Distinct relict fringing reefs in the northern shelf of the Gulf of Elat/Aqaba: Markers of Quaternary eustatic and climatic episodes

Quaternary reef development and demise have been shown to correspond to worldwide sea-level fluctuations and related environmental changes, yet the mechanisms and rates affecting this relationship are not well resolved. A set of high-resolution seismic reflection and multibeam bathymetric data were interpreted. Six distinct systems of relict fringing reefs embedded within the sedimentary cover of the northern shelf of the Gulf of Elat/Aqaba were identified. The two uppermost relict fringing reefs are also exposed on the sea floor in water depths of ca 20m and ca 60m, along the north-western corner of the northern Gulf of Elat/Aqaba and sub-parallel to the current northern coast, respectively. Two other relict fringing reefs are laterally correlated to each of the last two transgressive cycles, and are inferred to have formed during decelerations in sea-level rise during the last two deglaciations. These reefs and the units to which they are laterally correlated portray a repeating stratigraphic pattern of reef development during deposition of seismically homogeneous sediment and an ensuing demise during deposition of heterogeneous sediment. Correlation of the reef stratigraphy with rates of Late Quaternary sea-level rise and a sediment accumulation rate from one shelf core provide age estimations for the seismic stratigraphy. Two phases of fringing reef generation occurred during the last deglaciation (since ca 18ka); the older reef probably developed between 128ka and 115ka at ca 60m below present sea-level and the younger reef after 84 to 80ka at ca 20m below present sea-level. These last two phases of reef generation are separated by a lobate seismic unit that is interpreted as fluvial-deltaic deposits that backstepped across the shelf during the Early Holocene transgression. Results suggest that fringing reefs evolved along the northern shelf of the Gulf of Elat/Aqaba only during relative decelerations in sea-level rise, contemporaneous with low input of terrigenous sediment and probably during a period of aridity. At present, no fringing reef grows along the northern coast of the Gulf of Elat/Aqaba, suggesting that these relatively arid periods may have been drier than Recent. The pattern of slowdown in sea-level rise contemporaneous with conditions of increased aridity seems to have repeated during the last two sea-level rises, approximately at the same sea-levels, suggesting a common mechanism of short (millennium-scale) phases of eustatic and climatic alteration during deglaciations.