Ameki Formation Research Articles

Delineation of Aquiferous Zones in Some Parts of Umuahia and Uzuakoli Environs Using Vertical Electical Sounding Data

A delineation of aquiferous zones in some parts of Umuahia and Uzuakoli environs was carried out using Vertical Electrical Sounding (VES). A total of fourteen (14) VES data were acquired at different locations. Cross sections of the VES data were interpreted and correlated along profiles. The results showed that sands constitute the aquifer units while clay and shale made up the aquiclude. Aquifer units occur at shallow depths in some places such as Ibeku, Umule, Ohuhu, at 9m to 30m with thickness range of 9 m to 50m while some places such as Isingwu, Nkpa, Amachara, Ubakala, Lohum, Etitulo Bende areas have deep aquifer units with the depth to the top of aquifer ranging from 40m to 115m and the aquifer thickness ranges from 17m to 102m.The degree of the relationship of the aquifer parameters were investigated using some statistical analysis in which the coefficient of correlation between depth and resistivity is 0.6; From the analysis, it has been ascertained that there exist shallow and deep aquifer systems within the Ameki Formation and the depth to the top of these aquifers are in range of 40 m to 115m. The deep aquifer systems except the shallow units are confined. Recommended total drill depth (TDD) to guide a successful water borehole prospecting in the area should be 140m in the North, 180m in the south and west flank of the study area.

First potential occurrence of the large aquatic snake Pterosphenus (Serpentes, Palaeophiidae) from Nigeria, with further documentation of Pterosphenus schweinfurthi from Egypt

Pterosphenus was a genus of giant aquatic snakes distributed across North and South America, Asia and Africa. In Africa, the known occurrences of the genus are scarce, comprising isolated vertebrae and ribs from Egypt, Libya, Morocco and Angola. Here, a trunk vertebra from the middle Eocene Ameki Formation of Ameki in Nigeria is tentatively referred to Pterosphenus. For comparative purposes, multiple previously undocumented trunk vertebrae from the upper Eocene of Fayum in Egypt are also illustrated—these pertain to Pterosphenus schweinfurthi, the only named species of Pterosphenus currently recognized from Africa. The Ameki Formation vertebra is significantly smaller and likely represents an osteologically immature individual. This new find hints at a higher diversity of palaeophiids from Nigeria, which otherwise include Palaeophis africanus from the age-equivalent middle Eocene Oshosun Formation. Georgios L. Georgalis [georgalis@isez.pan.krakow.pl], Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Sławkowska 17, 31‑016 Kraków, Poland.

Palynostratigraphy and Palaeoenvironmental Interpretation of Outcrop Formations in Parts of Ini-Akwa Ibom State, Southeastern Niger Delta Basin, Nigeria

The palynological study of the outcrop Formations in parts of Ini Local Government Area of Akwa Ibom State, Southeastern Niger Delta Basin, Nigeria has contributed to unraveling the palynostratigraphy and paleoenvironments of the outcrops through the use of diagnostic palynomorphs. The section is made up of carbonaceous shales, sandstones, mudstones and claystones. The conventional maceration technique for recovering acid-insoluble organic-walled microfossils from sediments was used to prepare twenty outcrop samples for palynological studies. The samples produced poor to fair diversity assemblages of palynomorphs. A total of 176 palynomorphs species were recorded, with 48% pollen grains, 33% spores, 12% dinoflagellate cysts, 5% fungal spores, and 2% microforam test wall linings. Based on stratigraphically selected index taxa recovered,age determination and correlation wereestablished. The samples from Imo Formation were assigned Late Paleocene-Eocene based on Psilatricolporites Crassus, Retitricolporites irregularies, Psilatricolporites sp. and Leiotriletes adriennis with the presence of Paleocene dinoflagellate cysts such as Lejeunacysta beninensis and Selenopemphix nephroides. Ameki samples were dated Early-Middle Eocene based on Proxapertites operculatus, Retistephanocolpites williamsi, Mauritidites crassiexinius, Monocolpites marginatus and Longapertites marginatus. Ogwashi-Asaba shale samples were assigned Late Eocene-Early Oligocene due to the abundant presence of Verrucatosporites usmensis, Laevigatosporites discordatus and Retitricolporites irregularis while Eze-Aku samples were tentatively assigned Paleocene because of the presence of two pollen index fossils Proxapertites operculatus and Pachydermites diederixi. Inferred depositional conditions suggest that Imo Formation was deposited in a shallow marine or near shore brackish water estuarine environment. The Ameki Formation was accumulated in a marginal marine or near shore, brackish water-estuarine environment in the upper deltaic setting. The Ogwashi-Asaba Formation was deposited in a progradational shoreline moving between the brackish water and fresh water deltaic plain. The Eze-Aku Formation was deposited in an upper foreshore fresh water environment. The palynological study of the samples are Paleogene Formations while the paleoenvironment is in a costal deltaic to shallow-marine environment and are appropriate for hydrocarbon accumulations and exploration.

