Geology and depositional environment of the Ameki Formation in parts of Bende and environ Southeastern Nigeria

DEDICATION

I dedicate this B.Sc. thesis/ project to God almighty, whom has been so faithful to me.

ACKNOWLEDGEMENT

My profound gratitude goes to my parents DR. and Dr. (Mrs) Madumelu, Nwafor Ikechukwu Vincent for their financial and moral support all through my stay in the university, and to my siblings for their encouragements all this while may they be blessed immeasurably. I heartily thank my supervisor Dr. C.F.R Odumodu for his immense contribution towards the success of this project. I gratefully acknowledge my Head of Department Mr. E.I Okpoko also thank Prof. B.N. Nfor my genius and geological guru for proofreading the manuscript and the lecturers for their efforts in my academic pursuit.

ABSTRACT

This study is aimed at determining the geology and depositional environment of Ameki Formation in Bende and environs through field descriptions, textural analysis and Palynological analysis. The mapped area which covers an area of about 180sq km and is located around Bende, southeastern Nigeria. The study area is bounded by Longitude 07° 30` E and 07° 43` E and Latitudes 05° 30` N and 05° 39` N. The area is underlain by Paleocene Imo Formation and Eocene Ameki Formation. The Ameki Formation is a clastic unit that overlies the marine Imo Formation and it consists of sandstone, shales, limestone, ironstone and siltstones. The Eocene Ameki Formation in southeastern Nigeria consists, in its type locality of five lithologic units; calcareous sandstone, pebbly bioturbated sandstone, grey-dark shale, argillaceous sandstone and pebbly sandstone. The floral, faunal and lithologic studies of the Eocene Ameki Formation suggest sediments deposited in a continuity from nearshore (barrier-ridge estuarine complex) to shallow marine (intertidal and subtidal zones) environment. The sieve analysis unveils that the univariate parameters indicate a fluvially intercepted shallow marine environment with tidal crosscuts, the log probability plots suggest tidal environment while from the bivariate plots; a beach influenced fluvial environment is interpreted. The pebble morphological analysis showed that the pebble clast have being shaped by beach action as revealed by the bivariate scatter plots of pebble form indices while in multivariate aspect a fluvially dissected shallow marine environment with tidal interferences was interpreted. The palynological analysis indicated a marginal marine source for the sediment and that the formation (Ameki) is Eocene in age.

CHAPTER ONE INTRODUCTION

1.1 Background of study

GLY 492 is a project field course which centers on educating the final year students of Geology about the basic techniques necessary for the acquisition of geologic data, interpretation of the acquired data, the preparation of the geologic map, and to write a comprehensive technical report of the study area, this work is in partial fulfillment for the requirements for the award of Bachelor of Science Degree in Geology.

The participants are taking to a particular area, and the field work is carried out under the supervision of a professional, usually a tutorial staff from the department.

This work was carried out in Bende area of Abia state, south-eastern Nigeria. The aim of this study is to examine the Geology and Depositional Environment of the Ameki Formationin this area. The study area lies between latitudes 5⁰ 30’ N and 5⁰ 40’ N and longitudes 7⁰ 30’E and 7⁰ 40’

E. The age of the Ameki Formation has been established by different workers to be Eocene; the major Lithology of the Ameki Formation is the Sandstone with the presence of Mudrock bands and intercalations of limestone. The study area was selected because the area has an ideal rock exposure which enables easy acquisition of knowledge for the students.

The mapped areas includes: Bende-Idimabam, Okputong, Ugwuomeremma, Okwanka, Ndiagho, Elugwumba, Ozuitem, AmekeIbeku, Oduenyi, Ndiiwo, Amaba-ubibia, Uzoiyi-AmekeIsiegbu, UmukpubeIsiegbu. Outcrops in these areas were located and logged, systematically.

Finally, samples were collected for laboratory analyses and photographs were taken.

1.2 Aim of study

The aim of this project is to carry out a comprehensive study of the geology of the area and using data obtained to interpret the general geology, and produce a geologic map of the area. My study focuses on the Geology and Depositional Environment of the Ameki Formation in the Bende area of Abia State.

1.3 Objectives

To carry out a detailed study of Bende and its environs.

To use the textural data obtained to interpret the depositional environment of the sediment.

To identify various geological formations

To use data obtained to interpret the geology of the area and produce a geologic map that gives a detailed description of the mapped area.

To understand the physical and chemical properties of the Ameki Formation and the processes involved in their formation, including the transportation, deposition, and lithification of sediments, from the various analyses carried out.

