This project work covers Amaowelli town and its environs in Awgu Local Government area of Enugu state. It is bounded by Latitude N607’0’’ and 6011’0’’N and longitude E7023’0’’ and 7027’0’’. It is surrounded by the following towns; in the north by Enugu-Inyi, south by Obeagu, in the west by Mmaku and in the east by Awgunta. Three distinct geological formations were recognized in the study area based on outcrop study. These formations are Ajalli Sandstone, Owelli Sandstone and Mamu Formation. Their chronological ages are Maastrichtian and Campanian respectively. The Ajali Sandstone is a friable, non-fossilferous, whitish but sometimes ferruginised, cross-bedded sand, sometimes with silt intercalations. The Mamu Formation is largely made up of laterite and consists of fissile shale, mudstone, coal in some places and sandstone units. The method of study involved in the project work includes, detailed field mapping and laboratory analysis of the samples collected in the field. The major geologic materials of economic importance include sand, clay, shale deposit, ferruginised sandstone, and water resources. The grain size analysis carried out shows that the sandstone units in the study area are moderately sorted indicating a relatively high energy of deposition. Atterbergs limit results shows that the clay unit has high liquid limit and plastic limit. The geologic structures observed in the study area were cross-beds, ripple marks, parallel laminations to sub-parallel laminations, and biogenic structures like bioturbations and thalasonoides. Geologic materials of economic importance are ironstone, clay, sandstone, and laterite. some environmental hazards like gully erosion and road landslides were encountered.
The water analysis carried out on a water sample from the study area shows that streams of the study area are slightly acidic with pH value ranging from 5.23 to 5.80.
1.0 BACKGROUND STUDY
As part of the requirements for graduation, all final year Geology students are required to carry out a geological investigation of an area as may be determined by the student’s project supervisor. The investigation should involve field survey/descriptions, data collection and geological interpretations, including the production of a geologic map. Consequently, I was assigned to map, investigate and carry out a research on the geology of Amaowele and environs which is within the Anambra-Afikpo basin of Nigeria. The lithology and formation in the area include the Mamu Formation and Ajali Sandstone which were deposited during the second sedimentary cycle (Maastrichtian). The Mamu Formation (lower coal measure) was formed when the sea gradually became shallower and this led to the formation of low-lying coastal areas with lagoons and swamps. The Mamu is overlain by the continental sequence of the Ajali Sandstone. The Mamu Formation consists of sandstones, shales, and sandy shale with coal seams. The sandstones are fine to medium grained and yellowish in colour. The shales and mudstones are dark blue or grey and frequently alternate with the sandstones to form a characteristically striped rock. The coals are black to brownish black in colour. The Ajali Sandstone consists of friable, white, highly cross bedded, bioturbated and mud draped sandstone. Sandstones make up the higher elevations observed in the area, while the less resistant shale which is prone to erosion make up low lands and valleys in the area. This work is aimed at examining the lithologies and their statigraphic relationship with the view of drawing inferences on the geology of the area.
1.1 Location and Accessibility of the study area
The study area Amaowele and environs lies between longitudes 7°23′0″E and 7°27′0″E and latitudes 6°7′0″N and 6°11′0″. It is underlain by Mamu Formation and Ajali Sandstone of the Anambra Basin of South Eastern, Nigeria. It is surrounded by towns which include; Egwuashi, Ngeneugbo, Ugbuokpara, Obeagu, Owelle, Maku and lies on the western part of Awgu local government area of Enugu State, South eastern Nigeria (Fig. 1.1). Major road, Minor road and footpaths enhance accessibility to the study area and these include tarred and untarred road paths. To an extent, they are accessible with vehicles, motorcycles, and other means of transport but due to thick vegetation, traversing the study area was a bit difficult. Figure (1.1) and (1.2) shows the location and accessibility of the study area respectively.
Fig 1.1: Location map of the study area [Google, 2016]
Fig 1.2: Accessibility map of the study area
1.2 Aim and objectives of the study
The aim of this work is to study the geology of Amaowele and environs. The main objectives of this investigation include:
- To produce a detailed geologic map of the area and from outcrop description be able to produce a lithostratigraphic map that will show different formations encountered.
- To determine the structural features, economic geology, engineering geology, Sedimentological and stratigraphic characteristics and hydrogeology of the area with a view to delineating lithologic contacts and attempting the reconstruction of the paleoenvironment of deposition.
1.3 Geomorphology and Physiography
The area has an undulating rugged topography, characterized by the occurrence of residual hill sandstone ridges which are occasionally capped with rich vegetation (Fig. 3). The landform is controlled by the nature of the rock unit and agents of denudation like weathering and erosion.
