Rivers of the Hadramawt watershed (Yemen) during the Holocene: Clues of late functioning
Résumé
Recent geoarchaeological investigations have been carried out in the thick silty alluvial formations of the northern Hadramawt basin (Yemen). Field data was combined with a compilation of palaeoenvironmental records published from Arabia and its margins. Research performed on palaeolakes and other geoarchives indicates that the wet early-mid Holocene has little in common with the continuously arid period after 5.2 ka BP. The data sets allowed the authors to propose new perspectives for the Holocene palaeohydrological evolution of Southern Arabia, which was more variable and contrasting than previously thought. Furthermore, these data provide the opportunity to go deeper into the Holocene and to present a new precise palaeohydrological framework for the Late Holocene (7.0e2.0 ka BP). River functioning, fluvial aquifer dynamics and types of sedimentation are closely related to the rainfall regime, length and intensity (monsoonal or Mediterranean), and to the landscape conditions in the upper watersheds. The development of fluvial palaeosols in the Hadramawt valleys, often associated with high levels of the aquifers, is clearly in phase with humid periods until the beginning of the first millennium BC (5.9e5.3, 4.8e4.5 and 4.0e2.7 ka). River behaviour also impacted Neolithic and early Bronze Age settlement systems in this lowland area, as phases of floodplain stability favour site location. The hyperarid 4.2 ka event is associated with an unprecedented fluvial detrital phase with high energy discharges in the entire Hadramawt basin.