Geology, Petrogenesis and Determination of Paleoenvironment of the Sandstone in Offerekpe and Environs

Geology, Petrogenesis and Determination of Paleoenvironment of the Sandstone in Offerekpe and Environs

LOCATION
The study area Oferekpe and its environs are located at Ikwo local government area (Ikwo South East development centre) of Ebonyi State. It lies with the latitude of 60 00’Nto 60 05’N and the longitude 90 12’E to 90 17’E. The study areas are made up of many villages namely; Odomowo, Ochukwu, Ukwuanyim Omege Echara, Ekpa Omaka and Inyimagu.

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Fig. 1: Map of Ebonyi State Indicating the study area .

ACCESSIBILITY
The study area is accessible through roads network from Abakaliki-Ikwo, Abakaliki-Onueke and a division at Nkwagu through the Enyigba-Ikwo road and other minor road include; Odomowo-Ukwuanyim road Ukwuanyim-Ochokwu road.

Figure 2: accessibility map of the study area (Oferekpe).

AIMS AND OBJECTIVES OF STUDY
a. To map and demarcate different lithologic units within the study area.
c. To determine their paleoenvironment through the paleontologic content of the rocks.
d. To determine the economic viability of the map area.

METHODOLOGY
FIELD MAPPING
The mapping started with a review of literature of the area. This was followed by a reconnaissance survey of the area to determine the accessibility and familiarized with the area. Compass and traversing method was adopted in the field mapping. The materials used in mapping are; the base map, magnetic compass, sample bag, hammer, camera and field notebook. A detailed field mapping was undergone during which data were collected, contacts of different structures feature, lithology were identified and delineated samples were collected for analysis.

Sieve Analysis
Grain size (sieve) analysis was carried on the sampled sandstone unit. Fifty grams of the sampled was dried in the sun. The sample was shaken in the nest of U.S. standard sieve in the half Ø interval with an automatic sieve shaker. The sieve operation was conducted by continuous lateral and vertical motion for 15 minutes. The sieves were removed after the other. The sample retained I each sieve was weighed out accurately and recorded. Sieve loss was noted, the percentage and cumulative weight percentage materials retained in each sieve was calculated. Using Folk and Ward (1957).

Shale Washing
Shale samples were collected to determine their micro fossil contact each samples consist of about 0.5 to 1.0 kg of rock material were collected, soaked with white spirit for 24 hours and latter decanted, the decanted samples were re-soaked with de-ionized water for another 24 hours. The disaggregated samples were washed through a 63. micron sieve until all the mud was washed clear.
The washed samples were dried under the sun and taken to the laboratory for viewing under the microscope to locate and pick fossils for naming and for further analysis. Classification of the foraminifera follows the descriptions of Bronninann and others (1992), castelain and others (1962), de klasz et al (1963) Ellis and Messina (1940) Hart et al (1989), Ogbe (1980), and Petters (1979a, 1979b, 1980, 1982)

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GEOMORPHOLOGY
Topography
Oferekpe and its environs are characterized by undulating plain alternating from East- West of the high 200 feet and lowland of 100 feet above the sea level.

Climate and Vegetation
The rainfall within the rainforest belt of Eastern Nigeria has dry months ranging from October to March (Inyang, 1975) the driest month has less than 2-9cm rainfall annually (Ofomata, 1975). The wet months are within April to October and punctuated by few days of dry period in August after which comes a long period of dry season. This corresponds to periods of North-east dry winds (Inyang, 1975). The area has an average temperature of 280, the area lies in the rainforest/savanna vegetation (Igbozurike, 1975). In the rainy season the area is characterized by fill

grasses marshly and swampy terrain. Therefore, the geological mapping done effectively during the dry season between the December and March.

DRAINAGE PATTERN
The main drainage line that tranverse the study area is the Ebonyi River which is located east of the study area. Other area; Echara, Ukwuanyim, Odomowo and Ochokwu, these are tributaries of main river of (Ebonyi River), which link to the cross-river (River). The rivers are conforming to a dendritic pattern, although there is a limit of the trelli’s pattern suggested by a tendency for the drainage lines to be approximately straight.

CHAPTER TWO
LITERATURE REVIEW
Regional Tectonic Setting
The area studied falls with the South part of the Benue trough. The trough is the most important sedimentary domain of Nigeria and several other basins e.g. The Bida Anambra, Niger Delta basins were derived from it. It runs below the Anambra basin in the South, across the country northeastward below the Chad Basin and beyond the Northern border of Nigeria. The area of study is the southern part of the trough referred to the Abakaliki. The trough originated as a failed arm (Aulacogen) during the separation of South America from Africa as the Atlantic Ocean opened at the site of a triple junction (Burke et al., 1971).

The rift system developed by progressive mantle plume upwelling (Olade, 1979). The trough was filled with several depositional cycles which accumulated up to 6,000 meters of fluvial deltaic and marine sediments (Kogbe, 1989). The sediments consist of Albian. Cenomanian and Turonian lithofacies and were affected by the Pre-Santonian tectonic episode which resulted in folding, faulting and fracturing and igneous activity (Benkhelil 1987). Igneous activity related hydrothermal fluids were injected into the fractures to effect mineralization (Uzuakpunwa 1974). (Reyment 1965) described the volcanic rock and provided evidence of their genetic relation of Oferekpe and its environs.

