Palynology and stratigraphy of three deep wells in the Neogene Agbada Formation, Niger Delta, Nigeria. Implications for petroleum exploration and paleoecology

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Palynology and stratigraphy of three deep wells in

the Neogene Agbada Formation, Niger Delta,

Nigeria. Implications for petroleum exploration and

paleoecology

von Samson Ige BANKOLE

Diplom-Geowissenschaftler

von der Fakultät VI- Planen/ Bauen/ Umwelt

der Technischen Universität Berlin

zur Erlangung des akademischen Grades

Doktor der Naturwissenschaften

-Dr. rer. nat.-

genehmigte Dissertation

Promotionsausschuss:

Vorsitzender: Prof. Dr. U. Tröger

1. Berichter: Prof. Dr. W. Dominik

2. Berichter: PD. Dr. E. Schrank

3. Berichter: Prof. Dr. B.-D. Erdtmann

4. Berichter: Prof. Dr. S.O. Akande

Tag der wissenschaftlichen Aussprache: 13. August 2010

Berlin 2010

D 83

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Acknowledgements

This PhD thesis was started and completed at the “Fachgebiet Explorationsgeologie, Institut für Angewandte Geowissenschaften, Fakultät VI, der Technischen Universität Berlin, Germany” under the supervision of Prof. Dr. W. Dominik, Priv. Doz. Dr. E. Schrank and Prof. B-D. Erdtmann. Many thanks to Prof. Dominik for his guidance and assistance over the years from the beginning to the end of this project. Prof. Dominik’s scientific suggestions and advices have been of tremendous help to the successful completion of this thesis. My very sincere appreciations goes to Dr. Schrank for his supports without which this project wouldn´t have been reality. I am also grateful for the unhindered access to Dr. Schrank and his personal library during the quest for the solutions to the scientific questions ecountered during this project. Many thanks are due to Prof. Erdtmann whose moral and personal financial assistance initiated the start of this project. Acknowledgements are also made to Prof. Erdtmann´s scientific advices which have hugely added to the quality of this thesis. Special appreciations to Prof. S. O. Akande of the Geology and Mineral Sciences Department, University of Ilorin, Nigeria for his suggestions during the analytical stage of this project and also for his words of encouragement. I am deeply grateful to Dr. Schandelmeier for his inspirational support throughout my stay here at the Technische Universität Berlin. Thanks are due to Dr. O. J. Ojo of the Department of Geology and Mineral Sciences, University of Ilorin, Nigeria for his scientific advices, so also to Dr. O. A. Adekeye of the same department. Drs. K. Ladipo and E. Ganz of Shell Petroleum Development Company, Nigeria are greatly appreciated for their assistance during the sample collection stage of this project. My profound gratitude to Dr. P. Osterloff also of Shell Petroleum Development Company, Nigeria for his constructive criticism and also for his scientific suggestions which have hugely added to the quality of this thesis. Sincere appreciations are due to Mrs. R. Paul-Walz of the International Students Division, Technische Universität Berlin for her support.

I am deeply indebted to all the following non-academic staff members of the Fachgebiet “Explorationsgeologie, Technische Universität Berlin”, for their supports throughout the duration of this project: Mrs. U. Schroeder (departmental secretary), B. Dunker, Clova, C. Lange, C. von Engelhardt (retired), Messrs M. Thiel, V. Kola, and Kleeberg (retired). Mr. Thiel was of enormous assistance during the digital drafting of the graphics for this project. My sincere appreciations go to Dr. P. Luger´s scientific suggestions. Thanks are also due to Dr. A. Brall for his supports.

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Special thanks to Dr. A. Eisawi of the Al Neelain University, Khartoum, Sudan for his fruitful suggestions. The supports of PhD student colleagues: M. K. Barakat, V. Lorenz and A. Alwan at various stages of this work are greatly acknowledged. Sincere appreciations are due to Sarah Zeifelder for her assistance.

I wish to express my profound appreciations to the MD of Geotechnica GmbH Berlin, Mr. M. Voge and the company secretary, Mrs. M. Schildberg for their supports and understanding over the years.

I acknowledge the grant support by the VW-Foundation for the laboratory analysis and also for the provision of laptop for this project. Thanks are also due to Berlin Senat through the granting of one year “NaFöG Abschlußstipendium” which was of tremendous assistance to the successful completion of this work.

Thanks are also due to Shell Petroleum Development Company of Nigeria for the provision of ditch cutting samples and log data used for this study and also for the permission to publish the results of this project. The Directorate of Petroleum Resources (DPR) of Nigeria is immensely thanked for the mandatory permission to provide the materials for this project.

I am particularly grateful for the support and understanding of the following members of my family: Ribukat Bankole, Olumide Bankole and Omolola Bankole throughout the duration of my studies here at the Technische Universität Berlin, Germany.

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Table of contents

Page

Acknowledgements...i

Table of Contents...iii

List of figures and tables………...vii

Zusammenfassung………...ix

Abstract………...xi

Chapter 1: Introduction

1. Introduction……...1

1.1 Location of the basin and the study area...2

1.2 Geological evolution and history of the southern Nigeria basins and the Cenozoic Niger Delta ...3

1.3 Stratigraphy of the Tertiary Niger Delta...4

1.3.1 The Akata Formation...6

1.3.2 The Agbada Formation...6

1.3.2.1 Biostratigraphic outlook of the Agbada Formation...7

1.3.3 The Benin Formation...8

1.4 Sedimentological evolution in response to structural developments in the Cenozoic Niger Delta...9

1.5 Oil field structures common in the Niger Delta...11

1.6 Petroleum habitats in the Niger Delta...13

1.7 Petroleum exploration and exploitation history of the Niger Delta...13

1.8 Previous palynological work in the study area...15

1.9 Aim and objective of the present study...15

Chapter 2: Material and methods

2. Materials...17

2.1 Preparation techniques...17

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Chapter 3: Systematic descriptions

3.1 Pteridophyte and bryophyte spores...19

3.1.1 Monolete spores...19 3.1.2 Trilete spore...24 3.1.2.1 Smooth exine...24 3.1.2.2 Granulate exine...30 3.1.3 Alete spores...36 3.2 Gymnosperm pollen...37 3.3 Angiospermpollen...39

3.3.1 Inaperturates and monocolpates pollen...39

3.3.2 Monoporate pollen...42 3.3.3 Tricolpate pollen...43 3.3.4 Tricolporate pollen...49 3.3.5Triporate pollen...57 3.3.6 Tetracolporate pollen...60 3.3.7Polycolpate pollen...61 3.3.8 Polyporate pollen...62 3.3.9 Polycolporate pollen...65 3.4 Dinoflagellates...66 3.4.1 Gonyaulacoids...66 3.4.2 Peridinioids...69

Chapter 4:

Abundance and distribution patterns

4.1 Introduction...72

4. 2 Abundance and distribution patterns of Well 4...74

4.3 Abundance and distribution patterns of Well 6...77

4.4 Abundance and distribution patterns of Well 8...80

4.5 Assemblage Zones...82

4.5.1 Assemblage Zone I...82

4.5.2 Assemblage Zone II...83

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Chapter 5: Palaeoecology and palaeoclimate

5.1 Introduction...84

5.2 Palaeoecological consideration of the palynomorph groups...85

5.2.1 Mangrove group...85

5.2.2 Lower coastal plain group (including swamp species)...86

5.2.3 Savanna to upper coastal plain group...87

5.2.4 Montane group...87

5.2.5 Rain forest group...87

5.2.6 Marine group...88

5.2.7 Freshwater algae...88

5.2.8 The Indeterminate group...88

5.3 Palaeoecological discussions...89

5.4 Palaeoclimate...90

Chapter 6: Depositional sequence, wetter/drier climate cycles and their

implications to petroleum exploration in the investigated sections

6.1 Depositional sequence of the Agbada Formation...93

6.2 “Wetter” versus “drier” climate cycles...94

6.3 Relationship between climate cyclicity and transgression-regression...95

6.4 Petroleum exploration implications...98

Chapter 7: Age determination

7.1 Age determination...99

Chapter 8: Discussions and conclusions

8.1 Discussions...101

8.2 Conclusions...103

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Appendices

Appendix A List of species...117 Tables 2a-c…...124 Table 3...133 Appendix B Plates 1-13

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List of figures and tables

List of figures in the text

Fig. 1. Sketch map of Africa and South America.

