Occurrence and genesis of the exposed Oligo-Miocene Ghar Formation in Kuwait, Arabian Gulf

Abstract

A sequence dominated by fawn cross bedded sandstones that constitutes the basal part of the post Eocene Kuwait Group siliciclastics and has been assigned as Ghar Formation is well exposed within Bahrah coastal plain in the northeast of Kuwait. The geology of these exposures had been briefly described in the middle of the late century. The purpose of this paper is to assess in detail its sedimentology and specifically the diagenesis of its rocks. The exposures of this sequence have been investigated at several locations. A simplified geologic map was prepared and representative samples of the studied sequence were subjected to detailed petrographic examination and geochemical analysis including stable isotopes. Four main facies were recognized within this sequence; sandstones, palustrine dolomicrite, mudstone and carbonates. Structural, textural and geochemical characteristics of the sandstone facies indicated that the detrital constituents are mostly derived from the Arabian Shield to the west of the study area and transported for a long distance within relatively low to moderate relief terrains during tropical sub-humid to humid climate. The palustrine dolomicrite facies was precipitated within semi-closed lagoons that may be influenced by seawater intrusion. The occurrence of thin carbonate beds within this sequence suggests short lived marine incursions intermittent with the prevailed fluvial conditions. Sedimentation was episodic and significantly controlled by the regional tectonics particularly Red Sea rifting. It is, therefore, concluded that the studied sequence has been deposited by fluvial braided system close to a paleo-shore line. Due to its peculiar sedimentological and petrographic characteristics it is suggested to name it as Bahrah Formation. further detailed sedimentological and stratigraphic assessment of this Formation is recommended.