Abstract
The middle Benue Trough is one of the three segments of the larger NE-SW trending Benue Trough. As is the case with the Upper Benue Trough, there does not seem to be any recent work dedicated to the Geology of the Middle Benue Trough. Recent works on the stratigraphy and sedimentological studies of the Albian to Turonian sediments of the middle Benue Trough, covered areas around Keana and Awe respectively (all within sheet 232 NW). This work covered Areas within Lafia (Sheet 231NW). The study area is located southeast of Lafia town. It is accessible by some major roads which includes: Lafia to Makurdi, Doma to Agyaragu and Lafia to Keana. Reconnaissance study was first carried out in the study area on a scale of 1:100000 followed by a detailed field mapping on a scale of 1:50,000. In the course of the field work, the lithostratigraphic successions in the study area was established, sedimentary structures were identified and samples collected for petrographic and sieve analysis. Stratigraphic study in the study area indicates the occurrence of three formations namely; the fluvial Lafia Formation (Campano-Maastrichtian), the shallow marine Awgu Formation (Turonian-Coniacian) and the transitional Awe Formation (Albian-Cenomanian). A total of 12 samples were collected for granulometric analysis, and 11 samples for Petrographic analysis. The Lafia Formation consist of ferrugenised sandstone at the base, clay and clayed loosed sands. Petrographic and sieve analysis revealed that the Ferrugenised sandstone range from fine-medium grain. It is moderately sorted, strongly fine skewed and is a Quartz arenite. More than 60% of the crystals are monocrystalline which is indicative of igneous provenance. The Awe Formation consists of fine-grained white sandstone, with some intercalations of white clay and laminated shale. The sandstones are fine- grained and poorly-moderately sorted which coupled with the bivariate plot that indicates a transitional conditions between shallow marine and fuvial systems. The sandstones of the Awe Formation range from Arkose to Subarkose. The presence of monocrystalline quartz and plagioclase feldspars are all indicators of igneous provenance. The Awgu Formation consists of sandstones that are fine grained, very poorly sorted and strongly fine-skewed. The sandstones of the Awgu Formation are Quartz Arenites. There are ostracodes, echinoderms, and ammonites fossils within the shaley limestone and limestones of the Awgu Formation. This is an indication of a shallow marine environment of deposition. The Sedimentary structures in the study area include; beddings, mudcracks, faults, joints and veins and unconformity. The bedding planes are indications of break in deposition of the sediments while the mudcracks indicates long exposure to a dry warm climate. Other Methods of studies such as aeromagnetic studies, palynological studies and diagenetic studies should be carried out for more geological information of the study area to properly characterise the Middle Benue Trough
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication -iv
Acknowledgement -v
Abstract -vi
Table of Contents vii
List of Figures -xi
List of Plates xii
List of Tables xiii
CHAPTER ONE
1.0 Introduction 1
1.1 Background of the Study 1
1.2 Aim of the Study and Objectives 2
1.2.1 Aim 2
1.2.2 Specific Objectives 2
1.3 Location and Accessibility of the Study Area 3
1.4 Relief and Drainage 3
1.5 Climate and Vegetation 5
1.6 Human Geography 5
CHAPTER TWO
2.0 Literature Review and Geological framework 7
2.1 The Benue Trough 7
2.2 Origin and Evolution of the Benue Trough 8
2.2.1 Lee‟s Compressional Theory 8
2.2.2 Triple junction Theory 9
2.2.3 Triple Junction Theory -9
2.2.4 Strike-slip Fault and Compressional Theory 9
2.3 Stratigraphy of the Middle Benue Trough 10
2.3.1 Stratigraphy 10
CHAPTER THREE
3.0 Materials and Methods 17
3.1 Introduction 17
3.2 Desk Study 17
3.3 Detailed Field Work 17
3.4 Laboratory Analyses 17
3.4.1 Sieve Analysis 18
3.4.2 Petrographic Analysis 22
CHAPTER FOUR
4.0 Results 24
4.1 Introduction 24
4.2 Geology and Stratigraphy of the Study Area 26
4.2.1 Lafia Formation (Field description, Lithologs, and Petrographic Analysis) 26
4.2.2 Awe Formation (Field description, Lithologs, and Petrographic Analysis) 30
4.2.3 Awgu Formation (Field description, Lithologs, and Petrographic Analysis) 37
CHAPTER FIVE
5.0 Discussion 46
5.1 Introduction 46
5.2 Lafia Formation 46
5.3 Awe Formation 47
5.4 Awgu Formation 48
5.5 Provenance of the Sediments 50