Fig. 2. Simplified geological map of Africa showing the location of the Niger Delta and some other Nigerian basins.

Fig. 3a. Map showing the early evolution of the Niger Delta sedimentary Basin, Albian-Lower Santonian.

Fig. 3b. Map showing the early evolution of the Niger Delta sedimentary Basin, Lower Coniacian-Lower Eocene.

Fig. 4. Schematic representation of the diachronous nature of major lithofacies on the delta flanks.

Fig. 5. Map showing the regional elements and depobelts of the Niger Delta and the successive development of the depobelts.

Fig. 6. Escalator regression pattern and subsidence rates.

Fig. 7. Schematic diagramme to illustrate development of successive depobelts. Fig. 8. Sketch of the principal types of oilfield structures in the Niger Delta. Fig. 16. Vegetation belts during relative rise in sea-level.

Fig. 17. Vegetation belts during relative fall in sea-level. Fig. 19. Structural/depositional model.

List of figures in appendix A

Fig. 9. Lithostratigraphic sections with sample positions. Fig. 10. Vertical distribution of palynomorphs in Well 4. Fig. 11. Vertical distribution of palynomorphs in Well 6. Fig. 12. Vertical distribution of palynomorph in Well 8.

Fig. 13. Quantitative composition of palynomorph assemblages in Well 4. Fig. 14. Quantitative composition of palynomorph assemblages in Well 6. Fig. 15. Quantitative composition of palynomorph assemblages in Well 8. Fig. 18. Stratigraphic ranges of selected palynomorphs outside the study area.

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Tab. 1. Table of formations in the Niger Delta area.

Tables in appendix A

Tab. 2a-c. List of analyzed samples and their palynological status Tab. 3. List of taxa and their botanical affinities.

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Zusammenfassung

Drei Tiefbohrungen (Bohrungen 8, 6 und 4) aus drei verschiedenen Sedimentationsbereichen (Zentralsumpf I, Küstensumpf I und Küstensumpf II) im Bereich des Nigerdeltas von Nigeria wurden im Rahmen einer detaillierten palynologischen Studie untersucht. Diese Bohrungen wurden in den paralischen Ablagerungen der Agbada-Formation abgeteuft. Die angetroffenen Assoziationen der Palynomorphen werden von terrestrischen Formen dominiert, dennoch sind organischwandige Fossilien marinen Ursprungs (Dinoflagellaten und die organisch-wandigen Reste von Foraminiferen) in hinreichender Anzahl vertreten. Bei den untersuchten Palynomorphen treten die Gattungen der Pteridophyten und Bryophyten-Sporen wie Laevigatosporites, Verrucatosporites, Perimonoletes, Reticulosporites, Acrostichumsporites (eine Mangroven-Farn Spore), Crassoretitriletes, Cyathidites, Leiotriletes und Magnastriatites auf. Die Angiospermen-Pollen sind typisch für das Neogen in tropischen Bereichen und durch eine hohe Artendiversität in großer Häufigkeit gekennzeichnet. Von besonderer Bedeutung ist das Auftreten folgender Angiospermen-Arten: Psilatricolporites crassus, Zonocostites cf. ramonae (Mangroven-Art), Racemonocolpites hians, Racemonocolpites racematus, Retibrevitricolporites obodoensis, Retibrevitricolporites protrudens, Pachydermites diederixi, Psilastephanocolporites laevigatus, Psilastephanocolporites cf. perforatus, Peregrinipollis nigericus, Retitricolporites irregularis und Retitrescolpites cf. splendens.

Die untersuchen Palynomorphen weisen für die mächtigen Ablagerungen der Sedimente innerhalb der drei Bohrungen auf eine nur geringe vertikale und laterale Variation innerhalb eines relativ kurzzeitigen Intervalls des Miozäns hin. Dieser Umstand erschwert eine auf der stratigraphischen Reichweite der Palynomorphen-Arten basierende Gliederung für die Agbada-Formation erheblich. Deshalb wird in der vorliegenden Arbeit eine auf ökostratigraphischen Grundlagen – wie botanische Ähnlichkeiten und quantitative Verteilung der häufigsten Palynomorphen-Gruppen – basierende Unterteilung verwendet und auf die Verwendung der qualitativen Verteilung von Leitfossil-Arten verzichtet. Die phyto-ökologisch bedeutsamen Arten können in fünf phyto-ökologische Hauptgruppen unterteilt werden. Hierbei sind die Mangroven-, Küstensumpf-, Savannen bis Küstenebenen, montanen und tropischen Regenwald-Gruppen von Bedeutung. Auf dieser phyto-ökologischen Untergliederung beruhend, können feuchtere und trockenere Zyklen für die drei Bohrungen rekonstruiert werden. Der Vergleich der klimatischen Zyklen und der lithologischen Abfolgen,

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eine Korrelation. Die feuchteren Klimate, die auf einen relativen Meeresspiegelanstieg hinweisen, korrelieren mit Perioden von „Highstand system tracts“ oder „transgressive system tracts“. Trockenere Klimate weisen auf relative Meeresspiegelabsenkungen hin und stimmen gleichfalls mit „lowstand system tracts“ überein. Dies ermöglicht eine Vorhersage der Speicher- und abdichtenden Sedimente innerhalb der lithologischen Abfolge der Agbada-Formation.

Obwohl nur eine geringe vertikale palynologische Variation zu beobachten ist, können drei informelle Zonen von Fossil-Vergesellschaftungen ausgegliedert werden. Dies sind in stratigraphisch aufsteigender Abfolge: Vergesellschaftungen I, II und III, die durch die von oben gesehen erstmalig auftretenden bisaccaten Pollen (Podocarpidites) sowie das Erscheinen von peridinioiden beziehungsweise gonyaulacoiden Dinoflagellaten gekennzeichnet sind.

Das Auftreten von biostratigraphisch signifikanten Palynomorphen wie Crassoretitriletes vanraadshooveni, Magnastriatites howardi, Reticulosporis miocenicus, Caprifoliipites superbus, Cichoreacidites cf. spinosus, Echiperiporites minor, Ilexpollenites rarus und Tuberculodinium vancampoae weisen auf die Sedimentation der paralischen Ablagerungen der Agbada-Formation in den drei Bohrungen während des Neogens, höchstwahrscheinlich während des Miozän hin.

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Abstract

Three deep wells (Wells 8, 6 and 4) selected from three different depobelts (Central Swamp I Coastal Swamp I and Coastal Swamp II respectively) of the Niger Delta, Nigeria have been subjected to detailed palynological investigation. The wells penetrated the paralic Agbada Formation which is the focus of the present study. Although the encountered palynomorph assemblages are dominated by forms of terrestrial origin, marine-derived components including dinocysts and foraminifera test linings are adequately represented. Among the recovered palynomorphs are the pteridophytic/bryophytic spores of the genera Laevigatosporites, Verrucatosporites, Perimonoletes, Reticulosporites, Acrostichumsporites (a mangrove fern spore), Crassoretitriletes, Cyathidites, Leiotriletes, and Magnastriatites. The angiosperm pollen found are typical of Neogene tropical areas and show a high degree of diversity and abundance in all the wells. Important representatives of the angiosperms are Psilatricolporites crassus, Zonocostites cf. ramonae (a mangrove pollen), Racemonocolpites hians, Racemonocolpites racematus, Retibrevitricolporites obodoensis, Retibrevitricolporites cf. protudens, Pachydermites diederixi, Psilastephanocolporites laevigatus, Psilastephanocolporites cf. perforatus, Peregrinipollis nigericus, Retitricolporites irregularis and Retitrescolpites cf. splendens.

Evidence from the palynomorphs recovered indicates a low degree of vertical and lateral palynological variation as a result of the relative short geological time interval (Miocene) for the deposition of the sediments in the three sections. This makes detailed taxon range subdivision of the Agbada Formation using key palynomorph ranges difficult. Therefore, an ecostratigraphic approach with emphasis on the botanical affinities and quantitative distribution of the major palynomorph groups is employed, rather than a qualitative key fossil based approach. The phytoecological determination of the diverse taxa encountered yielded five main ecological groups, namely mangrove, coastal swamp, savanna to upper coastal plain, montane and tropical rainforest groups. Based on the phytoecological classification of the fossil content, wetter and drier climate cycles are constructed for the three wells. Comparison between the climate cycles and the lithostratigraphic sequences interpreted from the gamma ray log of the respective wells show some correlations. The wetter cycles which represent sea level rise events correlate with periods of highstand system tracts or transgressive system tracts. Drier cycles which signifies relative fall in sea level are also observed to correlate with lowstand system tracts. These allow the predictions of reservoir

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Despite the low degree of vertical palynological variation exhibited in the three wells, three informal assemblage zones are proposed. The zones in a stratigraphically ascending order are: Assemblage Zones I, II and III characterized by the first downhole appearance of bisaccates (Podocarpidites), first downhole appearance of peridinioid and gonyaulacoid dinoflagellates, respectively.

