Geology and Hydrochemical Characteristics of Surface Water in Okpo-ihechiowa Arochukwu

Geology and Hydrochemical Characteristics of Surface Water in Okpo-ihechiowa Arochukwu

The major source of water for all purpose in life is surface water, which has grossly become inadequate because of rapidly increasing demand for water due to urbanization. Prospecting for steady and reliable water supply from subsurface or ground water will rescue the nation from acute shortage of water. The quality of water is determined by its physical, chemical and biological characteristics.

Surface water (Rivers, Springs and Streams) which serve as source water for the people of Ihechiowa both for domestic purpose and agricultural usage. However, the urbanization process threatens the surface water quality because of the impact of domestic and industrial waste disposal.

This results in aquifer deterioration, since some of these waste products, including sewage and cesspool may be discharged directly into the water system. Water soluble wastes and other materials that are dumped, spilled or stored on the surface of the land or in sewage disposal pits can be dissolved by precipitation, irrigation waters or liquid wastes and eventually seep through the soil in the unsaturated zone to disturb the water (Wallis et al., 1998). Once contaminated, it is difficult, if not impossible, for the water quality to be restored.

The present day study was therefore undertaken to access the relative safety of the surface water, for this purpose by examining the geology and hydrochemical properties of the surface water in the study area.

1. The study area is Okpo Ihechiowa Arochukwu Local Government Area of Abia State
2. It lies within Latitude 05¬¬¬¬025iN and 5030iN and Longitude 7051iE and 7056iE. The entire mapped area covers approximately 68km2. The outcrops are not accessible by the road

The aim of this research work is to determine the geology and hydrochemical characteristics of surface water in Okpo-Ihechiowa, Arochukwu Local Government Area of Abia State, South Eastern Nigeria. To achieve this, the following objectives have been stated.

To demarcate the lithologic units of the study area as well as carry out a detailed description and interpretation of the rock types encountered.

This work is also aimed at conducting a hydrogeochemical investigation to evaluate the Chemical constituent of surface water resources of the area. Heavy metals will be investigated. This will help to evaluate potential pollution/contamination in these areas.

Charts and graphs will be plotted and drawn to show vivid explanations of results obtained.

The economic mineral potentials and land use significance of the different rock types or minerals are highlighted.


Climate and Vegetation
There are two seasons in the year, namely: the rainy season and the dry season. The rainy season begins in March and ends in October with a break in August usually referred to as the “little dry season.” The dry season which lasts for four months begins in November. Heavy thunderstorms are characteristic of the onset of the rainy season. The total rainfall decreases from 2200mm in the south to 1900mm in the north (Todd, 1980). The hottest months are January to March when the mean temperature is above 27°C. The relative humidity is usually high throughout the year, reaching a maximum during the rainy season when values above ninety per cent are recorded (Pipkin, 1994).

Relief and Drainage Pattern
The study area has a variety of land forms, despite the fact that it is dominated by flat and low-lying land, generally less than 120m above sea-level. The low-lying plain is the inland extension of the coastal plain from the Bight of Benin. The central part of the state is characterised by undulating land with many hills. The highland areas are part of the Enugu – Nsukka – Okigwe cuesta. This area has an average height of between 120m and 180m above sea-level. From Okigwe (Imo State), this escarpment extends in a west-east direction and, on getting to Afikpo (Ebonyi State), veers south-eastwards to Arochukwu where it terminates. There are nine main geological formations from south to north.

These include: The Benin Formation (or Coastal Plain Sand), the Bende-Ameki Group, the Nkporo Shale Group, the Nsukka formation (Upper Coal Measures), the Ijali sandstone (False- bedded Sandstone), the Eze-Azu Shale Group and the Asu River Group. The principal rivers in Abia State are the Imo River and its tributary, the Aba River. Imo River originates from the North-western part of the state and flows southwest through Abia and Imo state territories towards the Atlantic Ocean, passing through the southern parts of Ukwa-West and Ukwa-East local government areas. Other important rivers include lgwu, Azurnini Blue River and Kwa lbo River.

