FORAMINIFERA BIOSTRATIGRAPHY

1. UNIVERSITY OF NIGERIA NSUKKA
FACAULTY OF PHYSICAL SCIENCE
DEPARTMENT OF GEOLOGY
FORAMINIFERA BIOSTRATIGRAPHY AND PALEOENVIRONMENT OF
ANAMBRA BASIN
BY
PHILIP KOSI EZEAMUGWU
A SEMINAR PRESENTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE COURSE GLG. 591 (SEMINAR)
JANUARY, 2022

2. OUTLINE
 INTRODUCTION
 REGIONAL TECTONIC SETTING
 STRATIGRAPHIC OVERVIEW
 MATERIALAND METHODOLOGY
 FORAMINIFERAL BIOSTRATIGRAPHY
 FORAMINIFERAL ZONE
 PALEOENVIRONMENT STUDIES
 CASE STUDY
 CONCLUSION

3. INTRODUCTION
 Anambra basin is located in the South Central Nigeria and covers about 40,000 sq km.
 The roughly triangular Anambra sedimentary basin has its southern boundary coinciding with
the northern boundary of the Niger Delta Basin and the basin extends northwards beyond the
lower Benue River.
 A field work was carried out to map out the surface geological features within the area, with a
view to carrying out Biostratigraphical analysis.
 Samples from exposures of the road cut were taken and labeled to assist for easy laboratory
work.

4. REGIONAL TECTONIC SETTING
 The origin and evolution of the Benue Trough started the process that led to the
formation of the Anambra Basin
 A lot of authors have come up with various mechanisms which have been debated and
modified with time.
 (Burke and Whiteman, 1970; Burke et al., 1971 and 1972) compared the trough to the
Afar rift and suggested that there was a triple junction of the Ridge-Ridge-Ridge (RRR)
type with a new oceanic crust generated in the Abakaliki area, with a triple junction
development around a centre located beneath what is now called the Niger Delta.

5. REGIONAL TECTONIC SETTING
Sketch showing the separation of the African and South American plates around a triple
junction. The failed arm of the triple junction is the Benue Trough (after Wright, 1968).

6. STRATIGRAPHIC OVERVIEW
 The filling of the Anambra Basin took place within the time interval from Santonian to
Early Paleocene (Danian), a time span of 60 Mya.
 There were two marine transgressions (Nkporo and Nsukka).
 Nkporo Shale is a formation within the former which is early Maastrichtian and has several
lateral age equivalents namely: Enugu Formation, Owelli Formation, Afikpo Formation,
Otobi Sandstone and Lafia Formation (Nwajide, 2013).

7. STRATIGRAPHIC OVERVIEW
 The Coal measures namely: Mamu Formation, Ajali Formation and Nsukka Formation
overlie the Nkporo Group.
Geologic map of Nigeria showing Anambra basin

8. MATERIALAND METHODOLOGY
PREPARATION OF SAMPLES
 Fresh portions of each sample is taken, crushed into pieces in a mortar and is later transferred into a
pan, mix and soared with water and treated with 2 gram of sodium chloride salt and was left to boil for
30 minutes on hot plate at about 250°C.
 All this is done in order to disintegrate the clay and, shale particles and free the fossils from the matrix.
WET SEIVING/WASHING
 The boiled solution from each plate is discounted into a stack of sieve meshes arranged in decreasing
order 250µm, 100µm and 75µm.
 The coarsest is placed at the top while the finest is, at the bottom.
 The disintegrate sample are then allowed to pass through the sieves using a shower of water.

9. MATERIALAND METHODOLOGY
 The boiled solution from each plate is discounted into a stack of sieve meshes arranged in decreasing
order 250µm, 100µm and 75µm.
 The coarsest is placed at the top while the finest is, at the bottom.
 The disintegrate sample are then allowed to pass through the sieves using a shower of water.
 The washing continues until clear water observed on each of the sieves.
 Residues from each sieve size are collected in a filter paper tagged is label for each sample
depth and allowed for some minutes for water drip off before drying on the hot plate.
DRYING STORAGE AND PICKING
 The Filter paper containing the respective residual fractions of the sample is dried at temperature of
100°C on the hot plate after which the fossils are picked.
 To avoid contamination and loss of fossils , plastic mountain slides are used to sealed them with cover
slips.

