Abstract
The Upper Cretaceous Shilaif intra-shelf basin at the eastern margin of the Arabian platform contains rich source rock sequences in the hydrocarbon generation window, which are targets for ongoing exploration work. Time stratigraphy and sedimentology are key components to unravel the complex development of the hydrocarbon system. This paper presents detailed bio-, chemo- and sequence-stratigraphic data in combination with sedimentological analysis from core, well, seismic and outcrop data to support an analysis of basin architecture and regional time stratigraphic correlations.
The Late Albian to Turonian saw the final intra-shelf basin development and infill on the eastern margin of the Arabian plate Cretaceous carbonate platform. Basin development began with the deposition of the Late Albian Mauddud Formation. Mauddud cycles are laterally continuous over large distances but thin in western and central Abu Dhabi in the area of the future intra-shelf basin. Differential aggradation is likely to have been accentuated by unfavorable climatic and water-quality conditions related to the Albian/Cenomanian Oceanic Anoxic Event.
The Mauddud is overlain in the west and east of Abu Dhabi by the shallow marine aggrading & prograding carbonates of the Mishrif Formation with a SSW-NNE elongated intrashelf basin forming in central Abu Dhabi. This basin is filled by the Shilaif, Tuwayil and Ruwaydah Formations. Four depositional sequences with organic rich intervals are recognized in the Shilaif Fm corresponding in time to pulses of aggradation, progradation and retrogradation of Mishrif shallow-water platform margin sediments.
The Tuwayil is a shaly lowstand/transgressional sequence onlapping onto the Mishrif, which was at this time partially exposed based on erosional channel incisions on the platform top. The Ruwaydah Fm is composed significantly of calcispheres recording continued transgression, increased accomodation space and an increase of carbonate production. The Coniacian Laffan shales unconformably overlie the Cenomanian/Turonian sedimentary sequences.
Basin-fill sequences have been age dated with detailed chemo- and biostratigraphy. Based on carbon isotopes the Mauddud predates/coincides with the OAE at the Albian/Cenomanian boundary and is hence late Albian. Other carbon peaks, ammonites, calcispheres and planktonic foraminifera align the Shilaif with the Cenomanian reaching near its top the Cenomanian/Turonian boundary. The Tuwayil and Ruwaydah Fms are Turonian.
