CHAPTER ONE
1.0 GENERAL INTRODUCTION
Niger delta is one of the sedimentary basins in Nigeria. It is a pericratonic basin found at the margin of craton and therefore regarded as open ended basin. The inception of the delta started in the early cretaceous time and since that period, it has been the scene of at least three depositional cycles (Evamy, et al. 1978) The development of the delta has been dependent on the balance between the rate of sedimentation and the rate of subsidence. This balance and the resulting sedimentary pattern appear to have been influenced by the structural configuration and tectonics of the basement rocks. The barrier bars and fluviate sediments may precede the transgressive episodes which terminate the cycles. Details of the surface geology of the area have been published by the geological survey of Nigeria. The Formation Nomenclature has been improved and defined by Reyment (1957). It suffices to note that the tertiary Niger delta covers an area of about 75,000km2 and is composed of an overall regressive clastic sequence which amounts to a maximum thickness of 9,000 t0 12,000 meters (Evamy, et al, 1978).
Precisely Niger delta originated as a result of RRR triple joint development in the early cretaceous period (Burke et al 1975). The geologic history of the Niger delta has been dependent/controlled by three major tectonic phases. Two arms of the RRR-tripple generation spread continuously bringing the continent of Africa and south America to their present position. The third arm closed before the end of cretaceous after spreading for 30,000,000 years from Benue Abakaliki trough. The Formation within the Niger Delta includes Benin, Agbada and Akata Formations. Palynology is the science that studies contemporary and fossil palynomorphs including pollen, spores, orbicules, dinoflagellate cysts, acritachs, chitonozoans and scoledonts together with the particular organic matter (pom) and sediments palynology does not include diatoms. Foraminiferas or other organisms with silicaceous or calcareous exoskeletons. Palynology is an interdisciplinary science and is a branch of earth science (geology or geological science) and biological science (biology), particular plant science (botany). Stratigraphical palynology is a branch of micropaleontology and paleontology and paleobotany which studies fossil palynomorphs from the Precambrian to the Holocene.
The earliest reported observations of pollen under a microscope are likely to have been in the 1640s by the English botanist Nehimiah grew who successfully predicted that pollen was required for successful reproduction in plants. The earliest quantitative analysis of pollen was published by Lennant Van Post who laid out the foundation of modern pollen analysis in his Kristiania lecture of 1916. Pollen analysis was initially confined to Nordic countries because many early publications were in Nordic languages. This isolation ended with the publication of Gunnar Erdtmans thesis of 1921 when pollen analysis became widespread throughout Europe and North America for use in studies of quartenary vegetation and climate change. The term palynology was introduced by Hyde and Williams in 1944 following correspondence with the Swedish geologist Antevs, in the page of the pollen analysis circular (one of the first journals devoted to pollen analysis produced by Paul Sears in North America). Hyde and Williams chose palynology on the basis of the greeks words (paluno) meaning to sprinkle and pale meaning dust (and thus similar to the latin word pollen). Palynomorphs are broadly defined as organic walled microfossils between 5 and 500 micrometers in size.
They are extracted from rocks and sediment core both physically, by wet sieving often after ultrasonic treatment and chemically by using chemical digestion to remove the non-organic fraction. Palynology is used for a diverse range of applications that are related to many scientific disciplines such as pharmaco-palynology, paleo-botany, forensic-palynolgy, paleo-climate, paleoenvironment, archeology and anthropology, micropalynology and paleontology. Biostratigraphic and geochronologic geologists use palynological studies in biostratigraphy to correlate strata and determine the relative age of a given bed, horizon, Formation or stratigraphical sequence, paleocology and climate change. Palynology can be used to reconstruct past vegetation (land plants) and marine and freshwater phytoplankton communities, end to infer past environmental (paleoenvironmental) and paleoclimatic conditions. Organic palynofacies studies examine the preservation of the particulate organic matter and palynomorphs.
