Eustatic sea level rise and the transgression of the Abu Dhabi Coastline

The extremely low-angle ramp geometry of the southern shore of the Arabian Gulf offers an ideal setting for studying the effects of relative sea-level fluctuations on sedimentary systems and shoreline morphology. A late... [ view full abstract ]

The extremely low-angle ramp geometry of the southern shore of the Arabian Gulf offers an ideal setting for studying the effects of relative sea-level fluctuations on sedimentary systems and shoreline morphology. A late Holocene progradation rate of 0.75 m/yr has previously been established for the Abu Dhabi sabkha system. However, given a current estimated global sea level rise of 3.3 mm/yr, as derived from satellite altimetry and tide gauges we calculate a present-day marine transgression rate at the Abu Dhabi coastline of 8.25 m/yr. It is, therefore, inferred that the area has recently entered a broadly retrogradational phase.

This study utilised 12 years of fieldwork observations and satellite imagery to establish numerous lines of evidence for active retrogradation over an area of Abu Dhabi coastline lying between Al Dabb’iya in the east and Abu al Abyad in the west. The landward advance of spits and beach ridge systems was monitored at several locations with rates of retrogradation of up to 28 m per year being recorded in some instances. These are significantly greater than those predicted from sea-level rise and may indicate a local subsidence.

The landward and seaward limits of microbial mat belts are strongly controlled by their location in the intertidal zone. The seaward side of the Recent microbial mat belt in the Abu Dhabi Sabkha is being eroded while the landward side is backstepping over gypsum sands indicative of the uppermost intertidal to lower supratidal zone.

There has been a significant increase in denudation of the microbial mat with the unlithified underlying sediment has become increasingly susceptible to erosion. In some cases this erosion has reached the aeolian beach ridges marking the commencement of the supratidal zone. In the lowermost intertidal zone, erosion of the hardground and other facies has been observed. Clasts from the hardground have been transported landward onto the surface of the sabkha where they are incorporated into other facies.

We conclude that the current sedimentary regime of the Abu Dhabi coastline is regressive associated with the current marine transgression of the Quaternary sabkha system. From a sequence stratigraphic perspective, the current system would be identified as an unconformity or flooding surface prior to the onset of a new parasequence.