The study area is dominated by cuestas which were as a result of highly indurated nature of the sandstone unit in the area. These cuestas which was formed due to the resistant nature of the rocks to weathering has also aided to the development of present day drainage system.
This shows the surface feature of the study area which is the undulated and rugged topograghy discussed in the article above. The study area is characterized by highlands and lowlands with high rate of vegetation. The most prominent feature is the cuesta which is due to the resistant nature of sandstone to weathering and erosion. The study area has an elevation extent of not more than 450m above the sea level (Fig. 1.3).
Fig. 1.3: Topography map of the study area
1.3.3 Drainage Pattern
The drainage pattern refers to the design or plan which the streams collectively form. The study area, Amaowele and environs are sedimentary environment which have dendritic drainage pattern and contain water from some of the tributaries (Fig. 1.4). The drainage system in the study area is conspicuous in the rainy season and sparse in the dry season due to the drying up of some of the ephemeral streams and lakes. The angle at which the streams join each other and the direction of flow is a function of the lithology, topography and structural geology of the areas. Two springs encountered in the study area include the Olumu Okoli at N6o 8’ 20.6’’, E7o 26’ 2.1’’ and the Iyi n’ ogbu at N6o 11’ 0’’, E7o 25’ 31’’.
Olumu Okoli Iyi n’Ogbu
Fig. 1.4: Drainage map of the study area
- WEATHERING AND EROSION
The study area is affected by both physical and chemical weathering which tend to wear down the relatively resistant sandstone ridges and less resistant shale valleys. Temperature changes affect exposed rock surfaces which undergo alternate heating and cooling during the day and night respectively, especially during the dry harmattan season. The resulting expansion and contraction of rocks leads to fissure and fissility in shale and siltstones.
Mechanical weathering in the area is as a result of the vertical downward penetration of the plant roots into rocks which tends to weaken the soil compactibility and rock strength, making it prone to erosion and also through various anthropogenic activities. High temperature and heavy rainfall play a role in the ferroginization of the sandstone units and laterization of shale units. Ferroginization and laterization are the impacts of deep chemical weathering, which result from the oxidation of aluminium hydroxide [Al2OH] or iron oxide [Fe2O3] and the breakdown of feldsparthic minerals in the rocks. Various shales of reddish brown and yellowish brown indicates iron at various stages of oxidation.
1.5 Climate and Vegetation
The study area is part of equator which is located at the Greenwich Meridian. The equator location of the study area made it to have equatorial climate. The temperature in the study area is high throughout the year except during the harmattan.
The rainfall in Nigeria is high. It occurs mainly in form of orographic rainfall, frontal rainfall, and relief rainfall (Fig. 1.5). The rainfall is associated with strong wind and thunderstorm and it starts mainly from the months of April to September or October and sometimes November. Rainfall in Nigeria decreases towards august which is known as August break. The humidity is also high during the rainy season (Fig. 1.6). The harmattan in Nigeria starts from the month of November or sometimes December till the February or March of the coming year.
The atmospheric pressure is also high mainly at the mountaneous region in the area which is mainly on the Ngeneugbo plateau and many elevated area around Obeagu area. The atmospheric pressure in the mountaneous regions of Amaowele and its environs are about 880 to 960 mmhg (Iloeige, 1992). The atmospheric pressure in the low land is about 760mmhg to 780mmhg.
Rainfall distribution in Amaowele and its environs are highly affected by the atmospheric pressure and by vegetations in the area.
Fig. 1.5: Nigeria annual mean rainfall [Google, 2016]
Fig. 1.6: Histogram graph of climate in and around Enugu [Google, 2016]
The study area is located in south-eastern Nigeria which consists of main rain forest vegetation and few savannah vegetation (1.6). The rain forest vegetation consists mainly of trees with some shrubs, grasses and climber. The vegetation is thick during the rainy season and sparse during the dry season or harmattan.
The rainforest vegetation is assisted with the low land and deep gullies, this is because of variation in soil resistance to weathering and erosion which support the growth of luxuriant trees and shrubs.
Savannah vegetation also occurs in the region, by definition savannah vegetation is the type of vegetation which consists mainly of grasses and few shrubs and trees. Savannah vegetation occurs in the hills in the area. This is because those hills consists of hard rocks which did not support the growth of luxuriant trees but it support the growth of shallow rooted plants mainly grasses.
Generally, Amaowele and its environs consist of few main types of vegetation which are rainforest vegetation and savannah vegetation (Fig. 1.5). The rain forest vegetation is associated with low land while the savannah vegetation is associated with the hills in the area.
The vegetation is thick during the rainy season and sparse during the dry season except at the river bank and stream beds or banks in the area.
Fig. 1.7: Vegetation map of Nigeria [Google Map, 2016]
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