Geologic and Hydrogeologic Studies of East Kordofan Area, Sudan

Abstract

East Kordofan area lies within the declared thirst area of the Sudan. Data collected from more than 170 rotary drilled wells helped to reveal the geological and hydrogeological character of the area. The rock units from top to bottom are: A. Superficial deposits: These can generally be divided into i) typical eolian wind – blown Qoz sand, and ii) fluvial silstone deposits mainly in the southern part. B. Umm Ruaba Series: These consist of sands, sandstones, silty sandstones and clays which are silty and contain carbonate nodules (Kanker). It is characterised by rapid facies changes. Data from deep wells revealed that the greatest thickness is found in bastins within the Basement Complex, particularly the Para trough in which more than 1,500 feets of sediments occur. C. Nubian Sandstone Formation: This was detected for the first time in the area. The character of the formation generally shows that it is mostly composed of - 1) Basal conglomerates, 2) Sandstones and 3) Mudstones. D. Nawa Series: This is known only from boreholes data. It has a thickness of more than 935 feet. Thin sections cut from drilled core show that some degree of diagensis has acted on these rocks, indicated by the appearance of small euhedral crystals of sodic plagioclase concealed in the groundmass. E. The Basement Complex underlies all other rocks in the area. The only outcrop, at Jebel El Kon, is mainly equigranular pink granite. The Basement configuration shows a high subsurface ridge at the centre of the study area. Hydrogeologic studies reveal four aquifers: Superficial Qoz sand, Umm Ruaba Series, Nubian Sandstone Formation aquifers and to a lesser extent there is water in the weathered Basement Complex rocks. The most important of the proper aquifers is the one in Umm Ruaba Series. The transmissibility of the aquifer is estimated from pumping test to range between 100 gallons/day/foot, and 70,000 gallon/day/foot No pumping tests were made in the wells that tap the other aquifers. The main source of recharge in the area is the rainfall, which varies from 259 mm to 525 mm per year. The recharge is seen to come from the north and north – western side towards the southeast and the centre of the area. A second zone is the Nuba Mountains in the south. This is augmented by recharge from the surface represented by Khor Abu Habl. The presence of a subsurface ridge in the central part, results in shunting the water around it, producing high salinity stagnation prints behind it in shadow zones such as Umm Seaada and El Defis Goda