Aptian-Albian sediments exposed in Oman consist predominantly of shallow marine carbonates deposited on a broad shallow platform bordered to the west by the intrashelf Bab basin and to the east by the Tethyan basin. To improve the regional stratigraphic correlation and understand platform configuration, a study of outcrop and core data is being undertaken. Samples prepared for carbonate carbon isotope analysis will aid correlation between the platform and basin.
The two platform margins show contrasting styles of sedimentation. Tethyan platform margin sediments (Al Hassanat Formation) are dominated by coarse rudist-coral-stromatoporoid rudstones and floatstones, cross-stratified peloidal grainstones and rudist wackstones. Deposition was in a high energy environment with periodic reworking of rudist bioherms and progradation of isolated shoals. In contrast, intrashelf basin margin sediments show rapid vertical facies change between rudist-stromatoporoid biostromes and Orbitolina mudstones, and were deposited in a low energy subtidal environment with rapid episodic platform drowning.
Platform interior sediments (Shuaiba Formation) are 60-90m thick and consist of Bacinella-algae wackestones, and caprotinid rudists biostromes deposited in a relatively low energy subtidal environment. Biostromes are commonly reworked and winnowed, at the top to form several coarsening upward cycles with syndepositional firmgrounds. Shales of the Late Aptian-Albian Nahr Umr Formation lie unconformably above the Shuaiba Formation. The contact between the two formations is a laterally persistent, iron encrusted, and planar surface throughout central Oman. This surface is interpreted as a submarine drowninq disconformity formed during a marine transgression.
Initial results confirm that re-activation of platform margin faults, rather than eustasy, controlled sedimentation.
AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid