Sedimentology, Stratigraphy and Paleoenvironments of the Albian/Cenomanian Carbonates of the Arabian Platform, Southern Margin of the Tethys. A Platform-Scale Perspective

Abstract The Wasia Formation was deposited on the southern margin of the Shilaif Basin and comprises four 3rd order sequences and seven members (Khafji, Safaniya, Mauddud, Wara, Ahmadi, Rumaila, and Mishrif, in stratigraphic order). This study aims to refine the paleoenvironments of the Wasia Formation in the studied area, and to provide a detailed stratigraphic framework of the Albian–Cenomanian strata linked to the regional understanding of the Wasia Formation. Detailed sedimentological description and high-resolution bulk carbon isotope (δ13C) analysis, along with biostratigraphy, were performed in cores and sidewall cores from 17 wells from the Rub al Khali Basin. The biostratigraphic analysis includes micropaleontology (using both thin sections and disaggregated material), palynology (dynocysts and pollens) and nannofossils characterization. It is the first time that such an integrated dataset is presented for a single location at the scale of the Arabian Platform, which enables improved platform-scale correlations. The first sequence marks the initial Albian flooding of the platform with the argillaceous, shallow marine to estuarine deposits of the Khafji Member. The overlying Safaniya Member contains orbitolinid-rich limestones and deep marine deposits, with planktonic foraminifera. This marks a regional flooding event associated with slightly anoxic conditions (intrashelf basin). The top of the Safaniya Member marks the Albian/Cenomanian transition according to planktonic foraminifera, which differs from previously established stratigraphy. This sequence changes upwards to shallower deposits of the early Cenomanian Mauddud Member, which is capped by rudist-rich deposits that have been affected by a regional unconformity. The middle Cenomanian section includes the clastic-rich Wara Member and the carbonates of the Ahmadi and Rumaila members, characterized by shallow marine low-energy deposits rich in diversified benthic foraminifera and green algae, with sporadic rudist developments. Boundaries between these members are associated with terrigenous layers at sequence boundaries. The last 3rd order sequence, consisting of the mid to upper Cenomanian Mishrif Member, contains abundant planktonic foraminifera and coccoliths indicating the drowning of the platform and the development of the Shilaif Basin associated with the OAE2. Biostratigraphy and carbon isotopes indicate that the uppermost part of the Turonian deposits are missing, eroded by the pre-Aruma unconformity. This integrated study unravels paleoenvironmental changes on the southern margin of the Shilaif Basin and provides a new detailed stratigraphic framework for the deposition of these marine carbonates, in line with the regional understanding of the Wasia Formation on the Arabian Platform.