pjg.01.2021.08.12
ABSTRACT
ESTIMATION OF THE STRUCTURAL PATTERN AND SEDIMENTARY THICKNESS OVER PART OF ANAMBRA BASIN, NIGERIA USING AEROMAGNETIC DATA
Journal: Pakistan Journal of Geology (PJG)
Author: Priscilla E. Ikioda, Charles O. Ofoegbu, Etim D. Uko, and Olatunji S. Ayanninuola
This is an open access journal distributed under the Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
Aeromagnetic data acquired over part of the Anambra Basin is analyzed to determine the structural pattern and sedimentary thickness of the basin. The study area is covered by high resolution aeromagnetic data on sheets 301 (Udi), 302 (Nkalagu), 312 (Okigwe) and 313 (Afikpo), and lies between latitudes 5o30’0”-6o30’0” and longitudes 7o0’0″-8o0’0″. The whole area was divided into 25 overlapping blocks of 37.2km2 each and a 2D energy spectral analysis was carried out. Total magnetic intensity data was subjected to filtering and analytical techniques to determine the structural pattern, mineralization potential, depth to the basement, variation in the sedimentary thickness. The structural map generated using the vertical derivatives shows that the major structural orientation of the area is in the ENE-WSW trend and the minor trend is the NW to SE direction widespread all over the area. These structures are as a result of the various near-surface magnetic intrusion within the study area. The spectral analysis result shows two depth layers, the deep and the shallow depth, the depth to magnetic basement for the deep anomalous source ranges from 3.3km to 4.84km with an average depth of 3.99km, while the depth to shallow magnetic sources ranges between 0.46km to 0.67km and an average of 0.56km within the area. The mineralization pattern in this area follows the ENE-WSW direction.
| Pages | 08-12 |
| Year | 2021 |
| Issue | 1 |
| Volume | 5 |
The Siwalik sediments are widely distributed in foreland areas of Pakistan, India, Nepal and Bhutan. In Pakistan they are composed of four formations (Chinji Formation, Nagri Formation, Dhok Pathan Formation, Soan Formation) These post tectonic deposits contain vast phylogenetic trends of modern vertebrate species especially dating back to Miocene-Pliocene. Our study encompasses the Miocene-Pliocene Nagri Formation exposed at Kanati Section, District Khushab. The purpose of the study is to establish depositional modal based of Lithofacies and Petrographical studies. The Nagri Formation in the Kanati Section is 47 m thick and predominantly contains sandstone, silt and clay with sub-ordinate conglomerates. Four Lithofacies were established. These are Conglomerate Facies (N1) interpreted as channel floor deposits, Sandstone Facies with cross beds and extraclasts (N2), where extraclasts were deposited by the lateral movement of channel, Siltstone and Claystone/Mudstone Facies (N3) which were interpreted as crevasse splay deposits, and Clay Facies (N4) interpreted as flood channel deposits. The clay exposed here was mostly brick red in color showing oxidizing conditions due to subaerial exposure. Spheroidal weathering was quite common in sandstone. Petrographic analysis for sandstone thin sections revealed mostly moderate amount of quartz (59.53%), lithic fragments (39.9%) with minimal amount of feldspar (0.55%). The petrographic results for Nagri sandstone were plotted on a QFL diagram from where it was interpreted as belonging to Lithic Arenites. The provenance of this sandstone was established to be of Recycled Orogen based on the studies.
