AMS-dated mollusks in beach ridges and berms document Holocene sea-level and coastal changes in northeastern Kuwait Bay

Abstract

In northeastern Kuwait, ancient beach ridges and associated berms are separated from the present shoreline by a 4–6km-wide sabkha. A diverse mollusk fauna in the beach ridges attests to a former open marine environment. A total of 21 AMS dates were obtained in this study. Thirteen mollusk samples from beach ridges yielded AMS dates ranging from ~6990calyr BP in the southeast to ~3370calyr BP in the northwest, suggesting a southeast to northwest age progression during the Holocene transgression. In contrast, four samples from berms throughout the study area yielded AMS dates of 5195–3350calyr BP showing no age progression; these berms consist largely of Conomurex persicus gastropods that aggregated by storms during a highstand at ~5000–3500calyr BP. The berms are presently at ~+6m above sea level, 2–3m above the beach ridges. Human settlements were common on the ridge crests before and after the highstand. Regression to present-day sea level commenced after the highstand, which is when the sabkha began forming. A landward, marine-built terrace, which yielded AMS dates >43,500 14C yr BP, probably formed during Marine Oxygen Isotope Stage 5e and hence is not genetically related to the beach ridges.