1.4 Scope of study

This research will include the following:

a. Review of existing literature in the Geology and Paleoenvironment of the region.
b. Study of the topography and geology maps of the area to obtain accurate information about the area.
c. A proper reconnaissance survey of the Bende area followed by the detailed fieldwork in order to gather information pertaining to the Geomorphological, Stratigraphic succession, textural aspects of the rocks and the sedimentary structures.
d. Adequate interpretation of the depositional environment of the various rock units encountered during the fieldwork, based on data acquired during the fieldwork.
e. Production of a geological map showing the distribution of the various rocks units.
f. Finally the computation and compilation of the thesis that will be submitted to the Department of Geology.

1.6 Limitations

Inability to see an outcrop with reasonable sedimentary structures and cross beds that will enable us to take the strike and dip of the bed for paleocurrent analysis. Inaccessibility of roads to reach some outcrops for examination. Insufficient fund Unavailability of some laboratory equipment for analysis.

Some outcrops were already covered up with grass, this limited the contact with the outcrops though it was just very few of them Some of the outcrops were at risk of landslides this also limited contact with the outcrops as it is of great risk to life.

Most of the outcrops had undergone weathering, which made it difficult in some cases to obtain samples fit for analysis.

CHAPTER TWO GEOMORPHOLOGICAL SETTING

2.1 Topography and drainage

The prominent topography of the study area feature is generally an undulating topography made up of highlands which consist of the sandstones and the lowlands which consists of the shale. The highest elevation on the study area is 585ft. The drainage system of the study area is controlled by relief, topography and rock types. The major water bodies that drain the area are: River Inyang, Okwanka Stream, and River Idonyi as seen in Fig.1. The dominant drainage pattern of this area is dendritic in nature.

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Fig.1 Drainage pattern of the study area.

2.2 Climate

Bende is a humid zone; as seen in Fig.2, it has a tropical rainforest climate. It exhibits two major seasons, (rainy and dry season), harmattan is a minor season. The rainy season begins in March and ends in October with a break in August usually referred to as the August break. The rainy season is caused by the South West Trade Wind. The dry season which lasts for four months begins in November. Harmattan begins in December and ends in February; it is triggered by the North East Trade Wind. The total rainfall decreases from 2200mm in the south to 1900mm in the north. The relative humidity is usually high throughout the year, reaching a maximum during the rainy season when values above ninety per cent are recorded. Temperature is averagely 26 Celsius throughout the year. . The characterized annual rainfall is between 1,400mm and 2,500m. The relative humidity is 23% with annual temperature of 24⁰ C to 27⁰ C but as low as 17⁰ C to 20⁰ C at night. The annual pressure ranges from 1010.0millibars and 1072.9millibars (Monanu and Inyang, 1975).

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Fig.2. Climate Map of the Southeastern Nigeria (Iloeje, 1980).

2.3 Vegetation

The study area is ordinarily considered part of tropical rain forest which is the dominant natural vegetation in most parts of south-eastern Nigeria. This region (south-eastern Nigeria) is basically characterized by tropical rain forest belt as seen in Fig.3 (though, more of derived vegetation is dominating the area now because of urbanization, agricultural activities and uncontrolled deforestation). It has deciduous and occasional stunted trees like Palms, Iroko, Mahogany and other towering trees. The trees which grow in clusters are up to 6-7metres tall, interspersed with grasses which grow up to about three meters. The tall trees characterize the highlands (mostly composed of sandstones) in the area while the lowlands (mostly composed of mudrocks) are characterized by grasses. The major crops grown in the area include cassava, yam, plantain and palm trees. The vegetations turn greener in the rainy season with fresh leaves and tall grasses, but the land is usually open (barren) or nearly open during the dry season, showing charred trees and the remains of burnt grasses. The soils are not fertile and are prone to much leaching due to heavy rainfall. However, these vegetations in the study area are not in their natural luxuriant state because of the careless human use of the forest.

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Fig.3. Vegetation Map of the Southeastern Nigeria (Iloeje, 1980).

2.4 Location and accessibility

The study area is located in Abia state precisely Bende. It lies between latitudes 5⁰ 30’ N and 5⁰ 40’ N and longitudes 7⁰ 30’E and 7⁰ 43’ E. The towns and villages under the study area includes: Idima-Abam, Okputong, Uzuakoli, Ndiwo,Bende-Ndiagho, Elugwumba, Ozuitem, AmekeIbeku, Odonyi, Bende-Ohafia, Amaba-Ubibia, Uzoiyi-AmekeIsiegbu, Umukpube.The study area is accessible through road networks as seen in Fig.4 from Umuahia, Owerri, Aba, Arochukwu, and AkwaIbom State.

