Geophysical Study on Groundwater Structure at two localities in Central Butana (Sudan)

Abstract

ABSTRACT The study area lies between latitudes 14° 30‘ and 16° 00‘ N, and longitudes 33° 30‘ and 35° 30‘ E. A negative Bouguer gravity anomaly was identified in the area and referred to as Jebel Mundara. Also the drainage system shows the anomaly area as a delta of four Wadis (valleys). A number of isolated outcrops of l?re-Cambrian Basement Complex rocks scatter over the central plains of Sudan. In the Butana region, several hills occur prominent landmarks within the predominai;ttly flat clay plains. The solid geology of the Butana plain is rather concealed under a feneer of variable thickness of superficial clays covering over 70% of its total area. The present study was suggested in an effort to delineated and define the mentioned anomaly in more detail and to give a reasonable geological and hydrogelogical exploration for its existence. Also to check the delta of another four Wadies lying on the opposite side and shearing the same water divide with the mentioned ones. Integrated geophysical methods (Regional Gravity, EM Survey, and Electrical-Sounding) were applied to achieve the above aims. A total of 100 gravity points were conducted in the study area and they are compile to 275 gravity points acquired, by Sun Oil Company (approximately 2475 krnz were covered in the study area). Gravity data analyses were perfonned by "GEOSOFT" packages. The results show that the gravity lows is largely attributed to the occurrence of low-density rocks (granite intruded) into the high-density rocks (green schist) of the Butana region. On the other hand the gravity high zones unambiguously coincide with the areas of known shallow Basement Complex. A total of 57 VES were carried outs in the study area and distributed a long 7 profiles, cover almost the two interested areas. The results indicate‘ that the sedimentary cover'is relatively thin, and the Basement Complex is‘very shallow in the study area. The total length of the EM Survey is about 35 km. The EM measurements reflects considerable fracturing (faults and shear zones). Threc sets of fractures are identified with NE, NW and N-S trending. ' Finally, one of the objective of this work is to delineate lineaments in more details using geological informations and the geophysical data (gravity, resistivity, and electromaghetic) in the study area. They are also merged and combined with image data for a given geographic area using "GIS" software, to produce an integrated map of the area. Water supply'for settlement in the study area requires a different approach. The Basement rocks outcrop on the surface and the area is sloping to the north, therefore, seepage of water through the fracture system is negligible, in this case storing of rainwater through surface dams is more appropriate. ll