Regional Sedimentation along the Trucial Coast, SE Persian Gulf

Abstract

Sediment composition, surface patterns, and vertical sequences vary laterally along the Trucial Coast depending on three major factors:

• orientation of the shoreline with respect to the onshore “shamal” winds;

• proximity to Qatar Peninsula, an up-wind barrier;

• presence of the Great Pearl Bank coastal barrier.

This latter feature is paramount, its presence within the central parts of the Trucial Coast permits the subdivision of this regional shoreline into three sedimentary provinces:

The Western parts of the Trucial Coast which are protected laterally by Qatar Peninsula, the remote Great Pearl Bank having little effect. The shallow subtidal sediments are carbonate muds and the wide intertidal flats are composed of imperforate foram and pelletai sand. The protection decreases rapidly to the E where the wide Sabkha Matti embayment contains fringing reefs, oolitic and molluskan sands.

The Central parts of the Trucial Coast which are protected by the structurally-based Great Pearl Bank barrier. Because this ridge is oriented obliquely to the continental shoreline the lagoon varies in width and depth. The barrier axis rises progressively towards the E and becomes incorporated into the Arabian shore in E. Abu Dhabi. These lateral variations in the morphology of the barrier are reflected in its sediments as well as in those of the adjacent lagoon and of the mainland shoreline. The distribution of dolomite and other evaporite minerals is also related to these lateral variations.

The North Eastern parts of the Trucial Coast which are unprotected and face directly towards the entire length of the gulf. They suffer the effects of maximum wave fetch which has resulted in the development of major longshore spit systems. Although the Oman Mountain range overlooks the NE extremity of this shoreline, its detrital sediments barely contaminate the indigenous carbonates, presumably because of the arid climate. In contrast to those of the remainder of the Trucial Coast, the vertical sequence of coastal sediments in this area is transgressive, probably due to downwarping of the N end of the mountain range.

The 600 km Trucial coastline is essentially linear. Nevertheless, it is thus seen to exhibit very marked lateral variations in its sediments and their diagenetic modifications both of which are determined mainly by the proximity of up-wind barriers. An understanding of these relationships may help in the estimation of the proximity and orientation of ancient barriers and shorelines.