Using Palynomorphs (Pollens and Spores) to Biostratigraphic Zonation
Chapter One
AIM AND OBJECTIVES
This study is primarily aimed at using palynomorphs (pollens and spores) in order to achieve the following objectives:
- To establish biostratigraphic zonation
- To determine the relative age of the studied well ( age dating )
- To interpret and reconstruct the depositional environments
CHAPTER TWO
REGIONAL GEOLOGY
GEOLOGICAL SETTINGS OF THE NIGER DELTA
The Niger Delta is located between latitudes 4o00’N and 6o00’N and longitudes 3o00’E and 9o00’E. The Delta is bordered in the in south by the Gulf of Guinea and in the North by older (cretaceous) sediments of the Anambra Basin, Abakiliki uplift and the Afikpo syncline. The Niger Delta is bounded in the East and West respectively by the Dahomey Basin and Cameroon volcanic line (Figure 2.1)
Figure 2.1: Map of Nigeria Showing Niger Delta Province Outline (Modified from Whiteman, 1982 and Turttle et al, 1999).
During the Tertiary, the delta built out at the connection of the South Atlantic Ocean (Burke, 1972; Whiteman, 1982). The constituent clastic sediments are perceived as regressive wedge withall-out spreads depth of about 12 km (12,000 m).
Over the period, the delta plain has prograded southwards trending towards the oceanic crust, progressively developing a convex-to-the-sea-feature (Evamy 1978).The rate of sediment build up and rate of subsidence has been the major developmental factor and balance of the Niger Delta. (Doustand Omatsola, 1990).This observed balance originating from sedimentary patterns were well-ordered by the structural alignment and tectonics of the basement settings (Evamy et al, 1978).
TECTONIC SETTING AND GEOLOGIC EVOLUTION
The tectonic setting and geologic evolution of the Niger Delta is related to the tectonic setting of the lower Benue Trough, which is a mega configuration on whose coastal and ocean ward part lies the Niger Delta. On this wise, the Benue Trough is seen as an intercontinental Cretaceous Basin covering roughly 1000 km in length stretching NE – SW which rest uncomformably upon the Pre-Cambrian Basement (Figure 2.3). It represents a failed arm of a triple junction connected with the opening of the Gulf of Guinea and Equatorial Atlantic in Aptian through Albian time(Weber and Daukoru, 1975).
Much works have been carried-out by many scholars on the geologic development of the Benue Trough and the associated Niger Delta Basin Burke and Whiteman (1973), Short and Stauble (1967), Weber and Daukoru (1975), Reyment (1965), Murat (1970), Merki (1972).
According to Burke and Whiteman (1973), the history of the Niger Delta started after the development of the Benue Trough folded belt and now, the Niger Delta has masked completely the continental structures.
Three major depositional cycles have been identified within the south east Nigeria spanning from Late-early Cretaceous through Cenozoic.
According to Short and Stauble (1967), the first cycle occurred during the middle Cretaceous (Albian) and was terminated by a phase of folding, faulting and uplift occurring in the Santonian time. This led to the uplift of the Benue Trough into the Abakiliki Anticlinorium. While the Anambra basin subsided to the north and the Afikpo to the south giving rise to the Anambra platform and the Afikpo Syncline(Figures 2.5 and 2.6).The second cycle began during Campanian/Maastrichtian with the deposition of Campano-Maastrictian sediments and ended with the development of the proto-Niger delta.
The third cycle of deposition originated in the Eocene and lingers into the present-day. It is at this third cycle that the present Niger Delta was developed, which has remained the focus of hydrocarbon exploration till date.
CHAPTER THREE
METHODOLOGY
MATERIALS AND METHODS
Sample Material and Procedures 15 samples from Akaraja -I well, drilled on the central part of the Niger Delta were studied. The samples varied from silty shale, lignite/carbonaceous shale’s and sandstone. The lithostratigraphic description of the sample within the section are shown in table 4.1. Preparation of the palynologic samples was conducted according to the standard procedure using hydrofluoric acid.
