New Insights of Namibian Basins Using Regional Gravity and Magnetic Data

Abstract

Abstract Here we present a regional study of the offshore/onshore Namibia using gravity and magnetic data aiming to bring a new light on the structural configuration of the major Namibian basins. This has been achieved by integrating all the available wells, vintage seismic images and public domain information. We produced lineament maps at different scales with the aid of gravity and magnetic data enhancements in the attempt of differentiating between regional and local features. In general, volcanic centres and dikes are well recognized as well as two main structural trends: one oriented NW-SE being more prevalent in the offshore, near-onshore and in the Nama basin; the second oriented SW-NE more pronounced in the Owango basin and the Damara Belt. Satellite derived gravity is also used to delineate the transition zone between continental and oceanic crust (COB). Results are compared with information from seismic and well data to locate the COB on the achieved structural map. Magnetics was also used to estimate the depth to basement all over the studied area. Major basins and structural elements such as the SW-NE uplift in the Owango basin, a series of sub-basins with a significant depth in the Damara fold belt and the Nama basin, offshore basins and sub-basins plus structural highs were identified and mapped. 2.5D Gravity and Magnetic modeling over key areas was used to validate the structural interpretation. These models integrate interpreted seismic profiles, densities from stacking velocities, wells, refraction seismic interpretations and public domain data. We found thick piles of sediments could be present below the SDRs in the Walvis and Luderitz basins. While we found the SDRs probably be at direct contact with the continental crust in the Orange basin, generating an important magnetic anomaly, therefore no important sediment accumulation can be inferred below the SDRs in this basin. We also found the Owambo basin in the onshore dipping northward with important dike intrusions in the middle. The Nama basin is characterised by a high magnetised crust with a higher magnetised intrusion generating the large magnetic anomaly at its western end. Introduction Recently, exploration in new venture areas is relying more and more on integrated studies with all the available public domain information, low cost geological and geophysical data. More often the need of analyzing large areas of a regional extent to rapidly evaluate the petroleum potentials is requiring fast tools and large datasets. Gravity and magnetic data have the advantage of continuously cover large areas at a fraction of the costs of conventional seismic or geological field work. This type of data is more than sufficient for determining structural configuration, basement depth and geometry, COB, evaluate sediment thickness and lithologies at regional and basin scale. Here a regional interpretation of the onshore/offshore Namibia with focus on specific basins was undertaken, mainly using low cost GravMag data and public domain information.