Strontium-Isotope Chemostratigraphy and Rudists of the Qahlah and Simsima Formations (Campanian-Maastrichtian), United Arab Emirates and Oman

Thomas Steuber¹*, Stephen. W. Lokier¹, Malte Schlueter², and Mariano Parente^3
1The Petroleum Institute, UAE
²Ruhr University, Germany
³University of Naples, Italy
*[email protected]

The Qahlah and Simsima formations follow unconformably over the Semail Ophiolite, or various units of the Hawasina and Sumeini groups. Numerous studies focused on the biostratigraphy of the fossiliferous Qahlah and Simsima formations, concluding on a broadly Campanian-Maastrichtian age, but without further chronostratigraphic precision. Correlation – even over short distances – is complicated by lateral changes in lithofacies, intra-formational angular unconformities, and periods of nondeposition and subaerial exposure; all features indicative of a pronounced topography of the eroded allochthonous units, and active tectonics during the Campanian-Maastrichtian. We used numerical ages derived from strontium isotope stratigraphy to obtain a precise chronostratigraphical framework for the Qahlah and Simsima formations. The Qahlah Formation is diachronous, of Campanian age in the region of Al Ain and of Early Maastrichtian age in the north of the United Arab Emirates (UAE). This is also evident in significantly different associations of rudist bivalves, which provide excellent index fossils. While the Simsima Formation shows a deepening upward trend in the UAE-Oman border region, a continuous shallow-water carbonate platform sequences that straddles the Cretaceous/Palaeogene boundary is exposed in the region of Sur (Oman). Previous stratigraphical interpretations of this sequence are revised, and the importance of this locality for the evaluation of environmental change at the K/P boundary is discussed.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain