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European Journal of Applied Sciences – Vol. 11, No. 2

Publication Date: April 25, 2023

DOI:10.14738/aivp.112.14365.

Chiazor, F. I., & Ideozu, R. U. (2023). Sedimentology and Mineralogy of Sedimentary Sequences in Nanim Field in the Niger Delta

basin, Nigeria. European Journal of Applied Sciences, Vol - 11(2). 498-508.

Services for Science and Education – United Kingdom

Sedimentology and Mineralogy of Sedimentary Sequences in

Nanim Field in the Niger Delta basin, Nigeria.

Fortune I. Chiazor

Geology Department, University of Port Harcourt

Richmond U. Ideozu

Geology Department, University of Port Harcourt

ABSTRACT

A total of nineteen ditch cuttings from the sedimentary sequence of Nanim Field,

were subjected to both sedimentological and mineralogical analysis with the aim of

investigating the mineralogical composition of the studied section (1810 m -

2650m) in the study area. The shale samples were grinded, pulverized and sieved

with less than 75μm and analyzed using X-ray diffraction techniques (XRD) for

mineralogical composition. Results of the sedimentological analysis, suggests four

lithofacies made up of sandstone, shaly sand, shale and sandy shale in he studied

section. The studied section has been interpreted as a shallow marine environment

divided into two broad lithofacies sequences made up of beach sand (1810 m - 2290

m.) and upper shoreface (2300 m – 2650m) respectively. The beach sand sequences

comprise thick sands, brownish, grey to black, fine to coarse grained, whereas the

upper shoreface sequence is essentially a heterogeneous sequence of alternating

sand medium to very fine-grained sand and shale - grey. Results from the XRD

analysis shows that the mineralogical composition of the basal part (upper

shoreface) of the studied section is characterized by kaolinite a dominant in

sediments of fluviatile environments and is known to concentrate in many near- shore sediments (shallow marine) with a decrease in abundance from the shoreline

as other clay minerals increase basin ward.

Keywords: mineralogical composition, sedimentological analysis, Sedimentary Sequence

and lithofacies

INTRODUCTION

Shales are fine-grained laminated or fissile clastic sedimentary rocks with predominance of silt

and clay as the detrital components (Krumbein and Sloss, 1963). They make up at least 65

percent of earth’s sedimentary rocks (Ehlers and Blatt, 1982). They are found in major

depositional basins throughout geologic history and are formed from the weathering of igneous

rocks. Shales are major source beds for hydrocarbons, and host for metallic minerals. Shales

have definite chemical and mineralogical compositions. Their properties are controlled by the

parent rock and depositional environment. Bogg(1995) used texture, mineralogical

composition, cementing materials, depositional environment, organic matter content and

strength to classify shales. Shales that contain fine grained silt and clay particles are classified

as silty shale and clay shale depending on whether clays or silts dorminate the constituents of

the rock. Shales that contain some amounts of sands can be referred to as sandy shale. They can

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Chiazor, F. I., & Ideozu, R. U. (2023). Sedimentology and Mineralogy of Sedimentary Sequences in Nanim Field in the Niger Delta basin, Nigeria.

European Journal of Applied Sciences, Vol - 11(2). 498-508.

URL: http://dx.doi.org/10.14738/aivp.112.14365.

also be classified mineralogically as quarrtzose, feldspathic or micaceous shale depending on

the predominance of the mineral’s quartz, feldspar or mica respectively. Several scholars have

used mineralogical and bulk chemical composition of clastic sedimentary rocks to determine

provenance, evaluate paleoclimates and tectonic setting (Adebayo et.al, 2016; Akinyemi et al.,

2014; Mohammed et al., 2022; Tobia et al., 2016). The paper was therefore aimed at using both

sedimentological and mineralogical analysis to investigate the mineralogical composition of

selected shale deposits in Nanin field within the Niger Delta basin.

GEOLOGY AND LOCATION OF THE STUDY AREA

The study area is Nanim Field is located Offshore Niger Delta, Nigeria (Figure 1) within the Gulf

of Guinea on the West Coast of Africa.

Figure 1: Location of the Study Area

The Niger Delta basin is located within the southern part of Nigeria bordering the Atlantic

Ocean. Its formation is linked to the failed arm of the rift triple junction that became the trough

which formed the center for sedimentary accumulation, after the separation of South America

from the African plate and the opening up of the South Atlantic Ocean in the Cretaceous times.

