Study Of Sedimentary Rocks, Sandstone – Field Mapping Exercise By 300level Students Of Geology And Exploration Geophysics Department Of Ebonyi State University To Afikpo
Sedimentary Rocks, SandStone – Field Mapping Exercise By Geology And Exploration Geophysics Department
The fieldwork to Afikpo commenced on the 13th-17th December.
A five (5) days field mapping embarked upon by 300Level students of geology and exploration geophysics department of Ebonyi state university. To place an order for the Complete Project Material, pay N5,000 to Then text the name of the Project topic, email address and your names to 08060565721.
Account Name – Chudi-Oji Chukwuka
Account No – 0044157183
To place an order for the Complete Project Material, pay N5,000 to
Then text the name of the Project topic, email address and your names to 08060565721.
Research on the study of sedimentary rocks have shown that sediments, pieces and fragments of sedimentary old and pre-existing rocks have created some features and rock attributes which are especially distinct and useful in the sedimentary terrain.
This concept makes up about 80%-90% of mineral products that are being utilized in our day to day living and up building. Product of sedimentary rocks which have been a major commodity which has sustained living economics of major developed or developing nations and detailed study on its further use and maintenance is necessary so as not only to develop new uses but also to preserve products of sedimentary rocks for future generations.
Location and Accessibility
The duration of the field work/trip lasted for about five days and the main area of interest has the Afipko region area and its environs and the area has mainly a sedimentary environment in southeastern part of Nigeria located in Ebonyi state Nigeria.
The base map under consideration showed the scale of 1:25, 00 approximately 1.8 on ground. It had latitude and longitudinal co-ordinates in which the latitude is 7.55E to 8.00E longitude 6055N to 60 55N of the meridian respectively. The various locations visited are mostly accessible by the main roads minor road and foot paths (largely used during the work) and it is all easily located on the base map. Some of the area that were covered during the field work are listed below (conclude the areas on the map and those not on the map).
Areas on the map include:
1. The out crop behind Government college
2. Why worry spring, Ozara ukwu afikpo road, Akpoha junction in Afikpo Amasiri Road junction.
3. Out crop beside Ezesco hotel about 600km from the ndible road,
4. Ebonyi Hotels Afikpo branch
5. Macgregar road (along Afikpo Amasiri road) 8. Afikpo-Abakaliki road (about 800m from Amasiri junction towards Ai)
6. Out crop that is about 200m from Afikpo Abakaliki road.
7. Out crop that is abot 800m towards Ibii junction along Afikpo Abakaliki road.
8. Out crop that is 200m along Ibii junction Amesiri-Edde road,
9. Ezi Edda village (Afikpo south L.G.A.).
10. Oziza town (along the road to cross river about 150m to cross river)
11. Out crop about 100m along Ndibe beach
12. Ndibe beach.
Afikpo as an area of study has been visited by many renounced geologist and researches on the past, base on these fact many detailed map literature has be done and some of them have been revisited during the course of the field work.
The Afikpo base on was formed during the santonian orogeny in the upper cretaceous time (companian mastrictian).
Some of the research works on Afikpo where carried by notable researchers like Dr. L.F. Spath, Dr. R.C. Wilson, Dr. A. O N Bain, A. Sampson, Rayment 1965, C.S. Wajide 1976 Mckay 1939, Murat R.C among others.
During their basin is completely a sedimentary basin with lithological rariations. Majority of the shale’s and silt stone sediments are carbonaceous as observed in an outcrop where Ammonite fossils, Echinods, Bryozons and other fossils where collected majority of the sediments where sand stone deposits where found, charges from calcerous sand stone along the Abakaliki enticlinorium to arenaceous sand stone towards the core of the basine. The also observed that an igneous intrusion occured along the axis of the abakaliki anticlinorium which is dated to be about 55 million years.
Also mckay 1939 dated the age of Afikpo synclinorium to be midcretaceous base on the observation made and the outcome from the structural and lithological difference that exist between Amasiri and Afikpo sand stone.
The santonian event on the region resulted in fracturing and folding of the post santonian sediment found on the Afikpo synclinorium.
Geomorphology simply means the scientific study of land form and the process by which the land forms are formed.
The geomorphic setting associates with geomorphic features like topography and land form, climate, superficial deposits and drainage pattern that are found in Afikpo region and these features are define below at page 1.3.1
Topography and Land Form (Physiography)
The Afikpo lies around on elevation of about 170m above the sea level. Sand stone ridges forms the topographic highs of the area. Areas of moderate relief are often characterized by an intermediate condition of erosion between the extremes on area with high relief on one hand where the underlying shales are easily eroded.
In Afikpo region also erosion is more pronounced from N-S along the Abakaliki anticlinorium, most generally occurring are planes underline by shales and silt stones, within the hills and ridges are composed of sand stone lithology
Drainage simply means the arrangement in which a stream erodes the channels of its network of tributaries. It all depends on soil type, vegetation relief, topography etc.
Afikpo drainage pattern is controlled by Ndibe beach, Ozizza beach and tributaries from Iyowa and Iyogue river which flow eastward to Ebonyi river running from Akpohrgha to where the form a Y junction flowing into cross-river and depositing large amount of sand sediment (alluvium) because of the decrease intensity, capacity and velocity of the river.