Facies Analysis, Sedimentology and Petrographic studies of the Eocene Ameki Formation, SE Nigeria

Detailed sedimentology and petrographic studies of outcrop sections of the Eocene Ameki formation exposed in the Northern depobelts of the Niger Delta was done to, characterize the sediment facies, determine the depositional environment and also to development a depositional model for the study area. Three facies associations were have been identified in the study area based on lithology, primary sedimentary structures, fossil content, geometry, lateral and vertical succession of beds and the nature of bedding contacts,and they include; brackish swamp, braided fluvial channels and Tidal creek environments. Results from polished section study showed the percentage distribution of the maceral groups as Huminite = 58.25%, Liptinite = 34.35%, Inertinite = 7.5%. The lignites are mainly Duroclarite in nature, deposited in swamp vegetation with preserved cell structures in a slightly oxic to anoxic condition. Furthermore results from petrographic studies of representative sandstone samples showed that the predominant mineral is quartz with a greater number of them showing Monocrystalline features, while the feldspars are mostly of the plagioclase type. Ternary diagram plots for the sandstones suggest a subarkose to lithic subarkose, and Arkose to lithicarkose for the sandstones, a mixed provenance of plutonic, metamorphic and recycled sedimentary sources which are consistent with humid climatic conditions.   Â

Geochemistry and paleoenvironment of the phosphorites from the Ameki Formation, Niger delta, Nigeria

The phosphorites of the Ameki Formation occur as nodules, pellets as well as primary phosphatic shales and siltstones. Geochemical analysis of the phosphate samples was carried out to determine its chemical composition as well as its depositional environment. The methodology applied include XRF, INAA, XRD and thin section petrography using Polarizing Microscope. The XRF result identified CaO- P2O5- F as the major mineral group, SiO2, Al2O3, Fe2O3, MgO and TiO2, which show minor occurrences and Cr, U, Pb, V, Cu, Zn, Se and Cd that occur in trace amounts. The nodules and pellets are of medium to high grade (25- 34wt% P2O5) whereas the primary phosphatic shales and siltstones are of low to medium grade (4.5– 22wt% P2O5). The phosphorites comprise mostly of francolites. The mean index of refraction estimated by Becke-line method using Standard Polarizing Microscope gave 1.634 and1.636.XRD analysis yielded an average values of 9.243 (± 0.002) A° and 6.715 (± 0.002) A° for a and c crystallographic axes respectively with an axial ratio (c/a) of 0.726for unit cell parameter, suggestive of low degree of carbonate substitution. An increase in P2O5 content is found to be accompanied by increase in CaO, CO2 and F contents, but by a decrease in H2O, organic carbon, SiO2 and Fe contents indicative of amorphous solid phase of calcium phosphate. The phosphorite is interpreted to form under high biologic productive, shelf setting. High nutrient availability in the ancient sea is linked to upwelling along the West African Coastline during the Eocene.
 Keywords: Phosphorites; Geochemistry; Paleoenvironment; Ameki; Francolites; Nodules

Palynomorph assemblage biozonation of Paleogene strata in Bende\u2013Umuahia Area, Niger Delta Basin, southeastern Nigeria

Cenozoic sediments form extensive outcrops in the Niger Delta Basin. Detailed palynostratigraphic study was undertaken across Paleogene sequences exposed in Bende–Umuahia Area in up-dip sectors of the Niger Delta Basin, southeastern Nigeria, to establish different palynomorphs assemblage zones, with their corresponding ages. Palynological analysis was carried out on 27 selected outcrop samples, using the conventional maceration technique for recovering acid-insoluble organic-walled microfossils from sediments. Three Cenozoic lithostratigraphic units, including Imo Formation, Ameki Formation, and Ogwashi Formation, are exposed in the study area. Lithologies are sandstone, carbonaceous shale, mudstone, limestone, and the lignite. A total of 65 species of sporomorphs and 51 dinoflagellate cysts were identified. The recovered spores and pollen grains were used to establish six informal palynomorph assemblage zones, labeled as zone A – zone F, based on the first and the last occurrences of two or more species. These palynomorph assemblage zones include: (1) zone A — middle Paleocene Scabratriporites simpliformis–Bombacidites annae zone; (2) zone B — late Paleocene Foveotricolporites crassiexinus–Mauritidiites crassiexinus zone; (3) zone C — early Eocene Striatopollis catatumbus–Momipites africanus zone; (4) zone D — middle Eocene Margocolporites umuahiaensis–Gemmastephanocolporites brevicolpites zone; (5) zone E — late Eocene Cicatricosisporites dorogensis–Perfotricolpites nigerianus zone; and, (6) zone F — Oligocene–early Miocene Verrucatosporites usmensis–Magnastriatites howardii zone. The erected palynozones were correlated and compared with existing biozones in subsurface, down-dip sectors of the Niger Delta Basin, with pantropical palynological zones in tropical areas of Africa, and with palynofloral provinces of northern South America. A comparison of palynozones studied in southeastern Nigeria with other international palynozones, in this study, will assist in establishing the correlation of sediments for these areas.

Facies Analysis of Eocene Sediment of Umuahia Area, Southeastern Nigeria

This research work is the detailed facies analysis of the depositional environments and paleogeographic setting of the Eocene sedimentary sequence (Ameki Formations) exposed in the Umuahia area and paleoclimate during that periods. The study area was mainly concentrated around Amaudara inUmuahia South and Ekeoha in Umuahia North. And the co-ordinate are as follows,location-1 0.5°30.80N, 0.7°26.93E, location-2 0.5°30.39N, 0.7°26.62E, location-3 0.5° 32.83N, 0.7°27.24 E and location-4 0.5°32.19 N, 0.7°26.13 E.
 The aim of the study is to analyze the detailed sedimentary facies and describe the depositional environment in other to predict the depositional environment of the Eocene sediment (Ameki Formation) of the study area, which is underlain by rock unit of Ameki and predominately contains Laterite, mudstone, siltstone, claystone, sandstone and shale and Burrows were identified.
 The rock sequence consist of reddish lateritic material, highly weathered mudstone capped with ripped bedded kaolinite clay unit, light grey claystone, cross-bedded sandstone with claystone, whitish sandstone, siltystone, fine-medium grained sandstone with pockets of mudclast capped with ferruginized ground and dark grey shale.
 On the basis of gross lithology, sand-silt-clay percentage, color, texture and assemblage of sedimentary structure, eight distinct lithofacies type were recognized, grey shale facie (Gs), clay stone facie (Cs), cross-bedded sandstone facie (Cbs), mudstone facie (Mf), lateritic facie (Lf), mudstone facie (Bms), ferruginized sandstone facie (Fsf), sandstone facie (Bsf) are recognized within the lithosuccesion.
 From the analysis, the facies are grouped into two facie association on the basis of grain size. The Fine-grained facies association (FFA) which consist of Gs, Cbs, Cs, Mf and Fst and the Medium to Fine-grained facies association (MFA) which also consist of Bms, Bsf and Lf. It also shows medium grained sand, moderately sorted to well sorted sandstone, Skewness ranged from symmetrical to positive skewed and kurtosis showed leptokurtic.
 Deduction from facies analysis and grain size analysis shows that Ameki Formation consist of foraminifera and Mollusca which indicate that Ameki Formation was deposited in the estuarine(Marine) environment.

