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The Niger delta is one of the most prolific oil and gas producing Tertiary deltas in the world, yet its ... the geology

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Research Journal in Engineering and Applied Sciences 2(2) 86-94 © Emerging Academy Resources (2013) (ISSN: 2276-8467) www.emergingresource.org

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SEQUENCE PALYNO-STRATIGRAPHICAL STUDY OF DEL-2 WELL SOUTHWEST OF THE NIGER – DELTA BASIN NIGERIA 1

Ojo, A.O and 2Gbadamosi, A.O. 1 Department of Geology, Ekiti State University, Ado – Ekiti, Nigeria. 2 Department of Geology, Obafemi Awolowo University, Ile – Ife, Nigeria. Corresponding Author: Ojo, A.O ___________________________________________________________________________ The Niger delta is one of the most prolific oil and gas producing Tertiary deltas in the world, yet its biotratigraphy is less well understood. Despite the fact that a lot of exploration activities have been carried out in the basin, very little information has been published on its microfossils. Most of the information is kept as confidential reports in the archives of the oil companies for confidential reasons. Forty ditch-cutting samples from Del-2 well in the Southwestern part of the Niger delta basin were studied for their palynomorph content to date and deduce the depositional environment of the strata penetrated. A sequence stratigraphic interpretation was also attempted for the strata whose depth ranged from 609.60 m – 975.36 m. Of the 88 palyno-species, 60 pollen grains, 14 spore species and 14 other species made up of dinocysts, acritarchs, and algal cysts were identified. Other components of the palynomorphs include charred graminae cuticle, and microforaminiferal wall linings. The strata penetrated are dated Early – Late Pliocene based on the occurrence of, Racemonocolpites hians, Retistephanocolpites gracilis, Praedapollis obodoensis, Peregrinipollis nigericus, Multiareolites formosus; Verrutricolporites rotundiporus and Gemmanocolpites sp. The Early/Late Pliocene boundary was put at 710.18m, based on the first occurrence of Gemmanocolpites sp and regular occurrence of Retibrevitricolpites obodoensis and R. protudens. Three depositional environments, shallow, deep and open marine were deduced based on the relative abundance and diversity of the miospores and marine microfossils. The four proposed biozones (A B C and D) were based on the miospore distribution and abundance, especially, those of Monoporites annulatus and Zonocostites ramonae. One candidate sequence boundary and three system tracts: highstand, transgressive and low stand systems tracts, were deduced to occur within the studied interval. A candidate maximum flooding surface (mfs) occurred at 746.7 meters, depth. Thus this study has significantly contributed to the data base of published palynoflora records of the Niger delta basin and equally establish palynnofacies records and sequence stratigraphy of Pliocenc age of Agbada Formation. This will aid further studies in biostratigraphy and correlation of strata within the basin and other basins in the Gulf of Guinea. ©Emerging Academy Resources KEYWORDS: Sequence- Stratigraphy, Palynospecies, Niger – Delta Basin, Monoporites Annulatus, Maximum Flooding Surface. ________________________________________________________________________________________ INTRODUCTION stratigraphic techniques – The biostratigraphical Forty ditch – cutting samples from a well in the techniques applied during exploration in the Niger southwestern part or the Niger delta basin were delta are palynology, micropaleontology and analyzed in this study. The location and name of the calcareous Nannoplankton study. well were not made available for propriety reasons; consequently, it is hereby designated as Del - 2 well. The application of palynology to stratigraphy, The Niger delta (Fig. 1) is the most significant paleoecology and correlation began in the 1960s hydrocarbon province on the West African (Hopking, 1967) and the demand for palynological continental margin. It lies mainly in the Gulf of application in solving other geologic problems has Guinea to the southwest of the Benue – Trough and been on the increase since then. In the exploration for constitutes the most important Cenozoic deltaic oil, palynology alongside sedimentology, construction in the south Atlantic. paleontology and seismic stratigraphy plays an important role. This is as a result of the durability, Several methods are applied during exploration to get diversity and statistical value of palynomorphs, thus enough information about the well(s) of interest in their study has contributed significantly to the Niger delta. Such methods include biostratigraphy and hydrocarbon exploration. Also, sedimentological, biostratigraphical and seismic the application of sequence stratigraphy to the study 86

Research Journal in Engineering and Applied Sciences (ISSN: 2276-8467) 2(2):86-94 Sequence Palyno-Stratigraphical Study Of Del-2 Well Southwest Of The Niger – Delta Basin Nigeria

of sedimentary rocks has provided a good chronostratigraphic model for a more efficient exploration and exploitation of hydrocarbons.

Inspite of all these studies, no work has documented a sequence palynostratigraphic study of the palynomorphs of the Niger delta sediments, thus this study is embarked upon with the aim of carrying out a biozonation, datation and paleoenvironmental interpretation of the sequence penetrated by Del-2 well. The information thereon obtained will contribute towards better understanding of fossil floral diversity of the basin.

Numerous works have been undertaken on the Tertiary Niger delta. Some of the pioneer workers on the geology of the Niger delta include Short and Stauble (1967) and Frankl & Cordry (1967), who first provided the initial information on the sediments and subsurface distribution of the stratigraphic units in the Niger delta. Short and Stauble, (1967) studied the outline of the Niger delta and suggested that the major source rocks were shales of the Agbada Formation. Some works have also been done by Avbovbo (1978) and Oyede (1992) on the environment of the Niger delta. Oyede (1992) based on palynofacies principle pioneered by Whitaker (1985); identified the following environments in the Niger delta, mangrove swamp, channel deposits, shoreface and marine.

GEOLOGY OF THE STUDY AREA The geology of the Niger delta is known through, the numerous subsurface data acquired during oil prospecting. Part of these data has been published. The history and structure are relatively well known through several syntheses (Short & Stauble, 1967; Hospers, 1971; Murat, 1972; Weber & Daukoru, 1975 and Whiteman, 1982). Generally, it is agreed that the modern Nigeria delta is built on an oceanic crust. Argument supporting this view comes from the reconstruction of its precontinental drift positions (Stoneley, 1966). The evidence indicates an important overlap of NE Brazil on the present Niger Delta and a series of linear subdued and alternating positive ands negative anomalies beneath the Niger delta. These anomalies have been interpreted by Burke et al (1971) as sea floor spreading lineation (Mascle, 1976). Three major sedimentation cycles have been established in the Niger delta as well as other parts of the southern Nigerian sedimentary basin.

Palynostratigraphic studies undertaken to date on the Niger delta include those of Va-Hoeken – Klinkenberg (1964), Germeraad et al. (1968), Knaap (1971), Kogbe and Sowumi (1975), Legoux (1978), Jan du Chene et al (1978), Jan du Chene and Salami (1978), Biffi and Grigani (1983), Morley and Richards (1983) Poumot (1989), Oboh, et. al. (1991), and Oboh (1992). Clarke (1966) identified Peregrinipollis nigericus, as a new sporomorph in the Upper Tertiary of southern Nigeria subsequently; it has been extensively used as middle Miocene marker in the Niger delta. The most comprehensive palynological research to date was carried out by Germeraad et. al., (1968) on some Tertiary sediment from the world’s tropical areas. It is largely a comparative study of palynomorphs of Tertiary sediments from tropical South America, Asia and West Africa. Knaap (1971) provided a good time correlation across the continental deposits of the Benin Formation and the transitional sequence of the Agbada Formation and considered the sudden appearance of Podocarpus milanjianus, a montane conifer as a time marker.

These are: (i) Lower Cretaceous to Santonian cycle and (ii) Campanian to Paleocene cycle and (iii) Paleocene/Lower Early Eocene to Recent (Youngest) The third sedimentary cycle, which started in the Paleocene/Early Eocene, is responsible for the main part of the delta’s growth (Short & Stauble, 1967). The Niger delta oil province with its commercial oil fields is confined to the area covered by a thick sequence of rocks belonging to the youngest (Tertiary) sedimentary cycle.

Evamy et al. (1978) adopted an informal palynological zonation for the Niger delta using alpha numeric nomenclature. Legoux (1978) analyzed and used Praedapollis africanus, P. flexibilis, Verrutricolporites rotundiporus and other taxa for the zonation of some parts of the Neogene Niger delta. Sowumi (1981) analyzed pollen grains of thirty – six meters deep cores from the Niger delta and concluded from the report that in the Quaternary, there were shifts in the extent of rainforest and that the savannah had been reduced. Biffi and Grignani (1983) worked on dinoflagellate cysts assemblage that penetrated Oligocene strata and they proposed seven new species belonging to the Lejeunecysta, two new species of the Phelodinium and one new species of the Selenopemphix.

Megatectonically, the Niger delta is framed by a set of older and stable megatectonic elements that enhanced and controlled the development of the present day Niger delta (Fig. 2). Rift faulting during the Precambrian developed these structures (Weber, 1971). Deep-seated faults associated with this rifting controlled the outlines of the delta. These structures are (i) the Benin flank, a NE – SW trending flexure or fault zone called the Benin Hinge Line, (ii) the Calabar flank N.W-SE hinge line which is the subsurface continuation of the Oban Massif. It marks the eastern fringe of the delta, (iii) the Senonian Abakaliki uplift and (iv) the post Abakaliki Anambra Basin. These units are found to the north of the delta, 87

Research Journal in Engineering and Applied Sciences (ISSN: 2276-8467) 2(2):86-94 Sequence Palyno-Stratigraphical Study Of Del-2 Well Southwest Of The Niger – Delta Basin Nigeria

and were also stable elements throughout the Cenozoic (Fig. 2).

Niger delta sediments are controlled by the adjustments of the shale either by the downward movements in response to the pressure impacted by the overlying sediments or lateral motion of the shale on the continental slope or its upward diapiric motion. These movements are believed to have assisted in the formation of the growth faults and roll over structures, which are common features of the main Niger delta basin.

Stratigraphy Since the inception of the Cenozoic delta in the Paleocene/Lower Eocene, the history has been one of a major regression with a gradual southward offlap of thin, quite extensive lenses of sediments formed as result of deposition occurring simultaneously under full terrestrial (fluviatile) conditions with the interplay between terrestial and marine influence (i.e. paralic) and under fully marine conditions (Frankl & Cordry 1967). Thus the sequence observed laterally (i.e. starting with coarse sandy deposits and ending with marine clays) is also observed vertically in the Niger delta.

Its thickness is unknown because most wells drilled in the Niger delta did not encounter the base of the Akata Formation, except for the northern part of the delta where the formation has been drilled into the Cretaceous. Agbada Formation: This sequence of strata forms the hydrocarbon prospective sequence in the Niger delta. The formation is characterized by alternating sandstones and shales of the delta front, distributary channel, and deltaic plain origin.