This simply means that the studied area exhibits dentritic drainage pattern.
The tributes of the studied area like the woo-owo stream, flows towards Ndible.
Some minor stream like why worry steam is developed by erosional processes, resulting to contact spring on the area i.e. where an impermeable rock layer is intersected by permeable layer.
Dendritic pattern: is an arrangement of stream course that, on a map or viewed from the air, resemble branching habit of certain trees, such as oak or maple This drainage patter is mainly associated width coastal area and clay, silt-dominated environment
Climate and vegetation
Vegetation in Afikpo is characterized by trees shrubs with abundant palm trees. Climate is the average condition of a place over a long period of time. Like 45 and above.
The climate of Afikpo basin is hot and humid with mean annual rainfall of about 152-203cm, which corresponds to its adjacents basin (Anambra basin)
There two main seasons that dominates the climate in Afikpo. They are the rainy season and the dry season.
The rainy season usually begins minimum temperature towards the end of the rainy season is about 18-210c.
While dry season, lasted only from late November to early April.
Finally the climate of the studied area is not stable due to seasonal variation.
Soil and superficial deposit
In Afikpo there are two main types of soil present. There are silty clayey hydromorphic soil and the grey sandy clay hydromorphic soil.
Two types of superficial deposition are of hydrogeological importance they are laterites and alluvium.
Laterites can be found on sedimentary deposition, lateritic ironstones on different stage of consolidation can be found on scattered hills over all the formation on some cases they are general square killometres in extent as we saw in Afikpo field trip. Laterite crust is a thin layer of ironstone which is believe to be of a pedogenetic origin de Swandt (1964) it over lies the weathered bed rock directly and covers the top of the remnants of the higher pediment to form low flat-topped hills.
Laterite: red residual soil developed in humid tropical and subtropical regions of good drainage. It is leached of silica and contains concentration of iron oxides and hydroxides sand aluminum, manganese or nickel.
This simply deposit of sediment left by stream in the channel or flood plain.
It is generally believe that alluvial deposits cover the third and lowest erosional level in Nigeria that is the valleys of rivers and streams the thickness and nature of the alluvium however varies with type of the river.
Generally the behaviour of the rivers and their depositional process were influenced by fluctuating river-levels of quaternary time.
Methodologies and Equipment Used
This simply refers to all procedures plans and principle applied by both lecturers in ensuring that the field work is completed successfully.
i. Location of oneself in the field.
ii. Observation of various lithologic unit
iii. Studying every lithology of an outcrop to obtain information like grain size, grain shape composition, sedimentary structures, textures. Lithology etc
iv. Accurate measuring of attitude of different geological structures.
v. Taken note of the trends of every geological structures.
vi. Collection of fresh samples at every location for further analysis in laboratory.
vii. Measuring the thickness of the bed
viii. Taken photography.
Material that were used in the field Trip and their importance are listed below
Base map: is very important, it can be regarded as the first aid to every field trip in field mapping in geology. The base map shows the outcrop and the directions of a place under-consideration or mapping.
Compass: it is used to measure the attitude of the outcrops; it enables the trends of fault planner and trough crossbeds to be measure.
Measuring tape and meter rule: It is used to measure the thickness of beds during logging
hand Lens: it is used for magnification
Field note book: for recording information
Sample bags: for collection of rocks samples, for analysis in the laboratory.
Geological hammer: it is mostly used to extract samples from the rocks
Camera: for taking photography (image) of an outcrop.
Pen and pencil: pen for recording information while the pencil for sketching or drainage out crop.
Regional Geological Setting
This refers to the regional settings that are taking about the scientific study of the origin, history and the structure of earths crust.
There has been a lot of argument among researches and geologist for several years about the origin of Benue trough
Origin and evolution of Benue trough
Benue trough was under a tensional regime from the time when it originated as the failed arm of an RRR triple junction (C.F Burke et al; 1970) through out its history of sedimentation and deformation and that this tensional regime was the result of continued but intermittent uplift of so called Gulf of Guinea dome (le Bas, 1971) following the opening of the south Atlantic.
Nature of Folding
Differential vertical movements, the Benue trough has often been described as elongate partly fault-bounded depression occupied by up to 6,000m of marine and fluvideltaic sediments that have been compressionally folded in a non-orogenic shield environment (might 1976) Olade (1975, 1976) he emphasizes the wholly ensiabic nature of the trough, the thinned crust beneath it, and the dominate influence of vertical movement as a causes of the folding.
Concede that the weight of evidence may eventually prove that the folding was infact due to compressional movements, albeit accompanying broad regional uplift of the “Guinea dome” (cf Olade 1975) but (cf Wright 1968) prove it wrong.
So there is no obvious cause of the necessary compression movements. Figure 4.2 the lemuroid anticline, south of Gombe, one of the more impressive folded structures of the upper reaches of the Benue trough there is no question that it is a double plunging anticline, but its two virtually value-straight limbs provides evidence that at least some of the folding in the Benue trough may be controlled by a system of East-north east-trending faults in the underlying basement, along which blocks have been differentially uplifted. Straight limbs of folds such as those in fig. would thus be the surface expression of particular large basement fault Wright 1976-best available present day analogue for the crustal structure of early Benue trough is the afar triangle and its extension to the Ethiopian rift.
