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AJOSR Vol. 1, Issue. 2, October 2016 Volume 1, Issue 2, pp 37 - 52, October 2016
ISSN 2504-0141
Available Online at www.achieversjournals.org
Sedimentological, Palynological and Foraminiferal Biostratigraphic Studies of the (Upper Cretaceous) Mamu Formation at Imiegba, Anambra Basin, Edo State, Nigeria A. O. Jayeola1, O. A. Oluwajana1, O. A. Olatunji1, M. U. Udofia2 and O. Danjuma1 1 Department of Earth Sciences, Adekunle Ajasin University, Akungba, Nigeria 2 Pioneer-Alfa Petroleum Services, Benin City, Edo State Corresponding author: Email:
[email protected]. Phone Number - +2348034077969 Submitted: May 25, 2016; 2016
Revision Accepted: July 9, 2016;
Published: October 1,
____________________________________________________________________________________
Abstract Five representative samples from two exposed road-cut sections of the Mamu Formation, Anambra Basin along Imiegba-Apana road, were retrieved, processed and analyzed for their palynomorphs and foraminiferal contents. The lower part of the section is characterized by the maximum development of Cingulatisporites ornatus Zone, dated Maestrichtian. The upper part comprising of light grey coloured rock defined by intercalation of sand and shale with coal seam layers belong to Retidiporites magdalensis Assemblage Zone. The occurrence of Syncolporites marginatus, Retidiporites magdalenensis, Foveotriletes margaritae, Ephedripites americana, Ephedripites ambonoides, Longapertites marginatus, Syncolporites sp and Monocolpites marginatus suggest that the analyzed samples were deposited during Upper Maestrichtian times. The analysis of the identified foraminifera shows that
arenaceous benthics taxa predominate with no planktics counterparts The predominant foraminiferal assemblages include Ammobaculites coprolithiformis, Haplophragmoides saheliense and Ammobaculites amabensis which suggest a Maestrichtian age. Marine incursion during the Maestrichtian resulted in the deposition of basal shale sequence of Mamu Formation however the recovery of greater than 70% continental palynomorphs suggest probable continental with marine invasion. Key Words: Coal seams, Palynomorphs, Maestrichtian, Foraminifera, Mamu Formation _________________________________________________________________________________
INTRODUCTION The Late Cretaceous sediments of the Mamu Formation in the Anambra Basin are described by Nwajide and Reijers, (1996) as a distinctive sedimentary sequence of sandstone, shale, mudstone and sandy shale, with several horizons of coal seams. A well exposed section of the Mamu Formation investigated in this study is located in the western flank of the Anambra Basin along Apana-Imiegba road in Etsako East Local Government Area of Edo State (Figure 1). Only few reports on the lithostratigraphy and biostratigraphy of Mamu Formation in the western Anambra Basin have been published (Petters, 1982; Nwajide, 1990); thus necessitating the present study. Five representative samples from two exposed road-cut sections along Imiegba-Apana road, were retrieved, processed and analyzed for their palynomorphs and foraminiferal contents. The study was carried out with the aim of determining the age and paleoenvironment of deposition of the studied sections of two exposed outcrops of the Mamu Formation along ApanaImiegba road using palynological and foraminiferal biostratigraphy as a basic research tool.
Figure 1: Map of Edo State Showing Location of Study Area
LOCATION OF STUDY AREA
The study area is located in the western part of the Anambra basin along Apana-Imiegba road in Etsako East Local Government Area of Edo State on the latitude of N071230'' and longitude E0062733'' with an average elevation of about 182meters (597feet). The study area is accessible by road and exists as a road cut at a location between neighboring communities known as Apana and Imiegba along Auchi road. Other neighboring communities to Imiegba include Okpekpe, Imakebu, Ogbona, Ukho, Fugar and Agenebode in Uzairhue. This exposed section of Mamu Formation outcrops in several places along Apana-Imieagba and also along Okpekpe (figure. 1). Field observation shows that both sections of the road cut clearly depict same lithology.
GEOLOGICAL SETTING The study area belongs to the western sector of the Anambra Basin (Figure 2) which was a prominent structural depression formed during the Late Cretaceous Abakaliki post-folding phase of the early Benue Trough, and shows the most complete stratigraphic section. In the Anambra Basin, the strongly folded Albian-Coniacian succession is overlain by nearly flat-lying sediments of Campanian-Eocene succession. The sedimentary cycle (Upper Campanian-Maastrichtian) started with the deposition of the marine Nkporo Shale. In the Anambra Basin, the regressive phase is marked by the development of a large offlap complex starting with a parallic sequence, the Mamu Formation, followed by the continental sequence of the Ajali Sandstone. Although the overlying parallic sequence of the Nsukka Formation belongs genetically to the transgressive phase of the next cycle, (Murat, 1967) considered it here together with the Upper Cretaceous deltaic sediments because of their lithological affinities. Upper Cretaceous outcrops west of the Niger River showing a sandy continental facies. Downdip in the subsurface of the Benin Flank, the deposits are of marine origin (Reyment, 1960). The Mamu Formation is an important stratigraphic unit within the Anambra Basin. The lithology is characterized by intercalation of laminated fine-grained sand and light, dark grey fissile shale with interbeds of coal seams. It is also worthy of note that the Maastrichtian sediments of the Mamu Formation in the Anambra Basin as described by Nwajide and Reijers (1996) is known to be characterized by a distinctive sedimentary sequence of sandstone, shale, mudstone and sandy shale with several horizons of coal seams (Figure 3). The sandstones are fine to medium grained and yellow in colour. The shales and mudstones are dark blue or grey and frequently alternate with the sandstone to form a characteristically striped rock. Coal seams vary in thickness from a few inches to 12ft (Reyment, 1965, Simpson, 1956 and Whiteman, 1982).The age of the Formation is Lower-Middle Maastrichtian (Simpson, 1954 Reyment, 1965). It consists of interbeds of carbonaceous shales with sparse arenaceous microfauna and coal seams which often range from few centimeters to about four meters thickness. The coal beds and carbonaceous shale are concentrated in the lower section of the Formation and became rare towards the top.
MATERIALS AND METHODS OF STUDY Two surface sections (two road cuts) of the Mamu Formation were measured, described lithologically and sampled along Imieagba -Apana road. Ten samples of fresh shale, shaly coal and siltstone were taken from outcrop sections of the Mamu Formation for foraminiferal and palynological processing. The samples were prepared according to standard foraminiferal and palynological procedures. The slides were studied for identification, counting and photographic documentation. Field work involved reconnaissance field study, examination of exposed section and sampling from intervals of depth. The compositional and textural characteristics of the lithologic units were carefully examined and described.
Figure 2: Stratigraphic Setting of Anambra Basin
Figure 3: Geological Map of Study Area Field observation reveals that the basal sandstone is fine to medium grained and the overlying shales are hard, dark grey; fissile and carbonaceous (figure 3). Alternation of shale, thin fine-grained sandstone that grade into coarse-grained sandstone and thin coal seams were observed overlying the basal sandstone (Figure 4). The lithologic assemblage that is basically dominated by argillaceous strata (Figure 4) suggests deposition by suspension settling mode in the low energy setting, similar to deposition in coastal, near shore to non-marine environment. The shales appear very dark in the bottom thus suggesting a more anoxic condition during their initial depositional process. Observed sedimentary structures at Imieagba section include sand pinch out, ripple lamination in the siltstone, massive and consistent planar lamination, parallel and wavy lamination in the siltstone, sole marks and lenticular bedding in the interbedded sandstone. The presence of coal seams in the lithologic section suggests deposition of some marine plants removed from active clastic environments. Study reveals that the coal-bearing strata suggest a peat type of coal which are formed in swamps and are being characterized by high percentage of inorganic materials introduced by floods. Hence, the presence of coal seams geologically suggests a hiatus between the period of the deposition of the underlying and overlying
strata.
