Sedimentation around Bathymetric Highs in the Southern Persian Gulf

Abstract

Bathymetric highs in the Persian Gulf have been grouped into three classes based on their setting on the Arabian homocline: outer (basin centre), intermediate and inner (coastal). In general, sediments on these highs range from open marine, perforate foraminiferal or coral/algal sands on the basin centre highs to pelletoidal sands, carbonate muds with restricted faunas, and algal stromatolites and evaporites on the coastal highs.

Sediment patterns on and around highs vary according to the regional setting of the high. They tend to be concentric around basin centre highs and become progressively asymmetric towards the coast, due to the accretion of bioclastic sands on their leeward sides. These accretion tails may even link coastal highs with the adjacent mainland shore. Peninsulas are thus formed which can completely alter the system of coastal currents and the types and patterns of coastal sediment.

Sediment patterns are also related to the diameter of the high. When highs exceed 5 km in width, double sediment tails (“bulls horns”) are formed by curving, elongate barrier sand ridges on the windward quarters of the high. The shelter due to these barriers creates lagoonal environments in the centre of the high where somewhat restricted, muddy sediments accumulate. Sediments on the leeward flanks of wide highs are also muddy and contrast markedly with the sand tails that accumulate on the lee sides of smaller highs.

Sediment around salt domes may contain minor amounts of exotic material brought to the surface by the diapir. This exotic fraction remains close to, and downwind of the dome. In addition, some domes are ringed by faint bathymetric depressions which may reflect rim synclines. These lows also favour the accumulation of muddy sediments. The diapiric salt itself, although close to the surface in some domes, does not outcrop and does not seem to influence contemporary sedimentation. In all other respects, sedimentation around salt dome highs is similar to that around other highs in the basin, irrespective of their origin.

Diagenetic processes are also distributed systematically, partly according to the regional setting of the high. Highs submerged below about 10 m, especially in basin centre and intermediate settings, favour active submarine lithification on their crests. Emergent highs in exposed settings favour beach rock lithification and vadose leaching, but no dolomitisation. This latter process is active on the extensive tidal flats accreting around the lee sides of wide coastal highs.