10. FORAMINIFERAL BIOSTRATIGRAPHY
FORAMINIFERAL BIOSTRATIGRAPHY IN ANAMBRA BASIN
The planktonic foraminiferas are particularly used for biostratigraphy, especially
for Cretaceous and tertiary periods because:
 They are generally abundant in open marine samples.
 Generally have short time range and this delimits short time interval
 Occurs in sediments representing water depths from less than 200m to over 3,000m, thus
allowing some correlation between events in the shelf and in the deep sea.

11. FORAMINIFERAL BIOSTRATIGRAPHY
UPPER CAMPANIAN-MAASTRICHTIAN.
 The Upper Campanian-Maastrichtian has yielded abundant foraminiferal assemblages.
 Deposits of this age are widespread in Nigeria.
 They bear witness of the widespread marine transgression that followed after the Santonian
regression.
 The Campano-Maastrichtian Nkporo Shale has yielded the following planktonic foraminifera;
Globotruncana Helvetica, G. fornicata, Globorotalia variabilis, Heterohelix globulosa, H.
planate, H. pulchra, Rugoglobigerina rugosa, Hedbergella,

12. FORAMINIFERAL BIOSTRATIGRAPHY
UPPER CAMPANIAN-MAASTRICHTIAN con’t
 The Campano-Maastrichtian Nkporo Shale has yielded the following benthonic foraminifera;
Afrobolivina afra, praebulimina Bantu, Gabonita elongata, Gavelinella,
Haplophragmoides excavata and Anomalina.
 The Mamu Formation has yielded the following benthonic foraminifera;
Haplophragmoides saheliense, Haplophragmoides sp., Ammobaculites amabensis,
Ammobaculites sp. Gavelinella saheliense, Lenticulina sp. and Marginulina sp.

13. FORAMINIFERAL BIOSTRATIGRAPHY
UPPER CAMPANIAN-MAASTRICHTIAN con’t
 The Maastrichtian Ajali formation has yielded the mainly benthic arenaceoustexa which is
recorded as;
Gevelinella guineana, Ammobaculites amobensis, Haplophraomoides sahariense,
Haplophragmoides coprolithiforms.
 The Maastrichtian Nsukka has yielded diagnostic foraminifera which include
Afrobolivian afra, Rugoglobigerina rugosa, Orthorkarstina parva, Gabonite elongata, and
Heterohelix globulosa

14. FORAMINIFERAL ZONE
NIGERIAN MAASTRICHTIAN FORAMINIFERAL ZONES

15. PALEOENVIRONMENT STUDIES
FORAMINIFERA PELOENVIRONMENT OF ANAMBRA BASIN
Studies of modern foraminifera ecology have provided at least five distinct criteria for the
reconstruction of marine paleoenvironments:
 Both the number of species and specimen abundance increase away from shore and with
increasing depth of water to maximum values on the outer shelf and on the upper and middle
bathyal zone:
 Diverse porcellaneous species are abundant in shoal nearshor marine environments;
 Arenaceous Foraminifera with simple interior may be abundant in shallow waters whereas
more complex types with labyrinthic interiors are more characteristic of bathyal depths.

16. PALEOENVIRONMENT STUDIES
FORAMINIFERA PELOENVIRONMENT OF ANAMBRA BASIN con’t
 Deposition of planktonic species occurs most abundantly on the outer shelf and in the upper
bathyal one, with even greater abundance in deeper waters under the right conditions; and
 Similar environmental adaptations of modern species and fossil homeomorphs may be
assumed, especially for groups of species.

17. PALEOENVIRONMENT STUDIES
FORAMINIFERA PELOENVIRONMENT OF ANAMBRA BASIN con’t

18. ENVIRONMENTALADAPTATIONS OF SPECIES
 Species Abundance-Studies by a number of workers off the Atlantic, coast, in the Gulf of
Mexico, and in the Eastern Pacific have that shown that species increase in number with
increasing depth of water and distance from the shore.
 Specimen Abundance-The percentages of Foraminifera in sediments of modern seas increase
away from shore toward the edge of the continental shelf.
 Porcellaneous Foraminifera- Diverse porcelaneous species of foraminifere, especially the
miliolidae, are characteristic of the intertidal zone and the inner part of the continental shelf of
modern oceans.

