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Within onshore Abu Dhabi,UnitedArab Emirates,the Middle-LateEoceneDanunamFonnation can be separatedinto three distinctunits on the basis of lithologicalanalysis. Petrographicanalysis showsthese units to consistof interbeddedyellow-brown marl and shale with gray bioclastic packstone/grainstones and mudstone/wackestones. Dolomite and gypsum occur locally in the upper half of the section. A lithostratigraphy and facies analysis of the Danunam suggests cycling between the grain-supported and mud-supported limestones, and with pulses of terrigenous material producing the marly and shaley interbeds.The diagenetichistory of the Dammamis dominantlya reductionof porosityprimarilydue to secondarycementationby two generationsof calcite and the recrystallizationof unstable grains and cement, as opposed to dissolution. In addition, dolomitization, which often has the effect of creatinggood secondaryporosity,which is only local in extentThe Dammamof the onshore Abu Dhabi is interpretedin the area to representa transitionalperiod between the more restrictedlimestones of the underlying Lower Eocene RusFormation and the more complexsub-environments of the overlyingOligocene Asmari Fonnation.