A Geophysical Investigation of the Area Around Abu Deleig Town, Khartoum State, Sudan.

Abstract

In mid-seventies, the campaign for hydrocarbon exploration in the Sudan was intensified. The gravity survey conducted by Sun-Oil Company in 1984 for the above mentioned purpose revealed numerous low gravity anomalies distributed in various parts of central Sudan. In the area located between latitudes 15°00" & 16° 15' N, and longitudes 33° 30' & 34° 30' E., two strong negative Bouguer gravity anomalies were identified and they are referred to as Wad Burwa and Qeili, (Ibrahim, 1993) with magnitudes of approximately -70 and -65 mGals respectively. Both anomalies were interpreted as caused by sedimentary basins, (Ibrahim, op. cit.). The present study was suggested in an effort to delineate and define these anomalies in more detail and give a reasonable geological explanation for their existence. Integrated geophysical methods (gravity, magnetic and electric), were applied for this purpose. A total of 67 gravity measurements were taken along four, E- W and one NW-SE trending profiles, with a spacing of 2.5 Km between the stations. In addition, a number of 1525 pre-processed gravity measurements acquired by Sun-Oil Company were later merged with the a fore mentioned measurements, hence the total coverage reached to approximately 15,000 Km2. In the geoelectric survey, a total of 50 V.E.S. were measured in various surveys, but only 40 soundings have been utilized in this study, because the rest lie outside the area of study. The magnetic survey covered a total of 383 measuring points. The station spacing is mostly around 500m, and sometimes less, depending on the investigated feature. Gravity data analysis was performed by "GEOSOFT" package, whose analytical techniques utilizing Fourier Transform enabled attempts on various approaches of field isolation such as directional derivatives. Likewise, filtering processes by "Magmap" have been applied to the magnetic data. The resistively data was processed and interpreted using" RESIX " software © Interpex Co. Colorado, USA. Its results have indicated that the sedimentary cover is relatively thin and increases to the north as well as to the west. The magnetic data had been processed by using, "GEOSOFT" package. The results of the magnetic survey revealed lithological boundaries more clearly especially Qeili Ring Complex. Modeling of both, gravity and magnetic data have been achieved by the use of "GRA V2DC " and" MAG2DC " programs © J. Cooper, South Africa. Re-processing and interpretation of the available gravity data suggested that, these low anomalies could only be explained by an emplacement of granite-syenite bodies which are characterized by relatively low densities with respect to the regionally extensive basic rocks within the area. This indicates that previous interpretations did not satisfy the available geological and geophysical data. A test borehole was sited at Sheikh Ali Abu Deleig village (i.e. chosen within the -50 mGal contour line), to examine the extent of the anomaly (basin). The drilled bore hole encountered basement rocks at a depth of 37.5 m. Surface geological information as well as, more geophysical investigations are then requested to give a proper interpretation of the gravity anomalies identified in the Sudan