afikpo feild trip report
DESCRIPTION
DelineationTRANSCRIPT
-
~ 1 ~
CHAPTER ONE
INTRODUCTION:
1.1 LOCATION
The area of study is in the south eastern part of Nigeria, found in Ebonyi
State. Afikpo is located within latitude: 55300N and longitude, 7 56 0 E. It
covers an area of about 635.4 square kilometres.
The area is accessible by road through three different axes: Abakaliki rout
in the North East, Okigwe in the South East and Erei in Akamkpa local
Government Area in the South. The area is also accessible by river through the
major drainage in the area: the Cross River which drains to Calabar and to the
Atlantic Ocean.
1.2 CLIMATE, VEGETATION AND SOIL
The study area generally has a tropical climate with an average temperature
of 20C, over the day and the relative humidity is about 95% and 100% at dawn
and decreases to 70% and 80% during the time of maximum temperature in
the early afternoon. The vegetation of the study area is situated at the
transition between the guinea savannah and the rain forest. The areas with
thick vegetation are mostly the area dominated by sandstone and probably
indicates the nearness of the water table to the surface whereas the
swampy areas are dominated by shales. Evapotranspiration is between
1350mm to 1450mm per year.
-
~ 2 ~
The soil type is hydromorophic and alluvium because of the impervious nature
of the soil due to the geologic formations. The predominant formation is
marine argillaccus impervious hard shale but siltstone, Mudstones and
interspersed sandstones are also frequently formed. The soil are generally
drained due to run-off and the adequate drainage pattern.
1.3 TOPOGRAPHY AND DRAINAGE
Afikpo is characterised by an undulating topography mainly; sandstone and
shale. The shales were subjected to denudation because of its low resistance,
thus forming plains and valleys, whereas sandstones being more resistant to
denudation, formed the hills and ridges.
The shale plains are dissected by a number of small streams, some of
which are seasonal and issue out from near by sandstone ridges, which are
generally bare and supports vegetation as well as the percolation of swampy
rain through the sandstone ridges to form streams. Consequently, the
sandstone are aquifer forming.
Amasiri sandstone is faulted and has a stream flowing in the fault zone
implying that mechanical and chemical weathering are very active in the area
and causes rough surface on the sandstones outcrop.
Afikpo drainage is mainly by the Cross River and its tributaries Iywka river in
the North, Ubei and Tiara river in the South and their numerous tributaries
traverse the area in a general east west direction.
-
~ 3 ~
Dendritic drainage is highly common as well as radial drainage in hilly areas.
These tributaries empty into the Cross River which in turn empties into the
South Atlantic Ocean.
-
~ 4 ~
CHAPTER TWO
General Geology
General geologic studies carried out by geologist reveals that, the study area
lies the Afikpo syncline a depression formed on the eastern flank of the
South Eastern edge of the Benue trough as a result of Santonian tectonism and
uplift of Abakaliki anticline.(Nwachukwu, 1972, Murat, 1972, Olade et al 1972).
The upper cretaceous static graphic succession of southern Nigeria comprises
strata of three marine depositional sequences. The midalbians to
cenomaruiam phase is represented by the Asu River group and Odukpani
formation. This is succeeded by the Turonian Ezeaku formation and the
Campano Maastrichtian Nkporo state. The regional geology has been
described by Rryment et al (1965, 1972). Simpson (1954) first described the
Ezeaku formation as comprising hard, grey to black shales and siltstones
deposited in a shallow marine environment. Offodile (1976), established the
existence of an unconformity between the Turonian Ezeaku formation and the
overlying companion Nkporo shale in the Southern Nigeria. He explained the
absence of Awgu formation in the Afikpo syncline as a result of extensive
erosion of older beds which accompanied the santorian uplift.
In a petrographic study of the sandstones Hogue (1977) described the first
cycle sandstones (which include the Ezeaku formation) as being dominantly
texturally and compositionally immature and attributed this to proximity of the
course area to the depositional basin. Ezeaku and Awgu formation are
equivalent because they are indistinguishable in the field both in lithology and
-
~ 5 ~
fauna (Patters 1980). Consequently, while sedimentation in the Afikpo
syncline was replaced by a period of erosion an non deposition during the
santonian sedimentation in the adjacent Anambra basin continued
uninterrupted through the turonian unto the santonian leading to the
preservation of the Awgu formation in the basin, Petters (1980).
Mamu formation consist of interlaminated shale, siltsone and coal deposited
under as having laminated shale with carbonaceous coal deposited under
shallow marine.
Afikpo sandstone is described as feldspatic intercalated with pebble
essentially deposited under shallow marine.
The Waterworks sandstone member found in Afikpo, is a transition between
the Ezeaku and Nkporo formation because the Waterwork sandstone is older,
thus they are highly deformed.
-
~ 6 ~
CHAPTER 3
GEOLOGY OF AFIKPO AREA
The southeastern Nigeria and other parts of the country in the Pre-Cretaceous
times, consist of uplifted continental land mass made up of Pre-Cambrian
basement rocks, conformably overlain by Cretaceous sediments. Pre-marine
transgression occurred during the middle Albian and was mainly confined to
southern Nigeria and the Benue Valley, Kogbe (1972). The Albian end
witnessed the beginning of regressive Cenomanian phase and the only dated
deposits are those near Calabar. The Cenomanian was characterised by
extensive deltaic developments. There was the resumption of another marine
transgression which deposited shales and limestone in the Abakaliki are ,
Reyment (1965). The Benue Trough was partly filled with sandstones of the
Makurdi formation. Regression followed during the late lower Turonian and
continued up until the Santonian times. The extensive Maastichtian
transgression began during the Campanian with the deposition of
the Nkporo shale.
Maastrichtian outcrops occurred in the southwestern, southeastern and
northwestern Nigeria and themed Niger parts of the country, Murat (1970).
The Turonian transgression all over West Africa, happened to have affected a
wide area of the southeast of Nigeria. Its was this transgressive deposition
cycle of the Turonian that the Eze-Aku shale formation was deposited, Murat
(1971). In the upper Turonian periods, there were local periods of emersion
and erosion resulting in the intercretaceous unconformity, which has been
detected in the southeastern beds overlying the more disturbed strata ranging
-
~ 7 ~
up to lower Turonian.
3.1 Sratigraphic Event from Albian to Maastrichtian in Southeastern
Nigeria
3.1.1.1 Albian to Santonian Period
Earlier marine transgression In Nigeria occurred during Mid Albian and was
limited to the Benue Valley and southeastern Nigeria where the Asu River
Group was deposited. Some sediments deposited include:
1. The Asu River Group of Sediments
2. The Abakiliki Shale members, which were deposited in moderately deep
marine waters.
3. Calabar formation or Odukpani Formation
4. The Eze Aku Shales (Simpson 1955)
3.1.1.2 Coniancian to Santonian Period
The period is characterized by shales, limestones and an increasing amount of
sandstone deposited in southeastern Nigeria.
1. Awgu Shales: The formation is about 800m thick and consists of bluish
grey, well-bedded shales with occasional intercalations of fine grained
sandstone and almost thin marly shelly limestone
2. Santonian Uplift sediments: There are no sediments (no deposits) of this
age in southeastern Nigeria except the basic igneous intrusives but exit in
-
~ 8 ~
other areas in the country.
3.1.1.3 Campanian Maastrictian Period
Sediments in this period include:
1. Nkporo Shale: which has a lateral equivalent, the Enugu shale and
Owelli sandstone constitutes the basal beds of the Campanian, which began
with a short marine transgression.
2. Mamu Formation: Formed by a paralic sequence as the broad narrow
sea gradually became shallower.
3. Ajali Formation: A continental sequence overlying Mamu Formation.
4. Nsukka Formation: Formed as a result of return to partially paralic
conditions during regression of the maastrichtian Epeiric Sea.
In the midwest ,the Ajali formation transgresses directly above the Pre
Cambian.
Table 3.1 southeastern Nigeria stratigraphic succession
Series Formation Lithology Thickness (m)
Pleistocene
Holocene
Marine deltaic
sediments, Alluvium Sand and mud 200
Miocen -
Pleistocene Benin Formation Sand 200
Oligocene -
Miocene
Ogwashi Asaba Formation
Shale, sandstone,
Lignite 300
-
~ 9 ~
Eocene Ameki/Nanka
formation Shale/ sandstone 300
Paleocene Imo Shale Shale/sandstone 300
Upper
Cretaceous
Nsukka Formation Shale,
sandstone,coal 300
Ajali sandstone
Mamu formation
Cross bedded
Shale,coal,sandstone
330
390
Upper
Cretaceous
Enugu/ Nkporo shale
Awgu Shale
Shale, sandstone
Shale, sandstone
750
Eze Aku Formation Shale, sandstone 1500
Lower
Cretaceous Asu River Group
Shale, micaceous,
sandstone,mudstone 1800?
