Oligocene karstification of the Dammam Formation in Qatar

Karst features develop due to dissolution of carbonate and evaporitic rocks, producing geomorphologically complex and hydrologically sensitive landscapes. While karst development in humid and temperate regions is well documented, its occurrence in arid environments is less documented and understood. In Qatar, major unconformity occurs between Dammam (Eocene) and Dam formations (Miocene). Karsts occurs primarily within the Dammam Formation (Eocene) and are manifested as depressions and caves generated by dissolution, subsidence, and collapse processes. Field observations along with petrographic, cathodoluminescence, strontium isotope, and X-ray diffraction analyses were performed to determine the origin and timing of karstification affecting the Dammam Formation. Textural, geochemical and isotopic affinities between karstic infills and sediments of the overlying Dam Formation - particularly the Al-Kharrara and Al-Nakash members - indicate that material from the Dam Formation was trapped within Dammam cavities. Thus, Dam age sediment fills are found in karst features where the Dam is now absent by erosion suggesting a broader areal extent of the Dam Formation during the Miocene. Diagenetic and lithological relationships suggest that karst sediment infilling—and thus karst formation—postdates Oligocene dolomitization and silicification, with major speleogenesis occurring during the Oligocene. This event coincides with regional eustatic regression and tectonic uplift associated with the reactivation of the Qatar–South Fars Arch during the Zagros Orogeny. This study identifies a previously unrecognized karstification phase predating Pleistocene features, refining current models of Qatar’s landscape evolution and related geohazards. This suggests that geohazards associated with karsts are relatively stable due to the age of the major karst event.