Late Holocene Stratigraphic History of the Gulf of Aqaba Coastal Plain, Jordan

Abstract

Construction of the lower tidal lagoon at the Ayla Oasis Development in Aqaba, Jordan provided a unique opportunity to study the 3-D architecture of coastal plain sediment of the northern Gulf of Aqaba. Previous studies of sediment cores had identified a mid-Holocene transgression and a late Holocene regression. In this study, one cross-section of buried structures adjacent to the archaeological site of Tel el-Kheleifeh (8th-4th C. BCE) and two stratigraphic columns of 7 m-high outcrops that extended to a depth of 3.2 m below sea level were described and sampled for grain-size, SEM, and radiocarbon age analyses. The base of the section contains subtidal and beach sand and cobble gravel containing abundant shells and coral fragments. Three vertically stacked beachrock layers that developed in the intertidal zone indicate a rising sea level. The uppermost beachrock is found at an elevation of 1.3 m above present sea level and is constrained to be younger than 3.5 ka based on radiocarbon dating of shells. Raised reef, wave-cut notches, and other sea level indicators across the Gulf of Aqaba and northern Red Sea attest to a mid-Holocene highstand. A down-cutting event that eroded the beach sediment and is marked by an irregular unconformity and channels cut to depths below modern sea level. The channels are filled with a blue-gray gravel and sand with abundant rip-up clasts, terrestrial organic material, cross-bedding and convolute bedding which denote high flow velocities and rapid sedimentation. Radiocarbon dating of sediment above the channel constraint its age to before 3.1 ka. As rapid sea level change is not supported by regional evidence, the erosion and deposition of blue-gray channels are interpreted to represent inundation and drawdown of the sea by a tsunami. Similar erosion and deposition in low-lying areas has been documented in tsunamis in Sumatra, Chili, and the Kuril Islands.