5.6 Cycles/History of Sedimentation 51
5.7 Geological Structures 52
5.8 Economic Geology 54
CHAPTER SIX
6.0 Summary, Conclusion and Recommendation 57
6.1 Summary 57
6.1.1 Awe Formation 57
6.1.2 Awgu Formation 58
6.1.3 Lafia Formation 58
6.2 Conclusion 58
6.3 Recommendation -59
6.4 Contribution to Knowledge -59
6.5 Limitations 59
REFERENCES 60
APPENDIX 64
List of Figures
1: Map of Nigeria showing Sedimentary Basins and the Benue Trough 2
2: Map of the study area 3
3: Map of the study area showing relief and drainage 4
4: The Triple Junction Diagram 9
5: Lithostratigraphic subdivision of the Cretaceous 11
6: Graphic illustration of sorting in clastic sediments 19
7: Degree of roundness of the sediments 19
8: Smoothed Frequency curve 21
9: The Pettijohn classification of sandstone chat 22
10: Updated map of the study Area showing the three different formations 25
11: Lithostratigraphic log section of the Lafia Formation 28
12: A lithostratigraphic log section of the Awe Formation 32
13: Another lithostratigraphic log section of the Awe Formation 33
14: Lithostratigraphic log section of the Awgu Formation 40
15: Another Lithostratigraphic log section of the Awgu Formation 41
16: A model showing the cycles of sedimentation within the study area 52
17: Cumulative Frequency Curve for Lafia Sandstone sandstone 64
18: Cumulative Frequency Curve Awe Formation sandstone 67
19: Cummulative Frequency Curve for Awgu Formation sandstone 69
20: Bivariate Plot of Skewness versus Standard deviation 73
21: Bivariate plot of Skewness versus sorting showing fluvial environment of deposition 73
22: Age range of macrofossils preserved in stratigraphic record 74
List of Plates
I: Lithologic section of Lafia Formation exposed along Agyaragu-Doma road 27
II: Photomicrograph of sandstone of the Lafia Formation (Subarkose) 29
III: Photomicrograph of Basalt (dyke) sample intruding the Lafia Formation 30
IV: A lithological section of Awe Formation occurring along Lafia-Keana road 31
V: Photomicrograph of the Awe sandstone (Arkosic Arenite) 34
VI. Photomicrograph of sandstone of the Awe Formation (Arkose) 35
VII: photomicrograph of sandstone of the the Awe Formation (Subarkose) 36
VIII: A lithological section of the Awgu Formation 38
IX: Ammonites within Shelly limestone of the Awgu Formation 39
X: Photomicrograph of sandstone of Awgu Formation (Subarkose) 42
XI: Photomicrograph of the Awgu sandstone of the Awgu (Quartz Arenite) 43
XII: Photomicrograph of limestone of the Awgu Formation showing echinoderm 44
XIII: Photomicrograph of shaley limestones showing showing foraminifera and ostracodes 45
XIV: Location of Paraconformity 54
XVa: Brine associated with the Awe Sandstone found at Keana town 56
XVb: A coal mine associated with the Awgu Formation found at Bukan kwato 56
List of Tables
4.1: Results of Granulometric analysis 24
4.2: Statistical parametres for Lafia sandstone 1 64
4.3 : Statistical parametres for Lafia sandstone 2 65
4.4 : Statistical parametres for Lafia sandstone 3 66
4.5 : Statistical parametres for Awe Formation 1 67
4.6 : Statistical parametres for Awe Formation 2 68
4.7 : Statistical parametres for Awgu Formation 1 69
4.8 : Statistical parametres for Awgu Formation 2 70
4.9 : Graphic mean standard values 71
5.0: Graphic standard deviation values 71
5.1: Graphic skewness standard values 72
5.2: Graphic Kurtosis standard values 72
CHAPTER ONE
INTRODUCTION
1.1 Background to the Study
The Benue Trough is a sediment-filled elongated NE-SW trending depression that originated from the opening of the Atlantic Ocean. It is a failed arm of a rift-rift-rift triple junction developed over a Cretaceous hotspot located below the present-day Niger Delta (fig 4). (Cratchley and Jones 1965; Burke et al., 1970). This trough has been divided into three sections namely Upper, Middle and Lower Benue Trough by Cratchley and Jones (1965). The structural and stratigraphic settings of the trough have attracted the attention of geologists and many hypotheses have been advanced for its origin (King, 1950; Lees, 1952; Carter et al., 1963; Cratchley and Jones, 1965; Dessauvagie, 1969; Burke et al., 1970; Olade, 1975; Offodile, 1978). The rift tectonic/strike model seems the most widely accepted mode of origin. The Nigerian Benue Trough is an intracratonic rift structure whose evolution is related to the Early Cretaceous opening of the South Atlantic Ocean and the Gulf of Guinea (Akande et al., 2011). Fig. 1 is the map of Nigeria showing sedimentary basins.