The occurrence of age diagnostic palynomorphs such as Crassoretitriletes vanraadshooveni, Magnastriatites howardi, Reticulosporis miocenicus, Caprifoliipites superbus, Cichoreacidites cf. spinosus, Echiperiporites minor, Ilexpollenites rarus and Tuberculodinium vancampoae suggest the deposition of the paralic Agbada Formation in the three wells during the Neogene, most likely Miocene.

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Chapter 1

1. Introduction

For nearly six decades, the Cenozoic Niger Delta, Nigeria has played host to intensive hydrocarbon exploration and production. The 1956 discovery (Kulke, 1995) of commercial quantity of hydrocarbons in the basin signalled the establishment of the Niger Delta as a world-class petroleum province. Since then, exploration and production activities have moved from the continent into shallow-water offshore and presently into the deep-water. This very important hydrocarbon province is considered among the world’s top ten in terms of oil and gas reserves.

The last two decades has witnessed a tremendous increase in the demand for petroleum products both for domestic consumption and for industrial purposes. This increase in demand has been the major driving force behind the high cost of per barrel of petroleum until the last year (2009). Coupled with demand, the recent political unrest in some of the major petroleum producing areas of the world such as Nigeria and Iraq has hugely contributed to the high cost of petroleum products. Though the outset of global recession which has crippled the world’s economy since mid-2008 resulted in a significant crash in price, but the cost of the product still remains a major factor in the world economy. With demand not showing any sign of slowing down, the search for petroleum in new frontiers and the reassessment of the ageing fields is the preoccupation for petroleum geologists and engineers around the world.

Improvements in seismic data acquisition (including 3D seismic data) and processing over the last decades have led to the discovery of several giant oil reservoirs in petroleum provinces around the world. As effective as seismic stratigraphy may be, it is not without known scientific limitations such as the limit of resolution especially when applied in deep basins. The huge cost of seismic acquisition and personnel hiring for interpretation is also a major factor. Besides, the science of petroleum exploration and production is multi-tool based with each tool complementing the other. One of these important tools is palynostratigraphy. Palynology finds its use in petroleum exploration essentially as a stratigraphic tool in depositional settings such as continental, coastal and marginal marine environments. When integrated with other tools including wireline logs and seismic stratigraphy, it is useful mainly for

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chronostratigraphic correlation, palaeoenvironmental studies, evaluation of potential source, reservoir and sealing rocks (Copestake, 1993). Despite the effectiveness of palynology as an important tool in sequence stratigraphic analysis and resolution, it is still being grossly under-utilised in petroleum exploration and production.

Optimal hydrocarbon recovery from the existing fields and improved exploration at new frontiers require a good understanding of the depositional settings of the source, reservoir and sealing sequences in a basin. The present study looks into the application of palynostratigraphy (ecostratigraphy) as an important tool in the determination of the precise depositional settings of the reservoir sequences in the Niger Delta specifically the Agbada Formation (Table 1).

1.1 Location of the Niger Delta basin and the study area

The Cenozoic Niger Delta Basin is located at the centre of a triple junction, a fracture zone which initiated the separation of continental Africa from that of South America (Fig. 1) between the Late Jurassic and the Cretaceous (Weber and Daukoru, 1975). The basin is geographically located between Latitudes 3º and 6ºN and Longitudes 5º and 8ºE (Fig. 2.; Reijers et al., 1997). The southeastern boundary of the Niger Delta

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is delineated by the Calabar flank with the Abakaliki anticlinorium (Abakaliki Foldbelt) defining the northeastern limit (Fig. 2). To the west, the Niger Delta basin is bounded by the Dahomey Basin. The Anambra Basin is situated to the north of the Niger Delta; to the south is offshore Gulf of Guinea.

1.2 Geological evolution and history of the southern Nigeria basins

and the Cenozoic Niger Delta

The geological evolution of the Cenozoic Niger Delta cannot be completely understood in isolation of the other sedimentary basins in southern Nigeria, most especially the aulacogen Benue Trough (Figs. 3a-b). Reijers et al. (1997) considered the Niger Delta to be the youngest among the chain of sub-basins

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(the Gongola, the Yola, the Abakaliki, the Anambra and the Afikpo sub-basins) in the Benue Trough.

The evolutionary history of the Cenozoic Niger Delta has been extensively researched and documented by the following authors: Hospers, 1965; Short and Stäuble, 1967; Weber and Daukoru, 1975; Lehner and De Ruiter, 1977; Evamy et al., 1978.

The Benue Trough evolved during the opening of the South Atlantic margin which lead to the separation of the African and South American continents during the Cretaceous (Figs. 1 and 3a inset). The trough represents the failed arm of a triple junction (aulacogen). Since its Early Cretaceous opening, the trough has witnessed a series of depositional cycles from Aptian through Paleocene (Short and Stäuble 1967; Weber and Daukoru, 1975). The first marine transgression into the trough, which took place in the Albian, resulted in the deposition of Asu River Group (Fig. 3a, Table 1; Short and Stäuble 1967; Reijers et al., 1997). This was followed by a mid-Cenomanian regressive phase which resulted in a deltaic environment leading to the deposition of the Keana Formation (Fig. 3a). Another major transgression, which took place in the Turonian, lead to the deposition of the Eze Aku Shale (Table 1, Fig. 3a). This transgression was succeeded by a Late Turonian regression. The third major transgression took place during the Coniacian and was terminated with a brief phase of folding of Santonian age (Short and Stäuble, 1967).

During the Santonian regional folding, the Abakaliki Trough was uplifted to form the Abakaliki High (Fig. 3b), the Anambra Platform downwarped to form the Anambra Basin and there was also the formation of the Afikpo Syncline (Fig. 3b; Weber and Daukoru, 1975; Reijers et al., 1997). After the folding and uplifting, the deltaic sedimentation became permanently established in the southern Benue Trough which culminated in the formation of the present Niger Delta.

1.3 Stratigraphy of the Tertiary Niger Delta

The lithofacies of the Cenozoic Niger Delta reflects the various depositional environments peculiar to most deltas. These depositional environments, which prevailed in the sequences of the Cenozoic Niger Delta can largely be grouped into continental, transitional and marine. The Tertiary Niger Delta covers an area of

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approximately 140,000 km2, with cumulative sedimentary sequence of about 12,000 m (Knox and Omatsola, 1989). The sequences of the Niger Delta have been subdivided into three major sedimentary units, namely the Akata, Agbada and the Benin Formations (Table 1 and Fig. 4). The oldest of these three formations is the Paleocene to Recent Akata Formation (Short and Stäuble, 1967; Reijers et al., 1997). The Akata Formation, characterised by continuous, uniform shale deposition was laid down in a marine environment. On top of the marine sequence is the Eocene to Recent Agbada Formation. The paralic Agbada Formation constitutes the actual deltaic portion of the sequence. It is considered to have been accumulated in deltaic front, delta-topset and fluviodeltaic environments (Corredor et al., 2005). Capping the sequence is the mainly continental Benin Formation, deposited during the Oligocene to Recent (Reijers et al., 1997).

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1.3.1 The Akata Formation

The formation is characteristically composed of dark gray shale, sometimes sandy or silty of prodelta origin (Short and Stäuble, 1967; Akpoyovbike, 1978). The shales of this formation are largely undercompacted (Akpoyovbike, 1978).

1.3.2 The Agbada Formation

The Agbada Formation which herein is subjected to detailed palynological investigation, is composed mainly of alternating sandstone/sand bodies with mudstone. The Agbada Formation, according to Weber (1971), is considered to be composed of cyclic sequences of marine and fluvial deposits. Evidence from ditch cuttings used for the present study indicates fine to medium-grained sand/sandstone and mudstone. Lots of fairly clean coarse-grained sands have also been encountered in the samples. They are also locally calcareous, shelly, and contain pyrite. The formation as observed in the present investigation yields abundant and diverse groups of palynomorphs. Gamma ray log data indicate high shale to sand ratio at the base of the Agbada Formation. This gradually reverses itself as the middle part of the formation is approached and persists to the top. The formation grades vertically into

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the mainly continental deposits of the Benin Formation, but could also be a time-gap with some erosion suggested at “base-Benin”.

