Index Fossils of the Late Palaeocene-Early Eocene Jafnayn Formation, Al Batinah Coast, Northern Oman
Abdul Razak S. Al-Sayigh* and Osman S. Hersi
Sultan Qaboos University, Oman
The Jafnayn Formation is an Early Paleogene carbonate unit that crops out widely along the Al Batinah coastal plain of northern Oman. It unconformably overlies the uppermost Cretaceous Al-Khod Conglomerates and is overlain by the Lower to Middle Eocene Rusayl Formation. The Jafnayn Formation is informally divided into two members that are separated by a biostratigraphically identified unconformity. The lower member comprises an upsection sequence of low to moderate energy, inner-shelf to lagoonal strata of (1) mudstones and wackestones, (2) massively-bedded, pseudonodular, bioturbated wacke-packstones, and (3) bioclastic mudstones. The lower member is dated as Late Palaeocene (Thanetian) based on the occurrence of the foraminifera Lockhartia diversa, Daviesina persica, Kathina sp. and Nummulitoides margaretae (NP8?). The upper member is Middle to Early Eocene (Ypresian) as suggested by the occurrence of Sakesaria cotteri, Heterostegina ruida and Nummulites globulus. It comprises coral and red algal-rich, well-bedded, occasionally rudaceous, nodular packstones-grainstones and cross-bedded calcarenites deposited in a shallow (less than 10 m), fairly high-energy open-marine shoal environment with nearby patch reefs supplying coral debris. The base of the upper member is marked by a locally distinctive thin (1–3 m) pebble bed rich in various siliciclastic grains and clasts reworked from the underlying member. The pebble bed was deposited immediately after a distinctive depositional hiatus corresponding to the upper part of the Upper Palaeocene and lower part of the Lower Eocene i.e. approximately two nannoplankton zones (NP9–NP10) representing the upper part of the Alveolina (Glomalveolina) levis zone to the lower part of the A. cucumiformis/A. trempina zones. Although this hiatus is recognised lithologically and biostratigraphically at Wadi Rusayl, at other localities it is only detected through detailed micropalaeontological analysis.
AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain