Paper short abstract:

Fossil pollen and 40Ar/39Ar dates from a core drilled from West Turkana in Kenya record vegetation changes from 1.87Ma to 1.38Ma. The vegetation data reveal salinity/alkalinity, conditions and, interactions of climate change, hominin and herbivores during desiccation period.

Paper long abstract:

1Stephen M. Rucina, 2Andy S.Cohen,

1Palynology & Palaeobotany Section, Earth Sciences Department, National Museums of Kenya, P.O Box 40658 00100 Nairobi Kenya

2 Department of Geosciences, University of Arizona, Tucson, AZ 85721 USA

Fossil pollen and 40Ar/39Ar dates from a core drilled from West Turkana in Kenya, record vegetation changes from 1.87Ma to 1.38 Ma. The data reveal savanna vegetation composition driven by interaction of climate change, hominin and herbivore activities. The abundance of Poaceae until 1.67 Ma indicates a drier climate. Amarathanceae, Asteraceae and Typha recorded in the same period reflect of salinity or alkaline soils in a desiccation period recorded between 1.87 to 1.52Ma. The abundance of Cyperaceae in the same period suggests similar conditions recorded by the Poaceae, Asteraceae and Amaranthaceae when the lake was getting shallow forming a swamp and getting more alkaline as it became drier. A major observation from 1.67 to 1.62Ma is the disappearance of Poaceae suggesting a mega drought. Such major change supported establishment of Amaranthaceae, Asteraceae, Cyperaceae and Typha resistant to increased alkalinity as drought intensified. The afromontane pollen taxa recorded probably was washed in from regional dry montane forests especially Ethiopian highlands. From 1.62 to 1.52Ma Asteraceae, Amaranthaceae, Cyperaceae, Poaceae and other taxa recorded in the landscape were sporadically present in the ecosystem. Such changes suggest variability in climate between 1.87 to1.52Ma, emphasizing that West Turkana region was occupied by heterogeneous vegetation mosaic of savanna grassland.