POWER SPECTRAL ANALYSIS OF RESIDUAL AEROMAGNETIC MAP OF SOKOTO BASIN, NORTH WESTERN NIGERIA

Aeromagnetic data obtained from a recent aeromagnetic survey of Sokoto Basin, northwestern Nigeria has been studied using Power Spectral (PS) analysis. The Sokoto Basin is an arm of the Iullemmeden Basin is situated between latitudes 10°30’’ N to 14° 00" N and longitudes 3° 30” E to 7° 00" E in the Nigeria national grid. The PS analysis was carried out to determine the depth to magnetic sources in the Basin. By splitting the study area into 16 spectral model blocks, the spectral probe of 27.5 by 27.5 km2 for each block was carried out respectively. The results of the PS analysis revealed two prominent magnetic source depth layers. Depths determination of the magnetic sources showed that the first layer has average depth of 0.28 km which is interpreted as shallow magnetic zones attributed to the intrusions of magnetic rocks into the sedimentary formation. The second layer has average depth of 1.86 km and was interpreted as the deep magnetic source representing the depth to magnetic basement. Hence the results show that the maximum thickness of the sedimentary layers to be 1.86 km is the limit of the depressions on the basement surface of the basin. Hence it suggests that exploration of hydrocarbon which would require a minimum sedimentary thickness of about 2.3 km as obtainable in the coasts of West Africa region is also not feasible.

Relevance of topographic control on hydrogeological properties of the weathered granite gneiss aquifer in watershed perspective -- Usri sub-basin, Giridih, India

Usri, a southward sloping fourth order drainage sub-basin of Barakar river, is located in the northern margin of Chhotanagpur plateau, Giridih, India. Gently sloping undulating landforms devoid of hills and outcrops is main characteristics of this sub-basin. Topographic elevation varies between 310 to 390 m MSL. Geographically it is located between lat 24.38° N to 24.54° N long and 86.07° E and 86.28° E longitudes. Thick weathered horizon developed over homogenous Archean granite-gneiss is the principal unconfined aquifer system. Basement topographic (weathering depth) and water table have been correlated with the surface topographic features (landforms). Presence of considerably thick weathered horizons, devoid of rock exposures, regional uniformity in geomorphic characters and its location at fringe of plateau provides favorable condition for correlation of surface topography with basement topography and water table. It has been observed that basement surface is replica of ground surface only in regional or watershed perspective with reference to common datum. The basement surface is not always exact replica of ground surface at micro watershed scale. In many cases, basement surface is reverse of ground surface. The depth basement has remained constant along the basin water-divide situated near the margin of the plateau. The depth of basement (weathered horizon) is higher in upper reaches than lower reaches on the micro water-divides (upland) as well as in the drainage depressions (channels) within the sub-basin. The upper reaches of the sub-basin mainly along the basin water-divide has better groundwater prospects than lower reaches. There is no definite trend of water table with respect to ground and basement topography. Many places water table is shallow on the micro water-divides (upland) and deep in drainage depressions (channels). The established correlations are likely to be applicable in the other geographical area where similar watershed and geological characteristics exits.

Paleoenvironmental reconstructions and a sedimentological evidence of paleoseismic activity ca 9000 yr BP in Karelia, NW Russia, based on lake sediment studies on Mount Vottovaara

Karelia, like the entire Fennoscandian Shield, is a region with a low seismic activity. An example of the best-studied locality is a paleoseismic dislocation on Mount Vottovaara, which bears traces of disastrous Holocene geological events following the degradation of the last ice sheet. The evolution of the study area falls into three stages. At pre-Quaternary stage I, an uplifted block broken by numerous fractures and faults was formed. At glacial stage II, coarse clastic moraine was formed, the moving ice polished the crystalline basement surface and glacial scars were formed. At final deglaciation stages, the mountain top remained a nunatak. As Salpausselkä II marginal sediments retreated by about 70 km from the mountain, a postglacial stage in the region’s evolution, at which an earthquake occurred, began. It could have been triggered mainly by the consequences of the degradation of the Late Weischelian glaciations such as the rapid removal of the glacial load that contributed to the rejuvenation of various old faults. Changes in paleoecological conditions for the Mount Vottovaara area were reconstructed based on the results of lithological, palynological, diatom and radiocarbon studies of bottom sediments from a small lake on the mountain top. Vegetation dynamics from the Younger Dryas to the Subboreal period is presented. Small lake evolution stages were distinguished based on analysis of diatom complexes and the pollen and spores of aquatic and aquatic-subaquatic plants and Pediastrum algae. The data obtained show that minerogenic sediments were abruptly succeeded by organic in the late Preboreal-early Boreal period. The thickness of Boreal sediments and changes in the composition of diatom complexes and spore-and-pollen spectra suggest a depositional hiatus triggered by a strong earthquake which changed the water level of the pond and its basin structure. The earthquake is also indicated by numerous dismembered, displaced, thrown-away and shifted rock blocks and seismogravity downfalls. Deflation and other types of weathering are responsible for the formation of seide-shaped piles of blocks and boulders on the mountain top.

Subsurface Structural Mapping over Koton Karifi and Adjoining Areas, Southern Bida Basin, Nigeria, using High-Resolution Aeromagnetic Data

In this current work, we aim to delineate the subsurface structural trends, determine the depth to basement surface, and provide an illustrative 3D model for its subsurface structure. Four digitized aeromagnetic maps were acquired from the Nigerian Geological Survey Agency, Abuja. The total field aeromagnetic anomalies over Koton Karifi and adjoining areas have been evaluated. In order to map the subsurface structures and estimate the depth to basement surface the spectral analysis method was applied. To achieve such goals, a detailed analysis of the aeromagnetic data for the study area was performed. 2D interpretation was carried out for the aeromagnetic data. The processes used include contouring of the Total Magnetic Intensity (TMI) data, separation of regional and residual anomalies, structural detection methods such as analytic signal, vertical derivatives, and magnetic lineament mapping were used to map the contacts and faults within the study area. The first vertical derivative and the magnetic lineament maps show major geologic lineaments trending in East-West with minor ones trending Northeast-Southwest. In the south-eastern part of the study area, there is a dome-shaped linear feature. The result obtained using the spectral analysis method reveals two source depth models. The depths to deeper magnetic sources range from 2.81 km to 3.24 km with an average depth of 2.90 km. The deeper magnetic source bodies are identified with the magnetic basement. The shallower magnetic sources which range from 0.45 km to 1.81 km with an average depth of 1.13 km could be attributed to near surface magnetic sources which are magnetic rocks that intruded into the sedimentary formations or magnetised bodies within the sedimentary cover. Based on the sedimentary thickness range of 0.45 to 3.24 km, there is an indication that the possibility of hydrocarbon generation in the study area is feasible.

Deep gravity data interpretation using seismic reflection and well data: A case study of the West Gharib-Bakr area, Eastern Desert, Egypt

A rigorous processing and analysis of the gravity data with seismic reflection and borehole information enabled a general view of the deep-seated regional structures in the West Gharib-Bakr area, Eastern Desert, Egypt. In this context, several interpretational techniques were applied to learn more about the supra-basement structures and intra-basement sources. The interpretation started with a review of the seismic data to clarify the structural elements on top of the Miocene strata, where a number of isochronous reflection maps were constructed and had migrated into depth maps. The Bouguer anomaly map was processed using Fast Fourier Transform filtering based on spectral analysis to separate the gravity anomalies into its components. Gravity stripping was also performed under the seismic isopachs and density controls. The gravity effect of each rock unit was calculated and progressively removed from the original data to obtain a new gravity map on top of the Pre-Miocene. To ensure more reliable results, further filtering and analytical processes were applied to the stripped map. The results of seismic analysis show simple structural configurations at the Miocene level, with a significant increase of evaporite thickness along the Gulf of Suez coast. In contrast, analysis of the stripped gravity map reveals a more intricate structure at the Pre-Miocene level, with increasing numbers/lengths of faults on the basement surface. Lineament analysis shows two major peaks trending N0–20°W and N50–70°E, produced by two main forces in NNW–SSE (compression) and ENE–WSW (tension) directions. The models confirmed a rough and ruptured basement surface, with no evidence of any magmatic intrusions penetrating the sediments. The basement relief map delineates five basins/sub-basins in the area which are separated from each other by ridges/saddles.

Investigations on Ni-Mo Alloy Microstructure with Mo Atom Content

Using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) to describe the relationship between Mo content and the amorphous content in deposites from the effects of the molybdate concentration on microstructure, phase content and morphology of the deposits. It is found when the Mo content is low to 18at.%, the deposits are composed of nanocrystalline main phases and the grain size is below 10nm with tiny particle at the basement surface. When Mo in 18~33at.%, the deposits are composed of amorphous phase up to more than 60wt.% proportion, and the grain size of the nanocrystalline existing in the deposits is stability of 3~10nm with tiny particle and well-distribution of the basement surface. When Mo content is exceeding 33at.%, the deposits performance is of the crystalline properties with more crystal defects in the coating.