Geology and Paleoenvironmental Analysis of Shales Using Its Fossil Contents (Amangwu)

Amangwu and its environment which is located within the Afikpo Syncline has shale as one of its lithostratigraphic units. The use of foraminiferal and palynological data in the lithologic units of Amangwu shale has helped in determining paleoenviroment. The result from six (6) outcrop samples analysed for foraminiferal and Palynological distribution shows that fossils like Ammoastuta nigeriana, Textularia biafrae, Ammobaculites amabensis, Miliammina onyeamensis, Ammobaculites pindigensis, Ammobaculites bauchensis, Textulariopsis gidankukaensis, Praebulimina Bantu, Haplophragmoides nigeriense are present in the area. The age interpretation was based on the diagnostic fossil assemblage in the sample, which typify upper Cretaceous (Maastrichtian) age, with markers being predominantly of Nkporo Shale. (Gemeraad et al, 1968, Every et al 1978 and Petters 1982). The Paleoenvironment of the study area was interpreted based on the abundance and the presence of environmentally significant fauna.

LOCATION AND EXTENT
The study area (Amangwu Edda), is located at Afikpo south local government area of Ebonyi State in south Eastern Nigeria
The extent of study is within latitude 70501E and 70551E and longitude 50501N and 50551N.

Fig 1 Map of Ebonyi State showing the study area (Afikpo south)

ACCESSIBILITY
The study area (Amangwu Edda) is accessible through a network of roads; thus through Abakaliki-Afikpo road, Afikpo-Okigwe road then through Amasiri –Edda road. Some of the outcrops are located along the Amasiri-Edda road, Amasiri- Afikpo road, while some outcrops you trek few metres into the bush and others are along river channels.

PEOPLE, CULTURE AND SETTLEMENT
The people of Amagwu Edda are Igbo’s however the speak their indigenous language but English is widely spoken as the second language and a visitor will be understood almost anywhere in the area, if he can speak English language or its local variant the pidgin.
The study area is richly endowed culturally, the traditional mode of dressing for men is an overflowing jumper or shirt worn over a George wrapper tied around the waist and flowing down to the ankles. This is complimented with a cap and with and a walking stick for support and defense. For the women the traditional dress is a blouse over an agbada or George wrapper around the waist. This outfit goes with a headgear, earnings and necklaces.
Two important traditional festivals are observed every year; the masquerade and the new yam festivals, the masquerade is a very important and colorful institution and features the Okpaa, egede, olikonte, the New yam festivals is known by various names but the Edda’s call it Ikeji, the festival marks the end of the farming season and ushers in the harvest and consumption of the new yam.
Settlement patterns in Amangwu Eda is dispersed over much of the farmland, in almost every community, however there are vast unoccupied areas set aside as farmlands and somewhat removed from the settlement. This dispersed pattern of village settlement is traditional among the people of southeastern Nigeria. Beach homes stand is made up of houses in an oblong form around a compound.
RELIEF
The study area (Amangwu Edda) lies in an area of moderate relief (between 125 -245m above sea level, sandstone ridges form the topographic highs.

DRAINAGE
The study area Amangwu Edda is drained by Okpuko, otoni, Iyioka and Ubei rivers through the Ebonyi River. The drainage pattern in this area is dentritic pattern; low level sheet erosion is experienced in the study area.

SOIL
Two main types of soil can be found in the study area, these are the silty clayey hydromorphic soil and the grey sandy clay hydromorphic soil, the former has a brown loamy top horizon which overlies reddish brown silty clay subsoil. It is moderately to imperfectly low natural fertility, with appropriate agro technique and regular application of fertilizer, this soil can produce good yields of a wide variety of crops ranging from cassava to vegetables, plantain and groundnuts. The sandy clay hydromorphic soils occur in the low lying areas of the study area (Amangwu Edda) where the soil is grey, fine loamy sand, clay to clayey. In addition to poor fertility, strong acidity and lack of nutrients, this soil suffers from poor drainage. Due to the excess of moisture it is mostly suitable for rice cultivation.

Vegetation
The study area falls within the rain forest and savannah belts of southeastern Nigeria. The dominant vegetation is characterized by tree shrub, with abundant palm trees.

Climate
Two main climates exist in the study area, which are the rainy season which usually begins in late April and ends in early October and the dry season which last from late November to early April.

AIMS AND OBJECTIVES
This work is aimed at the following
– To map and demarcate the lithologic units within the study area
– To make a detailed description of the different rock types encountered
– To study the paleoenvironment of the Amangwu shale using its fossil content
– To make a detailed study of the economic potentials of the area

MATERIALS AND METHOD
Among materials that made the mapping exercise easy are:
– A base map, which serves as a guide to the journey and depicting of an outcrop
– Compass and clinometer, which measures the attitude of an outcrop such as strike, dip, dip amount
– Geologic hammer and sample bag for the collection of samples for analysis
– Field note
– Photograph for taking images of an outcrop

FIELD MAPPING
In the mapping of Amangwu Edda principles and ideas were adopted by me which involve careful observation of the various lithologic unit, location of oneself in the field and attitude measurement of different geologic structures. Thus compass and traverse method was the method adopted. Exposed sections of outcrops were measured at some locations in the study area. On the basis of stratigraphic continuity and degree of visible exposure I selected fine outcrops of Amangwu shale as a focus of study, reconnaissance was conducted at the whole locations in the map.
In describing the Amangwu shale I concentrated on the lithology, texture and presence of fossil.

