Palynomorphs and lithofacies distribution of the Cretaceous northern Anambra Basin, southeastern Nigeria: Evidences depicting continental environment of deposition.

Organic geochemical studies and fossil molecules distribution results have been employed in characterizing subsurface sediments from some sections of Anambra Basin, southeastern Nigeria. The total organic carbon (TOC) and soluble organic matter (SOM) are in the range of 1.61 to 69.51 wt% and 250.1 to 4095.2 ppm, respectively, implying that the source rocks are moderately to fairly rich in organic matter. Based on data of the paper, the organic matter is interpreted as Type III (gas prone) with little oil. The geochemical fossils and chemical compositions suggest immature to marginally mature status for the sediments, with methyl phenanthrene index (MPI-1) and methyl dibenzothiopene ratio (MDR) showing ranges of 0.14–0.76 and 0.99–4.21, respectively. The abundance of 1,2,5-TMN (Trimethyl naphthalene) in the sediments suggests a significant land plant contribution to the organic matter. The pristane/phytane ratio values of 7.2–8.9 also point to terrestrial organic input under oxic conditions. However, the presence of C27 to C29 steranes and diasteranes indicates mixed sources—marine and terrigenous—with prospects to generate both oil and gas.

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Geology and Geotechnical Investigations of the Anambra Basin, Southeastern Nigeria: Implication for Gully Erosion Hazards

10.21203/rs.3.rs-201366/v1 ◽

2021 ◽

Author(s):

Azuka Ocheli ◽

Ovie Benjamin Ogbe ◽

Godwin Okumagbe Aigbadon

Keyword(s):

Mean Value ◽

Gully Erosion ◽

Plasticity Index ◽

Sand Content ◽

Southeastern Nigeria ◽

Average Value ◽

Compaction Test ◽

Silt Content ◽

Anambra Basin ◽

Geotechnical Investigations

Abstract BackgroundGeologic and geotechnical conditions of soils where Nanka and Ajali Formations outcropped in Anambra Basin, Southeastern Nigeria were investigated and accessed. This was done using detailed mapping and mechanical soil laboratory tests to unravel the genesis and continued expansion of gully erosion in the study areas. ResultsField study revealed that gully erosions are more pronounced in the study area with poor vegetation cover and a high degree of slope steepness. Grain size analysis revealed that the soils of the Nanka Formation have an average sand content value of 90.90% (sandy) and silt content value of 3.0% (low fine portions). The plasticity index of the fine portions indicates that the soils are weak plastic, with a mean value of 5.29%. The soils have an average cohesion value of 0.30kg/cm2 indicating a very weak cohesion. The soils are highly permeable; with an average value of 2.67x10-3 cm/sec. The compaction test further revealed that the soils are loosely compacted. The soils for the Ajali Formation have an average sand content value of 95.10% (sandy) and silt content value of 1.43% (low fine portions). The plasticity index of the fine portions indicates that the soils are weak plastic, with a mean value of 2.70%. The soils have an average cohesion value of 0.30kg/cm2 indicating a very weak cohesion. The soils are highly permeable; with an average value of 2.70x10-3 cm/sec. The compaction test revealed that the soils are loosely compacted.ConclusionsAfter field surveys and laboratory analyses, it was found that the gully erosions have been developing respectively on steep slopes and non-vegetated areas, and their genesis facilitated by the cohesionless and very permeable nature of the sandy formations. Following those key findings, it was proposed many practices (agronomic and engineering mainly) that can help mitigate the formations as well as the expansion of this very damaging hazard type. The potential implications of these gully erosion include damaging of buildings, residential houses, bridges and roads, loss of farmland and vegetation, isolation of villages and towns, increased migration of inhabitants as well as degradation of agricultural fertile land.

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Sedimentary controls on the reservoir properties of the Paleogene fluvio-tidal sands of the Anambra Basin, southeastern Nigeria- implication for deepwater reservoir studies

American Journal of Scientific and Industrial Research ◽

10.5251/ajsir.2011.2.1.37.48 ◽

2011 ◽

Vol 2 (1) ◽

pp. 37-48 ◽

Cited By ~ 1

Author(s):

U. Nwachukwu

Keyword(s):

Reservoir Properties ◽

Southeastern Nigeria ◽

Anambra Basin

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Geochemical Characteristics of the Campano-Maastrictian Sediments of the Anambra Basin, Southeastern Nigeria - Implication For Provenance, Paleodepositional Environment, Maturity and Tectonic Setting

10.2118/207170-ms ◽

2021 ◽

Author(s):

Michael Edirin Okiotor ◽

EDeh Desiree Ogueh

Keyword(s):

Inductively Coupled Plasma ◽

Tectonic Setting ◽

Passive Margin ◽

Source Rocks ◽

Sediment Provenance ◽

Southeastern Nigeria ◽

Inductively Coupled ◽

Anambra Basin ◽

Plasma Mass Spectrometry ◽

Chemical Index Of Alteration

Abstract The present study investigates the Anambra Basin shales to determine the provenance and maturity of the sediments using standard geochemical techniques. Twelve (12) representative samples recovered from shale sequences of The Mamu Formation and Nkporo Group of The Anambra Basin were studied to determine the sediment provenance, paleoenvironment, diagenetic conditions, maturity as well as the tectonic setting. To consider in detail and establish the inherent constituents of the Major minerals, Trace and Rare Earth elements, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analyses techniques was employed. The detrital minerals determined are Al2O3 (18.27% and 21.16%), TiO2 (1.73% and 1.63%) and Fe2O3 (2.78% \ and 2.85%), for Nkporo Group and Mamu Formation respectively. The enrichment of SiO2, Al2O3 and TiO2 (1.14, 1.94, 3.67 respectively) supported by Chemical Index of Alteration (CIA) of 93.54 & 39.55 and Rb/Sr ratio of 0.57 & 0.40, indicate that the Anambra Basin sediments are matured. TiO2/AL2O3 binary plots, Th/Co Vs La/Sc crossplots, Th-Sc-Zr triplots and Cr, Ni concentration suggest mixed provenance of felsic to mafic source rocks for these sediments. From the log (K2O/Na2O) Vs SiO2 crossplots, a passive margin tectonic setting was determined for these sediments.

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