Arochukwu and environs falls within the south-eastern part of the Anambra basin. The south-eastern part of the Anambra basin is part of the scarp lands of south-eastern Nigeria. The north-south trending of Enugu escarpment forms the major watershed between the lower Niger drainage system to the west, and the Cross-River and Imo drainage systems to the east (Ibe et al., 1998). It is an asymmetrical ridge stretching in a sigmoid curve for over 500 km from Idah on the river Niger to Arochukwu on the Cross-River.

The geology of Arochukwu local government area falls within the Deltaie marine sediment of Cretaceous to recent age. There are essentially three principal geological formations in the area namely: the Ajali (false bedded sandstones) Formation, Bende-Ameki Formation and the Asata Nkporo shale Formation. The Ajali Formation of Cretaceous age consists of red earth sands which form the false bedded sandstones. These in turn consist of great thickness of friable but poorly sorted sandstones.
The formation spans through narrow country in Abia state from Isuochi north in Isuikwuato local government area, through Eluama, Ovim and Alayi where it narrows down to south of Nguzu before running south. It is overlain by Bende-Ameki formation.

The Bende- Ameki formation of Eocene to Oligocene age consist of medium to coarse-grained white sandstones which contain pebbles, gray-green sandstones, bluish calcareous sit with mottled clays and thin limestone. Indeed, there is a considerable lateral variation in lithology in the area. The Asata-Nkporo shale in north of Uturu in Abia State stretches laterally up the Agwu sandstones. In east of Uturu, the shale increases in thickness and have their greatest development along eastern limb of the anticlinorium where Nkporo village is located. The formation consists mainly of blue or dark grey shale mudstones with occasionally sunstones. The main water-bearing geological formation in the area is the late Maastrichitan Ajali Formation (Hoque and Ezepue, 1977; Ibe et al., 1998).

The formation consists of a quartz arenite, loose angular to sub-bounded grains. The grain size of the area has a multi-model distribution (Ibe et al., 1998). The Ajali is underlain by a shaly rock unit, which belongs to the Mamu formation. The shaly unit of the Nsukka formation overlies it. The Ajali formation is a confined aquifer in most locations in the area. The Ajali formation is very permeable. The groundwater flows from the recharge areas in the east and northeast to southwest below the younger formations over which artesian conditions develop (Offodile, 1992). At locations where artesian condition develops, springs usually occur. Prominent among such springs include Muri and Obayi River.

The Ajali Sandstone in the area has two distinct units. These are the quartz-rich lower unit and the overlying iron-rich variety. The lower unit is cream-colored, passingthrough an iron-stained sandstone to the iron oxide cemented sandstone that contains glauconite. The ironstone unit underlies the foraminiferal limestone that distinguishes the Nsukka Formation in Ohafia area from the type locality where coal seams are recorded, (Reyment, 1965). However, no such coal seams were recorded in the study area. There is thus a prominent facies change from north to south in late Cretaceous sediments in eastern Nigeria, (Ibe, 1999).

The Stratigraphic history of the region is characterized by the three sedimentary phases (Murat, 1972) during which the axis of the sedimentary basin lifted, these three phases were.

• Abakaliki-Benue phase (aptian-santonian)
• The Anambra-Benin phase ( Campanian-mid Eocene)
• The Niger-delta phase (late Eocene – paleocene)

Our main concern is on the first phase, there more than 300 meters of rock comprising the Asu River Group depositing sediments made up of shale, limestone and fine grained sandstone are found within the shale in Abakaliki and its environs. The Ezeaku formation and Awgu formation, the Benue valley and Calabar flank, the Ezeaku sediments comprises of shale, limestone ( Nkalagu), and sandstones ( Amasiri and Makurdi sandstone)

Asu River Group
This is a sequence of marine shales occupying the core of the Abakaliki Anticlinorium. It has a thickness of about 6000ft, embedded with shale and micaceous sandstone and the shales are deeply weathered and contain radiolarian echinoids, pelecypods and gastropods. The Age is Albian.
Eze-Aku Shale Group
The Eze Aku Shale group consists of hard grey to black shale having thick flaggy calcareous and non-calcaroeus shale. The Eze-Aku Formation represents a shallow water deposit. The fossils consist of mainly pelecypods, gastropods, echinoids, e.t.c which indicate basal Turonian age.