In a cross-section, a time stratigraphic unit of such deltaic sediment is characteristically S-shaped or sigmoidal (Merki, 1972). The formations are therefore strongly diachronous, their ages becoming progressively younger in a downdip direction and ranging from Paleocene to Recent. Thus the established tertiary sequence in the Niger delta demonstrates a tripartite lithostratigraphic succession (Fig.3) from marine prodeltaic shale (Akata Formation) through a sand/shale paralic unit (Agbada Formation) to continental sands (Benin Formation). The strata compose and estimated 8535 m of the section at the approximate depocentre in the central part of the delta (Short and Stauble, 1967). The characteristic features of these formations are outlined below:

Weber (1971) showed that the alternating sequence of sandstones and shales of the Agbada Formation is of cyclic sequences of marine and fluvial deposits. The sand content ranges from 50 to 75 %. The sandstones are medium to fine grained, fairly clean locally calcareous, and shelly. They consist dominantly of quartz and potash feldspar with subordinate and illite. The shales are dark to grey, fairly consolidated and silty with local glauconite. They consist dominantly of kaolinite (average value 73 %) with small amount of mixed layers of illite and montmorillonite.

Akata Formation: It is characterized by a uniform shale development. The formation is a marine sedimentary sequence laid down in front of an advancing delta. These prodeltaic shales are medium to dark grey, fairly hard or at places soft, gumbo-like and sandy or silty in several places, the shales of this formation were found to be undercompacted, and therefore mobile, and may contain lenses of abnormally high-pressured siltstone or fine-grained sandstone (Allen, 1965; Reyment, 1965; Short & Stauble, 1967 and Oomkens 1974). The upper boundary of the formation has been structurally deformed, while diaprism and high-pressure zones developed in it, on a large scale.

The formation has a maximum thickness of 3940 meters at the central part and thins northwards and towards the North western and Eastern flanks of the delta. Although, the thickest known section is about 3480 meters, the maximum thickness may well be much greater (Short and Stauble 1967). Generally, the boundary between the sand and shales is sharp. Where the sands grade into shales, shell fragments, glauconites, limonite coatings are common. The shales are denser at the base than higher up in the column because of compaction. They become silty and sandy towards the Benin Formation while shaliness increases downwards and laterally into the Akata Formation.

Generally, the Akata Formation contains rich foraminiferal fauna. Planktic foraminifera may constitute moiré than 50 % of the microfauna. The benthonic foraminiferal assemblages indicate that the shale was deposited on a shallow marine shelf and slope. The Akata Formation is considered to be the main source rock in the Niger delta (Evamy et al, 1978; Bustin 1988 and Schlumberger, 1985). The known age of the Akata Formation is Eocene to Recent (Asseez, 1976; Doust and Omatsola 1990). The shale is continuous in the subsurface with its probable outcrop equivalent the Paleocene/Eocene Imo Formation. The complex movements of the

The Agbada shales contain microfauna that are best developed at the base of individual shale units. The depth of the fossil assemblage ranges from littoral estuarine to marsh types of fauna developed at a water depth of approximately 100 meters. The slightly consolidated sand has a calcareous matrix, but most of the sand is unconsolidated. The coarse and poorly sorted sand indicates a fluviatile origin while the well-sorted sand represents beach or coastal barrier deposits. The mature Eocene to Miocene shales interbedded within the deltaic sands in the lower part of the paralic sequence is considered to be 88

Research Journal in Engineering and Applied Sciences (ISSN: 2276-8467) 2(2):86-94 Sequence Palyno-Stratigraphical Study Of Del-2 Well Southwest Of The Niger – Delta Basin Nigeria

a major source rock. (Nwachukwu & Chukwura, 1986; Knox & Omatsola 1989; Shannon & Naylor 1989: Doust & Omatsola 1990 and Reijers 1996). The Agbada Formation is held to contain most of the reservoir rocks of the Niger delta. The porosity is of excellent quality (ranging between 28 and 32 %) while permeability is in the darcies. Reservoir quality is closely dependent on the depositional environment.

the underlying paralic Agbada Formation Lithologically; it is laminated and has a maximum thickness greater than 8,000 m (Short and Stauble, 1967; Whiteman 1982; Doust and Omatsola 1990). The age ranges from Oligocene to Recent. Other subsurface clay members apart from a fan clay Member occur in the delta. The other anomalous shale bodies have been recognized within the Agbada and Benin Formations. The clay bodies within the Agbada Formation are the Opuama, Osare, Qua-Iboe and Elelenwa, while Makaraba, Soku and Amojie clays are members of the Benin Formation. The age of these clays; range from Oligocene to Recent.

The Agbada Formation is less carbonaceous and more marine than overlying Benin Formation there is also an increase ion microfauna with depth. This could be an indication of increasing rate of sedimentation and changes in salinity and temperature of the delta front. The age of the Agbada Formation varies from Eocene to Recent.

MATERIAL AND METHOD OF STUDY Forty ditch-cutting samples from Del – 2 well in the Niger delta were used for this study. The sample depth intervals extend from 609.60 m to 975.36 meters. The samples were composited.

Benin Formation: This is the uppermost unit of the Niger delta complex. The formation can be easily distinguished based on its high sand percentage (70 – 1000 %). The sand is dominantly massive highly porous and freshwater bearing with locally interbedded shale beds, which are considered to be of braided stream origin.

The 20 composite samples were subjected to standard technique of macerations for the preparation of acid insoluble microfossils.

The sands are poorly sorted, ranging from fine to coarse – grained and occasionally pebbly and they contain abundant wood, fragments, which become lignitic with depth. Composition, structure and grain size show deposition in a probably upper deltaic environment. The thickness is variable and may be more than (1990 m) in Warri – Degema area.

