Characterization of Subsurface Densities Using Aerogravity Data of Okigwe and Environs

Abstract

Isaac Owoicho Agada, Magnus Uzoma Igboekwe and Faustinus Chukwunweike Anyadiegwu

Density and its variations across rock materials govern gravity anomalies. As an important physical property of geologic materials, knowledge of rock densities provides vital information on subsurface structure and explorations. The study was carried out to model gravity anomalies and analyse the varying densities of subsurface materials within Okigwe and Environs located between Latitudes 5˚30’N and 6˚00’N, and Longitudes 7˚00’E and 7˚30’E in South Eastern Nigeria. Using Oasis Montaj geophysical data processing tool, aerogravity dataset for Okigwe and environs as contained in the Okigwe aerogravity sheet 312 obtained from Nigeria Geologic Survey Agency (NGSA) was analysed, mapped, profiled and modelled inversely to reveal the subsurface with varying and unique densities. There are huge masses of igneous/ gneiss intrusions with densities of 2.80g/cm³ in a diagonal array from the NE to SW of the study area, with locations such as Ihube, okigwe town and Umuna featuring strategically. The entire Okigwe and environs is underlain by a thick Precambrian basement complex, having varying densities of 2.67g/cm³ and 2.76g/cm³. The huge basement complex of the study area is overlaid with sediments of various densities, ranging from sandstones (2.25g/cm³), and clay/shale/laterite (1.98g/cm³). At the NW extreme and SE wing around Obowo, Umuahia and environs, the subsurface is dominated by low density materials as projected by the negative gravity signatures observed in the Bouguer anomaly map. Materials with the highest densities were observed at the NE axis around ihube, Okigwe, the southern part of Isuochi and their environs.