MASSE, J. P., J. BORGOMANO, and S. AL MASKIRY, University of Provence, Marseille, France

ABSTRACT: The Early Cretaceous Evolution of Carbonate Platforms from Northern Oman

In northern Oman (Jebel Akhdar and foothills) Hauterivian to early Aptian shallow carbonate platforms are widely extending and pass laterally to slope and basin environments in the Nakhl zone. Progradational geometries are identified in that zone where significant correlation between thickness and sediment types supports a prominent tectonic control.

The platform records four main sedimentary breaks (drowning events). Early Barremian (lower Lekhwair Formation), Late Barremian (basal Kharaib Formation), lowermost early Aptian (upper Kharaib Formation) and middle Aptian (Shuaiba-Al Hassanat formations boundary). The late Aptian-early Albian hiatus (pre-Nahr Umr unconformity) is regarded as an early Albian tectonically driven erosion.

In the Nakhl zone, coral-rudist limestones of late Aptian-early Albian (lower Al Hassanat Formation) document an east-west ribbon platform, the southward extension of which was obscured by the middle Albian erosions, and rudist limestones of middle to late Albian (upper Al Hassanat Formation), a lateral equivalent of the Nahr Umr circa littoral shaly sediments, document an east-west-trending linear platform.

The foregoing points out a northward progradation coeval with a southward transgressive major trend for the Hauterivian-early Aptian interval; a faulted margin corresponding with the Nakhl zone, active during the Aptian-Albian; a late Aptian ribbon platform coeval with the Bab basin initiation southward; a regional uplifting and truncation during the early-Albian (Austrian phase), whereas shallow-water carbonates are still forming at the edge of the former platform; and an active linear platform at the northern edge of the Nahr Umr basin, the corresponding drowning contemporaneous with the onset of the Cenomanian platform eastward.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.