-
~ 10 ~
Table 3.2 Stratigraphic Succession in the Study Area
-
~ 11 ~
CHAPTER FOUR
DESCRIPTION OF GEOLOGIC UNIT
The description of the rock units were based on the following parameters: Age
and generalized field occurrence, texture, structure and mineralogy.
The Afikpo sandstone is a sandstone member of the Nkporo group of the
Nkporo formation. Afikpo sandstone is more porus, less lithified, less
consolidated than the Amasiri sandstone.
The Afikpo sandstone has an outcrop called the Macgregor Sandstone; a
member of the Nkporo formation.
4.1 Macgregor Sandstone
It lies on Latitude 553.63N and Longitude : 75.304E at an elevation of 305ft
above sea level.
The sandstone has a dip direction of 160 and a dip amount of 14 in the
direction of southeast. It is a member of the Afikpo sandstone unit with a
geological age of Maastrichtian.
-
~ 12 ~
Plate 4.1 The surface view of the Macgregor Sandstone.
4.1.1.1 Field Occurrence
It shows a dirty white colouration with a flaggy structural look. It is pebbly in
some areas, implying that the sediments are unsorted as a result of a high
energy transport medium. It is highly fossilized showing numerous patches
made by Trace fossils. These biogenic features were produced by ancient
organisms, which once thrived in the oxygen rich environment provided by
their host.
4.1.1.2 Mineralogy and Texture
Macgregor sandstone is pebbly in some areas with big grains amongst small
ones. It is medium coarse grained sand averagely with a rough pebbly feel
-
~ 13 ~
when touched with the hands (See plate 4.2). It is kaolinitic i.e it is made up
essentially of quartz and kaolin.
Plate 4.2 Macgregor sandstone is coarse grain and kaolinitic.
4.1.1.3 Grain Size Distribution for Macgregor Sandstone
This is done by conduction sieve analysis for a given sample collected in the
field. The sample was washed in water and dried. It was later weighed.
The table below shows the result obtained after sieving and subsequent
weighing of the corresponding samples from the respective range of sieves, for
rounds of manual shaking lasting 10 -15 minutes.
The sieve analysis data for Macgregor sand stone is as follows:
-
~ 14 ~
4.1.1.4 Sieve Analysis data for Macgregor Sandstone
Weight of pan = 68.9g Weight of fines + clay = 76.9g
Pan + sample =423.5g Weight loss =3.0g
Weight of sample = 354.6g Correction factor = 0.008
Weight before washing = 431.5g
Table 4.1 Sieve Analysis Data for Works Sandstone
Clay
interval
Weight
retained
(gm)
Weight(gm) Corrected
weight
Cumulative
weight
Cumulated
weight%
mm-
scale
Scale Retained Corrected
2 -1.0 21.60 21.77 1.77 6.14 6.14
2-1 1.0-0.0 21.20 21.24 43.24 6.05 12.19
1-0.5 0.0-1.0 74.10 74.69 117.94 21.06 33.26
0.5-0.25 1.0-2.0 165.80 167.13 85.05 47.13 80.389
0.25-
0.125
2.0-3.0 52.10 52.52 337.58 14.81 95.20
0.125-
0.053
3.0-4.0 15.52 15.52 353.10 4.37 99.58
0.063 4.0 1.40 1.41 354.51 0.39 99.96
Weight
of pan
= 398.5g
351.60 354.50 354.51 99.97 99.98
-
~ 15 ~
Fig 4.1 Grain size distribution curve for Macgregor Sandstone
From the graph it can be seen that the Macgregor sandstone is made up of
grain sizes of the same class i.e it is well graded or sorted. This suggest that its
paleoenvironment is fluvial.
