GEOLOGY OF IGBARIAM AND ITS ENVIRONS, ANAMBRA STATE NIGERIA
TABLE OF CONTENTS
1.0 INTRODUCTION 1
1.1 Location and Accessibility 1
1.2 Method of Study 2
1.2.1 Desk Study 3
1.2.2 Field work 3
1.3 Field Work Mapping Techniques 3
1.4 Laboratory Analysis 4
1.5 Literature Review 4
1.6 Physiography 5
1.6.1 Drainage 5
1.6.2 Topography 6
1.6.3 Climate 7
1.6.4 Vegetation 8
1.6.5 Superficial deposit 9
2.0 GEOLOGICAL SETTINGS 10
2.1 Regional Tectonic Evolution 10
2.2 Local Geologic Settings 13
2.2.1: Nanka Sands 13
2.2.2: Imo Shale 13
3.0: RESULTS 14
3.1: Local Lithostratigraphy 14
3.2: Lithologic Description 15
3.3 Textural Analysis 19
3.4 Interpretation of Environment of Deposition 42
4.0 SEDIMENTARY STRUCTURES AND ECONOMIC GEOLOGY 44
4.1 Primary Sedimentary Structure 44
4.2 Economic Geology 45
4.2.1 Sand 45
4.2.2 Laterite 46
5.0 ENGINEERING GEOLOGY, ENVIRONMENTAL GEOLOGY AND
5.1 Engineering Geology 48
5.1.1 Rocks/Soils as Construction Materials 48
5.1.2 Rocks/Soils as Sites for Construction 49
5.1.3 Consistency Limit Tests 49
5.2 Environmental Geology 54
5.2.1 Environmental Hazards in the Area 54
5.3 Hydrogeology 56
5.3.1 Surface Water Hydrology 56
5.3.2 Groundwater Hydrology 57
5.3.3 Hydrochemistry 58
6.0 SUMMARY AND CONCLUSION 63
LIST OF TABLES
Table No: Title Page
2.1 Correlation Chart for Early Cretaceous-Tertiary Strata in south eastern Nigeria (Nwajide, 1990). 12
3.1 Verbal Terms and Scale (Folk and Ward 1957) 20
3.2 Outcrop 1 bed 1 21
3.3 Outcrop 1 bed 2 25
3.4 Outcrop 3 bed 1 28
3.5 Outcrop 3 Bed 2 31
3.6 Outcrop 4 Bed 1 34
3.7 Outcrop 4 Bed 2 38
3.8 Grain Size Parameter Calculated for Each Bed 41
3.9 Environmental Discrimination Model (After Sahu 1962) 43
5.1 Atterberg Limit Values for different Locations 54
5.2 Result of Hydrochemical Analysis of Water Samples from the Study Area. 59
5.3 Result of Microbial Analysis of Water Samples from the Study Area. 60
LIST OF FIGURES
Figure No: Title Page
1.1 Accessibility Map of the Study Area 2
1.2 Drainage Map Study Area 6
1.3 Map of Southeastern Nigeria showing Rainfall Pattern 7
1.4 Vegetation of the study 8
3.1 Description of the geologic map of the area 14
3.2 Log description for outcrop one 15
3.3 Log description for outcrop two 16
3.4 Log description for outcrop three 17
3.5 Log description for outcrop four 19
3.6 Graph of cumulative % retained weight vs. phi ∅ values (a) 22
3.7 Graph of cumulative % weight retained vs. phi ∅ values (b) 26
3.8 Graph of cumulative % weight retained vs. phi ∅ values (c) 29
3.9 Graph of cumulative % weight retained vs. phi ∅ values (d) 32
3.10 Graph of cumulative % weight retained vs. phi ∅ values (e) 35
3.11 Graph of cumulative % weight retained vs. phi ∅ values (f) 39
4.1 Desiccation crack at Ikem Nando mining site 45
4.2 Sharp sand mine along nando-otuocha road 46
5.1 Outcrop two excavation site at Nando-Otuocha road 52
5.2 Outcrop three laterite excavation site at Nando-Otuocha road 53
5.3 Ukwulukwu Steam at Isinyi Nando village 57
5.4 : Bar Chart Showing the Concentration of Notable Metal Ions in each of the Water Samples. 59
The study area lies between Latitude 6021ꞌ- 60 24ꞌN and Longitude 6054ꞌE - 6057ꞌE. the area is approximately 31.0km2. It covers parts of Igbariam and Nando. The lithologic unit encountered in this study area is the Nanka Sands, Ameki Formation, and Imo Shale. The study area has few outcrops due to the erodible nature of the Formation on which it lies, and the outcrops identified were found within road cut exposures and excavation site. The rock types observed include ferruginized sandstone, clay and sand, some of which constitute deposits of economic values