Bouguer Gravity Anomaly Expression of the Abbay (Blue Nile) Basin, Ethiopia

Ketsela Tadesse and G.R. Keller
University of Texas at El Paso, El Paso, TX

The Abbay (Blue Nile) Basin, in the north western part of Ethiopia has an area of about 70,000 km2. It contains more than 3000 meters of thick Paleozoic and Mesozoic sediments covered by a Tertiary volcanic series. Geological and geophysical studies have been carried out in the region to evaluate the hydrocarbon potential of the basin. Laboratory studies suggest that the Upper Hamanlei Formation is the major source rock. The Adigrat Sandstone, Debre-Libanos Sandstone and Middle and Upper Hamanlei Formations are known to be good reservoir rocks in the basin. In addition to these promising strata, the Were Ilu oil seep in the northeastern part of the basin is tangible evidence for the existence of hydrocarbons in the region. Analyses of ETM+ Landsat data together with STRM (Shuttle Radar Topography Mission) 90-meter Digital Elevation Model (DEM) data have allowed us to map lithologic units in remote areas and delineate regional faulted structures. A Bouguer gravity anomaly map generated for the basin shows a series of distinct gravity lows in the area of the basin, which could be due to thick sediments underlain below the basaltic cover. These anomalies indicate that the basin has a complicated subsurface structure and that one major depocenter coincides with outcrops of sedimentary rocks and the oil seep area in the basin. The residual gravity anomaly map of the Abbay Basin delineates a series of north-northwest south-southeast trending gravity minima that are probably associated with major depocenters. Various filtering techniques applied to the data have allowed us to define the depth extent of the sediments and their lateral variations. Results of gravity profile modeling across the basin will also be presented.