1.3.2.1 Biostratigraphic outlook of the Agbada Formation

Routine palynological information from the studied sections is not available due to the fact that most of the palynological investigations in the Niger Delta are carried out by the oil companies and such studies are always confidential. However, biostratigraphic studies on the Agbada Formation from other localities in the Niger Delta, largely based on foraminifera, have assigned an Oligocene - Pliocene age range to the formation (Peters, 1979, 1983; Ozumba, 1994; Adeniran, 1997). The same age range has also been assigned to most of the pollen recovered from the formation from other localities in the Niger Delta by Legoux (1978).

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1.3.3 The Benin Formation

The Benin Formation represents continuous continental deposits ranging from coarse to medium-grained sands/sandstone. Short and Stäuble (1967) have described the sand/sandstone of the Benin Formation to be coarse grained, generally very granulate and pebbly to fine-grained. Few samples of the Benin Formation included in the samples used for the present investigation indicate medium to coarse-grained sand/sandstones. It is generally fairly clean but evidence of organic remnants has been found in some of the samples.

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1.4 Sedimentological evolution in response to structural

developments in the Cenozoic Niger Delta

The Cenozoic Niger Delta exhibited successive phases of developments. These individual phase increments which are results of cyclic rapid progradation of the Niger Delta have been referred to by several authors as depositional belts or “depobelts” (Fig. 5; Knox and Omatsola, 1989; Doust and Omatsola, 1990; Reijers et

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development of the depobelts has been established and referred to as “Escalator Regression Model” (Fig. 6, Knox and Omatsola, 1989). This model is generally adopted among geologists working in the Niger Delta.

Seven depobelts, namely Northern Delta, Greater Ughelli, Central Swamp I, Central Swamp II, Coastal Swamp I, Coastal Swamp II and Offshore depobelts have been identified and delineated in the Niger Delta (Figs. 5 and 6). An individual depobelt is usually fault bounded both at the proximal and distal limits and essentially filled with paralic sediments (Fig. 7). The deposition of paralic sediments in each individual depobelt results from eustatic sea level oscillations active within the basin during the development of a depobelt. The sea level oscillations are the result of alternating transgressions and regressions depending on either rise or fall of the sea level. Marine/shallow marine sediments are deposited during transgression, whereas continentally-derived sediments are usually associated with regressive phases. Climatic changes associated with wet/dry climates have also been suggested to be responsible for cyclicity of paralic deposition (Burke and Durotoye, 1970). For a continued deposition of paralic sediments in a depobelt, there must be creation of accommodation space and sufficient sediment supply (Fig. 7). Ultimately, the creation

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of accommodation space is directly associated with subsidence, when subsidence ceases, accommodation space creation also ceases. The deposition of paralic sediments ceases within a depobelt at the outset of non-creation of new accommodation space. This results in rapid advance of “alluvial” sand over the proximal and central parts of the depobelt (Fig. 7) which eventually initiates the deposition of paralic sediments in the succeeding depobelt (Knox and Omatsola, 1989). As the deposition of paralic sediments starts in the new depobelt, simultaneous deposition (paralic) continues at the distal end of the successive older depobelt until the “alluvial” sediments advances further to the distal end, therefore rendering the depobelt inactive. The deposition of paralic sediments then shifts fully into the new depobelt (Fig. 7). The mechanism responsible for development of both the regional and counter-regional growth faults has been comprehensively explained by the following authors: Evamy et al., 1978; Knox and Omatsola 1989; Doust and Omatsola, 1990. The same process of development, fill and abandonment repeated itself in the development of all the depobelts.

Sedimentary fill in each successive depobelt show marked age differences, getting younger in the seaward direction (Fig. 7; Knox and Omatsola, 1989). The oldest of the depobelts is located further inland towards the continent and the youngest being farther offshore (Fig. 7).

1.5 Oil field structures common in the Niger Delta

Structures in the Niger Delta are dominated by growth faults, rollover anticlines and antithetic faults (Fig. 8). Other structures include: crestal faults and flank faults, shale ridges and salt diapirs (Doust and Omatsola, 1990; Weber and Daukoru, 1975). The development of growth faults in the Niger Delta has been suggested to be the result of gravitational slumping in the under-compacted marine Akata Shale during the deposition of the paralic (Agbada Formation) sequence (Weber, 1971). Growth faults, commonly referred to as structure building faults, define the up-dip limit of the depobelts. They are usually listric faults and tend to flatten at depth (Figs. 7 and 8). Growth faults in the Niger Delta exhibit a seaward or southerly dip. The angle of dip along the plane of these faults changes down to the particular depth where the plane almost flattens out.

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The down-dip or distal end of a depobelt is defined by counter-regional faults (Weber and Daukoru, 1975). The dips (landward dip) of counter-regional faults are usually opposite that of structure-building growth faults (Figs. 7 and 8). They have been suggested to be generated usually at a lithology change (sand to shale) (Doust and Omatsola, 1990). Immediately at the back of a counter-regional fault exists another structure-building growth fault which delineates the proximal end of a new depobelt. Such a combination of growth fault and counter regional fault to the south of the basin is referred to as “back-to-back faulting” (Weber and Daukoru, 1975).

Antithetic faults display similar dip direction like the counter-regional faults, but they are not associated with the delineation of depobelt boundaries (see Weber and Daukoru, 1975; Doust and Omatsola, 1990). Antithetic faults as depicted can actually be considered as bisectors of growth faults (Fig. 8).

Rollover anticlines are another important structure in the Niger Delta as regards the role they play in hydrocarbon trapping. Weber and Daukoru (1975) associated the development of these rollover anticlines with bed rotation along the growth fault as a

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result of rapid deposition. The same authors indicated that many oil fields in the Niger Delta are anticlinal rollover structures.

1.6 Petroleum habitats in the Niger Delta

Based on several literature accounts, there exists an incomplete understanding of the petroleum habitats of the Niger Delta, most especially the types of its source rock. While some authors considered the Akata Formation as the major source rock for hydrocarbon generation in the Niger Delta (Ejedawe, et al., 1984; Lambert-Aikhionbare and Ibe, 1984), some others are of the opinion that the Akata and the marine sequence of the Agbada Formations partly are the major sources of the hydrocarbons (Ekweozor and Okoye, 1980; Ekwezor and Daukoru, 1984; Weber and Daukoru, 1975; Evamy, et al., 1978). More recent publications by Haack et al. (2000) and Samuel et al. (2009) even suggest additional hydrocarbon source systems for the Niger Delta, especially the Cretaceous sub-delta successions.

While controversies exist on the source rock, there seems to be a general consensus on the reservoir rocks which are believed to be the marine and non-marine sequences of the Agbada Formation. Rollover anticlines associated with growth faults and a few stratigraphic trapping mechanisms constitute effective traps for the hydrocarbon in the Niger Delta (Evamy et al., 1978; Stacher, 1995).

1.7 Petroleum exploration and exploitation history of the Niger Delta

Petroleum exploration activities in the Niger Delta started in the 20th Century with the early wells drilled by the German-Nigerian Bitumen Corporation (Weber and Daukoru, 1975). However, the early exploration activities never resulted in discovery of petroleum of any commercial significance until in the 1950’s. In 1956, the first commercial oil discovery was struck at Oloibiri with the drilling of the Oloibiri-1 well. Since then oil exploration and production activities has drastically increased in the Niger Delta. With the oil boom of the 1970’s, petroleum became the main foreign earner for Nigeria accounting for 90% of her earning (Nigerian National Petroleum Corporation, NNPC-online). Presently, dependence on petroleum as the main foreign earner for Nigeria is well above 90%.

