The impact of sea‐level change on ramp margin deposition: lessons from the Holocene sabkhas of Abu Dhabi, United Arab Emirates

Abstract

Around the globe, the Holocene is replete with examples of the rapid accumulation and outbuilding of sediment wedges in response to, and associated with, a rise in sea level. It is particularly evident among the much-studied shallow-marine carbonate tidal flat association and arguably, nowhere better displayed than by the sabkha cycle developed along the coastal margin of the UAE. This cycle of rapid transgression and steady outward progradation throughout the last 10,000 years is only the most recent of a number of similar cycles that have been a characteristic of ramp margin sedimentation and a feature of stratigraphic associations in the Arabian Basin since the late Palaeozoic. It is not coincidental that these successions lying on top of earlier rifted basin sequences, many salt filled, are home to huge reserves of hydrocarbons.The sabkha cycle, as represented by the Holocene transgressive -highstand sequence found along the northern coast of the Arabian Platform is barely 2 m thick. Its sedimentary facies, associated mineralogical suites and early diagenesis are well documented. The gently sloping ramp margin setting is one that is extremely sensitive to even minor fluctuations in sea level and thin high-frequency sediment cycles are its hallmark. Fluctuations in sea level, however small, produce dramatic changes in sedimentation and groundwater chemistry in this environment, all of which can and do impact the rates of growth and destruction of the sequence. This may occur via increased erosion and ablation, leaching, alteration and replacement of existing minerals and precipitation of new ones, to aerobic destruction of organic material.Coastal flats are situated at the interface between groundwater, seawater and meteoric water which, especially in a sabkha setting, exposes the sequence to a multiplicity of diagenetic overprints. These, through their impact on porosity and permeability properties of potential reservoirs and seals, are of vital interest to the petroleum industry. The preservation potential, or lack thereof, in such tidal flat facies should be recognised as an inherent feature of high-frequency cyclicity. Despite this, relicts and indicators of highfrequency cycles can be observed in cores and wireline logs and offer some insights into the history of formation and preservation of porosity and hydrocarbon migration.

The mid-Holocene sea-level change in the Arabian Gulf

“…The study area is part of the Arabian Gulf’s homoclinal carbonate ramp (Read, 1985), the geometry and topography of which is a result of the eastward dipping foredeep basin and the carbonate factory. This factory operates year-round with 10–100 mm/a sedimentation rate (Reijmer, 2021) resulting in a flat-topped platform geometry with a steep slope at ~40 m water depth (Park, 2011). In the protected coastal zones behind barrier islands, the typical lateral sedimentary succession of the inner ramp is composed of low-lying sabkhas and their evaporitic components (e.g.…”