APPARATUS USED;
- Beaker
- Plastic cups
- Sieves (53micros)
- Glass slide
- Cover slip
- Hot plate (electric stove)
- Microscope
- Nylon sieve
- Mortal and pestle
- Sieve holder
REAGENT
- Norland adhesive
- Hydrochloric acid (HCl )
- Hydrofluoric acid ( HF )
- Potassium hydroxide (KOH)
LABORATORY ANALYSIS
Sediments samples are made up of a combination of organic and inorganic materials, and the microfossils that are needed for analysis can only be obtained from the organic materials therefore palynological sample preparation, involves the separation of the organic components from the inorganic components before analysis.
CHAPTER FOUR
RESULTS, DISCUSSION AND INTERPRETATION
LITHOSTRATIGRAPHIC DESCRIPTION:
15 samples were obtained from the study area and their lithological and textural characteristics were derived by the use of hand lens and physical examination.
The lithologic sequence of the studied interval covered a depth range of 6120m to 11,170m. The rock type shale have colour ranging from brownish grey to dark grey, fine grain and well sorted.
CHAPTER FIVE
SUMMARY/CONCLUSIONS
Four dinoflagellate cyst zones (1-4) have been recognized. The dominant species are Spiniferites Pseudofurcatus (zone 1), Multispinula quanta (zone 2), Chytroeisphaeridium, sp. (zone3) and Sumatradinium hispidum (base of zone 4). These zones correspond to the Verrucatosporites usmensis zone (Germeraad et al, 1968).
Combined palynologic, maceral and sedimentological data indicate that deposition occurred close to shore in a marine environment that became progressively shallower up section. This is indicated by: The dominance and abundance of terrestrial plant fragments in all samples; A marked increase in spores up section;
A decrease in the abundance of microplankton, in dinocyst species diversity and in chorate species diversity up section and an increase in the diversity of cavate and proximate dinocysts, in the abundance of reworked palynomorphs in sediment grain size and in sediment grain-size variability up section were observed in the study
REFERENCES
- AMERICAN COMMISSION ON STRATIGRAPHIC NOMENCLATURE 1961.Code of stratigraphic nomenclature. Bull Am. Asspetrol. Geol.,45;645-660.
- BIFFI ,U. and GRIGNANI, D.,1983. Peridiniod dinoflagellate cysts from the Oligocene of the Niger Delta, Nigeria. Micropalaeonto., 29, no. 2, 126-145, p1.1-7
- BROWN, S. and DOWNIE., C.,1984.Dinoflagellate cyst stratigraphy of paleocene to Miocene sediments from the Gabon spur. In initial Reports of the Deep Sea Drilling Project, 80. p. 643-651.
- BUJAK, J.P.,1984 Cenozoic dinoflagellate cyst and acritarchs from the Bering Sea and Northern North Pacific, DSDP leg 19. Micropaleont., 30 (2): 180 –212
- COSTA, L.I AND DOWNIE, C., 1979. Cenozoic dinocyst stratigraphy of sites 403 to 406 (Rockal plateau), IPOD, leg 48 In initial Reports of the Deep Sea Drilling Project, 48. p. 513-529.
- CROSS, A. T THOMPSON, G, G. and ZAITZEFF, J.B., 1966.
- Source and distribution of palynomophs in bottom sediments, southern part of Gulf of Califonia. Marine geology, 4, 467-524, 1p1., 14 figs.
- DOWNIE, C., HUSSAIN, M.A. and WILLIAMS, G.L. 1971 Dinoflagellate cyst and acritarch associations in the paleogene of southeast England. Geoscience and man, 3, 29-34.
- EDWARDS, LE. 1984 Miocene dinocysts from Deep Sea Drilling Projects, leg 81; Rockall plateau , Eastern North atlantic Ocean. In initial Report of the Deep Sea Drilling project, 8.1 p. 581-594.
