AGE CONSTRAINTS AND PALEOCLIMATIC IMPLICATIONS FOR THE LAST GLACIAL MAXIMUM PLUVIAL EVENT IN THE JORDAN VALLEY FROM WADI HASA, JORDAN

Late Quaternary wetland deposits outcrop intermittently throughout Wadi Hasa, a stream valley located in central Jordan that flows west from the Jordan Plateau into the Dead Sea. The paleo-wetland deposits are visible beginning at the narrows where the stream exits the plateau and continue for ~8km downstream from this location within the deeply incised channel and its tributaries.

Four time-stratigraphic units of wetland deposits have been identified within Wadi Hasa. Unit A deposits are mostly located downstream and consist of hard, consolidated, alluvial gravels cemented with secondary carbonate and gypsum with beds of wetland deposits. Unit A deposits are thought to be greater than 100 ka but as of yet have no age control. Unit B deposits are located in the central wadi area and consist of well-cemented wetland deposits that contain Middle Paleolithic archaeological materials that likely date between 100 ka and 45 ka. Unit C deposits are located at the narrows and at several downstream locations. Radiocarbon dating of Upper Paleolithic archaeological material within the loosely cemented wetland deposits of Unit C gives an age range of 35 ka to 20 ka. Unit D deposits are likely Holocene in age, less than 5 ka, and consist of uncemented alluvial gravels and wetland deposits that occur throughout the area.

Aggradation and incision of the wetland deposits is controlled by the height of the local water table. The main wet event recorded at Wadi Hasa in the wetland deposits of Unit C occurred between ~27 ka and 24 ka based on AMS 14C radiocarbon dating of archaeological charcoal. The main highstand (>164 m below mean sea level)of Lake Lisan, the Pleistocene precursor of the Dead Sea, occurred between 27 ka and 23 ka. The similarity in timing of the wet periods indicates that the water table fluctuations recorded in the wetland deposits at Wadi Hasa are indicative of regional climate change. The peak of Lake Lisan is likely due to a dramatic increase in total water input to the lake, causing a rise in base level reflected in the wet period at Wadi Hasa. The difference of ~1000 years in timing of the end of the wet period is likely related to the larger basin area of the lake relative to the wadi. The timing of the end of the wet period at 23 ka before present corresponds to the LGM and the resulting colder and drier climate conditions in the Near East.