Orbitally-driven evolution of Lake Turkana (Turkana Depression, Kenya, EARS) between 1.95 and 1.72 Ma: A sequence stratigraphy perspective
Résumé
Lakes act as major archives for continental paleoenvironments, particularly when the evolution of lake
levels over time serves as a guide for understanding regional paleohydrology and paleoclimate. In this
paper, two sections from the Nachukui Formation (Turkana Depression, East African Rift System) provide
a complete record of lake level variability and then paleohydrology for Lake Turkana between 1.95 and
1.72 Ma. This period corresponds to a key time during which important human evolutionary and
technological innovations have occurred in East Africa and in the Turkana area. Based on sedimentary
facies and sequence analyses on coastal deposits, one long-term regressive-transgressive cycle is iden-
tified between 1.95 and 1.72 Ma. Superimposed on this trend, five higher-frequency cycles of lake level
change are identified between 1.87 and 1.76 Ma. Origins of these periodicities are attributed to orbital
forcings. The extents of bathymetry change and shoreline migration during these periods are explored,
suggesting that the period between 1.87 and 1.76 Ma was relatively dry and that climate experienced a
relatively low variability. This finding differs strongly from most of the previous paleoenvironmental
investigations in the region that argue high climate variability during a relatively wet period. This work
emphasizes the importance of using sequence stratigraphy for analyzing lacustrine deposits.