Reselection of sea-floor spreading-sub-duction cycle. The supposed junction between those two plates has subsequently even identified as a major continent wide of Benue trough (Neev 1977)
Stratigraphic: mainly-pertaining to the composition, sequence, and correlation of stratified rocks
Southern eastern Nigeria
The oldest sediments on southern Nigeria are around Abakaliki on southeastern Nigeria. These sediments are unmoverd and undifferentiated. The constitute the “ASU River Group” (table 1) the type area of the group is along the ASU river (reyment 1965). The sediments consists of rather poor;ly bedded sand, shales known as the Abakaliki shales with sand stone and sandy limestone lenses.
The limestone beds can attain a thickness of thirty metres. Paleontologically, the shales is mainly characterize by species of montoniceras and elobriceras.
The sediments are folded particularly in the south of Abakaliki. The fold are stretch NE-SW. the beds are associated with a lead zinc mineralization.
The shales are deeply weathered and contain radiolarian, echinoids, some pelecypods and gastropods.
Beds of Cenomanian age is restricted to the south-eastern portion of the basin around calendar (fig 1) these beds have been assigned to the Odukpari formation and they have been dated as Cenomanian to lowet fortanian age. The deposition consist of arkose sandstone, limestone and alternating limestone and shales which becomes gradually more predominatly shally in its uppermost parts (Reyment 1956 pg 589) these sediment are of shallow water origin and they may be about 600 meters thick. They type locality is at the village of Odukpani near calabar.
The Turonian deposits manily belong to Eze-Aku formation (Eze-Aku river valley in south-easthern Nigeria. The formation comprises hand frey to black shales and siltstones with frequent facies changes, to sandstones or sandy shale. The thickness varies, but many attained 100 meters in places (reyment 1964 pg. 64) locally at amasiri the Eze-aku formation passes laterally into the Amasiri sandstone” facies, other lateral changes are into sahlly lime (as in the Nkalegu area) calcareous sandstone, and sandy limestone the Eze-aku formation represent a shallow water deposit.
The fossibles consist mainly of vascoceratids pelecypods, gastropods, echinoids, fish teeth etc, which indicate a based turonian age.
The Coniacian sediments are generally less thick than the turonian and they tend to give an impression of rather quickly lateral changes in facies these sediments have been assigned to the Awgu formation (Awgu shale of raiment 1965). The formation is about 800 meters thick consists of bulish grey, well-bedded shales with occasional intercalation of finergrain sandstones and thin often mainly limestones. The beds are rich in ammonites and other molluses. Fish teeth also occur.
The santonian is a regressive sub stage in Nigeria and sediments of this age have not been found in southern Nigeria.
A doubtful santonian locality in Agwu shale in Igumale area has yielded Ostracods possibly referable to this substage reyment (1960).
The total thickness of sediments of Albian to coniacian age in the eastern portion of the S. Nigeria basin is about 3,300meters.
In south-eastern Nigeria, Campanian sediments probably belong to the base of Nkporo formation (Nkporo shales taltan 1944).
Outcrops of the Nkporo formation are scarce but boreholes coves show that the formation consists of dark shales and mudstone with occasional thin beds of sandy shale sandstone. Thin beds of shelly limestone may be present. The estimated maximum thickness is 1000 meters. No typical companion. Ammonites have been found in Nigeria but it is probably that the base if the Nkporo formation and its lateral equivalents are campanian in age. The major part of the formation is maestrichtain.
The Campano- Maestrichtain in South-Eastern Nigeria beings with dark grey often friable, shale with occasional thin beds of limestone and sandstone. This part of sequence belongs to the Nkporo formation the owelli sandstone, Enugu shale and Asata shale are lateral equivalents of Nkporo FM these inner-basin sediment are of shallow water origin and there are frequently sharp facies changes the broad, shallow sea gradually shallowed further and coal-accumulating conditions resulted.
The basal part of the coal measure sequence, previously known as the lower coal measures but now known as mamu-formation contains marine intercalations composed of ammonitiferous shales (reyment 1964) the coal being part of the sequence consists of predominately fresh water and how salinity sandstone, shales, mudstones and sandy shales, coal seams occure at several levels (simpson 1955) excellent exposures of mamu formation can be seen along the Enugu-onitshsa road at the Milliken hill just on the out skirts of Enugu.
The mamu formation is overlay by the Ajali formation with its type locality along the valley of the Ajali River near Enugu. This formation was previously known as the false bedded sandstone and consist of thick friable, poorly sorted sandstones typically white in colour but sometimes iron-fragments are subangulay, with a sparse cement of white clay large scale cross bedding is characteristics
Ajali formation is well displayed along the road cut between mile (from Enugu to the foot of the milikin hill.
It consists of thin bands of white mudstone and shale occurring at intervals and increasing in number towards the base. The Ajali formation is often overlian by a considerable thickness of red earth, which consist of red, earthly sands formed by the weathering and ferruginisation of the formation of the formation. On the Udi plateau, the red earth may be as much as thirty meters thick. North of the Oji River, the higher slopes of the Enugu escarpment consist of the Ajali formation. Here, the formation has a thickness of about 45 meters. Good exposures of the sandstones occur in the deep gullies incised along the higher slopes of the scarp.
