Stratigraphy of the Kuwait Group in Umm -Gudair and Surrounding areas, Kuwait

Abstract

Stratigraphy of the Miocene-Pleistocene Kuwait Group is studied on the basis of core samples and bore-hole logs from Umm-Gudair, NW Al-Shagaya, Al-Salmi, Al-Wafra water wells, exposures at Jal Az-Zor escarpment and Ahmadi quarry. The over all stratigraphie sequence of the Kuwait Group bear clues for a gradual regional regression and accompanying increase in clastic material influx. The Kuwait Group starts with marine clays and continues upward as fluvial, river channel sands, and ends with alluvial fan conglomerates. Deposition of the Kuwait group was interpreted frequently by brief periods of quiescence and non-deposition. Pauses in sedimentation are marked by surfaces of carbonate and gypsum cementation in the pore spaces of sands by evaporation of capillary water, and alteration of clays. The lower parts of the Kuwait Group consist mostly of loose sands without cementation. The degree of cementation and frequency of cemented layers increase towards the top of the group. The Kuwait Group is subdivided into three formations in the pre¬ sent study from bottom to top. These are Ghar, Jal Az-Zor and Dibdibba Formations. The fossiliferous sandy limestone layer at the lower part of the group was selected as the boundary between Ghar and the overlying Jal Az-Zor Formations. The boundary between the Jal Az-Zor and Dibdibba Formations is hard to locate. The carbonate-cemented sand layers are included in the Jal Az-Zor, and overlying poorly-bedded and weakly cemented gravels are included in the Dibdibba Formation. Subsurface correlation suggests that the thickness of Ghar and Jal Az-Zor Formations are uniform, but Dibdibba Formation varies in thickness from north to south.