Geochemistry of the Lisan and Damya Formations in Jordan, and implications for palaeoclimate

Geochemical, mineralogical and sedimentological investigations, carried out on the lacustrine Lisan and Damya Formations of the Jordan Rift Valley, reveal three major and several minor transgressive depositional cycles, all terminating with massive gypsum precipitation. The highest level of Lake Lisan is reported in the literature at 130 m below mean sea level (b.s.l.). From 70-45 calibrated ka BP, the Lisan Formation is characterised by a high gypsum/aragonite ratio and a low lithogenic content, implying a regression of an initially high water level caused by reduced water input. In the following interval (ca, 45-36 cal. ka BP), two low water stands are marked by higher salt concentrations. After recovery and a period of higher water level, the Lake Lisan era ends with a strong regression at around 16 cal. ka BP. This date coincides with the period when Lake Van. Eastern Turkey also fell dry, thus marking a strong drought signal in the entire Near East. The overlying Damya Formation, containing more lithogenics records lake level fluctuations at around 300m b.s.l. The existence of a north-south precipitation gradient. as present today, is indicated by increasing Sr/Ca ratios in aragonite and a decreasing lithogenic content in a N-S direction. Secondary gypsum formed diagenetically, and aragonite and low Mg-calcite was transformed into high Mg/Fe-calcite. (C) 2002 Elsevier Science Ltd and INQUA. All rights reserved.