Recent studies in Lebanon conducted on multi-level caves propose new insights on incision stages of Kalb and Antelias valleys. The study area is located in central Mt Lebanon and comprises a dammed karst configuration close to the Mediterranean Sea. The suggested morphogenesis model of both valleys is based on the relation between the karst base level and the thalweg levels of both rivers. A crossover analysis between speleogenesis stages of Kanaan, Kassarat and Jeita caves, the geology settings of the area and marine terraces and paleosurfaces suggest three evolution stages for Kalb and Antelias valleys. The study highlights on: i) the sub-surface morphologies as indicators for the paragenesis process identified in all three caves in response to base level aggradation, ii) latter incision of Jeita and Kassarat canyons with the reorganization of the drainage system in response to the base level drop, iii) implications of regional eustatic changes of the Mediterranean sea and tectonic uplift of Mt Lebanon. Prelemenary chronology settings for the evolution of karst system is discussed based on U/Th datations of speleothems: Speleothem growth in Kanaan cave (100 m.) began at the end of Mid-Pleistocene (cf. 194 ka ± 0.98) and also at the end of MIS 6 (cf. 127 ka ± 0.7402). Speleothems dating from Kassarat cave (60m.) showed ages at the end of MIS 3 (cf. 37.590 ±0.82 and 33.921 ±1.09). Considering that the cave level identified at 90-160 m indicate that all three caves developed in the phreatic/epiphreatic zone of Antelias and Kalb karst basin, the passage to vadose conditions is occurred then at least from the end of Mid-Pleistocene. Cave levels are therefore, prior to this age inferring to the incision of Antelias and Kalb thalwegs probably during early or Mid-Pleistocene. The cave level identified at 90-160 m and 60-70 m correspond to the elevation of some low-gradient surfaces in the area. Based on the geomorphological work interpreted in the geological framework of Antelias and Kal valleys and compared to other cave levels around the Mediterranean basin, we suggest that the first cave level could be related to a former regional transgression of the Mediterranean sea during the Pliocene. Whereas abandon of the second and lower level could be related to a marine regression stage or to Mt-Lebanon uplift during the Pleistocene.

abstract, Geological Phenomena, landscape