Late Quaternary environmental change and anthropogenic landscape transformation in south-east Arabia: An assessment from piedmont oases in the Emirate of Ras al-Khaimah (U.A.E.)

In south-eastern Arabia, climatic reconstitutions mainly derive from the study of speleothems, dune sands, lacustrine deposits, and alluvial sediments. In the Hajar Mountain range, which covers a major part of SE Arabia, the Late Quaternary is relatively poorly documented, notably due to the lack of preserved archives. We explore the potential of oasis soil sequences as archives of past landscapes and climate in the Emirate of Ras al-Khaimah, in the piedmont oases of Dhayah, Sir, and Jiri. Geomorphological surveys, mapping and geoarchaeological investigations combined with luminescence and radiocarbon dating were conducted in these oases. We propose a detailed typology of the deposits and provide a first interpretation of their origin and depositional modes (alluvial, aeolian, anthropogenic). Our results show that Holocene agricultural activity has preserved natural archives from deflation and alluvial erosion. This allows us to identify phases of aeolian reactivation during Marine Isotope Stage (MIS) 4 (∼65 ka) and MIS 2 (∼21 ka), whereas alluvial sedimentation occurred in early MIS 3 (∼54 ka), the Late Glacial (∼15 ka) and the early Holocene (∼8-6.5 ka). Two important shifts of active lobe and distal incisions were identified in the Sir plain between 9-8 ka and 6-3.5 ka and potentially linked with base level evolution and/or climatic changes. Oases development is recorded during the second half of the Holocene. Despite a voluntary control of water supply, we identified phases of alluvial reactivation between ∼3.5 and 3 ka and ∼1.3 and 1 ka, and intense fluvial detritus dated to ∼2.7-2.4 ka. This study demonstrates that oasis pedo-sedimentary sequences in arid environments are valuable archives for the reconstruction of climatic conditions and landscapes evolution.