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The Oloibiri field at its inception in 1958 had a production capacity of about 5,100 barrels per day (Nigerian National Petroleum Corporation, NNPC-online). From 1958 until the start of the Biafra War in 1967, petroleum exploration and production increased steadily. This steady increase was curtailed until the end of the war in 1970 (Nigerian National Petroleum Corporation, NNPC-online). The end of the war in 1970 coincided with the worldwide increase in petroleum price and by the late 1970’s, Nigeria attained a production capacity of 2 million barrels per day making Nigeria a force to reckon with in world petroleum politics. Presently, Nigeria has a production capacity of 2.5 million barrels per day, but this cannot be fully realised because of the militant insurgence activities in the Niger Delta region. As at present, the Nigerian proven oil reserve stands at 37.2 billion barrels, with a target to increase the reserve to 50 billion barrels by 2020 due to new concessions granted to oil companies for offshore exploration (Nigerian National Petroleum Corporation, NNPC-online). In 2006, the Department of Petroleum Resources (DPR), the regulatory arm of NNPC, put the Nigeria gas reserve at between 185-189 TCF. In 1971, Nigeria joined OPEC as its 11th member and remains an important member till today.

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1.8 Previous palynological work in the study area

A great deal of palynological investigations has been conducted in the Niger Delta. Some of the pioneering palynological investigations in the Niger Delta include those of Van Hoeken-Klinkenberg (1966) on the Maastrichtian, Paleocene and Eocene pollen and spores from Nigeria and the systematic description of new sporomorphs from the Upper Tertiary of Nigeria (Clarke, 1966; Clarke and Frederiksen, 1968). The work of Germeraad et al. (1968) on the palynology of Tertiary sediments from tropical areas focused on the Niger Delta as one of the important basins on which the publication is based. Legoux (1978), Jan du Chêne et al. (1978) and Oloto (1992) have carried out palynological investigations including systematic description and age determination of the sedimentary sequences in the Niger Delta. The applied palynological studies in the basin include those of Morley and Richards (1993) who used Gramineae cuticle as a tool for climate change monitoring in the Late Cenozoic Niger Delta. The high resolution sequence stratigraphic work of Armentrout et al. (1999) from the Oso Field, Niger Delta emphasised the importance of palynology in detailed sequence stratigraphic resolution. Also van der Zwan and Brugman (1999), indicated the importance of palynology as one of a number of biosignals in the EA Field, Niger Delta. A recently published paper by Ige (2009) is based on the pollen and spore record from the Niger Delta and their palaeo-vegetational implications. Oboh et al. (1992) and Oboh (1995) are other important palynological contributions in the Niger Delta Basin.

1.9 Aim and objective of the present study

The present study is based primarily on the application of palynological results in determining the palaeoclimate and palaeovegetation which prevailed during the deposition of the Agbada Formation. These factors undoubtedly played an important role in the deposition of the paralic Agbada Formation in the Niger Delta.

The main objective, therefore, is to reconstruct palaeovegetation and palaeoecology trends as evident from the encountered fossil pollen and spores in the investigated wells. To achieve this, emphasis is laid on ecostratigraphy based on quantitative analysis as opposed to the classical conventional qualitative palynological study.

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The present study is also aimed at testing the correlatability of the paralic sequences between the selected depobelts.

The stratigraphic ranges of certain marker palymorphs as previously reported from West African and other African basins, South America and elsewhere also give more insight into the age of the Agbada Formation.

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Chapter 2

Material and Palynological Methods

2. Materials

Three wells from different depobelts are selected for this study, namely: Well 8 from Central Swamp I, Well 6 from Coastal Swamp I and Well 4 from Coastal Swamp II (Fig. 5). A total of 407 ditch cutting samples from the three deep wells together with their corresponding log data (Gamma Ray) yielded the data base for the present investigation. The samples and the location map of the selected wells were provided by Shell Petroleum Development Company of Nigeria. The wells are deliberately selected from different depobelts so as to give an insight into the relationship between the depobelts considering their evolutionary history. The geological formations penetrated by the wells are: the Agbada Formation and the lowermost part of the Benin Formation which was not palynologically investigated due to lack of meaningful organic content in the samples.

2.1 Preparation techniques

Following the standard palynological preparation method, with inputs from the procedures established at the palynological section of the Exploration Geology Department of the Technische Universität Berlin, Germany, 407 ditch cutting samples from the three wells were subjected to investigation.

Circa 10 g of each sample was treated with 10% HCl (in excess) for the complete removal of carbonates which may be present in the samples. This was followed by complete neutralization with distilled water before the next procedure. Then 35% HF was added to the sample which was placed on a shaker for 24 hours to speed up the reaction rate. The acid-resistant residue was then allowed to stand for another three days to ensure a complete dissolution of the silicates and for the particles to settle down. Thereafter, the HF was carefully decanted, then followed by complete neutralisation with distilled water. To remove fluoro-silicate compounds usually formed from the reaction with HF, the content was again treated with warm 10% HCl. This was again followed by another round of complete neutralisation with distilled water. It is important to point out that no oxidation was conducted on the samples

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because of the selective destructive effect this can have on some of the palynomorphs, especially on the dinoflagellates.

Using a 15 µm sieve, the residue was carefully sieved in an ultrasonic machine for a maximum of 5 minutes to improve palynomorph recovery. The collected residues are then stored in small glass bottles. One to two drops of the residue are carefully dropped at the centre of each slide. A drop of warm Kaiser´s Glycerol Gelatine is placed on a cover slip which is then gently lowered onto the slide containing the residue. This is then left in a relatively cool environment for about 15 minutes to ensure that the slide and the cover slip are firmly bonded together. A minimum of two slides were made from each sample.

2.2 Microscopic tasks

Microscopic scanning of the palynomorphs was carried out using a Leitz Diaplan Microscope (Leitz Wetzlar; Type 307-148.001). Photographic work was done using Olympus Digital Camera DP 12. All slides, sieved and unsieved residues, are stored at the Institut für Angewandte Geowissenschaften, Technische Universität Berlin, Germany.

During visual assessment of each sample, at least 200 palynomorphs (pollen, spores, dinocysts, microforaminiferal test linings, fungi, freshwater/marine algae and inaperturates) are counted where possible. Percentage contributions of the mentioned components in each of the samples were calculated and depicted in Figures 13-15.

Morphological comparison of the specimens recovered were made with reference to illustrations from systematic publications on Cenozoic palynomorphs, for example Germeraad et al., 1968; Van der Hammen and Wymstra, 1964; W. Krutzsch, 1959, 1962, 1963a, 1963b, 1967, 1970, 1971; Clarke and Frederiksen, 1968; Clarke, 1966; Salard-Cheboldaeff, 1978, 1979, 1990; Salard-Cheboldaeff et al., 1992; Van Hoeken-Klinkenberg, 1966; Legoux, 1978; Takahashi and Jux, 1989; Sah 1967 and Kar, 1992.

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Chapter 3

Systematic Description

Most of the forms encountered in the present study have been comprehensively described by respective authors cited for each species. In view of this, no major descriptions of the taxa were attempted in this chapter. However, remarks were made on specific taxa where necessary. Interested readers are therefore referred to the quoted references. Within the major palynomorph groups, the taxa are arranged in alphabetical order for ease of reference.

3.1 Pteridophyte and bryophyte spores

3.1.1 Monolete spores

Genus Laevigatosporites Ibrahim, 1933

Laevigatosporites discordatus Pflug, 1953 Plate 1, fig. 3

1967 Laevigatosporites discordatus Krutzsch, pl. 54, figs. 8-9. 1973 Laevigatosporites discordatus Roche, pl. 2, fig. 30.

1989 Laevigatosporites discordatus Takahashi and Jux, pl. 2, fig. 6.

Comments: The present specimen is morphologically similar to those described by Krutzsch (1967) and Takahashi and Jux (1989), but it is smaller.

Present record: 4-11340-3c (= 3456.4 m), coord. 40/100.9 and others.

Stratigraphic range: Paleocene to Miocene in Middle Europe, Late Cretaceous to Eocene in West Canada, Middle Tertiary, Nigeria (Takahashi and Jux, 1989); Eocene to Miocene in Eastern Europe (Krutzsch, 1967).

Measurement: Length 41.6 m.

Botanical affinity: Polypodiaceae (Takahashi and Jux, 1989).

Laevigatosporites haardti (Potonié & Venitz) Thomson & Pflug, 1953 crassicus Krutzsch, 1967

Plate 1, fig. 4

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1989 Laevigatosporites haardti crassicus Takahashi and Jux, pl. 4, fig. 7. Present record: 4-6540-1 (=1993.4 m), coord. 36.4/106.5.