19. ENVIRONMENTALADAPTATIONS OF SPECIES
 Arenaceous Forminifera –Arenaceous species occurs in high percentages in some brackish
water areas and at some localities on continental shelves and in deep cold waters.
 Planktonic Species- Planktonic foramminifera are abundant in Recent sediments of the outer
shelf and the upper bathyal zone at greater depth . An abundance of planktonic species may
indicate open sea conditions or a trend toward open sea conditions
 Adaptations of Modern and Fossil Homeomorphs- Homeomorphs are species which are
similar and related. Isomorphs are those species which are similar and not related. In either
case it appears that species of a general group have responded in similar ways under similar
environmental conditions

20. CASE STUDY
• Thirteen of the eighteen washed samples yielded foraminifera, six from Azagba Ogwashi,
one from Oba, and six from Ihioma.
• The yielded samples resulted in the identification of twelve benthonic foraminifera species
from the three locations, these seem to be suitable for defining the environment of
deposition of the successions. The most important recorded species are;
Ammobaculites, Ammotium, Bolimina, Dentalina, Gavelina, Lenticulina, Milliamina,
Planumina, Reophax, Orthokarsteina parva, Textularia hockleyensis

21. CASE STUDY CON’T
Distribution of benthic and planktic foraminifera

22. CASE STUDY CON’T
Distribution of benthic and planktic foraminifera continued

23. CASE STUDY CON’T
Typical benthic species showing infauna and epifaunal ratio at Azagba Ogwashi, Anambra basin

24. CASE STUDY CON’T
 From the distribution of benthic and planktic foraminifera above shows the infauna - epifauna
distribution ratio within the study area.
 The distribution is based on comparison with modern species of the same morphogroup
(Murray 1991; Kaiho, 1994; van der Zwaan et a1., 1999) and distribution patterns of
Cretaceous species (Koutsoukos and Hart 1990; Koutsoukos et al., 1991).
 The benthic foraminiferal assemblages of the Ihioma section were quiet distinct from the
Azagba Ogwashi and Oba Section.
 Generally, there appears to be scarcity of planktonic foraminifera as the samples yielded 3
species of Globorotalia fohsi, Morozovella and Globigerina which were have been identified
only in Ihioma .

25. CASE STUDY CON’T
Sketch of foraminifera identified in the Ogwashi Azagba
1. Ammobaculites sp. 2. Ammotium sp. 3. Dentalina sp. 4.
Gavelina sp. 5. Lenticulina sp. 6. Textularia hockleyensis 7.
Bolimina sp. 8. Orthokarsteina parva 9. Miliammina sp 10.
Planulina sp. 11. Haplophragmoides sp 12. Reophax sp.
benthic foraminifera
planktic foraminifera
1. Morozovella sp. 2. Globigerina sp. 3. Globorotalia foshi

26. CASE STUDY CON’T
 Result shows that the predominance of the low oxygen agglutinated genera as indicated in
most parts of the section was caused by increasing input of organic matter from nearby rivers.
 Based on occurrence of the species, the environment of deposition ranged from brackish
marsh (Ammotium, Ammobaculites, miliammina sp) with reduced salinities and dysoxic
conditions in the Azagba-Ogwashi, which was sustained at Oba, to an open-oceanic
conditions of an upper bathyal environment (Lenticulina, Dentalina, Bolimina, Reophax and
Textularia sp) with normal-marine salinity, dysoxic to anoxic conditions (100 – 250 m) at
Ihioma.

27. CASE STUDY CON’T
Depositional models of Ogwashi Asaba formation showing typical genera of foraminifera and their paleoecological water depth

28. CONCLUSION
 From the case study, an overview of the investigated environmental conditions based on the
foraminifera studies show high percentage of agglutinated species of benthonic foraminifera and a low
percentage of the planktonic foraminifera species.
 Calcareous, epifaunal and planktic species are very rare.
 The study inferred that the generally poor foraminifera abundance and preservation was attributed to the
high percentage of coaly fragments within the shales and the prevalence of siliciclastics in the shales.
 The sediment paleoenvironment within the Ogwashi Asaba as ranging from an inner shelf in the Azagba
Ogwashi area to the upper bathyal environment in the Ihioma area, consequent to tectonic subsidence.

29. THANKS FOR LISTENING