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Fig.4. Accessibility map of the study area

2.5 People and culture

The present day Bende LGA was formally called Old Bende which administrative and geo- political area stretched at that time,from Arochukwu to Umuahia and included such towns as Ututu, Ihechiowa, Ohafia, Abiriba, Nkporo, Abam, Umuhu, Bende, Igbere, Item,Alayi,Ozu-item, Isiukwu-ato, Uzuakoli, Nkpa, Umuahia, and Ikwuano with a population of 3 million people. Citizens from the Old Bende LGA area are simply referred to as "Bende People".The term Bende is in honor of a town called "Bende" which was the seat of Local Government under the Old Bende LGA era of governance. Even today, the Bende town is still the administrative seat of Bende in the present day Abia state local government areas structure. Bende today has many towns namely; Nkpa, Nkpokpa, Amaohoro, Eluama, Agbaiyi, Umuede, Umuewu, Ugwu, Obilaji, Okpobia ,Alayi, Item ,Okporoenyi, Ugwueke , Eziukwu, Igbere and Odua with atotal population of about 128227 people based on 2006 population census. The Bende people are predominantly farmers and local traders.The people cultivate yam, cassava, coco yam and Large Palm oil plantation for commercial and personal consumption which was formerly the heavy earner for the people in the LGA before the Oil boom and has now been neglected. Bende people are known for their bravery and self-reliance.They showed a lot of these great traits in the wars of survival during the Nigeria Biafra War. so also in those days and still being practiced total in some selected towns Victories over enemies were copiously celebrated with our trademark and famous Bende War Dance which is very unique and very popular, The War Dance is a constant staple in our cultural diet. Through their bravery, Bende people were able to survive during the era when Might was Power. They are known for their hospitality.

CHAPTER THREE LITERATURE REVIEW

3.1. Regional tectonic setting

A basin is equally produced by a major tectonic event which in the case of the Anambra Basin is the Santonian tectonic event and the Benue Trough,(Fig.5) the rifting of the African and South- American continents in the Mesozoic. The tectonism in Southern Nigeria probably started in Early Cretaceous, with the separation of Africa from South American and opening of the Atlantic. This resulted in the development of the Benue Trough which stretched in a NE-SW direction and resting unconformably upon the Pre-Cambrian Basement Complex. It extends from the Gulf of Guinea to the Chad Basin and is thought to have been formed by the Y-shaped (RRR) triple junction ridge system that initiated the breaking and dispersion of the Afro-Brazilian plates in the Early Cretaceous (Kogbe, 1989).The trough contains up to 6,000 m of Cretaceous - Tertiary sediments of which those predating the mid-Santonian have been compressionally folded, faulted, and uplifted in several places. Compressional folding during the mid-Santonian tectonic episode affected the whole of the Benue Trough and wasquite intense, producing over 100 anticlines and synclines (Benkhelil, 1989). Major such deformational structures include the Abakaliki Anticlinorium and the Afikpo syncline in the Lower Benue, the Giza Anticline and the Obi Syncline in the Middle Benue, and the Lamurde anticline and the Dadiya syncline in the Upper Benue Trough. Following mid-Santonian tectonism and magmatism, depositional axis in the Benue Trough was displaced westward resulting in subsidence of the AnambraBasin. The Anambra Basin, therefore, is a part of the Lower Benue Trough containing Post-deformational sediments of Campanian-Maastrichtian to Eocene ages. It is Logical to include the Anambra Basin in the Benue Trough, being a related structure that developed after the compressional stage (Akande and Erdmann, 1998).The Benue Trough is arbitrarily subdivided into a lower, middle and upper portion. No concrete line of subdivision can be drawn to demarcate the individual portions, but major localities (towns/settlements) that constitute the depocentres of the different portions have been well documented (Petters, 1982; Nwajide, 1990; Idowu and Ekweozor, 1993; Obaje et al., 1999).The depocentres of the Lower Benue Trough comprise mainly the areas around Nkalagu and Abakaliki, while those of the Anambra Basin centre around Enugu, Awka and Okigwe. The Middle Benue Trough comprises the areas from Makurdi through Yandev, Lafia, Obi, Jangwa to Wukari. In the Upper Benue Trough, the depocenters comprise Pindiga, Gombe, Nafada, Ashaka (in the Gongola Arm) and Bambam, Tula, Jessu, Lakun, and Numan in the Yola Arm. As recognised by Murat (1972), the megatectonic setting in the southern domain of the Benue Trough was a longitudinally faulted crust whose eastern half subsided preferentially to become the Abakaliki sub-basin (or the southern Benue Trough). The western fragment remained a platform up to the Santonian. Thus the subsided eastern part became an important depocentre relative to the platform which received only a clastic and chemical sediments. Following the Santonian folding and uplift, the main depocentre in the southern Benue Trough, i.e. the Abakaliki area, became flexurally inverted, displacing the depocentres to the west and northwest. This created the Anambra Basin. After the evolution of the Benue Trough, sediments started depositing into the trough with Asu River Group being the oldest sediment followed by Ezeaku Group, and Awgu Group respectively (Nwajide, 1990).Santonian age marked the stage when the basin experienced another phase of tectonic event that involved deformation, folding, faulting and up lift of the Pre-Santonian sediments leading to the formation of Anambra Basin which evolved as a depression to the west of the uplift (Benkhelil, 1987). Anambra Basin is a Cretaceous depo-centre that received Campanian to Tertiary sediments (Nwajide, 1990 and Obi, 2000). The stratigraphic setting of Southern Nigeria comprises sediments of three major sedimentary cycles. The first two cycles belong to the Pre-Santonian sediments while the third cycle belongs to Post-Santonian sediments which are found in the Anambra Basin and Afikpo Syncline (Nwajide, 1990).