10 grams of each sample were treated with 10 % hydrochloric acid (Hcl), then 40 % hydrofluoric acid (HF), 60 % Nitric acid for a period of 3 to 5 minutes, 2 % Potassium hydroxide (KOH). Separation by Zinc chloride ZnC2 (S.a.2.2)s solution and mounting in glycerin jelly. Identification and counting of palynomorphs were done using a Laborlux 6 (Leitz) light microscope using the objective magnifications of 25 and 40. The palynomorph species were identified with the aid of relevant publications such as Clarke (1966), Germeraad et al (1968) Legoux (1978), albums from shell, Agip etc. The identification was based on size, exine structure, shape, sculptures and aperture type.

Most companies exploring for oil in the Niger delta, arbitrarily define the base of the Benin Formation by the deepest fresh - water – bearing sandstone that exhibits high resistivity. Short & Stauble (1967), however, defined the base of the Benin Formation by the first marine foraminifera within shale, as the formation is non-marine in origin. Avbovbo (1978) partly agrees with Short & Stauble (op cit) but also demonstrated that the base of the fresh water in the delta sediments extends into the Agbada Formation and thus not coincident with the base of the Benin Formation.

RESULTS Analysis of the slides of Del 2 well yielded seventyfour palynomorph species. Pollen and spores are dominant and the other palynomorphs include a few dinoflagellate species, a few acritarchs and microforaminiferal linings. There are also charred graminae cuticle and a lot of fungal pores (Fig.4).

The Benin Formation is deposited across the entire Niger delta. It is a continental deposit and consists of various structures such as natural levees channel fills, ox-bow fills etc. these structures indicate a variability of the shallow water depositional medium (Short & Stauble, 1967). It becomes progressively younger from North towards the South.

The spores recorded belong to the species of corruporis, Laevigatosporites, verrucatosprites, Leotriletes, Lycopodiumsporites, Anthocerosporis, Stereosporites, Polypodiaceoisporites, Crassoretitriletes Magnastriatites and Retitriletes.

Subsurface Clay Members: A clay section in the subsurface of the Eastern Niger delta, the “Afam clay member” is locally recognized. The member has the form of a canyon fill that strikes in a SSE direction, from slightly north of Afam – 1 to the west of Imo estuary. It also grades southwards into Agbada and Akata Formations. The base is difficult to delineate where it contains basal sand intercalations and rest on

The pollen taxa recovered are: Zonocostites ramonae, Monoporites annulatus, Racemonocolpites hians, Retistephanocolpites gracilis, Praedapollis flexibilis, Striatricolpites catatumbus, Retibrevitricolporites protudens, Pachydermites diederixi, Arecipites sp, Psilatricoloporites crasssus, Retitricolporites irregularis, Fenestrites spinosus, 89

Research Journal in Engineering and Applied Sciences (ISSN: 2276-8467) 2(2):86-94 Sequence Palyno-Stratigraphical Study Of Del-2 Well Southwest Of The Niger – Delta Basin Nigeria

Sapotaceoidapollenites sp, Cyperaceaepollis spp Echitricolporites, spinosus; obodoensis, Nymphaepollis claus, Retibrevitricolporites obodoensis, peregrinipollis nigericus, Echiperiporites estelae, Gemamonocolpites sp, Multiareolites formosus, Echitricolporites icacinoides, Verrutricolporites rotundiporus, Polyporotetradites laevigatus, Nymphaepollis sp Polyadopollerites vacampoae, Psilatricolporites spp; Psilatriporites sp., Anthostema aubryanium Psitricolpites sp, Nummulipollis neogericus, Echimonocolpites minor, E. major Canthicimidites reticulates, Triporopetes neogenicus, clavainperturopollenites spp. Pandamites sp,Crototricolpites crotonoisculptus, Scherosperma sp, Psitricolpites operculatus, Elaeis guineensis, Ctenolophonodites costatus, Corylopollis avallena Retitricolpites sp., Bombacacidites sp. Corsinipollis jussiensis, Brevitricolporites guinetti, Polycolpites spp., Impatiencidites brevicolpus, Echriletes echinatus, Loranthicidites spp, Heterocolpites laevigatus, Alnipollis verus and Pinus haploxylon.

furmosus, Echitricolporites icacinoides, Verrutricolpites rotundiporis, Polyporotetradites laevigatus, Nympheaepollis sp., Polyadopollenites vacampoae, Psilatricolporites spp., Retitriporites sp., Nummilipollis concimus, canthiumidites reticulates, clavainaperturopollenites spp., pandanites sp., crototricolpites crotonoisculpties stereosperma sp., Psilatricolpites operculatus, Elaeis guineensis, Ctenolophonidites costatus, and Corylopollis avallene. Age: The studied interval has been dated early Pliocene to late Pliocene, based on the presence of the following marker species: Racemonocolpites hians, Retistephomocolpites gracilis, Praedapollis flexibilis, striatricolpites catatumbus, Retibrevitricolpites protudens, Pachydermites diederixi, Retibreviatricolpites obodensis, Psilatricolporites crassus, Retitricolpites irregularis, Fenestrites spinosus, Cyperaceaepollis spp., Echitricolpoeites spinosus, Nymphaepollis clarus, Peregrinipolllis nigericus, Echiperiporites estelae, Gemmamonocolpites sp., Multiareolites formosus, Echitricolporites icaciboides and Verrutricolporites rotundiporis.

