Quantification of Carbonate-Ramp Sedimentation and Progradation Rates for the Late Holocene Abu Dhabi Shoreline

Abstract

Abstract We utilize new radiocarbon dates and detailed sedimentological logging of the Abu Dhabi sabkha to produce the first well-constrained, internally consistent rates for late Holocene carbonate-ramp sediment accumulation and progradation for the southern shore of the Persian Gulf. These data are applied to test the hypothesis that, in low-angle carbonate ramp systems, ramp geometry is the primary control on sedimentation and progradation rates and, therefore, estimates acquired from other depositional environments cannot be applied to low-angle carbonate ramp systems. Average calculated progradation rates of 0.75 m/yr are higher than progradation rates proposed for other late Holocene and Recent carbonate settings; a relationship that is explained by the lack of accommodation space in the low-angle laterally extensive ramp system. In the sedimentary record, such relatively high progradation rates would produce laterally extensive lithologically uniform units with little or no evidence of progradational features and would appear to be largely contemporaneous across their extent. The total average sediment accumulation rate of 0.029 cm/yr is lower than those proposed from most other late Holocene to Recent shallow-water carbonate depositional environments; again, a relationship interpreted to result from the limited accommodation space of low-angle carbonate ramp systems. Calculated sediment accumulation rates show little variation over the past ~ 1,400 years, yet the calculated progradation rates exhibit a sharp decline from a maximum of 1.03 m/yr before 677–946 cal BP to 0.70 m/yr afterwards. This is interpreted to reflect a rise in relative sea level or distal steepening of the ramp system. Applying the progradation rates proposed in this paper, the lagoon system in the study area would be completely infilled in less than 4,000 years. Calculated sediment accumulation rates for syndepositional and early postdepositional interstitial displacive evaporite formation are higher than those for carbonate and microbial mat intervals. Continued precipitation of evaporite minerals during burial would result in a further increase in their relative contribution to the sediment pile. Conversely, compaction, particularly of microbial-mat intervals, will result in a decrease in apparent sediment accumulation rates for non-evaporite intervals. These processes need to be considered when modeling the basin evolution of mixed evaporite–carbonate sequences in the stratigraphic record. During calculation of sedimentation rates it is important to consider both a correction for compaction and a correction for evaporite formation.