Holostratigraphy of the Kahmah regional Series in Oman, Qatar, and the United Arab Emirates

The stratigraphic framework of the uppermost Jurassic - Lower Cretaceous interval of the Gulf area is revised using both historical and recently acquired paleontological (ammonites, calpionellids, foraminifers, 'calcareous' algae), sedimentological and sequential information. The Kahmah regional Series ranging in age from Late Tithonian to Gargasian (= middle Aptian) times is subdivided into regional stages, named from bottom to top: Rayda (with two substages, Bu Haseer and Belbazem), Salil, Zakum, Lekhwair, Kharaib, Hawar, and Shu'aiba. The Kahmah rests either on strata representing the Habshan regional Stage, which is the last term of the Sahtan regional Series (locally absent due to a stratigraphic hiatus in basinal areas), or on much older strata; it is followed either by the Bab regional Stage (locally absent due to a stratigraphic hiatus on platform areas), or by the Sabsab regional Substage (the lowermost part of the Nahr Umr regional Stage), both of which are assigned the Wasi'a regional Series. The Kahmah succession (as well as those of the Sahtan below and the Wasi'a above) is discontinuous, i.e. punctuated by sedimentary hiatuses due to forced regressions, some of significant importance (in the Zakum or in the Bab, and those bounding the Hawar and the Shu'aiba).