1.1 LOCATION OF NIGER DELTA
The Niger Delta occurs at the southern end of Nigeria boardening the atlantic ocean. It extends from the Calabar flank and Abakaliki trough in the eastern Nigeria to the Benin flank in mid western part of Nigeria and opens to the atlantic ocean in the south. It extends from a bout longitude 50-90E and latitude 3030N 6O20’N. it is separated from Dahomey basin in the west by the Okitipupa ridge. It is bounded in the north by the Anambra basin, in the east by the basement Oban massif. The Calabar flank lies at the Eastern part of the delta Calabar flank whose cretaceous rocks show a predominance of marine facies is traced to marine transgression in Cenomanian. These cretaceous trangression led to subsequent development of the stratigraphy of different sedimentary basins. After the first two main tectonic phases that took place in the Abakaliki-Benue trough and the Anambra basin (Albian to lower Campanian), a third phase connected at the end of Eocene. Major part of the areas in the eastern section of the delta downdip (the Abakaliki plunge and the Calabar flank) recorded constant erosional or non depositional periods in the middle or upper Eocene, whereas Anambra basin witnessed deltaic sediments. However, the NE-SW and NW-SE trending faults controlled the positive movement of blocks and brought about subsidence of the Oligocene and younger Niger Delta basin along the NW-SE fault trend. The fault also controlled the sedimentation. Maastrtchtian sediments encountered in coastal boreholes on the Benin and Calabar flanks are all of marine origin. They are similar to Nkporo shale while absence of coal-bearing beds in Benin and Calabar flanks was due to erosion or non-deposition.
1.2 PREVIOUS WORKS ON NIGER DELTA
The rocks of the Niger delta have been discussed in numerous studies, including frank and Cordy (1967), Short and Stauble (1967), Evamy et al (1978) and others. Short and Stauble (1967) suggested that the major source rocks where shales of the Agbada Formation. However Weber and Daukoru (1976) proposed deep Akata Formation hydrocarbon and migration rates that induced growth faults. Evamy et al (1978) and others have conclude based mainly on maturation studies, that Akata Formation is the main source rock in the eastern part of the delta. The Agbada Formation deposited in the mixed marginal or transitional environment consist of sand and shale ( paralic sequence) which becomes more sorted and sandy upward. This unlike Benin Formation is intensely affected by the syndepostinal deformational structures of the Niger Delta and rich microfaunal assemblage at the base. The oldest unit, the prodelta facies (Akata Formation) is composed mainly of shale. This unit is highly rich in microfaunal assemblage of which the planktonic forms may account over 50%. The geology 9 evolution, tectonic setting, stratigraphy, lithostratigraphy, biostratigraphy, chronostratigraphy, structure and petroleum geology) of the Niger Delta have been revealed based on the past works petroleum/oil exploration companied like SHELL BP, NAOC and MOBIL.
1.3 AIM AND SCOPE OF THE PRESENT WORK
1. These include the description of the ditch cutting samples collected from RAST WELL-13, so as to establish the lthostratigraphy of the well.
2. Identifying the recoverd palynomorphs.
3. Establishing the ages of the sediments penetrated by the RAST WELL-13
4. Biostratigraphy zonation of the sequence by RAST WELL-13.
5. Deducing the paleoenvironment of deposition of the strata based on the palynomorphs content
REFERENCE
Evamy, B.D., Haremboure, J., Kamerling, p., Knap, W.A., Molloy, F.A., and Rowlands, P.H., 1978, Hydrocarbon habitat of Tertiary Niger Delta; American Association of Petroleum Geologists Bulletin, V. 62, P.277-298
Reyment R.A 1957; The Cretacious Tertiary boundary of Nigeria Rep Geol survey Nigeria Pp 68-86
Short K.C and Stauble A.J. (1967) Outline of geology of Niger Delta
Petters, S.W (1979); Nigeria Paleocene Benthonic Foraminifera Biostratigraphy, Paleoecology and Paleobiogeograaphy marine Micropal., p. 85-95
