FLUVIAL SEDIMENTS RECORD MIDDLE HOLOCENE CLIMATE CHANGE IN SOUTHERN YEMEN

The arid highlands of the southern Arabian peninsula (Yemen) preserve abundant evidence of a climate shift that forced both human and environmental responses in the middle Holocene. The Roots of Agriculture in Southern Arabia (RASA) Project has been investigating archaeological and paleoenvironmental records in the region in order to understand the relationship between environmental dynamics and human responses at a time hypothesized to coincide with the advent of agricultural subsistence in the region. One of the primary RASA project geologic objectives is to better understand the shift in climate that occurred during the middle Holocene and reconstruct its timing and paleoenvironmental significance.

Fine-grained fluvial sediments preserved in wadi bottoms document past aggradation under considerably wetter, lower energy conditions, which differ significantly from the present-day environment. Charcoal samples collected from numerous hearths buried within these sediments provide evidence of greater human activity in the region and offer a means of dating the record. Radiocarbon dating has yielded a range of age estimates on the humid-phase fluvial sediments, representing a time span of approximately 5600 years. Our oldest and youngest samples were dated at 10,254 ± 55 and 4,633 ± 40 14C yr B.P., respectively. During the last field season, we identified a sinuous lens of organic-rich, laminated sandy silt, approximately 30m wide, traceable over 300m, which we interpret as an abandoned channel fill from the mid-Holocene period of increased precipitation. Abundant archaeological materials, including hearths, grinding stones, and stone structures, were recorded on the paleosurfaces adjacent to the former stream channel. Charcoal samples have been dated from the top and base of this dark sediment band, yielding radiocarbon dates of 5400 ± 40 and 5970 ± 70 14C yr B.P., respectively. Through GPS surveying, further sedimentological analysis, and flow modeling, a better understanding of the past flow conditions, sediment budget, and paleoclimate can be achieved.