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Tropical to semi-arid lacustrine environments and associated landscapes and ecosystems over the last 45 million years in the Turkana depression of northern Kenya

Abstract : The continent-scale East African Rift System is an impressively complex structure considering the large variety of relief and drainage - including fluvial and lake systems - that were created over millions of years by magmatic-, tectonic- and climatically-controlled processes. In the Turkana depression, such processes acting together over different time scales from 100 to 107 years, starting at the Eocene epoch, successively created high-altitude plateaus, axial or plateau-related volcanic edifices and complex horst and graben landscapes, that all acted as topographic barriers over long distances. Dramatic changes in climate, vegetation and hydrology occurred during these last 45 million years, as a consequence of major topographic changes affecting the rift. During the middle-late Cretaceous up to late Eocene, the Turkana depression was marked by a fully fluvial system of braided type, represented by the Lapur Sandstone, with a possible coeval fluvio-marine setting to the southeast, connecting through the Anza Rift with the Indian Ocean. Climate conditions were considered as semi-arid at that time. During middle-late Eocene, intense volcanic activity at the northern end of the Turkana depression resulted in the formation of a 3-km high topography made by lava flow accumulation. On the south and west sides of the depression, rifting processes began to create graben landscapes that connected with drainage networks issued from the south. Several lacustrine environments began to develop in this region, as represented by the Lokichar and North Kerio Basins of Eocene? to middle Miocene age. Pollen studies from the oil exploration well Loperot-1, indicate tropical climatic conditions during late Oligocene-early Miocene time with high rainfall conditions and a well-defined dry season. The presence of deep-water lakes with high organic productivity, surrounded by a mosaic environment of semi-deciduous forest and humid woodland, coincides with an abundant fauna represented by reptiles, fishes, and mammals of late Oligocene age. Active volcanism continued in the northern part of the depression during this period, before shifting to the south in the middle-upper Miocene. During the same period, south-north rift migration led to the end of lacustrine sedimentation in this region. A new single half-graben basin resulted from a new rifting phase during late Miocene-Pliocene time, corresponding to the present-day northern part of the Lake Turkana Basin. Regional climate change toward aridification resulted in major hydrological changes, particularly for the hydrographic network issuing from the south. The Plio-Pleistocene Lake Turkana was affected by successive lake level fluctuations indicating alternating humid and dry climatic phases. Large variations of lake level and water chemistry directly influenced the behaviour of hominin populations present in this region.
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Submitted on : Wednesday, February 1, 2012 - 1:26:30 PM
Last modification on : Friday, April 5, 2019 - 8:17:32 PM

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Jean-Jacques Tiercelin, Peter Thuo, George Muia, Mathieu Schuster. Tropical to semi-arid lacustrine environments and associated landscapes and ecosystems over the last 45 million years in the Turkana depression of northern Kenya. 5th International Congress of Limnogeology,, Aug 2011, Constance, Germany. ⟨insu-00665191⟩

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