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The “Carbonates” unit of the Oligocene-Pliocene Barzaman Formation, north of the Oman Mountains at Sultan Qaboos Campus, is at least 10 m thick. It consists of three coralline limestone beds in (1) bedded facies (base; eastern outcrop), (2) very thick-bedded debris facies (middle; western and eastern outcrops) and (3) bedded facies (top; western and eastern outcrops). These three beds can be correlated between two outcrops over a distance of 160 m based on facies, stratigraphic positions and thickness as well as on a seismic refraction survey. The most common bioclasts are poritid corals, red algae and benthic foraminifers. Dasycladacean algae are common, and, sporadically, small gastropods, bryozoans, echinoderms, echinoid spines, bivalves, worm tubes and ostracods occur. Based on facies analysis we suggest that the studied limestones formed in a lagoon with backreef coral facies and that the barrier that separated the lagoon from the open sea (and which is not exposed) was made of coral reefs. Because of the abundance of coral colonies we assume for the studied coral limestones a water depth within the light saturation zone, not deeper than 10 to 20 m for the lagoon. Based on the occurrence of the following foraminifer genera Praerhapydionina, Archaias, Dendritina, Operculina, Spiroclypeus, Lepidocyclina, Miogypsina, Amphistegina and Subterraniphyllum, the “Carbonates” unit can be dated as upper Upper Oligocene to Lower Miocene. This is the first indication of the Upper Oligocene of the Barzaman Formation for the study area.

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