Seismic stratigraphy of a Lower Cretaceous prograding carbonate platform (Oman) and implications for the eustatic sea-level curve

摘要

The Lower Cretaceous of northern Oman consists of a large carbonate platform that prograded over a distance of 280 km (174 mi) in approximately 23 m.y. The seismic stratigraphic interpretation of this system, based on a regional three-dimensional survey (40,000 km(2) [15,400 mi(2)]), revealed a complicated organization of nested clinoforms with changing depositional dips. The tectonic setting and stratal patterns suggest that different orders of sea-level fluctuations, ranging from 20 to 150 m(66-492 ft) in amplitude, have controlled the overall sedimentation. The Lower Cretaceous Lekhwair, Habshan, and Salil Formations form the lithofacies of this carbonate platform that prograded in a northeastward direction from the United Arab Emirates and Oman to northern Oman, filling in the Rayda Basin. The majority of this system is documented in seismic and well data, whereas the final part of the progradation is visible on outcrops in the Oman Mountains. Cored wells and outcrops have been dated with calpionellids, echinoids, and calcareous algae biostratigraphy; 14 sequences have been identified and are grouped into four sequence sets based on their seismic stratigraphic organization. The differences in stratal patterns between the sets are interpreted to be caused by variations in the amplitude of sea-level fluctuations. The sequence sets indicate a general increase of the amplitude of sea-level fluctuations to amaximumof 150 m(492 ft) in the early Valanginian, followed by a general highstand and low-amplitude fluctuations (20 m [66 ft]) in the late Valanginian. The Oman relative-sea-level curve shows similarities with the one proposed for the Vocontian Basin in France, providing strong evidence for the eustatic nature of these fluctuations. A glacio-eustatic control is invoked to explain this global trend.