Shale Washing
Shale samples were collected to determine their micro fossil contact each samples consist of about 0.5 to 1.0kg of rock material. were collected, soaked with white spirit for 24 hours and latter decanted, the decanted samples were re-soaked with de-ionized water for another 24 hours. The disaggregated samples were washed through a 63. micronsieve until all the mud was washed clear.
The washed samples were dried under the sun and taken to the laboratory for viewing under the microscope to locate and pick fossils for naming and for further analysis. Classification of the foraminifera follows the descriptions of Bronninann and others (1992), castelain and others (1962), de klasz and others (1963) Ellis and Messina (1940 etz.) Hart and others (1989), Ogbe (1980), and Pestan (1979a, 1979b, 1980, 1982)

Sieve Analysis
Sieve analysis was conducted on locations within the studied area from Ndiowere Amangwu, Along Amasiri –Amangwu road. Sieve analysis was conducted on four (4) samples collected from different location within the studied area; the aim of the sieve analysis was to determine the particle size distribution and then from the grain size analysis interprete the depositional environment.
Procedure
– The four (4) samples for the sieve analysis was broken into smaller particles to enable effective sieving.
– The sieves were arranged accordingly from below ranging from the pan, sieve sizes ‘250’, ‘180’, ‘120’, ‘100’, ‘80’, ‘60’,’36’, ‘24’, ‘14’, and ‘10’ on top.
– 50g of the samples was measured using the electronic weighing balance.
– The weight of paper which was used was 1g placed directly on top of the electronic weighing balance and the sample poured on it.
– The 50g measured sample was gently poured on to of the first sieve i.e. ‘sieve 10’ and covered, then placed on top of the electronic sieve shaker.
– The electronic sieve shaker was switched and the sieving was allowed for 5 minutes.
– The particles retained by each sieve was weighed and recorded as weight retained.
– This was replaced for all the samples and recorded accordingly.
However some safety precautions, was observed when carrying out the analysis and these include:
– Avoidance of excessive sieving.
– I maintained air tight environment for effective sieving
– Care was taken in removing each sieve and taking weight of particle retained.

 

CHAPTER TWO

LITERATURE REVIEW

TECTONIC SETTING

The Benue Trough extends from the south where it merges with the Niger-Delta to the north where its sediments are part of the Chad basin succession. The Trough Bifurcates near its northeastern end, and the northern branch continuous beneath the Chad formation as an elongate depression that extends well beyond Lake Chad.

The Benue rift is the failed arm of the Gulf of guinea, south Atlantic and Benue Mesozoic triple junction whose centre is occupied by the Niger Delta (Grant, 1971)

The origin of this trough has been discussed by many authors among whom are Ajakaije and Burke (1972), Nwachukwu (1972) Burke et al (1972), Olade (1975) (1978).

Murat (1972) proposed three major tectonic phases which took place in the Albian, Santonian and late Eocene or early Oligocene times these major tectonic phases resulted in the formation and subsequent remodeling of the Benue Trough.

There are folds, which consists of series of anticlinorium and synclinorium in the Benue rift suggesting that there was a deformational episode in the trough. The floor of the basin is irregular and sediments thicknesses vary from place to place. This occurs as a result of extensive block faulting initiated when the trough began to develop

REGIONAL STRATIGRAPHY

Regionally, the mapped area (Amangwu-Edda) is within the southern end of the Benue trough. The oldest sedimentary rocks in Nigeria are in this trough and they are of lower Cretaceous age. The Cretaceous stratigraphic record of the southern Benue Trough is represented by sediments deposited by three main marine depositional cycles. Albian-Cenomanian. Turonian-santonian and campanian-maastrichtian (Reyment, 1965, Ofoegbu, 1985).

Shortly after the break up of Africa and South America, a continental condition favourable for the deposition of fluvio-deltaic sediments occurred in the Aptian age. The Aptian sediments are represented by the Ogoja sandstones (Uzuakpunwa 1974).

The first marine transgression in this Trough occurred in the middle Albian age with the deposition of the Asu River Group sediments with type locality along the banks of Asu River (Reyment, 1965). The sediments consist of rather poorly bedded sandy shale’s with sandstone and sandy shale’s with sandstone and sandy-line stone lenses.

The regressive phase of the first marine transgression led to the deposition of the Cenomarian sediments. The beds of this age are located in the southeastern part of Nigeria, around Calabar. These beds been assigned as the Odukpani formation (Reyment 1965). It consists of arkosic sandstones, limestone and alternating limestones and shale which became gradually more predominantly shally in its uppermost parts (Reyment, 1965).

Unconformably overlying the Albian deposits in most parts of the southeastern Nigeria is the Turonian Ezeaku formation, it comprises hard grey to black shale and sandstone with frequent facies changes to sandstones and sandy shale.

The Turonian is overlain by sediments of Coniacian age. The Coniacian is represented by the Agwu formation (agwu shale of Reyment, 1965) the formation consists of bluish grey, well bedded shales with occasional intercalation of fine grained sandstone and thin shaley limestones.

The Santonian age was herached by a tectonic epierogenic event which led to the uplift, folding and widespread erosion of the pre-Santonian sediment in the Trough.

The Campanian-Maastrichtian experienced the third sedimentary cycle in this Trough. It started with the deposition of the Nkporo formation (Nkporo shale, Fattan, 1943). It consists of dark shales and mudstone with occasional thin beds of sandy shale and sandstones. A regressive phase of this transgression occurred in middle Maastrichtian with the deposition of the Mamu formation and subsequent deposition of Ajali sandstones. A minor transgression occurred in the late Maastrichtian with the deposition of Nsukka formation. The stratigraphy is represented in the table below.

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