Geology of Wadi Ka'am and Ka'am Dam Area, North Western of Libya

Abstract

This research is an attempt to investigate the different geological features of Wadi Ka'am area located along the Mediterranean coast about 25 km west of Khoms City. Geomorphologic, stratigraphic, and structural investigations were carried out. The most important geomorphologic features of the study area include the Wadi Ka'am tributaries, Targhlat, and Al-chusaiha as well as another minor wadi transect of Wadi Ka'am. The wadi is characterized by steep sides due to structural effects. Wadi Ka'am is surrounded by rocky cliffs and saddle areas. The conjunction area of Wadi Ka'am tributaries forms Ka'am Lake where the Wadi Ka'am Dam was built. Terrace areas in the form of steps were formed as a result of water erosion action and may remark water level fluctuations of the lake. A number of internal lakes were formed in low laying areas due to confinement of water in the direction of discharge areas of the wadi. Sand bars (spites) were formed parallel to Wadi stream as a result of decreasing flow of water and hence deposition. Mud cracks were formed in places where muddy areas of the wadi become dried. The highly curved stream meanders of Wadi Al-Chusaiha may indicate the maturity stage of the wadi. Field observations conclude that the stratigraphic succession of the area is represented by the Triassic rocks (Abu Shaybah Formation) made up of continental horizontal-bedded sandstone intercalated with siltstone and mudstone. This is followed by Cretaceous rocks which are separated by an unconformity from the underlying Abu Shaybah sandstone. Cretaceous rocks may have distinguished into two formations: the lower is Sidi As Said Formation which is distinguished into Ain Tobi Member at the base (Dolomitic Limestone) and Yefren Marl Member on the top (Marl with claystone and gypsum crystals as well as Oyster bearing horizons), and the upper Formation is Nalut Formation (Dolomitic Limestone to Dolomite with chert layers and nodules). The two Cretaceous Formations were separated by a distinct para-conformity. The structural investigation was focused on measurements of joint and fault directions in the entire area of study and may conclude that the western stratigraphic succession of Wadi Ka'am is represented by Sidi As Said Formation (Yefren Marl Member) followed up by the dolomitic Limestone of Nalut Formation, while the eastern stratigraphic succession is represented by the Triassic Abu Shaybah continental sandstones at the base followed up by the lower part of Cretaceous rocks of Ain Tobi Dolomite. This distribution may indicate the presence of a N58E- S58W directed fault (the fault is thrown to NW). The prevailing direction of faults affecting the western Wadi Ka'am area is generally parallel to the prevailing extent of joints (N32W-S32E). In general, the study area is affected by two prevailing fault directions, the first which is the older and extended (N32W-S32E) where the fault is thrown toward NE and appears in the form of a step fault. The second is relatively younger and represents the Wadi Ka'am stream directed (N58E-S58W) where the fault is thrown toward NE. As a result of structural effects, the flow direction of Wadi Ka'am is N58E.