The algal cysts present are: Pediastrum spp, Pediastrum bifidites, and Botryococcus branny and Concentricytes sp. The dinoflagellate cysts are: Selenopemphix nephroides, Lejeuncysta fallax, Lejeuncysta sp. Operaulonioduim centrocarpum and Nematophaeropsis labyrinthea. The acritarch taxon encountered was Leiosphaeridia sp. These forms are illustrated in photomicrographs (Fig.5).

The early/late Pliocene boundary was determined based on the first downhole occurrence Gemmamonocolpites sp., Multiareolites formosus and Echiperiporites icacinoides. Besides there is the regular occurrences of Retibrevicolporites protudens and R. obodoensis, abundance of Pereginipollis nigericus and sparse occurrence of Praedapolis flexibilis across the boundary were distinctive (Legoux 1978, Poumot 1989).

The distribution chart shows the different specimens encountered at the different depths interval. The different taxa vary in abundance; some are considered common while some are relatively rare.

However, other fossils of different ages occur within the studied interval, such as Heterocolpites laevigatus, Retitricolpites irregularis, Psilamonocolpites sp and Loranthacidites sp. They are probably reworked specimens because most of them are not well preserved, or probably due to contamination during sample processing.

The common forms are: Striatricolpites catatumbus, Retribrevitricolpites protudens Pachydermites diederixi, Psilatricolporites crassus, Retitricolpites irregularis, Sapotaoladopollenites sp, Nymphaeapollis clarus, Retibrevitricolporites obodoensis, Peregrinipollis nigericus, Anthostema aubryanium, Psilamonocolpites sp., Edumocolpites minor, Triporoletes neogenicus, currusporis spp., Ployapodiaceoisporites spp., Leotriletes spp., Laevigatosporites spp., Stereosporites spp., Verrucatosporites spp and Echitricolproites spinosus.

Biozonation: Four informal biozones were derived within the studied interval. These sub-zones have been termed subzone A, sub-zone B, subzone C and subzone D, following stratigraphic procedures.

The rare forms are: Cassoretitriletes vanraadshooveni, Magnastriatites howardii, Crassoretitriletes spp., Retitriatites spp., Lycopodium sporites sp., Echiperiporites estalae, Arecipites sp. Pinus haploxylon, Alripollis verus, Heterocolpites laevigatus, Loranthacidites spp., Echitriletes echinatus, jupatiencidites brevicolpus, polycolpites sp., Brevitricolporites guinetti, Corsinipollis jussiensis, Psilatricolpites operculatus, Bombacacidites sp, Retitricolpites sp., Anthoceroporite echinatus, Retistephanocolpites gracilis, Racemonocolpites hians Praedapollis flexibilis, cyperaceaepollis spp, Multiareolites

Subzone A. This zone ranges from a depth of 865.63 m to 975.36 m. An abundance of Monoporites annulatus, low occurrence of Zonocostites ramonae and a minimum recovery of spores characterize it. Other diagnostic features in this zone are the first down hole occurrence of Pinus haploxylon, Alnipollenites verus, Heterocolpites laevigatus, Crassoretitriletes vanraadshooveni, Echitricolporites icacinoides and Verrutricolporites rotundiporus. There is also a sparse occurrence of Arecipites sp., Corrusporis sp., Nymphaepolis clarus, Peregrinipollis nigericus, Echiperiporites estelae, 90

Research Journal in Engineering and Applied Sciences (ISSN: 2276-8467) 2(2):86-94 Sequence Palyno-Stratigraphical Study Of Del-2 Well Southwest Of The Niger – Delta Basin Nigeria

Psilatricolporites sp., Nummulipollis neogenicus, Edimonolcopites minor, Canthiumidites reticulates, Edimonocolpites major Triporoletes neogenicus and Crototricolpites crotonoisculptus.

Other diagnostic feature of this subzone is the first down hole occurrence of Peregnnipollis nigericus, Gemmamonocolpites sp., Multiareolites formosus, Ctenolophoridites costatus, Crototricolpites crotonoisculptus, Retitricolpites sp., Bombacacidites sp., Cornsinopollis jussiensis, Brevitricoloporites guinetti, Retritriletes sp., Magnastriatites howardii.

The sparse to common recovery of Retibrevitricolponites obodoensis and Brevitricoloprites guinetti was observed within this interval coupled with the low occurrence of Sapotacaeoidepollenites sp, Cyperaceaepollis spp. Psilamonocolpites sp., Leotriletes adriensis and Polypodiaceoisporites spp.

The common occurrences of Retibrevitricolporites protudens, Nymphae clarus, Retitricolporites obodoensis, Peregrinipollis nigericus, Leotriletes sp., and Stereosporites sp were also observed. Low recovery of Arecipites sp., Retitricolporites irregularis, Sapotacaeoidapollenites sp, Cyperaceaepollis sp., Gemmamonocolpites sp., Psilamonocolpites sp., Ploypodiaceoisporites spp., Psilamonocolpites sp., Polypodiaceoisprites spp., and the sparse to common occurrence of Striatricolpites catatumbus, Echitricolpites sp., Canthiumidites reticulatus, Brevitricolporites guninett; Lycopodium sp., Lejeunecysta sp and Pediastrum sp are additional characteristics of this biozone.

Top: Last downhole occurrence of the assemblage constituted by Retibrevitricoporites protudens and Crototricolpites crotonoisculptus at the depth of 865.63m Base: Undefined. It is here, taken as the base of the studied interval 975.36 meters. Age: Early Pliocene. Subzone B: This zone ranges from 755.90 in to 865.63m depth of the studied interval. It is characterized by an appreciable recovery of Zonocostites ramonae a low recovery of Monoporites annulatus and a considerable amount of spores. The sparse occurrence of Praedapollis flexibillis, Striatricolpites catatumbus, Echitricolpites spinosus, Pachydermites diederixi Echitricolporites icacinoides, Cathiumidites reticulates, Crototricolpites crotonoisculptus, Psilatricolpites operculatus, Elaeis guineensis and Brevitricolporites guinetti was also observed within this interval.

