INTERPRETING THE DEPOSITIONAL ENVIRONMENT OF NEOGENE COQUINA DEPOSITS IN JORDAN

Coquina deposits composed mainly of the bivalve Cerastoderma are located in the hyper-arid desert region of Jordan. These deposits are important as they have been used to reconstruct the northward migration of the African monsoon during interglacial periods as well as to infer ecological refuges for modern humans migrating into Eurasia through the Arabian Peninsula. However, the age and depositional environment of these deposits are unclear. The only age constraints on the coquina deposits in Jordan are U-series (alpha-counting) ages on Cardium shells, yet shells are notorious for being open systems with respect to uranium. Here we evaluate the age and depositional environments for the coquina deposits at Azraq (31.93°, 36.88°; 550 m), Umari (31.52°, 37.07°; 540 m), and Mudawwara (29.28°, 36.05°, 720 m) based on their fossil assemblages, the sediments and surfical deposits that contain the coquinas, as well as hydrologic modelling to assess the potential stability of lake environments in the basins. We ultimately evaluate three alternative hypotheses regarding the age and origin of these deposits. The first hypothesis is that these coquina deposits represent Pleistocene lakes, the second is that they represent Pleistocene wetland or spring-fed stream deposits, and the third is that they represent lakes, but that the deposits are actually Miocene or Pliocene in age.