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The Aptian Shu'aiba reservoir (eastern Arabian Plate) compared to outcrop analogues from the Maestrat Basin (eastern Iberian Plate)


The Aptian Shu'aiba Formation is a giant carbonate reservoir located at the southern part of the Arabian Plate. These reservoir rocks correspond to platform top to slope limestones, which pass basinwards to organic- or clay-rich carbonates. Fossil content is dominated by rudist bivalves, corals, orbitolinids, microbialites and Lithocodium aggregatum. Subsurface seismic data display aggrading to/or prograding sequence sets of normal regressive deposits, which were partly subaerially exposed and incised due to base-level fall. During subsequent transgression, the incised-valley system was back-filled with an estuarine succession. In the Maestrat Basin (E Iberian Chain), similar sedimentary results of Aptian long-term sea-level trends are observable in outcrop. In this regard, seismic-scale continuous platform-to-basin cross-sections and isolated rock exposures giving rise to kilometre-long hillocks are formed by highstand and lowstand normal regressive carbonate deposits, which exhibit prograding clinoforms, downlapping stratal terminations, and a comparable vertical and lateral lithofacies evolution. Lowstand platforms were drowned and buried by basinal marls during subsequent transgression. Highstand platforms terminated by subaerial exposure. Two forced regressive stages of relative sea level of Aptian age are identifiable. During relative sea-level fall, seismic-scale erosional incisions originated under subaerial conditions at the platform tops as a result of stream-cutting erosion and lateral planation. Later, incised valleys were back-filled with transgressive peritidal to shallow subtidal deposits. Incisions display a maximum down-cutting of 115 m into the Aptian succession (Fig. 1). The pace and magnitude of the two long-term drops in relative sea level identified fall within the glacio-eustatic domain. In eastern Iberia, terrestrial palynofacies indicate that the late Early and Late Aptian climate was cooler than the lower part of the Early Aptian and the Albian. In summary, the outcrops from the Maestrat Basin allow examination of the heterogeneity of rocks and stratal architecture resulting of Aptian changes in depositional trends of Tethyan significance within a comparatively reduced area. These rock exposures are of importance because the sedimentary expressions of these Aptian changes in accommodation are commonly only recognizable on seismic profiles such as for the Arabian Plate.