ABSTRACT
Rudist bivalves constitute an important component within the Cretaceous carbonates of the Arabian region, such as the Shu’aiba Formation. Their fossilized remains created highly porous and pervious hydrocarbon reservoirs, both within the rudist bank itself as well as the debris slopes on the proximal and distal flanks of the bank. The buildups were initiated along the margins of an intra-shelf basin and caused restriction of the shelf into vast lagoons. Optimum economic exploitation of the rudist-associated hydrocarbon reservoirs is dependent upon a comprehensive understanding of the three-dimensional architecture of the original buildup and its associated sedimentary facies. A modern analog with its readily studied biofacies and lithofacies variations could provide significant insights into the vertical and lateral developments of the palaeobiofacies and lithofacies.
The Great Pearl Bank Barrier is a positive submarine feature, generally located in water depths less than 8 m, which trends in a northwest to southeast direction for approximately 200 km between the Qatar peninsula and Abu Dhabi in the southern Arabian Gulf. The Barrier is composed primarily of bivalve sand and mud in which are embedded locally dense populations of the large bivalve species Pinna bicolor. This particular form lives vertically within the muddy sands, with only the upper 25% of the shell emergent above the sediment surface. Shallow seismic evidence suggests that the orientation of the Barrier may be influenced by underlying faults.
Uniformitarianism, the main method and basis of geological reasoning, is equally applicable to palaeoecology. Is it possible that the present distribution of the constratal pteroid ‘fan mussel’ Pinna bicolor could act as a Recent counterpart for the extinct Aptian constratal elevator rudist bivalves? If such an interpretation is correct, the available shallow structural data and environmental evidence from modern foraminifera and associated microfauna/flora should be integrated to form a model which should improve our understanding of the reservoir lithofacies distribution within the Aptian carbonate platforms of the Arabian Peninsula. Points of caution are numerous, and include the validity of comparing these extant pteroid ‘fan mussels’ with extinct rudists and also the problems associated with comparing the biological features adapted for the Recent hypersaline conditions of the Gulf with the normal, to slightly elevated, salinity conditions interpreted for the proposed Aptian fossil counterpart.