The Nsukka formation lies conformably on the Ajali sandstone. The formation was first described by tattarn (1944) as the “Upper coal measures” the lithology of the Nsukka formation is very similar to that of the mamu formation and the rocks consist of on alternating succession of sandstone, darkshale, and sandy shale, with thin coal seams at various horizons. The outcrops of the formation can be observed in the valley of the Nadu River and on road-cuts along the Enugu-Onitsh road.
Paleogene stratigraphic sequence south Nigeria.
Age Western Nigeria Eastern Nigeria
Ecocene Ameki formation
oshosun formation Ameki formation
Paleocene Akimbo formation
Ewekoro formation Imo formation
Maestrichtian Abeokuta formation Nsukka formation
Stratigraghic Succession of Afikpo Basin
Age Formation Member Lithofacies
Maestrictain campanian Nkporo shale Asaga shale
Afikpo sandstone Gysum, evaporates micaceous sandstone
Turonian Ezeaku shale Amasiri sandstone and water works sandstone junction shale Whit to light grey sandstone grey shale
Cretaceous Sequence in Southern Nigeria
Western Nigeria Eastern Nigeria
Maestrichtian Ajali Formation
Basement Complex Mamu Formation
(Lateral Equivalents are Asata Shale, Enugu Shale, Owerri SSt.)
Coniancian-santonian Agwu Formation
Turonian Eze-Aku Formation
(Lateral Equivalent Amasiri SSt.)
Cenomanian Odukpani Formation
Abakaliki Shales) “Asu River Group”
REGIONAL TECTONIC SETTINGS
The history of tectonic settings in Benue Trough
Important aspect of the tectonic history of Benue Trough concerns the relationship between movements of uplift and folding, marine transgression and regressions in the trough, and the major global transgression of the upper cretaceous, which probably resulted from Eustatic rises in sea level caused by Growth of the mid-Atlantic ridge as the Atlantic ocean opened (e.g Reyment et al. 1996) for example, Rement and Morner (1977) have identified no less than five transgression in the Benue trough, for of which are wholly or partly linked to global sea-level changes. We known that some of the intervening regression phases are characterized by earth movements in Benue, because a number of deformational events has been identified. (e.g Nwachukwu1972) Offodile and Reyment 1977; Patters, 1978). In addition, the sea ward migration of coarse fluviodeltaic deposit (now arkosic sandstones in the muri, Bima, Keana and Makurdi formations).during the cenomenian (e.g Offodile 1976) indicate rapid erosion at this time, perhaps as a result of rejuvenation of fault scraps along the trough margin. The most widespread transgression appears to have occurred during the Turonian, but there are conflicting views about whether this include a link up between the Benue trough and Tethys Ocean to the north (e.g Reyment and tait 1972. Kogbe 1976; morner 1978). This was a major global transgression (Reyment and Morner, 1977).
But the subsequently history of the Benue Trough probably owes much to relatively local tectonic movement in the uppermost cretaccous the main phase of uplift and folding occurred, the sea retreated into the Anambra Basin (Cf Petters 1978) and was displayed into the middle Niger basin (Kogbe 1976) and predominately continental (Fluviatile) sediments were deposited in the upper and middle parts of the Benue trough. “I have always thought, following carter et al(1963) that the unconformable paleocene and younger Kerri kerri sequence was made up of possibly remarked deposits eroded from the folded sediments (Cf. Wright, 1976), but a case for their derivations from uplift they may be derived from the Jos Plateau (Burke, 1976) for which there is some sedimentological evidence (E.O Ayeela, Pers. Comm..)
The timing of the final regression and folding is variously reconded, ranging from coniacian (Offodile, 1976) throng santonian (Olade, 1976; Petters 1978) to maestrichtian (Dessavuvagie, kogbe 1976); such variation might suggest the event was a diachronous one.
The lithostratigraphic units give a detailed description of the studied area (Afikpo and its environs) and for easy and convince purpose have been divided into seven  units, starting with the oldest formation to the youngest formation. The description starts from the formation, group, super group, member bed and complex.
1. FORMATION: The litostratigraphic from action identified in the studied area include the Eze-aku formation and the Nkporo formation. The Ezeaku formation is Turonian in age and contains the Amasiri sandstone, Ozara, Ukwu shale and the Amauro sandstone. The Nkporo formation is campanion in age and contains the Afikpo sandstone.
2. GROUP: The studied area belongs to the Asu river group.
3. SUPER GROUP: Stratigraphic group of Afikpo is categorized into lower Benue trough sediments. It is stratigraphy of the Albian sediment which is also called that Albian Asu River super group which contains the Afikpo Synclinorium.
4. MEMBER: This is the next in rank after bed in a lithostratigraph unit. The observed lithostratigraphic members in the studied area include Amasiri sandstone member, Ozara Ukwu shale member, Afikpo sandstone member and others. However, the Amasiri sandstone member consists of the Amasiri sandstone type. The Ozara Ukwu shale member consists of fossil reddish brown-black shale formed as a result of oxidation process the Afikpo Sandstone member consist of coarse grained sands and pebbles that is milky in colour.
5. BED: This is the lowest rank in lithostratigraphic unit it consist of layers of strat that ranges from 1cm-few meters ion thickness and can be distinct from one another either in colour, texture or thickness. With respect to the studied area, the beds studied include sandstone beds; shale beds coal beds and others.
