Cenozoic palaeodepositional conditions and terrigenous sediment influx in the Eyasi-Wembere Basin, Northeastern Tanzania: Insights from elemental proxies

Abstract Elemental proxies are widely used to study sedimentary deposits and reconstruct basin-fill history. The recent innovation of portable XRF (pXRF) offers a rapid and non-destructive method for acquiring elemental data from both core samples and outcrops. In this study, we present elemental data acquired from two shallow cores (well-1 and well-2) from the Eyasi-Wembere Basin, northeastern Tanzania to constrain spatial variations in terrigenous influx, depositional conditions, climate, and sediment sources, which to date have been poorly studied. Pearson correlation and binary cross plots were applied to determine the relationships between studied elements. In sediments from well-1, positive correlations among iron (Fe), titanium (Ti), potassium (K), and cobalt (Co) indicate a common sediment source. In contrast, Well-2 shows slight deviations from this trend, suggesting multiple sediment sources. Well-2, positioned near the source area, recorded massive terrigenous influx within a shallow, well-mixed oxic and unstable water column. Well-1, located in the deepest part of the basin, does not exhibit much variation in either terrigenous input or redox conditions. During wet periods, increased terrigenous input and higher lake levels promoted water-column stratification and reducing conditions, causing enrichment of redox-sensitive elements including vanadium (V), zinc (Zn), and nickel (Ni). Significant volcanic products were deposited at Well-2 location during Miocene. This is supported by Rb/Sr, Rb/K, Th/K, Fe/Ti and K/Ti ratios. Our findings demonstrate the strength of elemental proxies at understanding an interplay between volcanism, climate, terrigenous input, and palaeoredox conditions in a rift basin, all of which are key to reconstructing basin-fill evolution. Our findings highlight that both tectonic and climatic factors fluctuate throughout the Cenozoic, a pattern consistent with other observations from other basins of the East African Rift System (EARS).