ABSTRACT: The Aruma Formation is well exposed in central Saudi Arabia as a thin northwest-southeast trending outcrop. It consists of a carbonate-dominated succession dated asCampanian to Paleocene. Of the three members, theKhanasir and Hajajah are confirmed as being Cretaceous, but the uppermost Linah Shale Member is assigned a Paleocene age. Dolomitization and differential erosion of the Aruma has left exposures for which the lithostratigraphy can only be confirmed by biostratigraphy. At the study location, the Khanasir Member contains the dasyclad algae Cymopolia tibetica, radiolitid rudist fragments and rare small rotalid and miliolid foraminifera. The HajajahMember is confirmed by the presence of the characteristic larger benthonic foraminiferal assemblage including Loftusia persica, Omphalocyclus macroporus, Rotalia trochidiformis and Fissoelphidium cf. operculiferum of Maastrichtian age. The sparse microfossil assemblages indicate deposition undifferentiated shallow marine, normal salinity, probably lagoon depositional setting.