6. COMPLEX the stratigraphic complex of the studied are belongs to the sedimentary complex of Nigeria. They are cretaceous in age.
3.1.1 UNIT 1
This outcrop is located at about 800m, along Afikpo-Abakaliki raod. This shale contains clay minerals which clay minerals which also contains kaolinite, illite and montmorinite. This zone is transitional, contact that is that after will be no other shale after this outcrop. The deep were caused because of tectonism
In some areas, the shale were intruded by dolerite (Pyroclastic rock) mineral present: There is presence of Hematite (Iron mineral), clay mineral such as Kaolinite, illite, moutmorinite etc.
Colour: They are light grey, but brown weathered due to presence of iron mineral (Hematite)
Structure: This is presence of lamination.
Silicious Sandstone (Ezeaku-formation This outcrop is located at about 700m away from Amasiri junction. This outcrop is also a dip gully located along Afikpo Abakaliki Road. The outcrop is a silicious sandstone of Eze-aku formation called Amasiri Sandstone. On a fresh sample part, the sandstone is consolidated and not friable.
Mineral Present: Since the outcrop is a silicious sandstone, the mineral present are quartz, feldspar, muscouite, Mica, Biotite etc.
Structure Observed: There is cross-bedding in the area, also there is ripple of low amplitude. There is also presence of tectonic joint.
Colour: The colour of the sandstone is whitish in fresh sample due to presence of quartz but brownish in weathered.
Sample as an evidence of ferrogenization and also presence of iron mineral called Hematite.
Grain Size: It is medium grain size to coarse to pebble.
Grain shape: They are sub-rounded to sub-angular.
This outcrop has silica as its cementing material.
Measurement of trough cross bedding
1. N100oSE – N280oNW
2. N94oSE – N266oNW
3. N108oSE – N288oNW
4. N90oSE – 270oNW
5. N180oSE – 300oNW
6. N96oSE – 278oNW
7. N96oSE – 276oNW
3.1.3 UNIT 3
This outcrop is located at about 900m form outcrop 9A. The outcrop is beside Egoson Hotel along Ndibe beach. The outcrop is Nkporo shale under
Nkporo formation. The shale is laminated and the shale is located at the base of Afikpo sandstone as seen on the topmost layer, and it has a contact source of water which is seasonal. The shale is interbedded with Afikpo sandstone.
Sedimentary structure: There is some structure like mud cracks, orphomorphia showing the presence of some organic (fossil) and meaning that there is oxygen which support dwelling of organism. The drainage pattern here is dentric. The shale here is very soft as a result of age and depth of burial. The shale contains gypsum that has a hardnes of 21/2 the gypsum is grayish because of the action of weathering.
This location is 2km to Uwana polytechnic. The sandstone is Afikpo sandstone is also located at some are at opposite Ebonyi Hotel. The age of the outcrop is campanian-matritian. The outcrop is friable and consolidated not consolidated.
Mineral content: These are quartz, feldspar, fragment like, mica, biotite, muscovite etc.
Structure: There is presence of mega ripple or ripple bed forms. There is also tectonic structure like joint, fault, and fold in the area. There is also distorted due to some biogenic activities. That is burrow of sediment.
Gain size: Is medium to course to pebble in some area. And fine to medium in some area.
Grain shape: Is sub-rounded to sub-angular.
Colour: The colour is brown due to weathering but white due to in fresh sample.
Thickness of bed: 64m. And it is medium to course grain.
Grain shape: Is sub-rounded to sub-rounded to sub-angular in shape
Colour: is dirty white
The thickness is 40m
Grain size: medium to coarse
Grain shape: Sub-rounded to sub-angular
Colour: is dirty white
Thickness = 22m
Grain size: medium to coarse
Grain shape: sub-rounded to sub rounded
The outcrop is located about few meters away from Wowo River. The outcrop is a coal seam and it is Mamu formation. The coal were deposited in a detic environment and it is black in colour. The black colour is as a result of high content of carbon.
The coal was deposited from remains of plant and animal (organic material).
Thickness of bed is 6cm. the coal is used to generate electricity.
This formation is low per coal measure
Upper Nsukka formation. This formation is low maastrichtian
Dip direction N96o
Second strike – 44NE – 228oSW
Dip direction 28o
Dip amount – 10o
This location is beside Edda village. Afikpo South Local Government Area Ebonyyi State. The outcrop is Ajali sandstone and it represent the lower part of mamu formation. It is ferrogenized and consolidated. Hematite is present here due to deep chemical setting. There is deep weathering in this outcrop. There is absence of quartz. The feldspar found here has been weathered to clay. The bed here is coursing upward. The lowest bed is brown in colour and its about 20cm. ontop of this bed a yellowish brown bed of the grain. This bed is about 10-15cm. on top of this bed also is a reddish brown bed of medium. The beds of 25-30cm. on it are a brown bed of coarse gain. This bed is 50cm approximately.
Petrology lays emphasis on the origin, distribution, structure and history of rocks. The petrology of the structured area (Afikpo and its environs) is from igneous, sedimentary as dominated rock and metamorphic rocks which are distributed respectively and their history which is their mode of deposition either from molten magma, weathering and erosion and recrystalization of these rocks.
The processes leads to their difference in age distribution and their structures are as a result of the processes that acted on them.
Looking at petrology in terms of mineralogical composition in the studied area, the various rocks identified includes; shale siltstone, dolerite sill and coal seams.
1. Sandstone are mechanically formed sedimentary rock of areneceous components of quartz, feldspars, micas, garnet, and magnetite.
2. shale is a sedimentary rock of argiliceous components of both organic and inorganic types ranging from schist, silicate 15%, alumina (Al2O3), Kaolinate, chlorite, illite, sericite and micas.
3. coal is a sedimentary rock from organic matters with component
And high quantity of volatiles and ashes.
4. dolerite is an intrusive igneous rock identified in the area, dark in colour composed of Ca-plagioclase (Anorthite and Labradorite), Augite, Olivine and iron oxide.
Texturally, sandstone ranges from fine to coarse grain (1/16.6 2.0mm diameter) shale is fine grained argillaceous material, laminated and fissile (1/255-1/16m diameter).
Dolerite composed of hypabyssal (inter-mediate) rock which is made of medium to fine grained. Ophitic and sub-ophitic (porphyritic) texture as observe in out croop opposite block industry
Sieve analysis is a mass measurement used in determining the size frequency distribution of sedimentary particles especially in sand size range. (1/6-2.00mm).
The grain size parameters calculated from sieve data (eg) mean, sorting and skewness etc, are used to infer the genesis provenance, depositional process and depositional environment of the sediments.
These are small scale ridges and troughs formed by the flow of wind water over loose sand-grand sediment. They are usually less than three centimeters high, with spacing distances less than 30cm. in the studied are, current ripples which are asymmetrical in profile, with gentle upcurrent (stoss) slopes and steeper concave-upward (lee) slope and results from current flow in one direction was at outcrop in Ebonyi hotels. They may range from straight to sinuous crested or even liquoid (tongue shaped) forms, The ripple mark is pronounce inside Ebonyi hotel.
Concretions are distances segregation or nodules of common sedimentary materials found in shale as in location 16, and in sandstone as in location 14, (see plate, 2) and also found in limestone as well. Concretions can form at the same time as the enclosing sediments (syngenctic) or during diagenesis (Epigenetic), may be rounded or irregular and may vary in size from few (mm) to few (m) in diameter. The concretions ranges from calcite, iron oxide, pyrite to siderite type, and the identified once at the above locations are siderite type. Some concretions may be seen as psuedofossil.
This out crop is pronounced in outcrop before ndiebe beach.
The sediments of the Afikpo basin and its environs are marine and fossiliferous, containing abundant bivalves, pelecypods and gastropods that are seen int eh outcrops of shale and sandstone. The siderite gypsiferous containing calcite bands at location 16 these was observed. The gypsum indicates deposition in a reducing environment. The highly carbonaceous nature of the shale and their rich in organic matter content also support the deposition.
The cretaceous rocks were subjected to serious of folds which are thought to have resulted from repeated deformative forces. It is through that the Albian was probably folded before the deposition of the muri-keana-makurdi sandstone. Farrington suggests that to some degree all Basement took place in these fold, and further, indicates that most folding were accomplished before the coniacian. The cretaceous rock being incompetent to transmit organic thrusts, their deformation has been thougth to be a reflection of the movements, within the basement. This is believed to be more so because of the relatively thick cretaceous cover. The thickness of the sediments is about 1000-1300m.
In the middle Benue area the basaltic cones and vents reveal much thinner cover and in north give an impression of quick lateral facies changes caused possibly by oscillating shorelines of the sea. The upper part of the senonian is marked by a regressive phase starting about the santonian and probably continuing into the maestrichtian. The possible deltaic environment was ideal for the formation of the coal measures.
Regional Tectonic Settings
Post Tectonic Period
A SE to NW polarity relative to axial fracture system, resulted in the subsidence of the Anambra Basin which developed North of the Abakaliki Uplift. The development of the basin was controlled by the N25oE direction which became dominant in the structureal Evolution of the region. The subsidence is particularly strong and the basin is the locus of a proto Niger Delta which was formed on the stretched continental margin.
In the Bornue and Upper Benue Trough, the cretaceous basins are uplifted and subjected to compressive movements at the End of the cretaccous. The same tectonic sedimentary polarity from the SE to the NW, led to the some configuration of post-tectonic basin for the Paleocene kerri-kerri basin controlled by the N25oE fractures.
The tectonic regime in the region turned to a pure tensional activity accompanying the initiation and subsequently evolution of the cretaceous volcanic line.
Tectonic structures are structures that result from the action of forces generated with in the subsurface of the Earth at divergent or convergent plate boundaries. This external or endogenic force tries to transform the earth and its constituent there by leading to various structures and appearances retained by the rocks of the Earth involved, which serves as a criteria towards analyzing and interpreting the prevalent geological setting observed in the rocks.
Tectonic structures in other hand can still be a crustal deformation with different or similar structural behaviour. So in taking about tectonic structure as observed in Afikpo we will take knee look at structures like the fault (kinds of
fault present location of fault, fault plain and fault line) also the joints (materials that fill such joints and also folds, even unconformity.
It is a fracture or parting that cuts through and abruptly interrupts the physical continuity of a rock mass.
It can still be defined as a divisional plan or surface that divides a rock along which there has been no visible movement parallel to the plan or surface.