in places. The beds dip within the range of 4° to 9°. The structural features observed are ripple marks, mud cracks and lamination. The economic mineral and rock deposit in the area are sandstone, laterite and clay Results of grain size analysis showed that the sand units are fine to medium grained, moderately to well sorted, positively skewed (with values of 2.5 to 8.7) and the sorting values from 0.77 to 0.99). The result of the sieve analysis reveals that the environment of deposition was beach. The results of Atterberg limits tests indicate low plasticity index of 15.31. The results of water quality analysis show relatively high values of sulphate (0 to 852.99mg/l), chloride (17.75 to 355mg/l), total dissolved solids (600 to 1,300mg/l), iron (0.09 to 0.48mg/l), lead (0.30 to 1.60mg/l), total faecal coliform (0.8 to 1.0ml/l) and total microbial load (32.5 to 200ml/l). It is suggested that there should be pre- treatment of water for domestic uses, safe mining practices and further investigation of the area.
1.1 Location and Accessibility
The town of Igbariam, lies between Latitude 6021ꞌ- 60 24ꞌN and Longitude 6054ꞌE - 6057ꞌE. The area covers approximately about 31.0km2 within Igbariam and Nando in Anambra East and Awka North local government area Anambra State. It is accessible majorly through the Onitsha-Enugu express road, minor roads and minor tracks, and footpaths also made the accessibility of the area possible.
Fig 1.1: Accessibility Map of the Study Area
1.2 Method of Study
The method of study includes the desk study of existing literature, field work and laboratory analysis of the samples collected from the field area.
1.2.1 Desk Study
This involves consulting some available journals, reports and relevant textbooks on geological mapping techniques. The study of geologic and topographic map of the area was also carried out. This acquainted one with necessary information about the study area.
1.2.2 Field work
A reconnaissance survey was carried out to obtain a general view of the geology of the area. The topographic maps aided to note important landmarks and geomorphologic features in the area.
The field mapping exercise was done using geologic hummer, Brunton compass, tape, camera, sample bags, topographic map, pencil, eraser, field note book, ruler, biro and haver sack.
The geological mapping involved detailed examination and description of outcrops, taking note of the lithologic types, textures, sedimentary structures and distribution of the different lithologic units. The contact of the rock units were identified and plotted in the map. Dip and strike measurement were also taken. Rock samples, photographs and sketches of important features were taken in the field.
1.3 Field Work Mapping Techniques
The detailed mapping carried out in the study area involves the observation
and mapping of lithologic contact units, taking note of variations in lithology, rock types, structures and other geologic features. The altitude of beds were measured (dips and strikes), using a clinometers compass outcrops were carefully studied and logged. Rock samples for laboratory studies were collected at the outcrops and photographs of interesting geologic exposures were taken.
The study of the outcrop was carried out with the following procedure: The location is taken from the GPS and recorded, the rock type is recorded after which each bed is measured for thickness and the properties recorded which includes; color, grain size, sorting, roundness, the altitude of the bed is measured if a good surface is found. Geologic Structures are recorded if present and other properties.