In Anambra Basin, the strongly folded Albian-Coniacian succession (Pre-Santonian sediments) is overlain by nearly flat-lying Campanian-Eocene succession. The oldest sediment in the Anambra Basin is Nkporo Group (Nwajide, 1990). It was deposited into the basin in Late Campanian, comprising Nkporo Shale, Owelli Sandstone and Enugu Shale (Reyment 1965 and Obi 2001).

Nkporo Group is overlain by Mamu Formation. It was deposited in Early Maastrichtian (Kogbe, 1989 and Obi, 2000). It comprises succession of siltstone, shale, coal seam and sandstone (Kogbe, 1989). Ajali sandstone (Maastrichtian) overlies Mamu Formation (Reyment, 1965 and Nwajide, 1990) which is mainly unconsolidated coarse-fine grained, poorly cemented; sandstone and siltstone (Kogbe, 1989). Ajali Sandstone is overlain by diachronousNsukka Formation (Maastrichtian-Danian) which is also known as the Upper Coal Measure (Reyment, 1965 and Obi, 2000). Imo Shale (Paleocene) overlies Nsukka Formation (Nwajide, 1990). It comprises clayey shale with occasional ironstone and thin sandstone in which carbonized plants remains may occur (Kogbe, 1989). The Eocene stage was characterized by regressive phase that led to deposition of Ameki Group (Obi, 2000).

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Fig.5.Tectonic framework of the Benue trough (After Nwajide, 1990)

3.2. Regional Stratigraphic Settings

The Anambra basin which is in the southern Benue Trough, being that the trough itself is a continental large scale intra-plate tectonic range structure, which is part of the mid-African rift system initiated in the latest Jurassic to early Cretaceous and it is related to the opening of central and South Atlantic Ocean (Murat, 1972). The southern Benue Trough comprises the tectonically inverted Abakaliki Anticlinorium, Afikpo and Anambra basin flanking the anticlinorium to the east and west respectively. The development and evolution of the tectonics, of Anambra Basin, and the stratigraphic setting of the study area will be better appreciated by reviewing developments in the depositional area since early Cretaceous structural unit of the south-eastern Nigeria as represented by Murat 1972.

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Fig.6 Lithostratigraphic framework for the Early Cretaceous-Paleocene period in the Benue Trough (Modified after Nwajide, 1990).

3.3. Lithostratigraphic setting of the Anambra Basin

The Anambra basin found in the southern Benue Trough has been described to be a large scale continental intra-plate tectonic range structure forming part of the mid-African ridge stystem. The southern Benue Trough comprises the tectonically inverted Abakalikianticlonirium, Afikpo basin to the east and Anambra basin to the west. The lithostratigraphic succession in the Benue trough consists mainly of Cretaceous sedimentary rocks with thickness ranging from 3500m in the northwest to over 7000m to the southwest. This variation in length impacts a wedge shaped geometry to the sedimentary fill of the trough (Ezepue and Hoque, 1972).

The development and evolution of the tectonics of the Anambra basin and the Stratigraphicsettings has been widely reviewed. The basin has been shaped by sequences of events that has produced different sediment cycle and has largely shaped the nature of sediment that has defined the stratigraphy of the basin (Fig.6).

