Short-lived increase in erosion during the African Humid Period: Evidence from the northern Kenya Rift

• Published in: Earth and planetary science letters Vol. 459; pp. 58 - 69
• Main Authors: Garcin, Yannick, Schildgen, Taylor F., Torres Acosta, Verónica, Melnick, Daniel, Guillemoteau, Julien, Willenbring, Jane, Strecker, Manfred R.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-02-2017
• Subjects: African Humid Period; Baragoi; erosion; formula omitted; northern Kenya Rift; paleo-delta; erosion; African Humid Period; Be10; Baragoi; paleo-delta; northern Kenya Rift
• DOI: 10.1016/j.epsl.2016.11.017
• EISSN: 1385-013X
• ISSN: 0012-821X

The African Humid Period (AHP) between ∼15 and 5.5 cal. kyr BP caused major environmental change in East Africa, including filling of the Suguta Valley in the northern Kenya Rift with an extensive (∼2150 km2), deep (∼300 m) lake. Interfingering fluvio-lacustrine deposits of the Baragoi paleo-delta provide insights into the lake-level history and how erosion rates changed during this time, as revealed by delta-volume estimates and the concentration of cosmogenic 10Be in fluvial sand. Erosion rates derived from delta-volume estimates range from 0.019 to 0.03 mm yr−1. 10Be-derived paleo-erosion rates at ∼11.8 cal. kyr BP ranged from 0.035 to 0.086 mm yr−1, and were 2.7 to 6.6 times faster than at present. In contrast, at ∼8.7 cal. kyr BP, erosion rates were only 1.8 times faster than at present. Because 10Be-derived erosion rates integrate over several millennia, we modeled the erosion-rate history that best explains the 10Be data using established non-linear equations that describe in situ cosmogenic isotope production and decay. Two models with different temporal constraints (15–6.7 and 12–6.7 kyr) suggest erosion rates that were ∼25 to ∼300 times higher than the initial erosion rate (pre-delta formation). That pulse of high erosion rates was short (∼4 kyr or less) and must have been followed by a rapid decrease in rates while climate remained humid to reach the modern 10Be-based erosion rate of ∼0.013 mm yr−1. Our simulations also flag the two highest 10Be-derived erosion rates at ∼11.8 kyr BP related to non-uniform catchment erosion. These changes in erosion rates and processes during the AHP may reflect a strong increase in precipitation, runoff, and erosivity at the arid-to-humid transition either at ∼15 or ∼12 cal. kyr BP, before the landscape stabilized again, possibly due to increased soil production and denser vegetation.
•Erosion rate estimates in the northern Kenya Rift during the African Humid Period.•Comparison between delta-volume and 10Be erosion rates.•Increased erosion at the arid-to-humid transition between ∼15 and ∼12 cal. kyr BP.•Erosion rates declined during the early Holocene when climate remained wet.•Landscape later stabilized due to increased soil production and denser vegetation.