PETROGRAPHIC AND GEOCHEMICAL STUDIES OF IJEBU-IFE SANDSTONE IN SOUTH-WESTERN NIGERIA

Petrographic and Isotopic studies were carried out on carbonate facies obtained from somo and its environment with the aim of delineating the allochemical constituents, evaluating the depositional environment, the Paleotemperature and diagenesis alteration of the rock. Sixteen core samples retrieved from drill wells at 2m depth per hole in the study area were petrographically studied to determine the orthochemical and the allochemical contents. The carbon and oxygen isotopic signatures δ ¹⁸0 and δ¹³C from five pulverized samples were delineated using the Isotopic Ratio Mass Spectrometry Method (IRMS). Petrographic studies show the foraminifera, bivalves, echinoderms, brachiopods, which represents the skeletal content, intraclasts and ooids which represents the non skeletal grains. The microfacies deposited are groups of  bioclastic packstone, bioclastic wackestone, Pelloidal Wackestone deposited in a high temperature environment as a result of the present of foraminifera. The isotope signature valves for δ¹³C are -0.820, -2.82, -1.22, -2.52, -0.185 ‰ Vienna Pee Dee Belemnite and δ¹⁸O -7.73, -4.55, -4.62, -6.49, -5.19 ‰ Vienna Pee Dee Belemnite (VPDB). The calculated Z parameter is indicative of a mixed transitional environment of deposition. The negative trend in the δ ¹³C values gives a significant indication that the source rock was deposited in regressive phase and at an early stage of diagenesis. The somo limestone deposits are highly fossiliferous with numerous microfacies which were deposited in a quiet, high temperature, low energy and shallow marine or off shelf environment of deposition.

TABLE OF CONTENT

CHAPTER ONE

1.0       Introduction

1.1       General Statement

1.2.1    Aim and Objectives of study

1.2.2    Objectives of study

1.3       Scope of study

1.4       Physiographic Setting

1.4.1    Relief and Topography

1.4.2    Location and Accessibility of study area

1.4.3    Climate and Vegetation

1.4.4    Drainage Pattern

1.5       Review of Previous Work

CHAPTER TWO

2.0       Geological Settings

2.1       Regional Geology

2.2       Geology and Structural evolution of Dahomey Basin

2.2.1    Lithostratigraphy of Eastern Dahomey basin

2.2.2    Abeokuta Formation

2.2.2.1   Ise Formation

2.2.2.2   Afowo Formation

2.2.2.3   Araromi Formation

2.2.3    Imo Group

2.2.3.1 Ewekoro Formation

2.2.3.2   Akinbo Formation

2.2.3.3   Osohosun Formation

2.2.3.4   Ilaro Formation

2.2.3.5   Coastal Plains

2.2.3.6   Recent Aluminum

2.3       Sedimentation of Dahomey Basin

CHAPTER THREE

3.0       Methodology

3.1       Sample Collection and Description

3.2       Laboratory Analysis

3.2.1    Petrographic Analysis

3.2.2    Isotopic Analysis

3.3       Result Normalization

3.3.1    Delta Values

3.3.2    Standard Unit

CHAPTER FOUR

4.0       Results and Discussions

4.1       Results

4.1.1    Petrography

4.1.2    Isotope Result

4.2       Discussions

CHAPTER FIVE

5.0       Conclusion and Recommendation

5.1       Conclusion

5.2       Recommendation

REFERENCES                                                                                                                   

APPENDIX                                                                                                                          

  LIST OF FIGURES

Fig 1: Topographic map of the study Area

Fig 2: Location points and Accessibility of the study Area

Fig 3: Drainage of the Study Area

Fig 4: Sedimentary Basin of Nigeria with Red box on Dahomey Basin

Fig 5: Tectonic Framework and Structural Evolution of Dahomey Basin

Fig 6: Geological map of the eastern Dahomey Basin

Fig 7: Lithostratigraphic Section of Drill Hole 1

Fig 8: Lithostratigraphic Section of Drill Hole 3

Fig 9: Lithostratigraphic Section of Drill Hole 4

Fig 10: Lithostratigraphic Section of Drill Hole 6

Fig 11: Lithosection of the Holes in the study Area

Fig 12: Photomicrograph of Sample label Hole 1(Depth 16m)

Fig 13: Photomicrograph of Sample label Hole 1(Depth 20m)

Fig 14: Photomicrograph of Sample label Hole 1(Depth 25m)

Fig 15: Photomicrograph of Sample label Hole 1(Depth 28m)

Fig 16: Photomicrograph of Sample label Hole 1(Depth 37m)

Fig 17: Photomicrograph of Sample label Hole 3(Depth 16m)

Fig 18: Photomicrograph of Sample label Hole 3(Depth 18m)

Fig 19: Photomicrograph of Sample label Hole 3(Depth 20m)

Fig 20: Photomicrograph of Sample label Hole 3(Depth 24m)

Fig 21: Photomicrograph of Sample label Hole 4(Depth 24m)

Fig 22: Photomicrograph of Sample label Hole 4(Depth 29m)

Fig 23: Photomicrograph of Sample label Hole 4(Depth 32m)

Fig 24: Photomicrograph of Sample label Hole 4(Depth 32m)

Fig 25: Photomicrograph of Sample label Hole 6(Depth 15m)

Fig 26: Photomicrograph of Sample label Hole 6(Depth 17m)

Fig 27: Photomicrograph of Sample label Hole 6(Depth 20m)