CHAPTER ONE
INTRODUCTION
Geology is a field oriented and field dependent discipline. It is
not possible to appreciate the beauty of geology without a substantial portion
of time being spent on the field activities. This help to better understand the
theoretical background of geology provided in classroom. Geological field
mapping exercise require detailed survey, sampling, identification, examination
and interpretation of rock samples, fossils and minerals, and the production of
valid report including the geological map of the area
This presents the report of the intensive geological field mapping
exercise covering Ogunmakin and
environs between longitudes E 0030
45’ to 0030 50’ and
latitudes N 070 10’ 30’’
to 070 13’ (Fig. 1.1) located on part of Ibadan sheet 281NE (on
scale 1:100,000 topographical map), covering approximately 43 square
kilometers. Some of the villages in area of study include Omi-Leragun,
Omi-Fatokun, Fadipe, Bankole, Olonde, Sola, Seko, Dada, Onigbagbo, Abuku,
Olubadan e.t.c.
The geological field mapping exercise was carried out in these
areas between the 30th of August, 2015 and 9th of September,
2015. Ogunmakin and its environs lies
within the Pre-Cambrian Basement Complex of southwestern Nigeria composed
predominantly of migmatitic and granitic gneisses; quartzite; slightly
migmatised to unmigmatised metasedimentary schist and metaigenous rocks;
charnokitic, gabbroic and dioritic rocks; and the members of the Older granite
suite mainly granites, granodiorites and syenites.
1.2 Objectives
The objectives of the field exercise include the following:
- To identify the lithologic units in the study area.
- To determine the relationships of various lithologic units present in the area.
- To analyze the petrography of the rock samples.
- To produce a detailed geological map of the study area.
- To identify the structural features and determine their orientations.
1.3 Location and Accessibility
The studied section located
within coordinates longitudes E 0030 45’ to 0030 50’ and
latitudes N 070 10’ 30’’ to 070 13’. Important
settlements in the study area include Omi-Leragun, Omi-Fatokun, Fadipe,
Bankole, Olonde, Sola, Seko, Dada, Onigbagbo, Abuku, Olubadan among others.
The area is also well
accessible by networks of major and minor roads, as well as foot paths linking
the villages together. This facilitates easy movement during the mapping
exercise. Some of the footpaths have been upgraded to minor roads while new
ones have also been created see (Fig.1.2). Figure 1.1 shows the sampling
locations while Table 1.1 presents the geographical coordinates for the sample
locations
Table 1.1: Coordinates
of the outcrops in the area of study
|
Location No.
|
Outcrops
|
Northing
|
Easting
|
Elevation (m)
|
|
1
|
A
|
070 10’ 59.5”
|
0030 49’19.3”
|
117.2
|
|
|
B
|
070 11’ 03.8”
|
0030 49’19.2”
|
105.7
|
|
|
C
|
070 11’ 21.9”
|
0030 49’16.4”
|
119.6
|
|
2
|
|
070 11’
20.5”
|
0030 46’
50.4”
|
118.4
|
|
3
|
A
|
070 11’ 13.4”
|
0030 46’57.4”
|
106.6
|
|
|
B
|
070 12’ 20.5”
|
0030 46’
24.0”
|
110
|
|
4
|
A
|
070 12’ 31.9”
|
0030 46’
00.2”
|
94.4
|
|
|
B
|
070 12’20.6”
|
0030 46’24.0”
|
108.9
|
|
5
|
|
07⁰ 12’50.6”
|
0030 45’48.3”
|
118.6
|
|
6
|
|
070 10’56.6”
|
0030 48’44.8”
|
130.1
|
|
7
|
|
070 11’ 54.2”
|
0030 48’52.0”
|
128.4
|
|
8
|
|
070 12’12.6”
|
0030 48’28.4”
|
130.7
|
|
9
|
|
070 11’20.1”
|
003046’49.8”
|
109.2
|
|
10
|
|
07012’08.4”
|
003049’10.6”
|
142.8
|
|
11
|
|
07011’42.5”
|
0030 49’11.8”
|
127.6
|
|
12
|
|
07011’38.7”
|
003049’57.2”
|
143.2
|
1.4. Climate and
vegetation
The area is characterized by rain forest; derived savannah (Fig. 1.3a).
The rainy season and the dry season alternating each other are typical of the
rain forest belt, including the study area. The rainy season starts in March/April
and runs through September/October and with annual rainfall of 1000-1500mm
(40-60 in). The dry season is between November and March with mean annual
temperature of 210C-300C. These two seasons are caused by
the moist maritime south western monsoon winds which blow on land from the
Atlantic Ocean for the rainy season and dry dust laden winds which blow from
the Sahara deserts for dry season (harmattan).
The dry season is usually marked with bright sunshine, the
northeast trade winds known as the harmattan keeps the humidity/wetness
extremely low, most vegetation remains dry and most of the rivers and streams
in the area are dried up or at a relatively low energy level. However, the
vegetation of the area have been cultivated into secondary forest type
characterized by thick to light vegetation composed mainly of cultivated palm
trees, teak, mango, cashew, etc. During cultivation and farming, the natural
vegetation is mostly destroyed through bush burning. This has led to
deforestation of the natural and cultivated trees. A pictorial view of the type
of vegetation present in the area is shown in Figure 1.3b. Hence, this
vegetation is made up of palm trees, timbers of all kinds, averagely tall, long
grasses and resistant shrubs of various species.
Fig 1.3a: vegetation map of the study area
Fig. 1.3b: Photograph showing the vegetation of the
study area
1.5. Topography and Drainage
The studied area is characterized by moderate relief in some area
while in some other area there is presence of flood plain relative to the hills
around the area. The major rock
exposures are expressed as hills with the highest elevation being above 140m.
The drainage system is characterized by streams and rivers that
flow from the northern end towards the southern end. Most of the rivers and
streams are very dry during the period of this mapping exercise, this indicate
that they are seasonal. The streams and rivers flow almost parallel to the
strike of the rocks in the study area. This is an indication that they are
structurally controlled. Their tributaries form a dendritic drainage pattern
covering the study area (Fig. 1.4).
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