The Ziway-Shala lake basin system, Main Ethiopian Rift: Influence of volcanism, tectonics, and climatic forcing on basin formation and sedimentation

In the central sector of the Main Ethiopian Rift, the Ziway-Shala lake basi n system includes four present-day residual lakes, from north to south, lak es Ziway, Langano, Abijata, and Shala. This region of East Africa is under the influence of the Intertropical Convergence Zone seasonal migration. Thu s it has been designated as a potential core site by the ERICA Project ('En vironmental Research for Intertropical Climate in Africa'). The four lakes have been subjected to strong changes in water level and water salinity at least during the Late Pleistocene. The purpose of this study is to produce a model of basin formation and sediment accumulation for this system of lak es, in order to separate the effects of climatic change from environmental variations induced by local or regional factors such as volcano-tectonic fo rcings. In addition to an exhaustive synthesis of available data, various i nvestigations have been used to develop this model: 3D remote sensing, high -resolution seismics, coring, and structural, sedimentological, and hydrolo gical field studies. New AMS radiocarbon dating helped to refine the pre-ex isting stratigraphic framework for this region, and basin age estimations w ere calculated using mean sediment accumulation rates. The history of the Z iway-Shala lake basin system has been reconstructed from the Late Pliocene- Early Pleistocene period (10(6) yr), mainly characterized by catastrophic e xplosive volcanic eruptions. The early-middle Pleistocene-Late Pleistocene period (10(4)-10(6) yr) was marked by a regional volcano-tectonic paroxysm, resulting in major changes in the morphology of the area, with the formati on of the Abijata, Ziway and Shala lake basins. From similar to 0.20 Ma, th e Ziway-Shala basin history is marked by the eastward migration of volcano- tectonic activity, resulting in the development of the youngest basin of th e Ziway-Shala system, the Langano Basin. The joint history of sedimentation in the Ziway, Langano, Abijata, and Shala lake basins started during the e arly-late Pleistocene period (10(1)-10(4) yr) and is characterized from thi s period up to the present-day by a series of climatically controlled rises and falls of lake level. (C) 1999 Elsevier Science B.V. All rights reserve d.