-
~ 16 ~
4.2 Macgregor Shale
The sample collected at this location here were soils typical of the
unconformity between the Nkporo and the Eze Aku formations. It is the
Macgregor shale member of the Afikpo sandstone .unit of the Nkporo
formation of early to mid Maastrichtian age. It lies between longitude
7 55.444 E and Latitude 5 53.811 N and it is at an elevation of 255ft
above sea level. It is the boundary between Afikpo sandstone and Nkporo
sandstone with a width of 150m..
4.2.1.1 Field Occurrence
They are rarely exposed on the surface being wholly or partially overlain by the
pebbly and conglomeritic Macgregor sandstone. There exit an unconformity
between Works sandstone and Macgregor sandstone represented by the
Macgregor sandstone forming a thin band in between them.
4.2.1.2 Texture and Mineralogy
Like other shale it is rich in minerals containing mostly clay minerals like
montmorillonite, illite and large percentage of kaolinite. They are thin bedded.
-
~ 17 ~
4.3 Work Sandstone
It is a very high ridge and non-erodible, located on Longitude 7 55.407 E and
Latitude 5 53.840 N at an elevation of 187ft above sea level. They are
trending 150 and crossing the sandstone. The Works sandstone is used as a
cave zone, useful for defence. It is coarse sand and highly jointed with
open joints at its top. It is also highly sorted. It has a true dip of 170 and a dip
amount of 20.
Plate 4.3 ''Why Worry'' spring - a naturally good aquifer
It forms a good aquifer as seen at the Why Worry spring. The direction of the
-
~ 18 ~
joints is almost the direction of the flow of the local streams. The joints are
groundwater channels from which the Water Works near the Government
Secondary School Afikpo drew its source. The name Works Sandstone is
coined from it.
4.3.1.1 Texture, Structure and Mineralogy
Texturally, the works sandstone is coarse grained forming a high number of
pores, thus they are highly porous and permeable. It is cross bedded with the
structure overriding the stratigraphy. Its mineralogy is mainly quartz arenite
and composed of silica minerals.
4.3.1.2 Sieve Analysis Data for Works Sandstone
Samples of the works sandstone where collected, washed, dried and weighed
in preparation of for sieve analysis as follows;
Pan + sample = 240.3g Weight of sample = 171.4 Weight loss = 68.9g Weight of pan = 68.9g Weight before washing = 224.2g Weight clay and fines 52.8g Correction factor = 0.03
Table 4.2 Sieve Analysis Data for Works Sandstone
mm-scale Scale in phi Weight retained
Corrected Cumulated Corrected Weight
Cum. Weight
>2
-
~ 19 ~
0.5-0.25 1.02.0 54.90 56.54 147.29 32.99 85.93
0.125-0.063 3.04.0 10.10 13.90 166.34 8.11 97.05
4.0 4.20 4.33 70.67 2.52 99.57
165.90 170.67 170.67 99.57 99.57
-
~ 20 ~
Fig 4.2 Grain Size Distribution curve for Works Sandstone
-
~ 21 ~
The grain size distribution curve for works sandstone shows that the grain size
was probably decreasing from the source area. Consequent down-current
changes occur in fluvial and deltaic systems.
The cumulative frequency curve for the work sand stone shows that it is
unsorted, since it is not a straight line. The coarse grained particles in the
sandstone is an indication of the high energy of the transportation medium,
with the fine end members evenly sorted than the coarse end members. Thus,
the work sandstone is not well sorted.
4.4 Junction Shale
A shale member of the Eze Aku formation. Its Latitude is 5 55N and
Longitude is 7 54N and lies at an elevation of 110ft above sea level.
The shale beds are dipping SE towards Afikpo town.
4.4.1.1 Field Occurrence
During the Santonian tectonics, the dolorite intruded the junction shale thus
baking them close to their margins. The dolorite intrusion divides the junction
shale into two portions; Junction shale 1 and Junction shale 2.
-
~ 22 ~
4.4.1.2 Texture and Mineralogy
It is fissile in nature (ability to break along nearly horizontal planes). Contains
clay minerals like mica, illite and a few igneous minerals due to the intrusion,
contributing to the failure of roads.
4.5 Dolorite
It lies on Latitude 5 53.953N and Longitude 7 54.654N at an elevation 159ft
above sea level. It trends NE SW. It is the igneous intrusion between the
boundary between junction shale 2 and the dolorite sill. It belongs to the
gabbro basalt family. It is younger than Eze Aku because it is post
cretaceous.