Top: The top of the zone is marked by the first appearance of Echiperiporites estelae and Ctehonophonoides costatus, at 664.46 m. Base: The base coincides with the top of the biozone B at 755.90m. Age: Late Pliocene to early Pliocene. Sub zone –D: This zone occurs within the interval of 609.60 m to 664. 46 m depth. Characteristics features of this zone are the peak occurrence of Monoporite annulatus, a low recovery of Zonocostites ramonae and an appreciable recovery of spores. This zone is very rich is occurrence of Retistephanocolpites gracilis, Retitricolpiotes irregularis, Cyperaceaepollis sp., Psilamonocolpites sp., Edimonocolpites minor, Elaeis guineensis, Crassoretitriletes sp. and Currusporis sp. The sparse occurrence of Striatricolpites catatumbus, Anthostema aubryanium, Psilatricolpites sp. Nummulipollis neogenicus, Echimonocolpites major, Triporoletes neogenicus, Polypodiaceoisporites spp, Leotriletes sp., Laevigatosporites sp., Stereoporites sp., Verrucatosporites sp., microforaminiferal wall lining, fungal spore, Pediastrum sp and Oisphaeridia sp.

In addition, there was a low recovery of Psilatricolpites crassus, Retibrevicolporites irregularis, stereosporites sp. and heoisphaeridia sp. This zone also has the common occurrences of Retibrevitricolporites protudens, Sapotacaeoidapollenites sp, Peregrinipollis nigericus, Anthostema aubryanium Verrucatosporites sp, fungal spores and microforaminiferal wall lining. Top: The top of this zone occurs at a depth of 755.90m. It is marked by the first appearance of Polycolpites sp., Impatiencidites brevicolpus, and Echitriletes echinatus, and by the last appearance of Lycopodiumsporites sp and Crassoretitriletes sp. Base: The base corresponds to the top of subzone A. i.e. 865.63m

Low occurrence of Arecipites sp., Sapotaceoidapollenites sp., Retribrevitricoporites obodoensis, Canthiumidites reticulatus were also recorded. The rare/sparse occurrence of Sclerosperma sp., Selenophempix nephroides, Racemonocolpites lians, Anthocerosporites echinatus, Praedopollis flexibilis, Retibrevitriolporites protudens, Pachydermites diederixi, Psilatricolporites crassus and Echitricolpites spinosus were recorded in this biozone.

Age: Early Pliocene. Sub-zone C: This subzone ranges from a depth of 664.46m to 755.90m depths and is characterized by a low recovery of Zonocostites ramonae. The abundance of Monoporites annulatus also decreased, while spores are generally reduced in abundance.

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Research Journal in Engineering and Applied Sciences (ISSN: 2276-8467) 2(2):86-94 Sequence Palyno-Stratigraphical Study Of Del-2 Well Southwest Of The Niger – Delta Basin Nigeria

Top: This is undefined but it is assumed to coincide with the top of the studied interval at 609.60 m. Base: The base coincides with the top of sub-zone C at 664.46 m

some of the retrieved fossils to species levels due to lack of accessibility to archives of exploration companies and thier contradictory zonation schemes prevented the definition of upper and lower boundaries of Pliocene age in Del-2 well.

Age: Late Pliocene age. However, in conclusion, Del –2 well is characterized by eighty-eight palynomorph species, which include spores, pollen, dinocysts, algal cysts and acritarchs, fungal spores, microforaminiferal wall linings and charred gramineae cuticle were also identified.

Sequence Stratigraphy The sequence stratigraphic interpretation of the interval (609.60 m – 975.36 m) in Del-2 well is based on the abundance and diversity of the marine microfossils and the relative abundance and diversity of the miospores.

Based on the presence of some selected marked species, the studied interval was dated Early Pliocene to Late Pliocene and the boundary between the two epochs was placed at the depth of 701.04 m. In addition, the biozonation and paleoenvironmental determination of the Del-2 well was done using the relative abundance and diversity of miospore assemblages and the marine microfossils. Four biozones (informally designated biozones A, B, C and D) and three depositional environments; shallow, deep and open marine environments were established.

Four sequence boundaries were delineated at the following depths 701.04 m, 774.19 m, 865.63 m and 902. 21 m. Three system tracts, the lowstand (LST),Transgressive (TST) and the highstand (HST) systems tracts are represented. The highstand system tract is interpreted to have formed during the later part of the relative rise of sea level when the rate of relative sea level was decreasing. The rate of sea level rise decreases during the development of high stand systems tract. (Vail, 1987). It is characterized by intervals of coarsening and shallowing upwards.

The sequence stratigraphy of the well was attempted based on the relative abundance and distribution of the marine microfossils and miospores. Four sequence boundaries (at 701.04m 774.19 m, 847.34 m and 902.50 m) were established. Three systems tracts, High stand systems tract (HST) (701.04 – 774, 19 m and 865.63 m – 902.21 a transgressive systems tract (TST) (609.60 m – 701.04 m; 774.19 –847.34 m) and a lowstand systems tract (LST) 902.21m – 975.36 m were also identified.