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REGIONAL STRATIGRAPHY
(A). ALBIAN
The Abakaliki region was a major depocentre in the Lower Benue Trough, with accumulation of over 360 meters of marine sediments from Mid-Albian to the Coniacian (Ojoh, 1990). The Albian transgression occurred during the Middle Albian and was characterized by marine conditions, with a shelf environment of deposition for the Asu-River Group and later with the associated volcanic intrusions and pyroclastics. The sediments consist of poorly bedded sandy shales known as Abakaliki shales with less than the sandstone and limestone (Murat, 1972). Lithologically, the Asu-River Group consist of based Arkostic Sandstones, middle marine shales, Calastic limestone and upper regressive limestone. The shaly member are dark grey, fissile and weathered to needle shape bodies while the sandstone member are mostly fine grained friable and whitish to grey coloured (Reyment, 1965).

(B). CENOMANIAN
The Cenomanian was largely a regressive stage in most part of the country. The Benue valley, the Cenomanian regression was characterized by extensive deltaic developments with the continued deposition of Bima Sandstone in the lower Gongola and Upper Benue region (Koghe 1976), Tijani et al; (1976) noted that Cenomanian was characterized by a regressive continental to transitional marine environment, with a high clastic sediment in flux (Kanal Makurdi sandstone), which created a wide coastal plain predominantly to the siltstone with fragment facies changes to sandstone (Reyment 1965), (Nwachukwu, 1972) suggest the absence of Cenomanian deposits in the main Abakaliki basin itself.

(C). TURONIAN
The Eze-aku Formation comprises of hard grey to dark shales and siltstone with fragment facies changes to sandstone or sandy shale they varies in thickness but may attain 1000m in places (Reyment, 1965). The Amasiri Sandstone near Afikpo; Makurdi Sandstone around Makudi Sandstone. Also laterally shale, limestone around Nkalagu area.

(D). CONIACIAN-SANTONIAN
The sediment was assigned to the Awgu Formation (Reyment, 1965). During the Coniacian, beds of rapidly changing lithofacies, including shale, limestone, and increasing amount of sandstone were deposited. The facies changes has been interpreted as being the first indication of the one of the active tectonic phase of folding, faulting and uplifting which ended during the Santonian (Kogbe, 1976). These Santonian movements resulted in the folding and uplifting of the NE string Abakaliki Anticlinorium which is turn or led to exposure and subsequent erosion of the Coniacian, Turonian and Albian Formations (Kogbe, 1976). Awgu Shale was deposited in the basin about 800m thick, also consist well bedded shale bluish grey with intercalations of fine-grained sandstone and often mainly limestones (Nwajide, 1990).

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(E). CAMPANIAN-MASSTRICHTIAN
The Nkporo Shale and its lateral equivalent to the Enugu shale, Asata Shale and the Owelli Sandstone constitute the basal beds of the Campanian-Masstrichtian in the southeastern part of Nigeria. The formation witness a short marine transgression followed by a regression deposited the Mamu Formation (Kogbe, 1976). The Mamu Formation (lower coal measures) of carbonaceous shale, siltstone, coal and sandstone (Simpson, 1955). The formation was overlain by the Ajali Formation followed by a return to partially paralic conditions with the deposition of the Nsukka Formation (Kogbe, 1976).

 

TECTONIC SETTING
The Southern Benue Trough is a segment of the failed arm of a triple junction, which accompanied the rifiting that gave rise to the separation America from Africa, and the opening of South Atlantic Ocean in the cretaceous times (Burke et al., 1971; Fairhead and Okereke, 1987). Sediment thickness in the Southern Benue Trough is estimated to be about 6,500m and this was generated by repetitive transgressive, Regressive sedimentary cycles which however suffered two deformations in the Cenomanian and Santonian along NE-SW axis. These deformations produced multiple folds and fractures parallel to the fold axis (Ofoegbu, 1985; Nwachukwu, 1972), and Santonian deformation in particular produced the Abakaliki Anticlinorium with two synclinal basins (Anambra Basin and Afikpo syncline) on its main depocentres of the post deformation era. The deformation generate magnetic activities in the Asu River Group and Eze-Aku Formation (Okereke et al., 1988, Hoque, 1984), and the link between the deformation and magmatism is apparent in the emplacement of the igneous rocks in Southern Benue Trough along well-developed and steep anticlines (Ofoegbu, 1985). The Post Abian to Pre-Turonian deformational episode, which resulted to the restriction of Cenomanian to the Calabar flank, greater intensity of folding of the Albian sediments, and the distribution of lead-zinc mineralization (Nwachukwu, 1972).

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To Place An Order For The Complete Project Material Pay N,5000 To

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Then Send a text of your names, the topic you paid for, a valid email address to 07036785443

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