When rifting stopped in the late Cretaceous, gravity slumping became the primary

deformational mechanism that gave rise to several stages in tectonic and stratigraphic

developments in the Niger Delta (Wright, 1976)

The Tertiary Niger Delta is divided into three formations namely; Akata Formation, Agbada

Formation and Benin Formation, representing prograding depositional facies that are

distinguished mostly on the basis of sand-shale ratios. The type units of these formations are

described in Short and Stauble (1967)

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European Journal of Applied Sciences (EJAS) Vol. 11, Issue 2, April-2023

RESULTS AND DISCUSSIONS

The results of this work are presented in Table 1 and Figures 2 – 11.

Sedimentological Analysis

The results from the sedimentological analysis (Figure 2) of Nanim Field showed that the

lithology ranged from sandstone, shaly-sand, and sandy-shale to shale. The studied sections

were divided into two broad lithofacies sequences made up of Shallow Marine sequences

interpreted as beach sands (1810 m - 2290 m.) and Upper shoreface (2300 m – 2650m)

respectively. The Beach sand sequence comprises thick sands, brownish, grey to black, fine to

coarse grained whereas the upper shoreface sequence (2300 m – 2650 m.) is essentially a

heterogeneous sequence of alternating sand and shale components, the shale is grey and fissile.

Mineralogical Composition

The results from mineralogical studies using X-ray diffraction (XRD) analysis for bulk mineral

composition of the selected shale samples from Nanim Field Offshore Niger Delta is presented

in Table 1 and Figs. 3 to11, The results revealed the following minerals: quartz, kaolinite pyrite,

brookite, goethite, spinel, nacrite, sylvine, ileminite, crystobalite, augite, brucite, aluminite, k- feldspar, chloropatite, carnollite, dolomite, magenitite, rutile, fluorite, corundum, erionite,

halite, pigeonite, periclase, siderite, gypsum, dawsonite, halloysite, stillimanite, topaz, calcite,

talc, anhydrite, goethite, sylvite, uraninite, vaterite, crystobalite, natrolite, graphite, plagioclase,

serpentine, lime, albite, microcline, and others. The XRD patterns of all whole-rock samples

(Figs. 3to10), which were obtained following the method of Brown and Brindley (1984),

indicate the predominating presence of kaolinite peaks, accessory minerals included

microcline, quartz. Iron mineral peak was observed in all the samples, indicating their

incorporation in the clay minerals. Identification of secondary minerals was difficult, because

their peaks tended to be obscured by the greater peaks of the major mineral’s kaolinite and

quartz. However, there are differences in bulk mineral compositions between the individual

sediments (Table 1). All samples are, therefore, rich in kaolinite and quartz with exception to

Sample 2 and Sample 3 with no content of clay minerals and Sample 4 has traces of halloysite

(Table 1). Kaolinite is believed to form by weathering or hydrothermal alteration of

aluminosilicate minerals. Thus, rocks rich in feldspar commonly weather to kaolinite.

Halloysite, which consists of poorly ordered arrangement of kaolinite-like units, with variable

amounts of water between the layers, generally between 0.6 to 4H2O per formula unit, and often

with a tabular form. Kaolinites are indicators for its detrital origin in continental sediments

(Kassim, 2006). Furthermore, kaolinite is dominant in sediments of fluviatile environments

(Weaver, 1960). Kaolinite is known to concentrate in many near-shore sediments and to

decrease in abundance with distance from the shoreline as other clay minerals increase

(Parham, 1966). Increased kaolinite contents in marine sediments may have resulted from

increased runoff, which could be caused by sea level falls, or from increased rainfall (Robert et

al, 1994). Berner et al (1996) in their study established that kaolinite is formed under a good

drainage system where the water travel-distance was much greater, less rapid flushing of

sediments and less removal of silica. Hematite is the oxidation products of weathering of

ferrous minerals and constitutes a major source of detrital iron in sediments. During diagenesis

limonite may be dehydrated to hematite. For this to take place, the original sediment would

have to be relatively free from decomposable organic matter such that a high

oxidation/reduction potential (Eh) may be maintained to stabilize hematite. Since, organic