The stratigraphy of the Middle Eocene–Pleistocene sediments in Kuwait

The Dammam Formation and the Kuwait Group are the major aquifers containing useable brackish water in Kuwait. The Dammam Formation is a limestone–dolomite sequence of Middle Eocene age. It is underlain by Middle Eocene Rus evaporites and is overlain unconformably by the clastic sediments of the Kuwait Group. It is subdivided into three members. The lower member, A, is a nummulitic limestone with shale interlayers at its base. The middle member, B, is a highly silicified and dolomitized fossiliferous limestone which includes lignite and silty lignite interlayers. The upper member, C, is a friable, white dolomite which is silicified and karstified at the top, beneath the unconformity with the overlying Kuwait Group. Similar silicification and karstification occurs at the top of the B member, suggesting a minor but significant unconformity between the B and C members. The upper part of the Dammam Formation is dolomite of Lutetian age with fragmented and cherty zone on top. Secondary dolomite was formed from early dolomitization of fossiliferous micrites, pelmicites, intramicrites and fossiliferous pelmicrites. Silification was related to percolation of acidic ground-water during the non-depositional period in Oligocene time when the surface of the Dammam Formation was karstified. The Dammam Formation was deposited on a shallow marine shelf experiencing minor fluctuations from lagoon to tidal flat and swamp environments. This tectonically stable period was interrupted by small pulses in the source land and minor fluctuations in the sea level, which caused alternating transgressive and regressive cycles. Stratigraphy of Miocene–Pleistocene Kuwait Group is studied. The work is based on cores and bore hole logs from Umm-Gudair, NW Al-Shagaya, Al-Salmi and Al-Wafra water wells, and exposures at Jal Az-Zor escarpment and Ahmadi quarry. The Kuwait Group was subdivided into two or three formations. There is no general agreement on the boundaries of the formations and the number of formations. The confusion has persisted until present mainly because there is no clear cut criteria to delineate formations. There are no markers or distinct lithologic boundaries to set formations apart. The Kuwait Group is subdivided into three formations in the present study in agreement with previous work. These are Ghar, Jal Az-Zor and Dibdibba Formations from bottom to top. No clear cut stratigraphic clue could be obtained from wells to identify formations. The fossiliferous sandy lim