Agwu Shale
The Agwu Shale overlies the Eze Aku shale conformably and is between Agwu and Ndeaboh in Southern eastern Nigeria. The lithology is bluish-grey well-bedded shale interbedded with fine yellow calcareous sandstone and shaly limestone with a total thickness of 900m, the strata are greatly folded and contain oil seeps.

Nkporo/Enugu shale and Owelli sandstone
Nkporo shale of Late Campanian age is the basal facies of the late Cretaceous sedimentary cycle in the Anambra basin. Exposures are poor, bearing coarsening upward deltaic sequences of shale interbedded with sands. This interpretation is supported by the vertical association of distributary channel sands (basal Mamu Formation) and the lateral equivalents of lower flood plain carbonaceous shales (Enugu shales) towards the central and northern parts of the basin. The lithology of Enugu shales consists mainly of carbonaceous shales and coals within the upper half deposited in lower flood plain and swampy environments.

The sediments are normally associated with siderites and pyrites which are early diagenetic minerals. The Owelli sandstone is the major sand member of the Enugu shale formation and forms and elongate shoestring sand body elongated to the NE defining a meander belt of a fluvial/distributary channel system. Sedimentary structures of the channel sand exposed at the junction, for instance demonstrates possible tidal processes coupled with a few gastropod shells recovered, suggesting marine incursions into these distributary channel systems.

Mamu Formation
The Mamu Formation overlies the upper Campanian lateral facies associations described above. The age ranges from lower to middle Maastrichtian from south to north. Both vertical and lateral facies changes are observed, formation thickness ranges from 100m to 1000m across the basin and lithology includes shales and sandstones, with some limestones in the south and coal seams in the central to upper parts of the basin. Depositional environments include distributary/estuarine channels, barrier foot, swamp and tidal flats,

The Ajali Sandstones
The Ajali sandstone consists of mineralogically much matured, medium to coarse grained, moderately well sorted quartz grains, and intercalations of thin laterally extensive clay beds of normally less than 1m also occur. The formation thickness is about 300m extending across the entire basin and into the middle Niger Basin and slightly diachronous, ranging from Middle to Late Maastrichtian from south to north.

Nsukka Formation
The Nsukka Formation (Upper Coal Measure) lies conformably on the Ajali Sanstone. It occurs from the north of Awka to the Upper Ankpa sub-basin, with lithology of mainly shales, siltstones, sands and coals and lateritic cover. Age of the formation is from upper Masstrichtian to Danian, and depositional environment is similar in many respects to the Mamu Formation (lower coal measures), consisting of transitional/shoreline, mudflats and swamps, deposited during a largely regressive phase of sea level changes.

The history of the tectonic setting of the Benue Trough has also created a lot of controversies and debate among researchers, while Reyment (1965), Kogbe (1989) also believed the splitting of the South American and African plate during the lower cretaceous. Nwachukwu (1972), he believed that the Benue Trough itself is a part of the very expensive west and central African rift system in which it opened up as an extensive sinistral wrench complex. A reconstruct by Murat (1972) shows the southern part of Benue Trough as longitudinally faulted with eastern half subsiding preferentially to become the Abakaliki depression, an important depocentre relative to the west which remained stable and received only veneer sediments. As a result of the Santonian thermo-tectonic event, resulting in the folding and uplifting of the Abakaliki axis, it was flexturally inverted displacing the depocentre to the southwest, northwest and southward creating the Anambra and Afikpo basin.

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