is suggested to belong to marginal marine environment Interval 896e1234 m is defined by Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 12 S.A Bankole, A.O Ola-Buraimo Fig All magnification at ×400 1eGonyaulacysta sp.? 2eSubtilisphaera sp (Forma J); 3eMicroforaminiferal wall lining (Spiral type); 4eCallaiosphaeridinium asymmetrinun (Deflandre and Court) Davey and Williams, 1966; 5eAraucariacites sp.; 6eM marginatus Van der Hammen, 1954; 7eC edwardii (Cookson and Eisenack) Davey, 1969; 8eL microfoveolatus Jan du Chene and Adegoke, 1978; 9eP cursus Van Hoeken-Klinkenberg, 1964; 10eR williamsi in Salard-Cheboldaeff, 1990; 11e Cribroperidinium sp.1 Lawal, 1982; 12ePalaeocystodinium sp.; 13,14e Spinidinium sp.; 15eMonosulcites sp.; 16eTricolpites sp paucity of miospores mainly of terrestrially derived pollen and spores, thus, a continental environment of deposition is suggested for the interval The underlying interval 1234e1271 m is characterized by association of terrestrially derived forms and marine grains such as Batiacasphaera sp, A polymorpha and other forms of dinoflagellates The sediments were deposited in marginal marine setting Interval 1271e1320 m has similar characteristic like interval 896e1234 m, associated with continental deposit The basal interval 1320e1372 m has combined recovery of miospores and dinoflagellates Among the dinocysts present are Oligosphaeridium sp, Senegalinium sp, Polysphaeridium sp 1, dinoflagellate cysts and microforaminifera wall lining The interval is suggested to belong to marginal marine setting In a nut shell the analyzed interval varies alternately from marginal marine to continental environment of deposition Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 Biostratigraphy and palaeoenvironment, southeastern Nigeria 13 Fig 10 Palynolog of marker fossils appearances with depth in interval 847e1372 m Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 14 S.A Bankole, A.O Ola-Buraimo palaeoenvironment of deposition varies alternately from marginal marine to continental setting Acknowledgements The authors are grateful to Palystrat Limited for her continuous financial and material support in making this research study a reality We also appreciate the cooperation of Geological Survey Agency, Nigeria for providing ditch cutting samples and granting permission to publish these findings Fig 11 Depth-abundance plot for the upper part of interval 847e1372 m Fig 12 Depth-diversity plot for the upper part of interval 847e1372 m Conclusions Detailed palynological study of interval 847e1372 m revealed that the pollen, spores and dinoflagellates contained varied from moderate at the base through few to barren at the middle to very fossiliferous at the upper part of the interval The interval belongs to S baculatus assemblage zone based on the co-occurrence of S baculatus, C ineffectus, P spp, Monocolpites sp, and F margaritae The top of the interval is characterized by very high fossil abundance and diversity, and appearance of A luidonisis (marked Paleocene) in association with M crassibaculatus, R williamsi and other typical Maastrichtian grains such as P dehaani, E trianguliformis, P cursus, R magdalenensis and F margaritae The interval is mainly shaley lithologically with minor heterolith of sandy shale at the middle part of the interval while the References Agagu, O.K., Fayose, E.A., Petters, S.W., 1985 Stratigraphy and sedimentation in the Senonian Anambra Basin of eastern Nigeria Journal of Mining and Geology, 22(1), 25e36 Benkhelil, M.J., 1982 Benue Trough and Benue chain Geological Magazine, 119, 155e168 Benkhelil, M.J., 1987 Cretaceous deformation, magmatism and metamorphism in the lower Benue Trough, Nigeria Geological Journal, 22, 467e493 Boudouresque, L., 1980 Contribution de la paleopalynologie a la reconstitution floristique, stratigraphique et paleogeographique de la bordure occidentaledu Basin des Iullemmenden, au Cretace superieur et au Paleogene (Niger et Mali-Afrique de l'Ouest, These 3e cycle Niamey Geologie Sedimentaire, 244 Burke, K.C., Dessauvagie, T.F.J., Whiteman, A.J., 1972 Geological history of the Benue valley and adjacent areas In: Dessauvagie, T.F.J., Whiteman, A.J (Eds.), African Geology University of Ibadan, Nigeria, pp 187e206 Dessauvagie, T.F.J., 1975 Explanatory note, the geological map of Nigeria Nigerian Journal of Mining and Geology, 9, 1e28 Germeraad, J.H., Hopping, C.A., Muller, J., 1968 Palynology of tertiary sediments 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1964 A palynological study of the tertiary and upper cretaceous of British Guiana Leidese Geologische Mededelingen, 30(1), 183e241 Van Hoeken-Klinkenberg, P.M.J., 1964 A palynological investigation of some Upper Cretaceous sediments in Nigeria Pollen Spores, 6(1), 209e231 Wood, G.D., Gabriel, A.M., Lawson, J.C., 1996 Palynological techniques e processing and microscopy In: Jansonius, J., McGregor, D.C (Eds.), Palynology: Principles and Applications, vol American Association of Stratigraphic Palynologists Foundation, pp 29e50 Please cite this article in press as: Bankole, S.A., Ola-Buraimo, A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 ... A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 Biostratigraphy. .. A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 Biostratigraphy. .. A.O., Biostratigraphy and palaeoenvironment of deposition of Nsukka Formation, Anambra Basin, southeastern Nigeria, Journal of Palaeogeography (2017), http://dx.doi.org/10.1016/j.jop.2016.11.001 Biostratigraphy