Facies-based sequence-stratigraphic framework of the Lower Cretaceous rudist platform, Shu’aiba Formation, Saudi Arabia
Published:January 01, 2010
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Nasser Al-Ghamdi, Fred J. Read, 2010. "Facies-based sequence-stratigraphic framework of the Lower Cretaceous rudist platform, Shu’aiba Formation, Saudi Arabia", Barremian – Aptian Stratigraphy and Hydrocarbon Habitat of the Eastern Arabian Plate (vol. 2), Frans S.P. van Buchem, Moujahed I. Al-Husseini, Florian Maurer, Henk J. Droste
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The Cretaceous (Lower Aptian) Shu’aiba Formation in Shaybah Field, Saudi Arabia, is a giant carbonate reservoir that formed on a regional carbonate ramp bordering an intra-shelf basin. The main objective of this study was to construct a high-resolution facies-based, sequence-stratigraphic framework using cores, logs and available isotope data for reservoir characterization and development. This study will also help refine our understanding of global climate and sea-level history in the Early Cretaceous Aptian Stage.
The succession consists of a composite sequence of seven high-frequency sequences. Sequences 1 and 2 formed a deeper open platform of Palorbitolina-Lithocodium wackestone, with maximum flooding marked by planktic foraminifera mudstone. Sequence 2 built relief over the northern and southern blocks, separated by an intra-platform depression. Sequence 1 and part of Sequence 2 form the transgressive systems tract for the composite sequence. The remaining sequences developed a platform rimmed by rudist rudstone, backed by rudist floatstone back-bank and lagoonal fine skeletal peloidal packstone; slope facies are fine skeletal fragmented packstone. Aggradational sequences 3 to 5 make-up the composite sequence early highstand. Progradational sequences 6 and 7 are the composite sequence late highstand marking the deterioration of the Offneria rudist barrier and deposition of widespread lagoonal deposits, where accommodation may have been created by syn-depositional growth faulting that moved the northern block down. Shu’aiba deposition on the platform was terminated by long-term sea-level fall and karsting.
The presence of fourth-order sequences and ca. 100 ky parasequences, which are driven by long- and short-term eccentricity, suggests that the Early Cretaceous climate may have been cooler than generally believed and was not an ice-free greenhouse World. Small ice sheets may have been present. This is pertinent to the debate concerning whether the Aptian was a time of green-house climate typified by small precessionally-driven sea-level fluctuations, or whether small ice sheets at the poles generated moderate amplitude fourth-order fluctuations, perhaps driven by eccentricity.