Stratigraphy, subsidence and uplift history, and tectonic evolution of the
United Arab Emirates foreland basin
 Dr. Mohammed Ali and Prof. Tony Watts (Oxford University)

Summary

 
Seismic reflection profile, gravity, and commercial well data have been used to determine the structure and evolution of the sedimentary basin that flanks the Oman Mountains in the Abu Dhabi region. The basin is of tectonic significance because it is believed to have formed by ophiolite obduction and flexural loading of an underlying rifted margin. Existing stratigraphic data shows that the margin is characterized by an early syn-rift sequence of mainly Triassic age that is overlain by a post-rift sequence of early Jurassic to Late Cretaceous age. The rifted margin formed following the opening of the Tethys Ocean.

Backstripping of well data provides new constraints on the age of initial rifting, the duration and amount of extension, and the flexural effects of ophiolite load emplacement. The rifted margin subsidence and uplift history can be generally explained by a uniform extension model with an initial age of rifting of 210 Ma and a stretching factor,, of c. 2.75. The model accounts for the general exponential decrease that is observed in the tectonic subsidence between 210 Ma and 95 Ma. However, there are discrepancies that we attribute to uncertainties in paleobathymetry, sea-level, and stratigraphic ages. Irrespective of these uncertainties, the backstrip curves suggest that there was a significant thinning of the continental crust prior to ophiolite emplacement. The timing of ophiolite emplacement cannot be constrained precisely, but our backstrip curves suggest that orogenic loading was initiated during the Late Cretaceous and resulted in a broad flexure that was flanked by a peripheral bulge that migrated from east to west across the basin. The bulge is presently obscured by at least 2 km of sediment, possibly because of the dynamic effects associated with the subduction of the Arabian plate beneath the Eurasian plate.
 		  

 
Fig. 1. Seismic profile across Abu Dhabi foreland basin. The seismic stratigraphy of the basin has been divided into lower sequence of Mesozoic shelf carbonates, middle sequence of foreland deep sediments (Fiqa) and upper sequence of Tertiary shallow water carbonates. The foreland sequence is divided into lower and upper units.
 
 
 
 
Fig.2. The figure shows profile of the tectonic subsidence and uplift of the margin compared with the predictions of finite stretching model for different values of the amount of stretching, b. Subsidence pattern indicate three major tectonic events:
1. Passive margin subsidence under Tethyan control related to crustal thinning. The curve conforms well to the predictions of the finite stretching model. As a result the passive margin history can be explained by a thermal model with an initial age of rifting of 210 Ma and a stretching factor,b, of c. 2.75.
2. Uplift event prior to the main phase of Late Cretaceous subsidence in the foreland flexure area. This is the time when large portion of Wasia Group were eroded. It is caused by the flexural loading of the lithosphere that caused uplift due to the flexural bulge.
3. Foreland basin subsidence related to the loading of the ophiolite. The rapid subsidence since Late Cretaceous departs from the backstripped curves typical of extensional basins, as it is concave down. This is interpreted as the result of loading of Semail ophiolite and Hawasina thrust sheets on Arabian plate which formed foredeep basin.