--> Abstract: The Late Aptian-Early Albian Carbonate Crisis - Evidence for Glacio-Eustacy and Environmental Change from the Arabian Plate (Offshore Qatar), by Frans S. van Buchem, Radmila Pedersen-Tatalovic, Esbern Hoch, Michael Emang, and Noureddine Bounoua; #90105 (2010)

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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

The Late Aptian-Early Albian Carbonate Crisis - Evidence for Glacio-Eustacy and Environmental Change from the Arabian Plate (Offshore Qatar)

Frans S. van Buchem1; Radmila Pedersen-Tatalovic1; Esbern Hoch1; Michael Emang2; Noureddine Bounoua2

(1) PED, Maersk Oil Qatar, Dohoa, Qatar.

(2) Qatar Petroleum, Doha, Qatar.

The Mid-Cretaceous carbonate succession of the Arabian Plate is interrupted by a phase of exposure and condensed siliciclastic sedimentation spanning the Late Aptian and Early Albian. This dramatic change in sedimentation pattern is attributed to a glacio-eustatic sea level fall, dramatically documented with incised valleys in offshore Qatar, and was followed by a phase of condensed, iron-rich siliciclastic sedimentation at the end of the subsequent sea level rise. This anomalous facies pattern produced a unique, thin, but high-pay siliciclastic reservoir.

Based on a dataset of 25 cored wells, a high resolution seismic dataset, and extensive palynological analyses, a high resolution sequence stratigraphic model has been built. The lower sequence boundary is the incised valley floor that penetrates approximately 25 meters into the underlaying Shu’aiba Formation with a maximum valley width of 8 kilometers. A cored well in the middle of this channel shows that the fill sediment consists of plant material-rich, bi-directional cross-bedded, medium-grained sandstones changing upward to bioturbated sandstones. This succession is interpreted based on sedimentary facies and palynofacies as an estuarine environment, displaying a deepening upward trend of a transgressive back fill succession. The overlaying highstand deposits are thin (approximately 6 to 7 meters) and consist mainly of oolitic ironstone, locally admixed with glauconite and sandstones. This succession has been dated as Late Aptian and ?Early Albian age. The top sequence boundary is placed at the base of a thin, but regionally extensive sandstone bed, rich in glauconite, that has been dated as Middle Albian, and forms the beginning of the next sequence.

The offshore Qatar dataset provides detailed insight in this little known, but geologically and economically significant part of the Arabian Plate stratigraphy. It provides a conceptual depositional model, and unequivocal evidence for late Aptian sea level fluctuations and sedimentation that will have affected other petroleum systems on this Plate.