Depositional Environments and Geochemical Assessments of the Bende Ameki Formation Potential as Petroleum Source Rocks in the Ogbunike Quarry, South-Eastern Nigeria

This paper focuses on investigating the paleoenvironments and hydrocarbon generation potentials of the outcropping Eocene Bende-Ameki Formation at Ogbunike quarry, Anambra Basin southeastern Nigeria, which is the Niger Delta Agbada Formation subsurface equivalent. The fine to coarse sandstones interbedded with parallel laminated grey, coaly shales, and bioturbated claystones were the dominant rock facies. The shales contain Ammobaculities, Ammontium, lenticulina, and Reophax benthic foraminifera of brackish to outer shelf environments. The rock sequence and biofacies associations indicate a fluvial, shoreface to delta environments. The marine and continental paleoenvironments are supported by the concentration and association of redox-sensitive trace elements such as vanadium and nickel of oxic to dysoxic paleoconditions. The twenty shales have a range of TOC from 0.39 - 8.81 wt% (mean 2.2 2 wt%), suggesting a good to very good source rocks. The organic richness is highest within the depth of 2 – 6 m across the quarry. Their genetic potential (S1+S2) ranges from 0.22 - 27.35 (mean 2.8 kgHC/ton) of rock, and hydrogen index from 26 to 292 mgHC/gTOC with a mean of 67.3 mgHC/gTOC. This, however, indicates dominance of Type III gas prone kerogen of terrestrial origin. The oxygenated water column characterized by the presence of benthonic scavengers may not preserve lipidenriched organic constituents of anoxic paleoenvironments which could account for the rare Type II oil and gas prone kerogen in the source rock. The thermal history inferred from the Tmax between 401°C - 424°C suggests that the source rocks are immature at the present stratigraphic level.

Stratigraphic relations and habitat of the Bende fish teeth, southeastern Nigeria

The age and habitat of the Bende fish fossils have remained a matter of controversy with interpretations ranging between the Paleocene Imo Formation and the Eocene Ameki Formation. Outcrop-based sequence stratigraphic analysis presented in this work shows that the Imo and Ameki Formations together include three laterally extensive estuarine central basin/offshore mud rock units that are associated with the 59.7, 58.1, and the 56.8 ma maximum flooding surfaces, respectively. Field evidence and stratigraphic analysis show that the Bende fossil bones are hosted by the mud rock unit containing the 58.1 ma maximum flooding surface, while the Ameke bone fossils are contained within the condensed section associated with the 56.8 ma maximum flooding surface. Apart from highlighting the relevance of sequence stratigraphy in paleobiological interpretations, this study shows that the Bende fish fauna which Arua first assigned to the Eocene Ameki Formation indeed belongs to the Paleocene Imo Formation.

Evaluation of geotechnical properties of gully erosion materials in ORLU and its environs, IMO state, Nigeria

The evaluation of geotechnical properties of rock materials is used to ascertain the environmental factor that necessitated gully erosion in Orlu and its environs, Imo State, Nigeria. The study is aimed at geotechnically defining the characteristics, causes and formation of the gully erosion with particular emphasis on the current land degradation in the study area. Data used in the study were derived from field measurements, and laboratory analysis. Gully variables such as length, depth and widths were also determined. The result of the geological mapping revealed that there are three geologic formations encountered in the study area namely; Ameki, Ogwashi Asaba, and Benin Formations. The result of the field studies shows that 27% of the gullies observed occur in Ameki Formation while no gully was discovered in Ogwashi Asaba formation. The grain size distribution curves interpretation revealed that 80% (by weight) of the soils are medium to coarse grained sand and fine gravels, while the remaining 18% and 2% are for fine grained sand and coarse grained silt. The Atterberg Limit Test interpretation shows that the plasticity index of the formations ranges from 24.83% to 48.42%. Based on the results of the geotechnical properties of rock materials in the study area, the factors responsible for gullies occurrence in the study area were identified as topography, rainfall, geology, and anthropogenic factors. The devastating effects of gully erosion in the study area were observed to include loss of about 22km2 of arable lands; 2 major and 6 minor road failures; loss of many houses and other infrastructures; pollution of surface and underground water. Finally, it is recommended that the appropriate authorities, individuals and all stakeholders in the environmental protection agency should develop ideas in environment watch towards gully erosion control.