Characteristics of Joints and their Formation
– Joint can be formed from compression tensional and shear stress
– They are range in size from microscopic to kilometers in length
– Erosion can occur at a faster rate along joint
With respect to the studied area joint are located at out crop very close to magregor hill they are tectonic structures which are post depositional structures.
During their deposition spaces that were created in these joints are filed with later sediment/minerals. The trend of joint was measured during the filed trip as 365o NW and 148o NW, also in the out crop was a conjugated joint with a shear fractures in the rock this shear fractures mobile element/minerals fill up the joint and mostly iron minerals also fill up these joint but they cannot be seen or felt by eyes and the hand during the field work.
Surface of rock rupture along which has been differential movement.
Faults can be classified on
– The sense of movement (the direction in which the blocks or either side of faults move) this is controlled by the type of stress that is applied
– The articulation of the fault surface (the angle of the plane fracture)
In fault, as observe in Afikpo there is observable movement unlike in joint there is no movement.
e.g of faults, normal fault, reverse or strike slip depending on the movements of the blocks relative to each other.
Normal faults:- This is when hanging wall or block moves downward relative to the foot wall. It is caused by tensional or extensional force.
Reverse Faults:- This is when foot wall moves up wards relative to the hanging wall. It is cause by compressional forces.
Strike Slip Fault:- Here the fault plane is vertgical in nature, and is produced where the stresses act parallel to each other.
If the movement is to right it is called dextral fault but if it moves to left it is called sinitral fault.
With respect to the studies area we can appreciate the existence of fault in the following area. About 600m along Afikpo Amasiri, Road there is present of normal fault their and the dip amount has measure to be 51oNW. growth fault was observed in the Ozizza hill.
Why worry spring out crop, there is present of fault resulted by implacement at a hanging wall aquifer. The rock body present (Sst and shale) lies across the fault plane which resulted in the aquifer present their etc.
UNCONFORMITY AND FOLDS
Buried Erosion surface separation two rock masses, older exposed to erosion for long interval of time before deposition of younger if older rocks where deformed and not horizontal at times of subsequent deposition, surface of separation is angular unconformity, but if older rocks remained essentially horizontal during erosion, surface separating them from younger rocks is called disconformity. Unconformity that develops between massive igneous or metamorphic rocks exposed to erosion and other cover by sedimentary rocks is called nonconformity.
With respect to the studies area we saw unconformity on the following out crop angular unconformity was found in out crop between magregor hill and fork junction.
Folds are lands forms found in areas of anticline and synclinal structures.Land forms such as anticlinal mountains and synclinal mountains. Water gaps (which I breaks I the ridges due to water erosion and wind gap (breaks in the ridge but neo water flowing through the gap).
Igneous Activities was observed in presence of a dolerite sill in out crop located about 400m from Amasiri junction.[afikpo amasiri rd] The igneous intrusive rock is of tunonian time and was found in the boundary between the shale of the Eze-aku fm.
The environment was discovered to be a sedimentary environment with basic rock and basic rocks are mostly made of basalt and gabbro the texture of the rock ranges from fine (Basalt) coarse grain (gabbro) it contain plagioclase angite and K-feldspar, also there are present of iron oxides which exists in the form of magnetides and some other minerals that makes up the rocks are the pyroxene and olivine.
The igneous intrusive (dolerite sill) that was observed, was formed by an implacement of the intrusive by the fault plane fracture from the upper mantle. It intruded over 37 km running parallel to the strike plane it occurs as sill or dyke which can be either volcanic or plutonic. The dolerite sill observed with the bedding plane and was a result of uplift and erosion (hyper basal) and the exposure leads to the formation of basalt which is hyperbasal.The sill that was observed where horizontal in its orientation and they are also characterized as concordant intrusive contacts because they are intrusive rock formation in contact with the host or country rock in horizontal plane.
The sill also observe, hand a chilled zone a baked margin.
It is zone from the core to the surface the core is coarser indicating shower cooling while the surface is fine grain indicating faster cooling at the surface.
It is composing of pyroxene (mainly augite) phagiochase (ca-phagiochase such as labrodorite and anorthite, biotite, iron oxide, horrnblende, mica and magnetite.
Various strike of dip amount and dip direction of the out crop was taken.
STRICK DIP AMOUNT DIP DIRECTION
2440 SW 400 1560 SE
2740 NW 410 1820 SE
2220 SW 420 1400 SE
2340 SW 500 1460 SW
2460 SW 500 1600 SE
Hydrogeology is the area of geology that deals with the distribution and movement of ground water in the soil and rocks of the earths crust (commonly in acquifers)-ref-wikipredia.org. The occurrence of ground water in Afikpo and it’s environ is encouraging due to, the presence of aquiferous sandstone as the major rock type and also the present of ozizza beach and ndibe beach.
Generally pattern of water movement by evaporation from sea to atmosphere by precipitation to land and return to sea under influence of gravity causes the ending sequence of ground water occurrence known as hydrogical cycle
Subsurface ground water flow and seepage from stream, lakes, beach, and river like ndibe and ozizza beach are among the major process by which ground water is recharged naturally. Except recharging of ground these beaches (ndibe and ozizza) can be of great important to Afikpo inhabitant
Source of occupation fishing
It is also means of transportation
Source of food to inhabitant of Afikpo (Fish)
For recreation and tourism
The aquiferous sandstone due to its high level of porosity and permeability allows for ground water movement. This movement makes the generating of portable ground water possible.
