ABSTRACT

The field work was carried out at two different locations namely: Kompina and Kombe which are sedimentary terrains within the Douala basin and are part of the N’kapa formation.

They were accessible roads, foot paths, and bush tracks leading to the different outcrops at Kompina and they were other physical geographic features like vegetation, relief, soil, topography, and climate.

Also a geophysical method called Lithologging was used in the  field at arrival on each outcrop and a laboratory method known as granulometric analysis was used to analyse 6 samples mainly sandstones and also pebble morphometric analysis was also carried out in the laboratory using a total of 60 pebbles.

Furthermore, the outcrops were comprised with different sedimentary rock types namely; limestones, sandstones, and mudstones but with different lithologies.

Sandstones in the area are characterized by a range of texture from fine to medium and to coarse grained and some of which contained pebbles and some had sedimentary structures like porosity and some were very rich in iron that is ferrugineous sandstones.

The marl which is a type of limestone that contain terrigenous materials characterized by a fine grained texture, mainly made up of mould, cast and phosphate noddules.

The rest of the limestones in the area are characterized within the range from medium to fine grained texture and some of which contained high fossil population, others low and trace fossils.

Shales in the area are characterized by a clayey texture and showed fissility and some also contained fossils.

From the various sieve analysis plots most of the samples were well sorted and also from the pebble morphometric plots indicates that most of them were deposited by river process and fluvial process.

CHAPTER ONE

GENERAL INTRODUCTION

1.0 BACKGROUND

Cameroon’s geologic history dates back to the Archaean era between 3.5 and 2.5 billion years ago (Dumort, 1968). Its development is characterized by three orogenic cycles that resulted in the formation of the Ntem complex during the Archaean (2.5 billion years old), the Nyong which dates from the Proterozoic (2.5–1.8 billion years old) and the Pan African cycle composed of Formations from the Neoproterozoic era (1–600 Ma; Dumort, 1968).

The geology of Cameroon is further subdivided into five geotectonic units (Vicat, 1998) that comprise the Craton (south from Congo) made up mostly of metamorphic rocks (gneiss, charnokites, granodiorites);

the craton cover (eastern part of Cameroon) made up of sandstones, arkoses, shales and pillow lavas and the Pan African chain (which covers the majority of the country) compose of metamorphic and volcanic rocks. Two main periods characterize the history of Cameroon geology:

• Palaeozoic (northern part of Cameroon) characterized by volcano-detrital deposits overlying the PanAfrican.
• The Cretaceous composed of Flavio-lacustrine deposits and the coastal sedimentary Basins (Vicat, 1998; Kwankam et al.,2016).

The sedimentary basins in Cameroon are both coastal and continental and they include the following; the Douala/Kribi-Campo basin which is in its turn subdivided into two sub-basins: the Kribi-Campo sub-basin in the south and the Douala sub-basin which is the northern component, the Mamfe basin, Garoua basin, Benue basin, Tchad basin, Mbere/ Djerem basin, Rio Del Rey basin.

The two major basins are the Douala-Kribi/Campo basin and the Rio Del Rey basin which are coastal basins (Figure 1).

In the study area (Kompina), the major sediment outcrop belt of the N’kapa Formation is along River Bongoue and its tributaries. The nature of the rocks, fossil diversity and content have been analysed in N’kapa formation in order to infer sedimentary depositional environments. Few existing studies have focused on surface sediments in the N’kapa Formation within the Douala Basin (Loule et al., 1997; Agyingi et al., 2006a, b).

Following the previous studies carryout in N’kapa formation within the Douala basin by authors such as (F. N. Kwankam et al., 2016), this field work was aim at contributing to the lithology and distribution of different rock types using litho logging technique and coming up with geologic map.

To this effect, field study was carry out by the final year students (level 400) of the Department of Geology, University of Buea on the course title Field Geology Mapping Project under the supervision of Dr. Tiabou Feudjio Anicet. This field mapping exercise was carried out at Kompina and its environs from Sunday17^th March to Saturday 22^nd March 2019.

1.1 OBJECTIVES STUDY

1.1.1 Main Objective

The main objective of this course is the field geological mapping of Kompina.

1.1.2 Specific Objectives

• To locate outcrops and identify various rock types and logging the different rock types and theirdistribution.
• To study the stratigraphy, lithologic and structures characteristics of the formations.