Stratigraphic range: Oligocene in Germany (Takahashi and Jux, 1989), Mid Tertiary in Germany (Krutzsch, 1967).

Measurements: Length 38.4 m, width 27.2 m.

Botanical affinity: Polypodiaceae (Takahashi and Jux, 1989). Laevigatosporites javanicus Takahashi, 1982

Plate 1, figs. 1-2

1989 Laevigatosporites javanicus Takahashi and Jux, pl. 3, figs. 2-4; pl. 4, figs. 3-6.

Comments: Generally, this species is common in almost all the investigated samples. Therefore the record indicated in the “present record” below is for reference purposes. Present record: 4-7680-2 (=2340.9 m), coord. 59/102, (fig. 2) 4-6060-2 (=1847.1 m), coord. 48.4/101 (fig. 1) and others.

Stratigraphic range: Eocene in Indonesia, Middle Tertiary, Nigeria (Takahashi and Jux, 1989).

Measurements: Length 64 m, width 48 m, (fig. 2), length 54.4 m, width 36.8 m, (fig. 1).

Botanical affinity: Polypodiaceae (Takahashi and Jux, 1989).

Laevigatosporites nutidus (Mamczar, 1960) Krutzsch, 1967 Plate 1, figs. 6-7

1967 Laevigatosporites nutidus nutidus Krutzsch, pl. 53, figs. 4-12. 1989 Laevigatosporites nutidus Takahashi and Jux, pl. 4, fig. 1. Comment: The present specimens fit well to those described by the above mentioned authors.

Present record: 4-6960-1 (= 2121.4 m), coord. 47.5/98.7, (fig. 7) 4-7260-1 (= 2212.8 m), coord. 37.1/108.1, (fig. 6) and others.

Stratigraphic range: Eocene-Pliocene in Middle Europe and Miocene-Pliocene East Europe (Takahashi and Jux, 1989).

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Measurements: Length 64 m, width 48 m (fig. 7); length 67.2 m, width 48 m (fig. 6).

Botanical affinity: Polypodiaceae (Takahashi and Jux, 1989).

Laevigatosporites nutidus crassicoides Krutzsch, 1967 Plate 1, fig. 5

1967 Laevigatosporites nutidus crassicoides Krutzsch, pl. 53, figs. 13-15.

1989 Laevigatosporites nutidus crassicoides Takahashi and Jux, pl. 4, fig. 2.

Comment: The size of this specimen is larger than that described by Krutzsch, 1967. Present record: 4-6120-2 (= 1865.4 m), coord. 40.4/91 and 4-7380-1 (= 2249.4 m). Stratigraphic range: Early Miocene in Germany (Krutzsch, 1967); Eocene to Oligocene, Colombia (Schuler and Doubinger, 1970); Eocene to Pleistocene, Eastern China Sea (Song et al., 1985).

Measurements: Length 62.4 m, width 36.8 m. Botanical affinity: Polypodiaceae (Krutzsch, 1967). Genus Perinomonoletes Krutzsch, 1967

Perinomonoletes sp. 1 Plate 1, figs. 9-10

Description: Monolete spore. Bean-shaped in lateral view. Moderately long and straight dehiscence mark present.The exospore or inner exine layer is laevigate. The perispore or outer exine layer is made up of irregularly arranged folds.

Present record: 4-10020-1 (= 3054.1 m), coord. 41/97.9 (fig. 10); 6-9890-2 (= 3014.5 m) , coord., 46/94.1 (fig. 9), 6-9350-2 (= 2849.9 m).

Measurements: Length 56 m, width 40 m, (fig. 10); length 48 m, (fig. 9). Botanical affinity: Polypodiaceae (Krutzsch, 1967).

Perinomonoletes sp. 2 Plate 1, fig. 8

Description: Monolete spore. Exospore laevigate. Irregularly arranged folding on the ectexine. It is elongated in lateral view which differentiates it from Perimonoletes sp. 1.

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Present record: 6-8210-1 (= 2502.4 m), coord. 29.8/103.4. Measurement: Length 56 m.

Botanical affinity: Polypodiaceae (Krutzsch, 1967). Genus Reticulosporis Krutzsch 1959

Reticulosporis miocenicus (Selling, 1944) Krutzsch, 1959 Plate 1, fig. 13

1967 Reticulosporis miocenicus Krutzsch, pl. 81, figs. 1-6. Present record: 6-6230-2 (= 1898.9 m), coord. 37/111. 9. Stratigraphic range: Miocene, Germany (Krutzsch, 1967). Measurement: Length 68.8 m.

Botanical affinity: Unknown.

Reticulosporis sp. A Plate 1, fig. 12 Present record: 6-6290-2 (= 1917.2 m), coord. 38/111. Measurement: Length 56 m.

Botanical affinity: Unknown.

Reticulosporis sp. B Plate 1, fig. 11

Description: Monolete spore. Elongated bean-shaped in lateral and proximal view. Plate 1, fig. 11 is an oblique proximal view. The exine is foveolate. The dehiscence mark is long and straight.

Present record: 6-8510-1 (= 2593.8 m), coord., 36.2/109. 2. Measurement: Length 56 m.

Botanical affinity: Unknown.

Genus Verrucatosporites Pflug and Thomson in Thomson and Pflug, 1953 Verrucatosporites alienus (Potonié, 1931) Thomson & Pflug, 1953

Plate 2, figs. 1-2

1967 Verrucatosporites alienus Krutzsch, pl. 67, figs. 1-15.

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Comment: The species is widespread in the studied sections. Present record: 4-6720-2 (= 2048.3 m) , coord. 47.8/95.2.

Stratigraphic range: Oligocene to Pliocene in Germany, Miocene in Czechoslovakia, Early Miocene in New Zealand (Takahashi and Jux, 1989).

Measurements: Length 56 m, width 36.8 m (fig. 1). (fig. 2).

Botanical affinity: Polypodiaceae (Takahashi and Jux, 1989). Verrucatosporites balticus major Krutzsch, 1967

Plate 1, fig. 14

1967 Verrucatosporites balticus major Krutzsch, p. 178, pl. 65, figs. 18-26. Comment: The specimen fits very well into Krutzsch´s (1967) description. Present record: 6-6230-1 (= 1898.9 m), coord. 28.3/103.2, among others. Stratigraphic range: Miocene – Pliocene, S. Germany (Krutzsch, 1967). Measurement: Length 46.4 m.

Botanical affinity: Polypodiaceae (Krutzsch, 1967).

Verrucatosporites favus (Potoniè, 1931c) Thomson and Pflug, 1953 subfsp. favus Plate 2, figs. 3-4

1967 Verrucatosporites favus Krutzsch, pl. 68, figs. 2-8. 1989 Verrucatosporites favus pseudosecundus Takahashi and Jux, pl. 3, fig. 7. 2008 Verrucatosporites favus Eisawi and Schrank, pl. 6, fig. 17.

Comment: The species is widespread in the studied sections.

Present record: 4-6060-1 (= 1847.1 m), coord. 30/105.3, (fig. 3) 4-11940-1 (= 3639.3 m), coord. 32.7/94.1 (fig. 4).

Stratigraphic range: Oligocene-Miocene in Western Europe (Takahashi and Jux, 1989).

Miocene in Germany (Krutzsch, 1967).

Measurements: Length 52.8 m, width 43.2 m (fig. 3), length 64 m (fig. 4). Botanical affinity: Polypodiaceae (Takahashi and Jux, 1989).

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Verrucatosporites ornatus Sah, 1967 Plate 1, fig. 15

1967 Polypodiisporites ornatus Sah, pl. III, figs. 19, 20 and 22. 2007 Verrucatosporites ornatus Bankole et al., pl. 2, fig. 16. Comment: The species is widespread in the studied sections.

Present record: 4-6000-1 (= 1828.8 m), coord. 32.3/95.6.

Stratigraphic range: Neogene in Burundi (Sah, 1967), Paleogene in Nigeria (Bankole et al., 2007).

Measurements: Length 57.6 m, width 36.8 m. Botanical affinity: Polypodiaceae (Sah, 1967).

Verrucatosporites usmensis Van Der Hammen 1956 Plate 1, fig. 16

1968 Verrucatosporites usmensis Germeraad et al. pl. 2, fig. 3. 1978 Verrucatosporites usmensis Jan Du Chêne et al. pl. 7, fig. 10. 1990 Verrucatosporites usmensis Salard-Cheboldaeff, pl. 7, fig. 7.

