Former humid phases in the southwestern Arabian peninsula: climatic and environmental implications of the tufa record over the last 250 ka from the Harrat Al Birk, Saudi Arabia. &#160;
Authors: Stone Abi , Sahy Diana , Inglis Robyn , Candy Ian , Alsharekh Abdullah , Sinclair Anthony 
Published: March 2021

&lt;p&gt;Little is known about the tufa deposits within the volcanic Harrats of western Saudi Arabia. This research aims to characterise the fossil tufa system and examine its utility as a palaeoenvironmental archive. This requires us to understand the conditions under which the tufa was deposited. In particular, to ascertain whether they are cool, freshwater tufa, or geothermal travertine. In this presentation we show the extent of the tufa within the basin, describe the stratigraphy and settings, as well as their composition and petrology, alongside U-Th chronological control for a selection of suitable subsamples&lt;/p&gt;&lt;p&gt;The samples are composed of low-Mg calcium-carbonate&lt;strong&gt; &lt;/strong&gt;and their &lt;sup&gt;87&lt;/sup&gt;Sr/&lt;sup&gt;86&lt;/sup&gt;Sr composition shows there has been water-rock interaction with the mafic metavolcanic Neoproterzoic bedrock as well as metamorphosed marine carbonates from the Arabian Escarpment at the head of the Wadi Dabsa catchment. Their &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C composition (-6.3 to -12.9 &amp;#8240;) is indicative of a meteoric water and soil signature, rather than a geothermal source.&lt;/p&gt;&lt;p&gt;The tufa deposits are widespread within the Wadi Dabsa Basin, with at least three phases of deposition, recorded at the basin surface, within incised wadi channels and in a downstream fan region. In some locations, the size of tufa-cemented fluvial bedload represents very high magnitude events, whilst the lacustrine to paludal facies indicate more quiescent phases of increased moisture availability. The U-Th dating indicates that the basin was wet during interglacial stages (Marine Oxygen Isotope Stags [MIS] 7 and 5) with some indication, given the error ranges on dates from multiple-subsamples, that deposition occurred primarily during interstadials (e.g. MIS 5e, 5c and 5a). The MIS 7 age is from a vug-fill tufa deposits within an extensive tufa cascade, which indicates the cascade itself pre-dates MIS 7.&lt;/p&gt;&lt;p&gt;The major concentration of artefacts (&gt; 3000) in this basin make it one of the richest Palaeolithic assemblages so far recorded in southwest Saudi Arabia (Foulds et al., 2015; Inglis et al., 2019). This site is ~ 6 km from the current coastline, which is inland from the MIS 5e shorelines in this region (Inglis, pers comm), and these sites with freshwater mean it is important to continue to consider coastal sites as corridors with habitable landscapes for hominins.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;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&amp;#8211;1434.&lt;/p&gt;&lt;p&gt;Inglis, R. H., Fanning, P. C., Stone, A., Barford, D. N., Sinclair, A., Hsing-Chung, C., Alsharekh, A., Bailey, G. (2019). Palaeolithic artefact deposits at Wadi Dabsa, Saudi Arabia: A multi-scalar geoarchaeological approach to building an interpretive framework.&amp;#160; Geoarchaeology 34(3), 272-294. &amp;#160;&amp;#160;&lt;/p&gt;