3.3.1. Imo Formation

The Formation is typically developed as thick clayey shale of about several meters in thickness. The Imo shale shows lateral variation into sandstone in places in the eastern region of the mapped area. The Imo Formation is described by Anyanwu (1980) consist of thick clayey shale fine texture dark to bluish grey with occasional admixture of clay ironstone and thin sandstone bands. The Formation becomes sandier towards the top where it may contain of alternation of bands of sandstone and shale (Wilson 1925)

The outcrops of the Imo shale in the mapped shale in the mapped area consist of three lithologic units. Generally, the Imo shale is composed of fine texture, grey and bluish-grey shale with occasional clay ironstone, thin sandstone and sandy limestone bands. The sandy limestone bands are highly indurated. The fauna consist predominantly of marine mollusks (Gastropods).

The shale consists predominantly of dark grey carbonaceous shale with sandy limestone. There is presence of fossil fauna of marine mollusks predominantly the Gastropods.

The sandstone have texture ranging from medium to coarse grained, they are typically whitish in color on fresh surface and brownish on weathered surfaces. This is explained further in Table.1

3.3.2 Ameki Group

The Ameki Group was given an early attention by the Geological Survey of Nigeria. The references have been to the Bende Group and Bende Series (Wilson and Bain 1925, White, 1926, Tattam, 1944, Du Perez, 1947, Jones, 1948, Grove, 1951, Simpson, 1955, and Reyment and Barber, 1956). These studies did not fully distinguish the component formation of the group, although Reyment (1965) referred to the (1979, 1980) nominated three laterally equivalent units to constitute the components of the group the Ameki Formation, the Nanka Formation and the Nsugbe Formation. The facies of the Ameki Group conformably overlie the Imo formation. They pinched out both eastwards and westwards.

3.3.2.1 Nanka Formation

Demarcated as the loose sand facies of the Ameki Group (Nwajide 1979, 1980), the Nanka Formation outcrops over an area in excess of 1,400km² exclusively adjacent units are transitional and have had to be arbitrarily place. The name is derived from the Nanka Town, an extensive area of which has been so deeply gullied as to expose the bedrock which is elsewhere covered by thick lateritic soil development. Thus the best exposure are found I gullies, which have mostly been developed on the East facing scarp slope of the AwkaOrlu Cuesta, the main topography expression of the formation. The gullies also occur as the dip slope of the cuesta. The estimated thickness of the Formation is about 350m.

3.3.2.2 Nsugbe Sandstone

The third lateral equivalent within the Ameki Group has hardly been documented in any detail. It has only been suggested as possible a lithostratigraphic unit of Formation rank distinct from the contiguous Nanka Formation with which it has a rather unclear boundary. Its nomination as a lateral equivalent within the Ameki Group is here reiterated and reinforced based on the following observations:

a) It has a lithological succession with a motif considered significantly different from that typical of the Nanka Formation
b) Its texture characteristics set is apart, being composed in part of class of cobble size within beds of conglomerate.
c) It exhibits a degree of induration unknown in the Nanka Formation.
d) It underlines an area which can be conveniently cartographically represented at over 1,000km², a substantial part of which the acute angle between the Anambra and the Niger River.it may in fact be more extensive than the Nanka Formation.

Table 1.Characteristics of the stratigraphic components of the Anambra Basin.(Nwajide 1990)

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3.4. THE GEOLOGICAL SETTING

The Eocene Ameki formation overlies the Paleocene Imo formation, which is considered as the basal stratigraphic unit of the tertiary Niger Delta Basin. The Imo Formation is regarded as the outcrop equivalent of the Akata Formation in the subsurface of the Niger Delta, while the Ameki Group (Ameki Formation and Nanka Sands) and the Ogwashi-Asaba Formation are also considered as correlative of the Agbada Formation (Table.2) (Short and Stauble, 1967; Avbovbo, 1978). The origin of the Niger Delta Basin resulted from the sea level rise in the Paleocene, which halted the filling of the Anambra basin. The transgression led to the deposition of the Imo Formation, while the succeeding regression resulted in the formation of the Niger Delta Basin (Reyment, 1965; Murat, 1972; Nwajide and Reijers, 1996). The Ameki Formation comprises of an alternating sequence of shale, sandy shale, clayey sandstone, and fine grained fossiliferous sandstone with thin limestone bands (Reyment, 1965) and is about 287m thick (Arua, 1986; Arua and Rao, 1987). It overlies the Imo Formation, which consists of blue-grey clays, shales and black shales with bands of calcareous sandstone, marl and limestone (Reyment, 1965). The Ameki Formation is overlain by the Upper Eocene to Oligocene Ogwashi-Asaba Formation, comprising of alternalting succession of coarse grained sandstone, lignite seams, and light coloured clays (Kogbe, 1976).

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