In the studied sections, the HST is present within the depth interval of 701.04 m – 774.19 m. It is characterized by the peak occurrence and diversity of the marine microfossils (Fig.6). The trangressive systems tract is (TST) a systems tract found between the highstand (HST) and the lowstand (LST) is identified within the depth intervals 609.60 m –701.04 m; 774.19 m-847.34m and 902.21 m – 975.36 m. brackish environment developed in protected coastal plains during the TST are characterized by low diversity assemblages of low salinity tolerant plants and animal species. This is very evident at the intervals listed above.

It is hereby recommended that the section below the studied part should also be studied and that the seismic stratigraphic study of the whole well should also be undertaken. This will give a better picture of the strata penetrated by by the well. It will also help in identifying all the reservoirs in the strata.

The lowstand systems tract (LST), the stratigraphically oldest systems tract in a sequence that is usually deposited during an interval of sea level fall at the offlap break and subsequent slow relative sea level rise (Emery and Myers, 1999) is encountered within the interval 85.7.34 m to 902.21 m. “The LST is recognized most importantly in the proximal fossil record by an underlying hiatus, a sudden shallowing up of biofacies or the super imposition of non-marine assemblages on marine ones”.

Thus, an integrated study that combines sequence stratigraphy with palynostratigraphy should be used in erecting standard biozonation, age and paleoenvironmental scheme for the Niger delta basin. ACKNOWLEDGEMENT The authors wish to express their sincere thanks and appreciation to Professor M. O. Odebode of Obafemi Awolowo University, Ile – Ife, Nigeria for the initiation and supervision of this project. S.A. Akinyemi and D. Omagba helped in the computer graphics of this project The comments of the anonymous reviewer is highly appreciated too.

CONCLUSION AND RECOMMENDATIONS There are certain limitations which have prevented a high resolution of the biozones, age and paleoenvironmental deductions established in Del-2 well, these include among others: (i) the limited number of composited samples to the uppermost section of the well, (ii) the inability of identifying

REFERENCES Allen, J.R.L., 1965. Late Quaternary Niger Delta and adjacent areas: sedimentary environments and lithofacies. Am. Assoc. Petroleum Geol. Bulletin, Vol. 49, pp. 547-600. 92

Research Journal in Engineering and Applied Sciences (ISSN: 2276-8467) 2(2):86-94 Sequence Palyno-Stratigraphical Study Of Del-2 Well Southwest Of The Niger – Delta Basin Nigeria

Asseez, L.O., 1976. Review of the Stratigraphy, Sedimentation, and structures of the Niger delta. In Kogbe, C.A. (ed), Geology of Nigeria Elizabeth Pub. Lagos. Pp. 259-272.

Hospers, J., 1971. The geology of the Niger delta area. In: The Geology of the East Atlantic Continental margin. Inst. Of Geol. Sci. Dept. Grt. Britain. Vol. 70 (16), pp. 121 – 142.

Avbovbo, A.A., 1978. Tertiary lithostratigraphy of the Niger Delta. Am. Assoc. Petroleum Geol. Bulletin, Vol. 62, pp. 295-306.

Jan du Chene, R.E.; Onyike, M.S. & Sowunmi, M.A., 1978. Some new Eocene pollen of Ogwashi-Asaba Formation, southeastern Nigeria. Rev. Espanola. Micropal., Vol. X (2), pp. 285-322.

Biffi, U. and D. Grignani, 1983. Peridinoid dinoflagellates cysts from the Oligocene of the Niger delta, Nigeria. Pp. 132-133.

Jan du chene, R.E., and Salami, M.B., 1978. Palynology and Micropaleontology of the Upper Eocene of the well Nsukwa-1 (Niger delta, Nigeria) C.R. des Seantes, SPHN Geneva, Vol. 13 (1): pp. 5-9.

Burke, K. 1971. Opening of the Gulf of Guinea and the history of the Benue depression, and Niger delta. Nature Phys. Sci., Vol. 233, pp. 51-55.

Knaap, W.A., 1971. A montane pollen species from the Upper Tertiary of the Niger Delta. Nig. Journ. Min. Geol, Vol. 6 (1-2), pp. 23-39.

Bustin, R.M. 1988, Sedimentology and characteristics of dispersed organic matter in Tertiary Niger delta. Origin of Source rocks in a deltaic environment: AAPG Bulletin, Vol. 72, pp. 277298.SS

Knox, G.J., and Omatsola, M.E. 1989. Development of the Cenozoic Niger delta. In terms of the “Escalator Regression Model” and impact on hydrocarbon distribution.

Clarke, R.T., 1996 Peregrinipollis nigericus – A new palynomorph from the upper Tertiary of Nigeria. Grana Palynologica, Vol. 6 (3), pp. 540-54

Kogbe, C.A. and Sowunmi, B., 1975. The age of the Continental Terminal as suggested by sporopollenitic analysis. Savana, Ahmadu Bello University, Zaria, Nigeria, Vol. 4 (1), pp. 47-55.

Doust, H. and Omatsola, E., 1990. Niger Delta: Divergent/Passive margin basin (J.O. Edwards and P.A. Santoigrossi, Eds.) Am. Assoc. Petroleum Geol. Memoir. Vol. 48, pp. 201-238.

Legoux, O., 1978. Quelques especes de pollen caracteristiques de Neogene du Nigeria. Bull Cent. Rech. Explor. Prod. Elf-Aquitanie, Vol 2 (2), pp. 265-317.

