Petrography, diagenesis and isotope geochemistry of dolostones and dolocretes in the Eocene Dammam Formation, Kuwait, Arabian Gulf

Detailed petrographic and geochemical investigation of an exposed sequence of the Eocene Dammam Formation in Kuwait revealed significant gradational upward changes from friable chalky dolostone to hard dolocretic palaeoduricrust (karst carapace) passing through an extensively karstified dolostone enclosing cavity fill dolocretes. The dolostones were originally deposited as calcareous wackestone and mudstone within tidal flat and backshore lagoons that manifest cyclic sedimentation within minor sea regression and transgression cycles. Dolomitization of these sediments was early, pervasive, fabric selective and non-fabric destructive and it took place by Mg-rich sabkha brine mixed with meteoric fresh water. Regional sea regression was followed by chertification. Three sequential stages of dolocretization were identified within the karst dolostone and the karst carapace. Microscopic and SEM examination as well as stable isotopic analysis of Carbon and Oxygen indicate significant variation in the dolomite textures and genesis of the dolostone and the dolocretes. A suggested paragenesis model elaborated complex diagenetic processes. The results of this research may be applicable for analogues subsurface carbonate reservoir rocks.