An East African record of vegetation and climate as interpreted from the palynology of the terrestrial Late Neogene and Quaternary sediments of the southern part of Lake Albert, Uganda

Abstract

The Neogene of East Africa was a time and place of critical importance in hominid evolution, and yet our current understanding of its climatic history is a composite record based on different proxies from a series of stratigraphically (temporally) restricted outcrop sections. Whilst these studies provide an overall picture of progressively increasing aridity with a long-term trend toward more open savannah vegetation, there is as yet no single complete Neogene climatic record from a location in East Africa which epitomises this scenario. This study therefore aims to produce the first long-term vegetation and climatic records for the East African Neogene by undertaking a systematic palynological analysis of the plant communities recorded in two continuous Late Neogene lacustrine borehole sequences from Lake Albert, in the Western Riftof the East African Rift Valley, Uganda. Detailed systematic analysis of borehole cuttings samples has allowed the first comprehensive determination of the botanical affinities of the abundant and well-preserved palynomorphs recovered, permitting the identification of ecologically, climatically and stratigraphically significant taxa. The latter have been used to establish an age framework, which in turn have permitted accurate comparison with outcrops dated by macrofossils and tephrostratigraphy. A Nearest Living Relatives (NLRs) statistical analysis of the climatic “profiles” of the pollen and spores has produced a climatic profile which reveals a fluctuating, but overall gradual trend of decreasing rainfall and temperature through the Neogene. In addition, Principal Components Analysis (PCA), Discriminant Analysis (LDA) and Cluster Analysis reveals a central rift plant community which steadily increased in biodiversity through the Neogene, whereas the rift margin vegetation was less stable, taking considerable time to recover from the sporadic, tectonically controlled development of alluvial fans, which were characterised by much lower diversity plant communities. This palynological analysis of the lacustrine sediments from the Albert Rift has for the first time shown that palynomorphs can provide a long-term and continuous record of vegetation and climatic change in East Africa, providing pollen profiles which illustrate the increased development of savannah, and shifts in the profile which can be related to continent-wide climatic events of intra-Late Pliocene, Early Pleistocene and Mid Pleistocene age.

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ORCID for John Marshall: orcid.org/0000-0002-9242-3646

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