Paper No. 5
Presentation Time: 2:35 PM
PALEOCLIMATIC IMPLICATIONS OF PLUVIAL DEPOSITS IN MUDAWWARA, JORDAN
The presently hyper-arid region of Mudawwara in southern Jordan provides geomorphological evidence of more pluvial conditions in the past, however, the timing and source of these humid episodes has been unclear. A 3m sediment core from the dry playa Khabrat Ratiya (29¢ªN, 36¢ªE) was radiocarbon dated and analyzed to better understand the timing and conditions for wetter periods in southern Jordan. The 14C results indicate Khabrat Ratiya was active from ~20-29 ka, which coincides with the highest lake levels of Paleolake Lisan. The age of the Khabrat Ratiya playa sedimentation suggests the same source of humidity as Paleolake Lisan: enhanced precipitation from Mediterranean cyclones. Coquina deposits also in the Mudawwara depression, consisting mainly of the bivalve Cardium sp., were interpreted to have been deposited in a large (>2000km2), shallow (<40m) perennial lake(s) (Petit-Maire et al., 2010, Global and Planetary Change 72: 368-373). Unlike the short-lived pluvial episodes of dry playas, these lacustrine deposits indicate past climatic conditions sufficient to sustain a perennial freshwater to brackish aqueous environment in the presently hyper-arid desert. Petit-Maire et al. argue that the existence of the paleolake was due to an intensified Indian Monsoon during interglacial periods OIS 7a-6e, 5e, and 5c-a based on Th/U dates on bivalve shells (88-170 ka). This interpretation, however, is reliant upon the validity of the Th/U ages; we argue that the Th/U ages on these deposits are problematic. Bivalve shells are prone to open-system behavior and several lines of evidence (e.g. high and variant U concentrations) suggest open-system behavior in the Mudawwara bivalve shells. Moreover, geomorphological evidence such as the lack of preservation of lacustrine landforms and poor exposure of deposits suggest that the coquina deposits are older than late Pleistocene We argue that in southern Jordan (1) pluvial episodes occurred in Khabrat Ratiya ~20-29 ka and resulted from increased winter precipitation from the Mediterranean and (2) the Mudawwara coquina deposits should not be used as evidence for enhanced precipitation from the Indian Monsoon during Pleistocene interglacial periods.