1.4 Laboratory Analysis
The rock samples collected from the field were analyzed. Sieve analysis was done to evaluate the grain size parameters. Median, mean, sorting, kurtosis and skewness were calculated using folk and Wards (1957) inclusive graphic measures. Atterberg limits such as plastic and liquid limits were carried out to assess the engineering properties of the rocks.
1.5 Literature Review
The geological survey of Nigeria started mapping of south eastern Nigeria from 1922 (Bain 1924: Wilson 1925 and Tattam 1943)) in Reyment (1965). These studies described the stratigraphy and biostratigraphy of eastern Nigeria. Reyment (1965) using ammonites, pelecypods and foraminfera as index fossils established the biostratigraphic zones of the southern Nigeria sedimentary basin. Murat (1972) discussed the paleogeographic history of Nigeria from Albian times and noted that the Ameki/Nanka sand was deposited during the Eocene regressive period.
Egboka and Okpoko (1988) worked on gully erosion in Agulu- Nanka area and noted that over the years there have been losses of houses and land of the people there by rendering them homeless from varying periods of time .also, it has led to the loss of lives of people and livestock as well as the destruction of farms on with majority of the population depend on for survival. Egboka (1993) described Anambra basin as a basin formed during the Santonian tectonism, which resulted on the folding and uplifting of the Abakaliki- Benue Trough and the subsidence of the Anambra Platform. The Anambra basin filled from late Campanian to the Paleocene.
The regression that followed in the Eocene resulted in the deposition of the Ameki formation and Nanka sands. Investigation carried out by Nwajide (1979; 1980) on the Nanka sandstone indicated that the formation is a sequence of unconsolidated friabe sands and claystone, silt-stone and finely laminated shale. Reyment (1965) had earlier described the Nanka Sand as a lateral equivalent of the Ameki Formation.
Physiography is the science of landform. It has to do with the drainage, topography, superficial deposits and vegetation.
The major rivers draining the study area are Ezu River and Okwulukwu River while the stream found within the study area is Ukwuluku stream. The drainage pattern is dendritic which are tree like structures forming an acute angle. It structurally indicates the loose and consolidated nature of the formations within which the study area lies. The flow direction of the Rivers is North-West as they empty into the River Niger Drainage.
Fig 1.2: Drainage Map Study Area
The topography of the area is undulating, with highlands at the SE and SW directions and lowlands at the NE direction. The topography of the area is highly influenced by the lithology of the area.
The study area lies within the humid tropical rainforest belt of Nigeria. It is bounded by freshwater swamp to the south and the guinea savanna grassland to the north. The major climate variables are rainfall and dry season. The wet season begins from late march and ends in October and sometime November. The dry season starts from November to March. The rainfall is sometimes turbulent and accompanied by thunderstorms. The annual rainfall in the study area is about 1000mm-1500mm. The month with the highest rainfall is September, where rainfall can be as high as 2500mm, during the rainy season in the month of August there3 is the August break which last for about two weeks. It is characterized by very hot temperature with little or no rain fall. In the dry season, in the month of December (late December) the hamattan sets in. It is characterized by low humidity. The temperature of the study area leads to oxidizing conditions that cause chemical weathering of outcrops.
Fig 1.3: Map of Southeastern Nigeria showing Rainfall Pattern
The vegetation condition of the area is controlled by lithology of the area. Sparse shrubs and grasses cover the sandstone areas, while dense vegetation is characteristic of the clayey and shale areas. The major crops cultivated in the area are cassava, yam, vegetables and rice (especially towards Igbariam)
Fig 1.4: Vegetation of the study
1.6.5 Superficial deposit
Most of the rocks in the study area have been highly weathered chemically. The wide spread lateritic cover found in the area reveals the effects of chemical weathering. The exposed shale unit of the Formation in the mapped area has been highly weathered as revealed by the sharp contrast in colour. The exposure of lithostragraphic units within the area is a main effect of weathering, the oxidation of pyrite content in the shale of Ameki Formation and the irregular staining of rocks by iron oxides. The produce are white, pink, brown and purple sand stones, shale and iron stone the weathering of the area has a considerable economic importance.
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