The timing of humid phases on the west coast of Arabia: The chronological and palaeoenvironmental record of an archaeology-rich tufa basin in Saudi Arabia.

The south-eastern Red Sea region may have served as a refuge during Quaternary arid phases for hominin populations migrating out of the Saharo-African region (Bailey, 2009). Wadi Dabsa, within the volcanic landscapes of Harrat al Birk contains the richest and highest density of lithic artifacts (~3000) in southwestern Saudi Arabia (Fould et al., 2015; Inglis et al., 2019). It drains the western side of the Harrat Al Birk for a few 10s of km and the southern tributary opens into a basin (where the lithics are located) that is dominated by a tufa sedimentary unit indicating significantly, and consistently, wetter conditions at various points during the Late Quaternary, making it an attractive site for hominin populations. The range of tufa morphologies within the basin indicate that these wetter phrases involved both standing and running water. The stratigraphies include units of large tufa-cemented basalt bedload (boulder-sized) recording phases of high-energy fluvial flow, and units of tufa with little, or no bedload, recording a lower-energy surface water environment.
We investigate both a basalt handaxe that is partially encased in tufa as well as tufa units on which the surface lithic archaeology is located, in addition to a tufa unit ~ 1.5 m below the surface and a large tufa cascade downstream from the Wadi Dabsa basin . The palaeoenvironmental and chronological context of the tufa and the associated lithics can be reconstructed using facies descriptions in hand section and thin-section, geochemical analysis and stable isotopic data, alongside 234U-230Th dating. Here we present the analysis of 12 tufa samples across the basin, including the surface units associated with the lithic finds, a deeper unit (~1.5 m below the surface) and a fan, containing a large tufa cascade at the distal end of the basin. The results indicate wetter conditions during MIS 7 and MIS 5 (into MIS4), from a meteoric water source (not deep thermal groundwater) and a catchment covered in C3 vegetation. Comparisons are made with the timing and composition of tufa deposits on the western side of the Red Sea.
Bailey, G. N. (2009) The Red Sea, coastal landscapes and homin dispersals. In M. D. Petraglia and J. I Rose (Eds) The Evolution of Human Populations in Arabia. Amsterdam, Springer. pp15-37.
Foulds, F., A. Shuttleworth, A. Sinclair, A. M. Alsharekh, S. Al Ghamdi, R. H. Inglis, G.N. Bailey (2017) A large handaxe from Wadi Dabsa and early hominin adaptations within the Arabian Peninsula. Antiquity, 91:1421–1434.
Inglis, R. H., Fanning, P. C., Stone, A., Barford, D. N., Sinclair, A. G., Chang, H-C., Alsharekh, A. M., Bailey, G. N. (2019) Palaeolithic artefact deposits at Wadi Dabsa, Saudi Arabia: A multiscalar geoarchaeological approach to building an interpretive framework. Geoarchaeology DOI:10.1002/gea.21723