Episodic settlement and mound formation context at Cubalel and Siwré sites, Middle Senegal River

Recent analysis of sediments recovered in 1991 at the sites of Cubalel and Siwré in the Middle Senegal River Valley have revealed new insights into the context of mound formation beginning ca. 1900 cal BP. In this study, we utilized stable isotopes ( δ 13 C, δ 15 N) from Soil Organic Matter (SOM) and applied a Bayesian deposition model to radiocarbon dates to understand differences in the duration and nature of settlement between the two sites compared to nearby sterile levee deposits. The median calibrated radiocarbon ages dating the aggradation of sediments associated with Phase IB pottery at Siwré 2S occurs between ca. 1650 and 1490 cal BP in a generally stepwise fashion. However, previously identified Phase IIIA ceramic-bearing occupation at the Cubalel C1 mound occurs between ca. 1400 and 1370 cal BP within stratigraphically separated, but temporally indistinguishable contexts applying a Bayesian framework. The results indicate earlier phases of settlement at Siwré were longer in duration than the later occupations at Cubalel, yet isotopic indicators of vegetation cover remain relatively constant with a mix of C 3 and C 4 vegetation as the source of the SOM. Increases in δ 15 N from mound sediments at Cubalel C1 are interpreted as reflecting an increasing reliance on animal husbandry and sedentism, which is also indicated in the archaeological record. The data provide deep understandings of past pastoral systems combined with ecological data, which can be built upon in future studies.