Comment: The species is widespread in the studied sections. Present record: 4-5880-2 (= 1792.2 m), coord. 39.6/107.

Stratigraphic range: Eocene to Pleistocene in Nigeria and Borneo (Germeraad, et al., 1968)

Measurements: Length 60.8 m, width 40 m including gemmae. Botanical affinity: Unknown.

3.1.2 Trilete spores

3.1.2.1 Smooth exine

Genus Biretisporites Delcourt & Sprumont, 1955

Biretisporites potoniaei Delcour & Sprumont, 1955 Plate 2, figs. 5-6

1955 Biretisporites potoniaei Delcourt & Sprumont, p. 40, fig. 10. 1987 Biretisporites potoniaei Schrank, pl. 4, fig. 1.

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1990 Biretisporites potoniaei Schrank, pl. 1, figs. 6a-b.

1990 Biretisporites potoniaei Salard-Cheboldaeff, p. 13-14, pl. I, fig. 5.

Comment: With reference to the original and emended description by Delcourt & Sprumont 1955 and Delcourt et al. 1963, respectively, the spores could be triangular to subtriangular in ambitus. The specimens presented here are, however, subangular to subrounded in ambitus. This fits well into the specimen presented in Schrank, 1987. The size of the specimens ranges between 40 and 45 m.

Present record: 4-7200-1 (= 2194.6 m), coord. 52.2/101.5 (fig. 5), 4-7320-2 (= 2231.1 m), coord. 34.8/109.8 (fig. 6).

Stratigraphic range: Long-ranging.

Measurements: 43.2 m (fig. 5), 41.6 m (fig. 6). Botanical affinity: Unknown.

Genus Cyathidites Couper, 1953

Cyathidites congoensis Sah, 1967 Plate 2, figs. 7-8

1967 Cyathidites congoensis Sah, p. 10, pl. I, figs. 4-5. 2008 Cyathidites congoensis Eisawi & Schrank, pl. 7, fig. 15.

Present record: 4-12540-2 (= 3822,2 m), coord. 36.8/99.2, (fig.7), 4-7800-2 (= 2377,4 m), coord. 36.6/110, (fig. 8). Common in all the sections.

Stratigraphic range: Neogene, Burundi (Sah, 1967). Measurements: 35.2 m (fig. 7), 38.4 m (fig. 8).

Botanical affinity: Derived from either Cyatheaceous or Dicksoniaceous plants (Sah, 1967).

Genus Dictyophyllidites Couper, 1958

Dictyophyllidites trilobiformis Sah, 1967 Plate 2, figs. 9-10

1967 Dictyophyllidites trilobiformis Sah, p. 12, pl. 1, fig. 11.

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Present record: 4-6300-1 (= 1920.2 m), coord. 28.9/102.6, (fig. 9), 4-7980-1 (= 2432.3 m), coord. 38.1/104.9, (fig. 10), 4-6060-2 (= 1847.1 m), 6-7010-1 (= 2136.6 m), 6- 10430-2 (= 3179.1 m) among others

Stratigraphic range: Neogene, Burundi (Sah, 1967). Measurements: 36.8 m (pl. 2, fig. 9) 56 m (fig. 10). Botanical affinity: Dicksoniaceae (Sah, 1967).

cf. Dictyophyllidites pliocaenicus (Thiergart, 1940) Nagy, 1985 comb. nov Plate 2, fig. 11

1985 cf. Dictyophyllidites pliocaenicus Nagy, p. 84, pl. XVIII, fig. 10 Present record: 4-13160-1 (= 4011.2 m), coord. 37/96.7

Stratigraphic range: Pliocene in Europe (Nagy, 1985) Measurement: 40 m

Botanical affinity: Unknown.

Dictyophyllidites pessinensis (Krutzsch, 1962) Nagy, 1985 Plate 2, fig. 12

1962 Toroisporis (Toroisporis) pessinensis Krutzsch, p. 84, pl. 35, figs. 1-6. 1985 Dictyophyllidites pessinensis Nagy, p. 271, pl. XVIII, Figs. 8-9. Present record: 4-13340-1 (= 4066.0 m), coord. 37.2/103.8, 4-11280 (= 3438.1 m), 4-10980 (= 3346.7 m), 4-5880 (=1792.2 m), 8-13540 (= 4127.0 m).

Stratigraphic range: Lower and Middle Miocene in Germany (Krutzsch, 1962). Measurement: 33.6 m.

Botanical affinity: Unknown.

Genus Distancoraesporis (Krutzsch, 1963) Srivastava, 1973

Distancoraesporis cf. triangularis (Mamczar, 1960 ex Krutzsch, 1963) Grabowska in Stuchlik, 2001

Plate 2, fig. 13

1963b Stereisporites (Distancoraesporis) triangularis Krutzsch, p. 54, pl. 9, figs. 15-19.

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Present record: 8-7675-1 (= 2339.3 m) , coord. 23/105.7.

Stratigraphic range: Middle to Upper Miocene in Poland (Stuchlik, 2001). Measurement: 47 m.

Botanical affinity: Unknown. Genus Gleicheniidites Ross, 1949

Gleicheniidites sp. Salard-Cheboldaef et al., 1992 Plate 2, fig. 14

1992 Gleicheniidites sp. Salard-Cheboldaef et al., pl. II, fig. 12.

Present record: 4-6300-2 (= 1920.2 m), coord. 36.5/104.4, 4-6180-1 (= 1883.7 m), 8-9160-1 (= 2792.0 m).

Stratigraphic range: Tertiary, Cameroun (Salard-Cheboldaef, 1992). Measurement: 44.8 m.

Botanical affinity: Not known.

Genus Intrapunctisporits Krutzsch, 1959

cf. Intrapunctisporis gracilis Krutzsch, 1962 Plate 2, figs. 15-16

1962 Intrapunctisporis gracilis Krutzsch, p. 62, pl. 24, figs. 4-8.

Comment: The species fits to Krutzsch’s (1967) description. However, the present specimen has a size range of 60-75 m which is much larger than Krutzsch’s (1967) size range of 40-45 m.

Present record: 6-11210-1 (= 3416.8 m), coord. 24/102.1 (fig. 15), 4-7920-2 (= 2414.0 m), coord. 41.1/108.3 (fig. 16). Relatively common in the sections investigated.

Stratigraphic range: Early Tertiary, Germany (Krutzsch, 1962). Measurements: Length 67.2 m (fig. 15), Length 70.4 m (fig. 16). Botanical affinity: Unknown.

Intrapunctisporis intrapunctis Krutzsch, 1959 Plate 2, figs. 17-18

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Present record: 6-10550-1 (= 3215.6 m), coord. 51/108.5 (fig. 17), 6-10430-2 (=3179.1 m), coord. 31.5/109.2 (fig. 18). Fairly common.

Stratigraphic range: Mid Eocene, Germany (Krutzsch, 1959) Measurements: Length 67.2 m (fig. 17), length 60.8 m (fig. 18). Botanical affinity: Unknown.

Genus Leiotriletes (Naumova) ex Potonié and Kremp, 1954

Leiotriletes maxoides maxoides Krutzsch, 1962 Plate 2, figs. 19-20

1962 Leiotriletes maxoides maxoides Krutzsch, p. 18, pl. 2, figs. 1-5.

Present record: 8-11740 (= 3578.4 m), coord. 31.9/102 (fig. 19), 8-13180-2 (= 4017.3 m), coord. 33/98.2 (fig. 20). Common in the sections.

Stratigraphic range: Middle Oligocene to Pliocene in Germany (Krutzsch, 1962). Measurements: 79 m (fig. 19), 60.8 m (fig. 20).

Botanical affinity: Lygodium? (Krutzsch, 1962).

Leiotriletes maxoides minoris Krutzsch, 1962 Plate 3, fig. 1

1962 Leiotriletes maxoides minoris Krutzsch, p. 16, pl. 1, figs. 2-4.

Present record: 6-6230-2 (= 1898.9 m), coord. 38.8/105, 6-7670-1 (= 2337.8 m), 4-9000-2 (= 2743.2 m). Common.

Stratigraphic range: Early Miocene to Late Oligocene in Germany (Krutzsch, 1962). Measurement: 60.8 m.

Botanical affinity: Unknown.

Leiotriletes microsinuosoides Krutzsch, 1962 Plate 3, fig. 2

1962 Leiotriletes microsinuosoides Krutzsch, p 36, pl. 11, figs. 1-15.

Present record: 6-7910-1 (= 2411.0 m), coord. 24.1/100.1. Common in all the sections. Stratigraphic range: Oligocene to Miocene in Europe (Krutzsch, 1967).

Measurement: 44.8 m. Botanical affinity: Unknown.

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Genus Matonisporites Couper, 1958

Matonisporites rarus Sah, 1967 Plate 3, fig. 3

1967 Matonisporites rarus Sah, p. 13, pl. I, figs. 15-16.

Present record: 6-6290-1 (= 1917.2 m), coord. 45.2/107.8, 6-10910-1 (= 3325.4 m). Stratigraphic range: Neogene, Burundi (Sah, 1967).

Measurement: 62.4 m.

Botanical affinity: According to Sah (1967) the spore resembles Matonia. Genus Todisporites Couper, 1958.

Todisporites major Couper, 1958 Plate 3, figs. 4-5

1958 Todisporites major Couper, p. 134, pl. 16, figs. 6-8.

1997 Todisporites major Samant & Phadtare, p. 13, pl. 2, figs. 7-8.

Present record: 6-7670-2 (= 2337.8 m), coord. 40/110, (fig. 4), 6-6230-1 (= 1898.9 m), coord. 36.7/97.4, (fig. 5), 6-10490-1 (= 3197.4 m), 6-6350-1 (= 1935.5 m), among others.

Stratigraphic range: The species been reported from the Middle Jurassic, England (Couper, 1958); Paleocene to Neogene in India (Samant & Phadtare, 1997). Measurements: 70.4 m (fig. 4), 62. 4 m (fig. 5).

Botanical affinity: Osmundaceae (Samant & Phadtare, 1997).

Todisporites flavatus, Sah & Kar, 1969 Plate 3, fig. 6

1969 Todisporites flavatus Sah & Kar, p. 111.

1997 Todisporites flavatus Samant & Phadtare, p. 13, pl. 2, fig. 6.

Present record: 6-6290-1 (=1917.2 m), coord. 25.7/105, 6-7190-1 (= 2191.5 m), 6- 10430-1 (= 3179.1 m), 6-10550-1 (= 3215.6 m), and others.

Stratigraphic range: Early Eocene to Pliocene in India (Samant & Phadtare, 1997). Measurement: 67.2 m.

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Genus Triplanosporites (Pflug) in Thompson & Pflug, 1953 Triplanosporites microsinuosus Pflanzl, 1955

Plate 3, figs. 7-8

1962 Triplanosporites microsinuosus Krutzsch, p. 42, pl. 14, figs. 1-16.

Present record: 6-7070-2 (= 2154.9 m), coord. 37.8/107.2, (fig. 7) 6-7480-1 (= 2279.9 m), coord. 30.2/95.1, (fig. 8).

Stratigraphic range: Oligocene to Pliocene in Europe (Krutzsch, 1962). Measurements: 32 m (fig. 7), 41.6 m (fig. 8).

Botanical affinity: Unknown.

Genus Undulatisporites Pflug in Thomson & Pflug, 1953

cf. Undulatisporites structuris Krutzsch, 1962 Plate 3, figs. 9-10

cf. 1962 Undulatisporites structuris Krutzsch, p. 76, pl. 31, figs. 1-5. cf. 2001 Undulatisporites structuris Stuchlik et al., p. 53, pl. 32, fig. 6.

Present record: 6-6530-2 (= 1990.3 m), coord. 46.6/101.5 (fig. 9), 6-10970-1 (= 3343.7 m), coord. 39/107.2 (fig. 10).

Stratigraphic range: Miocene to Pliocene in Germany (Krutzsch, 1962); Middle Miocene in Poland (Stuchlik, 2001).

Measurements: 36.8 m (fig. 9), 40 m (fig. 10). Botanical affinity: Unknown.

3.1.2.2 Granulate exine

Genus Acrostichumsporites Kar, 1991

Acrostichumsporites meghalayaensis Kar, 1992 Plate 3, figs. 11-13

1992 Acrostichumsporites meghalayaensis Kar, p. 34, pl. 1, figs. 1-9.

Present record: 6-6350-1 (= 1935.5 m), coord. 39.2/112.7 (fig. 11), 6-6470-2 (= 1972.1 m), coord. 46/110 (fig. 12), 6-6290-2 (= 1917.2 m), coord. 41/109 (fig. 13), among others.

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Botanical affinity: Acrostichum, Polypodiaceae (Kar, 1992). Acrostichumsporites sp. 1

Plate 3, figs. 14-15

Description: Trilete spore, anisopolar, single grain, radially symetrical with triangular amb. The trilete mark can be indistinct depending on view position. Exine thicknesses range between 1 and 2 m. Verrucae which may be as high as 2 m and are irregularly arranged on the surface. Folding is a common feature of the surface of the exine.

Present record: 4-11520-1 (= 3511.3 m) , coord. 33.8/98.2 (fig. 14), 6-6350-1 (=

1935.5 m), coord. 50.5/101.1 (fig. 15). The species in very widespread in the

investigated sections.

Measurement: Diameter 57 -70 m.

Botanical affinity: Acrostichum, Polypodiaceae.

Acrostichumsporites sp. 2 Plate 3, figs. 16-17; plate 4, figs. 1-2

Description: Single grain, radially symetrical, spherical but has been observed to be subspherical or ellipsoidal in some specimens. Trilete mark is indistinct. Exine: irregularly arranged verrucae cover the surface. The verrucae are higher and more densely distributed in some specimens than in others. Acrostichumsporites sp. 2 is different from A. meghalayaensis based on its round outline.

Present record: 6-7190-2 (= 2191.5 m), coord. 30.6/103, (fig. 16), 6-8570-2 (= 2612.1 m), coord. 33.3/97.2, (fig. 17) 6-7070-1 (= 2154.9 m), coord. 47.3/92, (fig. 1), 6-7250-2 (= 2209.8 m), coord. 39.8/94, (fig. 2). Widespread in the investigated sections. Measurements: 67.2 m (fig. 16), 64 m (fig. 17), 76.8 m (fig. 1), 65.6 m (fig. 2). Botanical affinity: Acrostichum, Polypodiaceae.

Genus Crassoretitriletes Germeraad, Hopping and Muller, 1968

Crassoretitriletes vanraadshooveni Germeraad et al., 1968 Plate 4, figs. 3-4

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Present record: 6- 6530-1 (= 1990.3 m), coord. 46/107, (fig. 3), 6-7070-2 (= 2154.9 m), coord. 54.7/93.4, (fig. 4). Widespread in the investigated sections.

Stratigraphic range: Miocene – Pliocene in Nigeria (Germeraad et al., 1968), Mid- Miocene to Pleistocene in Venezuela (Lorente, 1986), Miocene and Pliocene in Taiwan (Huang, 1978 and Li & Huang, 1990 respectively).

Measurements: 91.2 m (fig. 3), 88 m (fig.4).

Botanical affinity: Lygodium (Germeraad et al., 1968).

Genus Foveosporites Balme, 1957

Foveosporites cf. canalis Balme, 1957 Plate 4, fig. 6

1967 Foveosporites canalis Sah, p. 18, pl. 2, figs. 1, 2 and 5. 2008 Foveosporites canalis Eisawi & Schrank, pl. 7, fig. 11. Present record: 6-6050-2 (= 1844.0 m), coord. 33.4/96. 8.

Stratigraphic range: Neogene, Burundi (Sah, 1967); Late Miocene to Pliocene in Sudan (Eisawi & Schrank, 2008).

Measurement: 36.8 m. Botanical affinity: Not known.

Genus Foveotriletes (Van der Hammen, 1954) ex Potonié, 1956

Foveotriletes margaritae (Van der Hammen) Germeraad et al., 1968 Plate 4, fig. 5

1968 Foveotriletes margaritae Germeraad et al., p. 268, pl. 1, figs. 1-2. Present record: 6-8810-2 (= 2685.3 m) , coord. 39.6/101.2, 6-8750 (= 2667.0 m). Stratigraphic range: Maastrichtian-Palaeocene in Nigeria (Germeraad, et al., 1968). Measurement: 44.8 m.

Botanical affinity: Unknown.

Genus Intrapunctisporis Krutzsch, 1959

Intrapunctisporis balinkaënse Kedves, 1973 Plate 4, fig 7

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