afikpo feild trip report

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~ 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: 5°53’00’’N 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 20°C, 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.

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    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.

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    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

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    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

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    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

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    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

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    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.

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    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

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    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:

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    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

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    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.

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    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

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    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.

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    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.

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    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.