A reconnaissance study of a clastic coastal sabkha in Northern Kuwait, Arabian Gulf

Abstract

A clastic, tidal flat-sabkha complex characterizes the mesotidal coastline of Northern Kuwait. The Holocene tidal sediments of this area represent the western-most limit of the Shatt Al-Arab delta sediments. The area under study in Bahrah is subdivided according to its geomorphological features and depositional setting into eight sub-environments. The sediments are characterized by two distinct size populations; a coarse fraction of siliciclastic sand derived from a local source area (the Jal-Az-Zor escarpment); and a dominant, mud-size mode of more distinct origin. The mud-size, clastic fraction is dominated by detrital carbonates (low-Mg calcite with minor dolomite). The latter sediments are brought to the area through direct aeolian fallout and through the reworking of the delta sediments by counter-clockwise currents in the northern Arabian Gulf. Since the coastal areas are bordered by the hypersaline basin of the Arabian Gulf, biological activity is limited in the tidal zones. As a result, most of the internal sedimentary structures are preserved, with minor disruption caused by intra-sedimen-tary gypsum growth. Progradation of the coastline has been going on since about 3040 years B.P. at the rate of 1·5 to 2 m per year. The ‘early Holocene’ transgressive sediments are made up of patchily distributed, autochtonous carbonates (aragonitic oolites, pellets and micrite) similar to those of other Recent carbonate provinces on the southern coast of the Arabian Gulf.A unique tidal regime characterizes the northern coastal zone. Maximum flooding of the supratidal area is dependent on the coincidence of high water spring and/or storm tides with south-easterly winds. This results in a very small area (0·6–0·7 km) of the tidal zone being subjected to flood recharge during the normal tidal cycle. The study area therefore, can be described as a ‘wind tidal flat’.This area is unique among modern sedimentary environments and a similar example is not known from either modern sedimentary settings elsewhere or from ancient analogues. The closest comparable example is the Colorado River delta. Bahrah area contrasts with the southern shoreline of Kuwait and the southern Arabian Gulf coastline which are characterized by carbonate-hosted sabkhas.The semi-quantitative model developed in this study may be used to characterize similar ancient analogues from the geological record.