Lake level history of Paleolake Siriata and hydrological sub-basin connectivity in the Southern Kenya Rift during the African Humid Period (AHP)

Citation:
Dommain, R., S Riedl A. L. D., deMenocal P. B., Olaka L. A., Strecker M. R., & Potts R. (2016).  Lake level history of Paleolake Siriata and hydrological sub-basin connectivity in the Southern Kenya Rift during the African Humid Period (AHP). American Geophysical Union, Fall General Assembly 2016. , December 2016, San Fransisco

Date Presented:

December 2016

Abstract:

The AHP is one of the most dramatic examples of late Quaternary hydroclimatic change in the tropics. During this wet period numerous large and deep lakes existed in the eastern arm of the East African Rift System (EARS) as testified by paleo-shorelines and lacustrine sediments. The tempo of onset and termination as well as the duration of the AHP is a matter of ongoing research and are still poorly established for the Southern Kenya Rift. Here we present new paleo-shoreline and sedimentary evidence for the existence of a freshwater lake during the AHP to the east of alkaline Lake Magadi. The AHP lake - Paleolake Siriata - was a critical link in the paleodrainage network that connected the central with the southern Kenya rift lakes and northern Tanzania. To establish the timing and spatial extent of Paleolake Siriata we mapped elevations of paleo-shorelines and associated shoreline facies and diatomaceous lacustrine sediments along the former basin margins. Morphometric and topographic details were mapped using a dGPS and an UAV to create a DEM with a resolution of 5 cm to define shoreline elevations and the characteristics of the former basin outlet. Reservoir age-corrected radiocarbon dates of gastropod and bivalve shells and 40Ar/39Ar ages of pumice from the lacustrine strata provide the chronological framework of the Lake Siriata highstand. In addition, oxygen-isotope measurements of gastropod shells indicate past variations in the former lake water-balance. Paleolake Siriata formed abruptly immediately after the dry Younger Dryas interval and reached a maximum depth of 55 m and a surface area of 30 km2; during highstand conditions the lake overflowed into adjacent Lake Magadi while it received inflow from Lake Naivasha via the Kedong Valley and the Olorgesailie Basin in the north. This hydrological connectivity provides important context for the interpretation of the sediment records from the recently collected Olorgesailie-Koora and Lake Magadi drill cores.

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