Stratigraphy, foraminiferal paleontology and facies architecture of the Late Cretaceous post-emplacement units (Qahlah and Simsima formations) in Oman

From late Paleozoic to the late Cretaceous time, the Arabian Shield lay along the southern margin of the Tethys Ocean. During the late Cretaceous, outer parts of the continental shelf and adjacent Tethyan deep-sea floor were thrust southwestward onto a passive continental margin of the Arabian plate, and the Oman Mountains were emergent in the late Campanian (?) and early Maastrichtian times. The Qahlah and Simsima formations are the first autochthonous deposits on the obducted ophiolite complex in Oman, characterized by the dominant occurrence of benthic foraminifera and rudists along with corals, algae, gastropods and echinoids. The Qahlah Formation is mainly a conglomerate unit, ranging in thickness from several meters to more than 700 m in the Oman Mountains, deposited by streams draining the allochthonous ophiolite and Hawasina complex. The formation comprises interbedded conglomerate, sandstone and siltstone suggestive of stream dominated alluvial fans, mostly devoid of fossils. At its type-section, the Qahlah Formation (ca. 140 m-thick) consists of conglomerates, sandstones devoid of fossils and limestones containing abundant Loftusia at its upper part. The most fossiliferous beds of the unit are known from Jabal Huwayyah in the Buraymi region where green claystone/siltstone beds in the upper part of the Qahlah Formation consists of Omphalocyclus, Orbitoides, and Loftusia, accompanied by abundant rudists. The Simsima Formation, with a thickness of 2.5 to 200 meters, is a shallow marine bioclastic limestone characterized by the abundant occurrence of larger benthic foraminifera, rudists, molluscs, corals, echinoids and algae. In Oman Mountains, the unit locally overlaps the Qahlah Formation and rests directly upon the older units (Hawasina or Sumeini Group) with an angular unconformity and elsewhere, sandstones of the Qahlah Formation may interfinger with the lower limestone beds of the Simsima Formation. The Simsima Formation is highly fossiliferous, dominated by Lepidorbitoides minor-socialis, Sirtina orbitoidiformis, Ilgazina unilateralis, Siderolites sp., Omphalocyclus sp., Pseudorotalia sp., Rotalispira sp., Fallotia sp., Planorbulina sp., Fissoelphidium sp., algae, miliolids, gastropods and agglutinated foraminifera. A progressive deepening upwards in the sequence was reported by previous studies, documenting some planktonic foraminifera in the Buraymi region. In this study, we aim to describe and interpret the stratigraphic development, foraminiferal paleontology and facies architecture of the late Cretaceous Qahlah and Simsima formations in various outcrops between Sur and Buraymi areas. A special attention will be given to the sections in Buraymi region since most fossiliferous outcrops of these formations are located in this part of Oman.