4.4.1.2 Field Occurrence
It intrudes the boundary between Works sandstone and Junction shale. In the
Field, fresh samples are dark grey to black in colour. However, the weathered
parts are clearly brown in colour.
-
~ 23 ~
Plate 4.4 Dolorite quarry
4.4.1.3 Texture and Mineralogy
Dolorite is medium grained and ridge like in structure with boulders. Its
mineralogy consists of plagioclase feldspar, olivine, pyrite (dark colour). The
olive brown colour of plants is due to the high presence of, Fe in olive( a
geobotanical anomaly). Dolorite is used in road construction, railway road
making and of course, used for quarrying.
-
~ 24 ~
CHAPTER FIVE
STRUCTURAL GEOLOGY
5.1 Joints
These are common features in sandstone found in the area at station 2 (a joint
filled with iron deposit), but are visible in the works sandstone area.
Plate 5.1a - joint filled with iron oxide mineral vein & Plate 5.1b - An open Joint on the work sandstone trending 150
5.2 Ripple marks
They were observed in works sandstone. They are formed in response to the
velocity of the turbidity current that deposited the sediments. They look like
stretch marks on the body.
-
~ 25 ~
Plate 5.2 - Typical Ripple mark on Afikpo sst
5.3 Trace fossils: Trace fossils were present in the Macgregor sandstone and
works sandstones in form of marks made by burrowing animals
Plate 5.3 Macgregor sandstone is highly fossilized with burrowing animals e.g Annelids
-
~ 26 ~
5.4 Pebble Beds
Pebble beds are seen on Macgregor sandstone. The period of their deposition
must have been in between the Turonian transgression and regression.
5.5 Unconformity
An unconformity beds between Nkporo and Eze-Aku formations represents
short periods of non-deposition that existed between the Maastrichian and
Turonian periods.
Plate 5.4 Angular Unconformity in Nkporo formation with hills trending NE
-
~ 27 ~
5.6 Strike and dips
Below are the strikes and dip values of the stations observed in the field.
Table 5.1 Strike and dip values of the stations observed in the field
STATIONS STRIKE DIPS DIP VALUES
1 160SE 14 SE
2 105SE AND 10 SE
3 190 SE 4
5
6 7
8 9 160 SE 15 SE
10 170 SE 20 SE 11
12
13 14
15 42 SE 170 SE 16
17
18 19
-
~ 28 ~
CHAPTER SIX
Environmental Geology or Economic Geology
Rocks encountered in the study area were mainly igneous and sedimentary
rocks. Sedimentary rocks, as processes of their formation and nature of
cementation agents, they have high porosity, as a result of this they are
generally low in rock hardness and their grains are less tightly held together.
Unlike sedimentary rocks, igneous rocks have generally higher rock hardness in
case of fine grained igneous rocks such as basalt to that of coarse grained
igneous rock such as granite, gabbros.
As a result, the mineral grains of fine grained igneous are more tightly held
together than that of coarse grained igneous rocks.
6.1 Shales
The Macgregor shale and the junction shale were encountered in the study.
The shale formations mapped in the study area are not favourable for
engineering construction as they can easily swell when saturated with water.
They cannot support heavy structures since they contain weathered clayed
materials.
-
~ 29 ~
However, shale has a wide variety of economic uses. The plans and valleys are
used for various agricultural purposes such as cultivation of food crops. Shale is
fertile and useful for blanketing at the base of water.
Weathered shale (Clay) is used in pottery.
6.2 Sandstone
The works sandstone and Macgregor sandstone were encountered.
1. The works sandstones were indurated and crystalline.
The calcareous materials from them can be used for fermentation of
cassava, extraction of palm oil and production of other materials important is
man.
2. Sand is elastic and can bear load, therefore roads can be constructed on
it.
Its disadvantage is that with time, the iron cement and pregimation will be
dissolved out, thus making the sandstone loose and friable.
-
~ 30 ~
6.3 Dolorite
It was also mapped around the study area. Its economic value or importance
includes:
1. It is used by natives to make grinding stones.
2. It is used for caring because of its high hardness.
3. It makes a gird rock hammers as it on be harder than most other coarse
grained igneous rocks.