COMPARISON BETWEEN THE APTIAN SHU’AIBA RESERVOIR (E ARABIAN PLATE) AND OUTCROP ANALOGUES FROM THE MAESTRAT BASIN (E IBERIAN PLATE)

The Aptian Shu'aiba Formation is one of the most important carbonate reservoirs for oil in the Arabian Plate. The reservoir rocks correspond to platform top to slope deposits characterized by the presence of orbitolinids, corals, rudist bivalves, microbialites and Lithocodium aggregatum. In the basin, organic- and clay-rich carbonates are found. Seismic data show aggrading to/or prograding sequence sets of highstand and lowstand normal regressive deposits. The highstand platform carbonates, which are of Early Aptian age, were subaerially exposed and incised due to base-level fall, starting in the latest Early Aptian. During subsequent marine onlap, the incised-valley system was back-filled with an estuarine succession. In the Maestrat Basin (E Iberian Chain), comparable and coeval sedimentary results of long-term sea-level trends are observable in outcrop. Seismic-scale continuous platform-to-basin cross-sections and isolated rock exposures giving rise to kilometre-long hillocks are constituted by highstand and lowstand normal regressive carbonates, which display prograding clinoforms and downlapping stratal terminations. Lowstand platforms were drowned and buried by marls during the following transgression. Highstand platforms terminated by subaerial exposure. Two forced regressive stages of relative sea level of latest Early and Late Aptian age are recognizable. During base-level fall, seismic-scale incised valleys formed under subaerial conditions at the platform tops as a result of stream-cutting erosion and lateral planation. Subsequently, erosional incisions were back-filled with transgressive peritidal to shallow subtidal deposits. Incisions exhibit a maximum down-cutting of 115 m into the Aptian succession. Glacio-eustasy is a plausible mechanism for explaining the sea-level changes identified. In the Maestrat Basin, terrestrial palynofacies reveal that the late Early and Late Aptian climate was cooler than the lower part of the Early Aptian and the Albian. The outcrops from the Maestrat Basin are of significance given that allow examination of Aptian long-term changes in depositional trends of Tethyan significance within a comparatively reduced area, whereas these trends are often only recognizable on much larger (seismic) scales such as, for example, the Arabian Plate.