Uses of ground water
It is use for agriculture (irrigation)
It is exploit for drinking
It is also exploit for industrial purpose
It is also use for domestic needs.
These aquiferous sandstone sometimes are interbedded with other rock like shales which results in eruption of springs. This was observed in almost every Conner of the studied area. Eg. They why worry spring and Ebonyi hotel
Engineering geology can be referred as a major aspect of geology which is concerned with the physical and mechanical properties of natural rocks structural fabrics and defects such as fault, folds foliation and point are international weak uses for rock which may affect the stability of human engineered structure such as dams, road cuts, open pits mine and underground mines or road turnel. Eg. As observed on the valley at the out crop along Afikpo Amasiri road where trace of dolorites were found such rocks are not considered for engineering usage on the Afikpo region due to the following factors.
That the dolorite rocks are made of high temperature minerals such that they are weak for cooling during raods construction. So bitumen is highly favoured for coating at road construction.
The bearing strength of dolorite is very poor in like high bearing strength of quartz weathering easily affects its dolorite (spheriodal weathering) also sandstone that is dominanted in Afikpo has a lot of uses in engineering field, it could be us as a durable material in the construction of road networks in Afikpo and its environs and also in the siting of building and structures due to the high cementing content agents found in them.
Also sedimentary rocks while are good aquifers in Afikpo could be used as sites for drilling boreholes and springs that could go along way in solving the hydro needs of individuals in other area also with the presence of beaches and rivers in the area the sitting of dams and water reservations can also be considered as an option in the generating of power for the Afikpo region. Also due to availability of coal-coal mines could be created due to cater for the industrial and commercial production and generating of electricity as on alternative source of power supply in Afikpo.
Environmental geology is the environmental audit of Afikpo is predominant by sedimentary environment.
It is noticed and discovered that a set of transgressive and regressive events led to the simultaneous deposit of sediment in the area.
There are presence of different rock types, sand stone, mud silt shale coal, pyroclastic rock etc but sandstone is the most predominant.
Afikpo lies in the cross river plain the area lies in the formation know as Ezeaku shale formation of the touranian age.
The result of sedimentation and folding on Afikpo gave rise to two major structural features, the Abakaliki antidinorium and the Afikpo synchiomium the transgression and regression occurs is cenomanian period.
Economic geology is a branch of geology the concerned with the earth material that can be used for economic and or industrial purposes.
Examples of out crop found on Afikpo regions that is of economic importants are coal, sandstone, pyroclastic rock kaoline, quartz.
Coal and its economic important coal is Nigerian’s earliest known fossil fund. It played a more prominent role in the country economic development before the development of crude oil began on 1958. Coal production in Nigeria started as early as 1915.
Economic important: it is used as fuel in rail transportation the major use of coal to day is to generate electricity so the lignite coal could be used to generate 25% of electricity if well harnessed and utilized
Quartz is silica occurring alone in its pure state? The higher temperature forms of silica namely tridymite and cristabalite are rarely found in nature. Silica deposite occur as sand deposits, sand stones, Quartzite and many other less significant forms.
Silica is used on the same way as kaoline as filler except where exreme finess is required. It is used on the paint industry to provide the point good scribbability and film toughness.
It also provides flexural strength to plastics.
GEOLOGICAL HISTORY OF THE STUDY AREA
Benue trough is a tensional feature throughout its entire history, the folding in the trough is seen as a result of differential block faulting in the underlying basement.
The principal supporting evidence being the straight limbs discernible on ERTS imagery of some of fold structures.
The trough is envisaged as being due to a combination down mapping and rift-type faulting of an attenuated silica crust, with sub-silence enhanced as a result of isocratic loading by the sediment filling the trough and over lapping the marginal faults.
The case for a seafloor spreading and sub-duction cycle in the trough are more recent applications of major transcurrent faulting and membrane tectonics to the structural history of the basin. The Benue trough has been wholly ensialic through out its evolution.
The Afar depression remains probably the best present-day analogue of Benue trough; there are several features of the latter that have their counterparts in east Africa and the middle valley of Scotland.
The striking elongated appearance of the valley tends to suggest some kinds of structural control of the sedimentary area and has lead to a number of propositions on it’s origin.
It has been generally accepted that the Benue valley has a kind of rift structure due to major faults along it (carter et al 1963).
A construction by murat (1972) shows the southern part of Benue through is longitudinally faulted, with eastern half subsiding preferentially to becomes Abakaliki depression.
Basin subsidence in southern Benue trough was being a high rate in pre-Albian depositing the Asu-river group. How in hover cenonanin high turonian, which was an important phase of plat form subsidence (ojoli, 1990) this was also believed to be actual initiation of the Anambra basin and Afikpo basin. This process gained momentum. In the Coniacian, deposition of Awgn formation and was at climax during the sentonian thermolutonic event following the sentonian folding and uplift the Abakaliki area become flexurally invented displacing the depocenter to southwest (Afikpo basin) northwest (Anambra basin ans southward. This was believed to the origin of Afikpo basin in south eastern Nigeria.)
Sedimentary Rocks, SandStone – Field Mapping Exercise By Geology And Exploration Geophysics Department
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