Ajali Sandstone Research Articles

Geotechnical evaluation of untreated and cement-treated Ajali Sandstone from southeastern Nigeria

Abstract The grain size analysis and the Atterberg limit values indicate that the Ajali Sandstone falls into the A-3 and SP-SW classes of the AASHTO and the Unified Soil Classification systems respectively. The low values of the coefficient of uniformity 2.9-3.4 show the deposit is uniformly graded and the soil is deficient in silt-clay fractions. At the optimum moisture content of 8% the untreated soil has a maximum dry density of 1.77 Mg/m3. The CBR of the soil when compacted to the standard Proctor optimum and soaked for three days is 10%. To establish the effective cement requirement of the soil, 5, 7, 9 and 110y weight of Portland cement was added to the soil. Results show that 80f the stabilizer meets the required minimum CBR of 100% and the 7-day uniaxial compressive strength of 1.4MPa (l.4 N/mm2). On ageing, the stabilized A-3 soil gains appreciably in strength.

Environmental pollution from coal mining activities in the Enugu area Anambka state Nigeria

Hydrogeological studies of the Enugu coal mining area were carried out which included hydrogeochemical analyses of water samples. These analyses revealed high sulphate and iron content in the acid mine drainage water as well as high total dissolved solids' (TDS) and low pH (acidity) values. The water issues from the Ajali Sandstone formation and the underlying carbonaceous Mamu Formation and is classified as hard water. As a consequence of under-mining this aquifer, huge volumes of (polluted) water has flooded the mines are channelled into some streams or rivers which in turn get chemically polluted. Remedial measures have been indicated which include the following:

Paleogeography, sedimentation and tectonics of the upper cretaceous Anambra basin, southeastern Nigeria

A reinterpretation of the depositional environments of the Anambra Basin succession in the light of modern sedimentological models has necessitated a revision of the late Cretaceous paleogeography of southeastern Nigeria. The phases of transgressions and regressions in the Campanian in the Campanian to Paleocene within the Anambra Basin are reviewed, based on these new interpretation. Thus, it has been shown, for example, that the Mamu Formation and the overlying Ajali Sandstone are both part of a continued controlled Maastrichtian transgression, which started in the late Campanian, superimposed on a regional geoidal eustatic sea level rise, which lasted until the Paleocene. This contrasts with the interpretation favouring a regressive phase of a short-lived Maastrichtian transregression, as has been previously thought by some workers. Tectonic movements within the basin have been shown to have been active during the late Cretaceous sedimentary cycles, as demonstrated by variations in the thickness patterns across the basin. Lateral facies variations both within and across formation boundaries, from north to south, as well as the occurrences of a large-scale slumps and other types of syn-sedimentary deformation structures attributed to tectonic activity further attest to the active nature of the basin during the period of sedimentation. The pattern of subsidence is also thought to have been influenced by earth tremors and periods of “quiescene”, particularly in the northern Ankpa sub-basin.

Paleocurrent, petrography and provenance analyses of the Ajali Sandstone (Upper Cretaceous), southeastern Benue Trough, Nigeria

Paleocurrent, petrographic and heavy-mineral analyses of the Ajali Sandstone (Late Cretaceous) in southeastern Nigeria show that the sedimentary rocks on the Santonian Okigwe-Abakaliki anticlinorium provided the major detritus, whereas minor contributions of the eastern Precambrian basement block (Oban massif) are confined along a narrow belt southeast of Alayi in the Afikpo Basin. The sandstones derived from the major sedimentary source are quartz arenites characterized by a zircon-tourmaline heavy-mineral assemblage and a radial paleocurrent pattern which parallels the paleoslope of the provenance. On the other hand, those sands generated from the eastern basement block are arkose and sub-arkose dominated by a garnet-apatite-rutile heavy-mineral assemblage and southwesterly directed paleocurrent modes. The results of this study support the previous hypothesis that most ancient quartz arenites are multicycle in origin.

Palynostratigraphy of the Ahoko sediments from the nupe basin, N.W. Nigeria

The Ahoko sediments of the Nupe Basin were sampled in four locations. Among others, the following Upper Cretaceous miospores were identified from locations 2, 3 and 4: Syncolporites marginatus, Proteacidites tengispinosus (Echitriporites trianguliformis), Gleicheniidites senonicus, Granulatisporites subgranulosus, Ericipites crassiexinus, Proteacidites fromensis, Cicatricosisporites sp., Retitricolpites sp., Monocolpollenites sp., Cingulatisporites ornatus, Tricolporopollenites sp., Longapertites vaneendenburgii, Tricolpites sp., Ephedripites sp. The fossil assemblage indicates a Maastrichtian age for the sediments. Location 1 could belong to the False Bedded Sandstone (Ajali Sandstone) and the shales, sandy shales and sandstones in locations 2–4, to the Upper Coal Measures. These two lithologic units, the Ajali Sandstone and Upper Coal Measures belong to the Ajali and Nsukka Formations respectively.

Tidal shelf depositional model for the Ajali Sandstone, Anambra Basin, Southern Nigeria

The Ajali Sandstone is a dominantly sandstone formation of Campanian-Maestrichtian age occurring within the Anambra Basin, Southern Nigeria. Previous interpretations of the Ajali Sandstone have suggested fluvial and fluvio-deltaic settings, with the sediments having been derived from westerly source areas of the Abakaliki-Benue fold belt and the granitic basement of the Camerounian Highlands. However, process interpretations of sedimentary structures and palaeocurrent analyses from the Ajali Sandstone south of Nsukka suggest a tidally influenced regime, possibly tidal shelf, characterized by shoreline-parallel sand bodies with intercalations of shelf muds. Evidence includes both planar and trough cross sets which display occasional herringbone cross-stratification, reactivation surface sets and the typical ‘bundle structure’ associated with these discontinuity surfaces, overlying storm-generated granular beds. A dominantly southerly (ebb) current is indicated by the large-scale planar cross beds interpreted as avalanche sets of sandwave bedforms. The trace fossils Ophiomorpha and Skolithos also indicate a shallow marine depositional environment for the Ajali Sandstones.