1.0 Introduction
1.1 Background of Study
Sandstones are sedimentary rocks formed by the cementation of sediment by material cements and they show a great deal of variation in mineral composition, degree of sorting and roundness and they possess quality reservoir characteristics and mineralogy. Sedimentological studies help to determine sediment characteristics of the rocks (sorting, sedimentary structures, grain size, shape, lithology, porosity, texture, maturity etc.). Similarly, petrographic studies are very useful in understanding and interpreting the mineralogical (petrographic) details of rocks - their composition, abundance, and morphology among others. Together, sedimentology and petrography are widely used in the reconstruction of the geological history of rocks - their distances from provenance, paleo environmental and conditions of formation and/or deformation, diagenetic processes acting on rocks, tectonic history as well as the stratigraphy.
The need to combine sedimentological and petrographic analyses for paleo environmental analyses is borne out of the fact that relying on textural analysis alone may result in gross interpretational errors, especially if diagenetic or disaggregation processes have significantly altered textural properties of such sediments (Wilson and Pittman, 1979).
The sedimentological investigation of some outcropping sediment in southern Bida basin and its environs employed the field mapping and the laboratory studies approach of the sediments sampled and it was used in deducing the porosity and permeability of the outcropping sediments in the study area.
This study involves the determination of the lithology, mineralogy and textural characteristics of the sandstone facies in order to predict the reservoir quality of the sandstone using Sedimentological and petrographic data as obtained from field evidence of some outcropping sediment of southern Bida basin and its environs.
1.2 Aim and Objectives of Study
The aim of the study is to investigate the Sedimentological and petrographic attributes of outcropping sediments in Lokoja and its environs. In achieving this aim, the following specific objectives were laid out as follows:
- To determine the lithofacies characteristics of the sediments of the study area;
- To ascertain the mineralogical composition of the sediments;
- To determine the paleodepositional environment in which the sediments where formed using available sedimentological and petrographic data sets; and
- To characterize the reservoir properties of the sediments by inferring the porosity and quantitatively determine the permeability.
- To investigate the reservoir sedimentological quality (facies, grain size, thickness) of sandstone samples.
1.3 Significance of Study
Sedimentological studies help to determine sediment characteristics of the rocks (sorting, sedimentary structures, grain size, shape, lithology, porosity, texture, maturity etc.). Similarly, petrographic studies are very useful in understanding and interpreting the mineralogical (petrographic) details of rocks - their composition, abundance, and morphology among others. This study will be of immense benefit to Geologist and other researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.
1.4 Scope of Study
The study focuses on the Sedimentology and Reservoir Quality of Outcropping Sediments using the southern Bida basin in Lokoja, Lagos State as a case study.
1.5 Limitations of the Study
During the course of this study, many things militated against its completion, some of which are:
- Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
- Research material: availability of research material is a major setback to the scope of the study.
- Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
- Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).
1.6 Location and Accessibility
The study area is located in Kogi State. It is bounded by latitudes 070 30' N - 080 30' N and longitude 006000'E- 0070 00' E. The area visited include outcrops on road cuts along the Lokoja-Abuja Express Road and include; Filele and Mount Patti.
The study area was accessible by main roads and footpaths. The main is the Lokoja-Abuja express road (Ojo, 2009).
Figure 1: Geologic map of Southern Bida basin showing (Ojo, 2009)
1.7 Relief and Drainage
The River Niger is present in the study area as the main hydrological element. The Niger River runs in an ESE direction in the southern marginal area/part of the basin. Its floodplain is broad and locally up to 20km wide and marked in most areas by a series of elongated ponds running parallel to the river channel. The main tributaries of the River Niger are River Kaduna (wuya) and Gurara which drain the Northern Nigeria Basement Complex.
The area of study has various elevations above sea level as recorded by GPS and shown below:
Filele (169m), Mount Patti (255m) and Agbaja plateau (407m). (the diagram is shown in the complete material which you will get before the end of this article)
1.8 Climate and Vegetation
The study area has an average maximum temperature of 33.20C and an average minimum temperature of 22.80C. It is generally hot throughout the year with an average relative humidity of 68-70 percent. The study area has two distinct weathers, dry and wet seasons. The dry season occurs between November and February while the rainy season is between March and October.
The vegetation type in the study area is Guinea savanna or parkland savanna with tall grasses interspersed shrubs and some trees. The shrubs shed their leaves during the dry seasons in order to withstand some amount of drought. Apart from shedding of leaves, some shrubs have stems with thick bark, thick leaves etc. as adaptive features by the trees or shrubs in low rainfall regions to check excessive transpiration
1.9 Settlement and Land Use
The study area is the headquarters of Kogi state with various settlements ranging from mainly urban to rural. Main towns in the study area include Ahoko, Kotonkarfi, Idu and Ozi. The main occupation of the residents is Agriculture. Trade and other cottage industries are also common in the area.