Organic and Trace Element Geochemistry of the Ameki Formation, South Eastern Nigeria: Implications and Hydrocarbon Generating Potential

Organic and Trace Element Geochemistry of the Ameki Formation, South Eastern Nigeria: Implications and Hydrocarbon Generating Potential

Lithofacies characterization of sedimentary succession from Late Cretaceous-Tertiary age in Benin west-1, northern Depobelt, Anambra Basin, Nigeria

Lithofacies and their relationships, textural content, sedimentary structures were used to delineate eight facies associations in the Benin west-1. Seven lithofacies are recognized; coarse grained sandstone with granules, laminated shaley sandstone, shaley siltstone, laminated shaley siltstone with fossil fragment, laminated shale, siltstone, coarse grained sandstone and micaceous sandstone facies. Each lithofacies is interpreted to represent different or similar depositional environments. Sediments of the Ameki Formation and Imo Shale encountered in the Benin west-1 were deposited in distributary channel and prodelta to marine shelf environments

Molecular composition and chemotaxonomic aspects of Eocene amber from the Ameki Formation, Nigeria

The molecular composition of fossil resin from the Eocene Ameki Formation, southern Nigeria has been analyzed by infrared spectroscopy, pyrolysis–gas chromatography–mass spectrometry and thermochemolysis gas chromatography–mass spectrometry to determine the structural class and botanical source of the resin. The pyrolysis products were dominated by bicyclic products derived from regular labdatriene structure and lacked succinic acid indicating Class Ib type amber. The biomarker compositions in the pyrolysates are dominated by sesquiterpenoids of the cadinane and bisabolane classes that are common constituents of higher plants and labdane type diterpenoids. The exclusive presence of labdane type diterpenoids and the absence of higher plant triterpenoids strongly suggest that the amber was derived from a gymnosperm (conifer) botanical source. This observation contrasts with the angiosperm source previously suggested for the resin based on the palaeobotanical studies of the host sediments. The specific family source within the conifers could not be ascertained based on the molecular composition of the resin. However, the presence of methyl-16,17-dinor-callitrisate pointed to the Cupressaceae family although other Cupressaceae biomarker indicators were not detected in the resin.

Paleocene ichthyofauna and paleoenvironmental setting, Imo Formation, southeastern Nigeria

The Paleogene vertebrate fossil record of Nigeria has until recently been limited to marine deposits in the Eocene-age Ameki Formation. New work in the Imo Formation of southeastern Nigeria has revealed a diverse ichthyofauna of Paleocene age. The Imo Formation overlies the Nsukka Formation, and underlies the Ameki Formation. The uppermost bone-bearing interval of the Imo Formation is separated from the overlying Ameki Formation by a NW-SE trending, shoreface- tidally-influenced sandstone ridge that dominates the Ozuitem-Umuahia landscape. The Ameki beds outcrop to the west of the sandstone ridge, whereas the Imo outcrops to the east. Fossils described herein were recovered from an interval of interstratified crudely laminated clay/shale and calcareous lenses of well-sorted sandstone/siltstone which outcrops to the east of the sandstone ridge in the Bende District. The fauna is represented by at least seven taxa, including an actinopterygian, five chondrichthyans (represented by one ray and four shark species), and Cylindracanthus, an enigmatic incertae sedis taxon. Five of the species in the Imo fauna appear to have survived into the Eocene, whereas the remaining two are hitherto undocumented in younger faunas of Nigeria.

Groundwater investigations: experiences in parts of South Eastern Nigeria

comAbstractTo serve as the basis for a preliminary estimate of aquifer potential in an area where there has been no successful water borehole, Vertical Electrical Soundings (VES) were carried out in conjunction with hydrogeological study in Okija. The study area is on the Ameki Formation. The interpretation of the resistivity sounding data indicates a depth of 59-81m to the aquifer. Interpretation of the field curves outlines the resistivity values (8955-9964 U-m) and the depths (59-81m) to the sand (aquifer) of thicknesses (65-73m) within the silt/sand intercalation of the Ameki Formation. The results also indicate generally the types and thickness of soil materials above the aquifer. Keywords :Aquifer potential, vertical electrical soundings, Ameki formation, Okija. Nigerian Journal of Physics Vol. 18 (2) 2006: pp. 255-260

Hydrogeophysical investigation of Southern Anambra Basin Nigeria

This study was undertaken to study the hydrogeophysical properties of the geologic formations that underlie the Southern Anambra Basin and to help in delineating sites for drilling of productive boreholes in the area. The North-south trending Awka-Orlu cuesta divides the study area into two relief features, viz; the western uplands underlain by the Eocene Ameki Formation and the Miocene Ogwashi-Asaba Formation and the eastern lowlands underlain by the Paleocene Imo shale Formation. Surface water is uncommon in the western uplands. Forty-two Schlumberger electrical soundings were carried in the study area to a maximum current electrode separation of 1200m. Eleven of the soundings were conduct besides boreholes already drilled in the area. From the data, variations of the depth to the water table, longitudinal conductance, transverse resistance and the thickness of the aquiferous layer have been established. The analytical relationship between the Dar Zarrouk parameters and the hydraulic characteristics were used to assess the hydrogeological condition of the basin. These have led to inferences about the aquifer hydraulic conductivities and transmissivities and K product across the area. Consequently favourable areas have been suggested for future groundwater development in the area. Hydrochemical analysis carried out on the water samples indicates that the water samples are suitable for human consumption as well as for industrial uses. KEY WORDS: Hydrogeophysical, Aquifer, Hydrochemical, Groundwater. Global Journal of Geological Sciences Vol.2(2) 2004: 221-233

The trace fossil Teredolites longissimus in calcareous concretions from the Eocene Ameki formation, southeastern Nigeria

An occurrence of the trace fossil Teredolites longissimus crowded within a woody core in calcareous concentrations is described and illustrated. The calcareous concentrations which vary in shape from spherical to oval are found in situ in dark grey-blue to black, silty to sandy, highly micaceous, shelly, lagoonal flat shales of the Eocene Ameki Formation near Umuahia in southeastern Nigeria. The wood, bored extensively by pholadid bivalves of the genus Teredo, drifted probably into the lagoonal flat from estuarine environment. Some relationships are noted between the bored wood and the calcareous concretions.

Morphology and origin of calcium carbonate concretions in Eocene shale, southeastern Nigeria

Calcareous concretions that have at their core woody fragments and masses of closely arranged Teredo tubes are common in Eocene lagoonal shales of the Ameki Formation, southeastern Nigeria, Association of the concentions with the woody material suggests that, during the decomposition process of the material, a microenvironment was created with a raised pH. The process is also responsible for the precipitation of Ca ++ ion, probably as adipocere. Conversion of adipocere to CaCO 3 brought about the splitting of the core into many pieces. The pieces are covered with a thin warty layer of calcite which derived from the pore waters in the cracks.

Fossil predaceous gastropod borings from Nigeria

Predation of naticids and muricids has been studied in the Ameki Formation (Eocene). The investigation shows that six types of holes are found in the Ameki gastropod and bivalve prey. In identifying the borers of a particular hole type, the mode of life of the most preferred prey species is used as a diagnostic parameter. Infaunal prey species are bored by naticids, epifaunal prey is bored by muricids. The presence of a boss at the base of an incomplete hole and countersunk holes are the additional criteria for identifying naticid borings. If the living habits of the preferred Eocene Ameki prey are used as a criterion to distinguish between naticid and muricid borings, then the steepness of holes, the presence or absence of correlation between hole-size and shell-size, the bevelled or ragged nature of the outer rim of a hole and the preferred site for boring become less valuable as distinguishing features.

Gastropod predators and their dietary preference in an eocene molluscan fauna from Nigeria

Boreholes produced by naticids and muricids can be recognized in molluscan prey from the Ameki Formation (Eocene) in southeastern Nigeria. Possible predators are four species of Naticacea and three species of Muricacea. A quantitative assessment of the occurrence and type (naticids or muricids) of borings in 1409 fossil shells belonging to seventeen species shows that there is a pronounced differential proneness to attack among the species. The most common prey species of naticids were the infaunal, feebly ornamented bivalve Tivelina newtoni and the infaunal, smooth gastropod Natica amekiensis. The principal prey of muricids was the epifaunal, strongly ornamented gastropod Bonellitia (A.) amekiensis.