CHAPTER ONE
INTRODUCTION
1.1 Background Information
Benin formation is identified within the Niger delta, it consists of 99.8% thick accumulation of massive, loose, friable sandstone and 0.2% mud rock. It also consists of pebble imbrications and conglomeratic horizons. Petrographic studies revealed quartz as the dominant mineral (97%) which places the sandstone as quartz arenite. Other minerals include feldspar, limonite, zircon, opaque and minor clay matrix consisting 3%.Mudstone are fine grained siliciclastic sedimentary rock composed predominantly of silt size (0.062-0.004mm) and clay sized (0.004mm) particle (prothero & schwab, 1996).when more than 50% of the constitute are siltstone can be used, whereas if more than 50% of the particle are clay-sized the term clay stone is more applicable. In both cases individual grain size are too small to distinguish without a microscope. If any rock fragment are present with quartz and feldspar being the predominant once. Similarly a sedimentary rock comprising more 50% either silt or clay-sized transport carbonate grain is referred to as calcilutile
Geochemical data of fine-grained clastic sedimentary rocks, such as shale and siltstone have been used to evaluate the nature of the parent rock and intensity of weathering, s well as to identify the tectonic setting of the source region (Bhatia,1983;Taylor and Mclennan,1985;Bhatia and Crook,Mclennan,1989,Feng and Kerrich, 1990; Mclennan and Taylor,1991;Cullers,1994; Hemming et al.,1995; John and Condie,1995; Girty et al.,1996; Etemad-saeed et al.; 2011; Verma and Armstrong-Altrin,2013; Armstrong-Altrin.,2015; Tawfik et al.,2015).(reff i work2) The major element composition of the siliclastics rocks is clearly influenced by the intensity of hydrothermal altaeration. Given the fact that the main alteration minerals recognized in altered mudstone samples are alunites,goethite,pyrite,quartz and clay minerals such as mineral as koalinite, phyrophillite and illite, alteration-induced major element variation are likely to primary involve the element AL203, K2O, FEO,SIO2.
These geochemical species represent a complex function of variable that comprises of source material, weathering, physical sorting and diagenesis (Nagaraja et al 2007;Madhavaraju 2015). Mudstone commonly account for average crustal composition of a source area more than any sedimentary rock and this provides important information on regional tectonic setting, provenance, weathering condition.(Cullers 1995;Melennan et al 2013;Spalleti et al 2012) Numerous investigation has demonstrated that the chemical and mineralogical composition of clastic sedimentary rock is controlled by the composition of source rocks, environmental parameter influencing the weathering of the source rock (atmospheric chemistry , temperature ,rainfall and topography).duration of weathering ,transportation mechanisms of clastic materials from the source area of the site of deposition, deposition environments (marine versus fresh water), and post deposition process (diagensis and hydrothermal alteration). A good knowledge and understanding of the chemical and mineralogical constituent of these siliciclastic sedimentary rocks can prove a useful tool in determining geological activities, processes and conditions that prevailed at the time of deposition of such sediment, which is the sole aim and objective of this research work. On the basic mean crustal abundance, geological elements are classified as major, minor and trace elements based on their percentage composition by mass in rock. some researcher noted that major element geochemistry of sedimentary rocks is more important in discriminating tectonic setting(10-11 from material); however trace elements are more useful in discrimination tectonic evolution of rocks and the provenance of clastic materials(12). Gritty et al (13) attribute this is low mobility during sedimentary depositional processes.
Although major oxide has been proven useful in the study of provenance and depositional setting, immobile trace element have been proven to be more useful in the study of provenance and depositional setting than major element (Bhatia and Crook 1986). it is also on this basic that the present work is aimed carrying out geochemical analysis of major and trace elements of mudstone within the Benin formation Southern Nigeria, implication for provenance, weathering, paleoclimate and weather, transport history as well as paleo-environment of deposition.
1.3 AIM AND OBJECTIVES
The study is aim to reconstructing and determines the provenance and paleo-depostional environment of mudstone accessed in the study area
The objectives are as follows.
To determine the mineralogical maturity of the present day.
To geochemically classify the mudstone of the present day.
To determine the transport history of the mudstone
To infer provenance and tectonic setting of mudstone within the study area.
Mapping of outcrops and collection of sample from the study area.
1.4 SCOPE OF STUDY
This research work dwell entirely on mapping and collection of mudstone sample exposed at Abak,Etinan,Nsit Ibom for chemical analysis and used the outcome result to determine mineralogical maturity, transport history, classification, provenance and tectonic setting of the mudstone.
1.5 GEOMORPHOLOGY AND PHYSIOGRAPHY
The geomorphology and physiograhy of the study area are influenced by the following
1.6 CLIMATE AND VEGETATION
The region has mangrove vegetation which consists basically of shrubs, trees and grasses. The study area is generally dominated by farmlands and forest with hot and humid climatic conditions that are controlled by two seasons, Wet (march-October) and dry (November-April). Annual precipitation is usually over 2,200mm, while annual temperature range between 230c and 320c.average relative humidity for the area is about 88%.
1.6.1 RELIEF AND DRAINAGE
The relief of an area is an indication of its topographic height relative to mean sea level. The relief of an area depends on the nature of the rocks. The type of erosion at work, the length of time which this erosion has been taking place and the vegetation of the area. Over 75% of Akwa Ibom state consists of level to gently undulating sandy plains. the drainage network in the upland part of Akwa Ibom State is not dense, as river are few and wide part. The state is drained by the Cross River on the east, Imo River on the south west, and Qua Ibom River in the south central parts. These Rivers flow from the northern highlands of the state and drain into the Atlantic Ocean in the south. Qua Iboe River is the only major river that traverses the entire state from north to south.