Emery, D. and Myers, K. J. (Eds), 1999. Sequence stratigraphy (with contributions from Bertram, G et al.,) Blackwell Science, 277pp

Mascle, J., 1976. Submarine Niger delta structural framework. Journ. Min. Geol., Vol. 13, pp. 12-28.

Evamy, D.D., Haremboure, J., Kamerling, P., Knaap, W.A. Molloy, F.A. and Rowlands, P.H., 1978. Hydrocarbon habitat of the Tertiary Niger Delta. Am. Assoc. Petroleum Geol. Bulletin, Vol. 62, pp. 1-39.

Merki, P., 1972. Structural Geology of the Cenozoic Niger Delta: 1st conference on African Geology, Ibadan, 1970, Proceedings: Ibadan, Nigeria, Univ. Press, pp. 635-646.

Frankl, E. J., and Cordry, E.A. 1967. The Niger Delta oil province: Recent developments onshore and offshore. 7th World Petroleum Congr. Mexico City. Proc. Vol. 1, pp.195 – 209.

Morley, R. J. and Richards, K., 1983. Graminae cuticle: a key indicator of late Cenozoic Climatic changes in the Niger delta. Rev. Paleobot. Palynol., Vol.77, pp. 119 – 127.

Germeraad, J.H., Hopping, C.A. and Muller, J., 1968. Palynology of Tertiary sediments from Tropical areas. Rev. Palaeobotany Palynol., Vol. 6 (3 and 4), pp. 189-348.

Murat, R.C., 1972. Stratigraphy and Palaeogeography of the Cretaceous and lower Tertiary in southern Nigeria: 1st Conference on African Geology Proceedings: Ibadan, Nigeria, Ibadan Univ. press, pp. 251-266.

Hoeken-Klinkenberg, P.M.J. Van, 1966. Masstrichtian, Paleocene and Eocene Pollen and spores from Nigeria-Leidse geol. Meded., Vol. 38, pp. 37-48.

Nwachukwu, J.I. and Chukwura, P.I., 1986. Organic matter of Agbada formation, Niger delta, Nigeria: Amer. Assoc. Petrol. Geol. Bull. Vol. 70, pp. 48-55.

Hopking, C.A., 1967. Palynology and the Oil industry. Rev. Palaeobotan. Palynol., Vol. 2, pp. 2348.

Oboh, F.E., 1992. Multivariate statistical analyses of palynodebris from the middle Miocene of Niger Delta and their environment significance Palaios, Vol. 7, pp. 559-573. 93

Research Journal in Engineering and Applied Sciences (ISSN: 2276-8467) 2(2):86-94 Sequence Palyno-Stratigraphical Study Of Del-2 Well Southwest Of The Niger – Delta Basin Nigeria

Oboh, F.E., Salami, M.B., & Chapman, J.L., 1991. Palynological interpretation of the palaeoenvironments of Miocene strata of the well Igbomotoru-1, Niger Delta. Journ. Micropal, Vol. 11, pp. 1-6.

Whitaker, M. F., 1985. Palynofacies analysis as applied to basin evaluation in the northern North Sea. Shell Exploration Bulletin No. 217 Whiteman, A. J., 1982. Nigeria: Its Petroleum Geology, Resources and Potential. I & II. Graham and Trotman, London. 394 pp.

Oomkens, E., 1974. Lithofacies relations in Late Quaternary Niger delta complex: - Sedimentology. Vol. 21, pp. 195-222. Oyede, A.C., 1992. Palynofacies in deltaic stratigraphy. Nig. Assoc. Pet. Explo. Bull., Vol. 7. pp. 10-16. Poumot, C., 1989. Palynological evidence for eustatic events in the tropical Neogene. Bull. Cent. Rech Explor. Prod. Elf-Aquitaine Vol. 13, pp. 437-452. Reijers, T. J. A., 1996. Selected chapters on Geology: Sedimentary Geology and Sequence Stratigraphy and three case studies and a field guide. Shell Petroleum Development Company, Corporate Reprographic Services., 197 pp. Reyment, R. A., 1965. Aspects of the Geology of Nigeria: University of Ibadan press., 146 pp. Schlumberger, 1985. Well evaluation conference, Nigeria. p. 16 – 54. Shanon, P. M. and Naylor, D., 1989. Petroleum basin studies. Graham and Trotman. 206 pp. Short, K. and, A. J., Stauble 1967. Outline of Geology of Niger – delta. Amer. Assoc. Petrol. Geol. Bulletin. Vol. 51., pp. 761 – 779. Sowumi, M. A., 1981. Late Quaternary environmental changes in Nigeria. Pollen et Spores. Vol. Xxii (2), pp. 125 – 148. Stoneley R. 1966. The Niger delta region in the light of the theory of Continental drift. Geological Magazine. Vol. 105 (5), pp. 385 – 357. Vail, P. R., 1987. Seismic Stratigraphy interpreted using sequence Stratigraphy interpretation procedure; In. Bally, A. W. ed., Atlas of Seismic Stratigraphy. Assoc. Petrol. Geol. Studies in Geology 27, Vol. 1, pp 1 – 10. Van Hoeken – Klinkenberg, P. M. J., 1964. A palynological investigation of some Upper Cretaceous sediment in Nigeria. Pollen et Spores. Vol. VI, pp. 209 – 231. Weber, K., 1971. Sedimentological aspects of oil fields in the Niger delta. Geol. En Mijnbow, Vol., 50, (3), pp. 559 – 575. Weber, K., J. and Daukoru, E. M., 1975. Petroleum geological aspects of the Niger delta. Proc. 9th World Petrol. Congr., Vol. 2, pp. 209 – 221. 94

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