Figure 4: A typical lithologic section of the Mamu Formation at Imieagba
RESULTS Foraminiferal Biostratigraphy Five (5) outcrop samples were processed and analyzed for their foraminiferal contents. Arenaceous benthics taxa predominated, however, these samples were devoid of planktics counterparts. Age designation was therefore interpreted based on the benthic (arenaceous) assemblage encountered in the analyzed samples. The predominant
assemblage: Ammobaculites coprolithiformis, Haplophragmoides hausa, Haplophragmoides sahariense, Ammobaculites amabensis, Haplophragmoides talokaense and Ammobaculites sp. points to Middle - Late Maestrichtian age (Gebhardt,H.,1998). Paleoenvironmental interpretations were carried out based on the abundance and diversity of the microfauna encountered from the analyzed sediments and the presence of environmentally significant fauna taxa. These sediments were deposited within the inner neritic paleo-water depths.
Figure 5: (1) and (2)Haplophragmoides sahariense, (3) Ammobaculites amabensis, (4) Miliammina telemaquensis, and (5) Ammobaculites coprolithiformis.
Palynological Studies The results of the five (5) samples subjected to standard laboratory palynological procedures and analysis are presented below in the form of distribution charts in the order of their successions. The prepared samples yielded fair to good recovery of palynomorphs. Some of the palynomorphs are well preserved. The palynostratigraphy of the studied section of Mamu Formation is based on the spores, pollen, dinoflagellates and some forms such as foraminifera test linings recovered from the two locations in the outcrop section. The identified marine palynomorphs (Dinoflagellates) include Andalusiella sp., Apectodium sp., Paleocystodinium sp, and Dinocyst indeterminate while the non - marine palynomorphs (pollen and spores) include Cingulatisporites ornatus, Foveotriletes margaritae, Leiotriletes adriennis, Lygodiumsporites adriennis, Longapertites sp., Ephedripites sp., Ephedripites procerus, Auriculiidites reticulates, Baculatisporites orluensis, Zonosulcites parvus, Longapertites marginatus, Syncolporites marginatus, Retidiporites magdalensis and Echitriporites trianguliformis (Figure 6). On the other hand,chitinous foraminiferal test lining were also observed within these sections. They consist of single chambered and uniserial forms in addition to the planispiral evolute test linings. The marker (palynomorphs) that occur in the studied outcrops section include short ranging and age diagnostic palynormorphs –Cingulatisporites ornatus, Echitriportites triaguliformis, Ephedripites ambonoides, Retidiporites magdalensis, Synocolporites marginatus, Zonosulcites parvus and Auriculiidites reticulates which are non - marines. Also recorded within the analyzed section is Andalusiella sp. which is a marine (dinoflagellates) flora. All the above forms suggest Maastrichtian age. Though admixture within these sections are some species of Senegalinium bicavatum which denotes a Campanian age and Proteacidited miniporatus also suggest a Paleocene age for the samples; one can likely infer the environment to be deposited during the Late Cretaceous - Early Tertiary time.
Figure 6: Distribution Chart of Palynomorphs showing Palynological Diversity, Abundance, Age and Paleoenvironment of Shale Samples from Imiegba-Afana,Mamu Formation.
DATA INTERPRETATION Biozonation Majority of the pollens and spores observed from the IMI-001 include marker flora such as Cingulatisporites ornatus and Ephedripites ambonoides and are similar to those recovered from various Maastrichtian sediments of Nigerian basins, (Ojo and Akande, 2006). Other forms present are Cyathidites minor, Monocolpopollenites spheroidites, Leitriletes adriennis, Tubistephanocolpites cylindricus, and Adenantherites sp. The presence of Proteacidited miniporatus probably suggest an Early Paleocene age for IMI-001. Thus, the sampled interval is therefore tentatively dated Late Cretaceous - Early Tertiary age (Maastrichtian-Paleocene times). However, the IMI-002 is characterized by the occurrence of Senegalinium bicavatum, Monocolpopollenites spheroidis, Retidiporites magdalensis, Cingularisporites ornatus and Ephedripites ambonoides (Figure 7).The sediment is dated Campanian – Maestrichtian age on the basis of the presence of Senegalinium bicavatum and Cingularisporites ornatus, Ephedripites
ambonoides respectively. The presence of Cingularisporites ornatus, Auricullidites recticulatus and Retidiporites magdalensis as the marker species found in IMI-003, and are significant because they had been reported on the world record as a stratigraphic marker pointing to Maastrichtian age (Omoboriowo et al., 2012) though some few species of Senegalinium bicavatum suggest Late Campanian age. Other forms present are Verrucosisporites sp., Longapertites sp, Foram lining, Foveotriletes margaritae, Longapertites marginatus, Ephedripites sp., Ephedripites multicostatus, Ephedripite procerus, Zonosulcites parvus, Chlorophytum tuberosum, and Tubistephanocolpites cylindricus.
Figure 7: Stratigraphic Distribution Chart for the Recorded Palynomorphs (Plot of Depth(m) against Numbers of Counts of Palynomorphs). The main Maastrichtian diagnostic species of pollens and spores include, Cingularisporites ornatus, Echitrisporites triaguliformis, Ephedripites ambonoides, Retidiporites magdalensis, Syncolporites marginatus, Zonosulcites parvus, and Auriculiidites reticulates. They are the index fossils that characterized the IMI-001 by their occurrences. Other forms present within the analyzed section also include; Chlorophytum tuberosum, Tubistephanocolpites cylindricus, Leiotriletes adriennis, Psilatricolporites sp, Baculatriporits orluensis. The marker species Proteacidited miniporatus proposed Early Paleocene age for the sample. Hence, the sample can therefore be assigned to the Maastrichtian - Paleocene age of deposition. The IMI – 002 contain characteristics form such as; Cingulatisporites ornatus, Tubistephanocolpites cylindricus, Syncolporites marginatus, Proteacidited miniporatus, Cyathidites minor, Paleocystodinium sp, Ephedripites sp, Leiotriletes adriennis; all assigned to Upper Maastrichtian age (Lawal and Moullade, 1982; Jan Muller et al, 1987).
Depositional Environment Paleoenvironmental interpretations were carried out based on the abundance and diversity of the microfauna encountered and the presence of environmentally significant fauna. These sediments were deposited within Outer Neritic paleo-water
depths. The high proportion of continental miospores (70-100%) in the studied outcrop show continental origin for the sediments encountered in the Mamu formation of the Imiegba area. However, the occurrence of dinoflagellates, foraminifera test linings is indicative of infrequent marine incursions. The environment of deposition of the Mamu Formation is that of progradation with occasional transgressive phases giving rise to the observed parallic sequences. The presence of heterolith lithologic facies show strong influence of wave action in mixed energy environment. The very fine to fine grained sandstones in Imiegba area bear mostly argillaceous cement probably indicative of continental origin in transitional environment, while the medium to coarse grained wave rippled sandstones with ferruginous cement obtained to the southern section of the exposed outcrop probably indicative of shallow marine wave dominated environment (Figure 8).
Figure 8: Depositional Environment of study area showing continental to marine
CONCLUSION The exposed sections of Mamu Formation along Imiegba - Afana road in Edo State was studied and it consist of carbonaceous shale with sparse arenaceous microfauna contents, fine to medium grained and interbeds of well sorted sandstone, thin film of coal seams which often range between few centimeters and a meter in thickness. Micropaleontological analysis of the Mamu shale probably suggests a deposition during the Middle to Late Maastrichtian age. The microfossils recovered are; Ammobaculites coprolinthiformis, Haplophragmoides hausa, Haplophragmoides sahariense, Ammobaculites amabensis, Haplophragmoides talokaense And Ammobaculites sp. all indicating a marginal marine environment of deposition. The dating of the studied outcrop sediments was based on index pollens, spores and dinoflagellates. These include: Retidiporites magdalensis (Maastrichtian - Recent), Cingulatisporites ornatus (Maastrichtian), Ephedripites ambonoides (Maastrichtian), Zonosulcites parvus (Maastrichtian), Syncolporites marginatus (upper Maastrichtian), Foveotriletes margaritae (Maastrichtian - Recent), Andalusiella sp (Maastrichtian). The main Maastrichtian diagnostic species of pollen and spores include Cingulasporites omatus, Echitriporites triaguliformis, Ephedripites ambonoides, Retidiporites magdalensis, Syncolporites marginatus, Zonosulcites parvus, and Auriculiidites reticulates. The recovery of greater than 70% of continental palynomorphs shows that the depositional environment of Mamu Formation is probably continental with frequent marine incursions. The environment of deposition of the Mamu Formation is that of a prograding pattern with occasional transgressive phases giving rise to the observed parallic sequences.
REFERENCES
Adeleye, D. R.,(1975): Nigeria Late Cretaceous Stratigraphy and Palaeogeography: American Association of Petroleum Geologists Bulletin 5a(12). Pp. 2302-2313. Chiaghanam, O.I., et.al (2012) : Sequence Stratigraphy and Palynological Analysis of Late Campanian to Maestrichtian Sediment in the Upper- Cretaceous Anambra Basin. A case study of Okigwe and its Environs, South- Eastern Nigeria. Gebhardt, H., (1998) : Benthic Foraminifera from the Maastrichtian Lower Mamu Formation near Palaecology and Palaeogeographic Significance. Hoque, M. and Ezeque, M.C.,(1977): Petrology and Palaeogeography of the Ajali Sandstone, and Geology, 14pp. 16-22.
Leru (Southern Nigeria):
Nigeria. Journal of Mining
Ladipo, K.O., (1988): Paleogeography, Sedimentation and Tectonics of Upper Cretaceous Anambra Basin, Southeastern Nigeria: Journal of African Earth Sciences 7(5/6). P.865 – 871. Lawal, O. (1982): Biostratigraphic Palynologique es Paleoenvironment des Formations Cretacee de la Haute- Benoue, Nigeria Mord- Oriental. These- 3 cycle, University of Nice.,2a (1),p61-68. Nwajide and Reijers (1996): Sedimentology and Sequence stratigraphy of the Nkporo Group (Campanian to Maastrichtian), Anambra Basin, Nigeria. Vol. 2, Issue 2, pp192- 208.
Omoboriowo et al.,(2012): Geochemical Characterization of Afikpo Basin, Arochukwu Area, South East, Nigeria. Pelagia Research Library. Vol. 3, Issue 6, pp3652 -3657 Ojo, O.J. and Akande, S.O.,(2006): Sedimentological and Palynological Studies of the Patti Formation, Southern Bida Basin, Nigeria: Implications for Palaeonenvironments and Palaeogeography:Nigerian Association of Petroleum Explorationists Bulletin 19: 61-77. Reyment, R.A. (1965): Aspects of the Geology of Nigeria. University of Ibadan Press. Ibadan, Nigeria, 145pp. Salard- Cheboldaeff, M.,(1991): Intertropical African Palynostratigraphy from Cretaceous to Late Quaternary Times. Journal of African Earth Sciences, 11(1/2): pg 1-24. Simpson, A., (1954): The Nigerian Coalfield: The Geology of Parts of Onitsha, Owerru and Benue Provinces. Bulletin of the Geological Survey of Nigeria. 24:85pp. Tattam, C.H.,(1944): A Review of Nigeria. Report of the Geological Survey of Nigeria. No. (13) 61pp.
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