Palaeoclimatic and tectonic implications of Neogene microflora from the Northwestern Ethiopian highlands

Abstract

Climatic changes in East Africa have been well documented although the record is far from complete. Palaeoclimatic data for both the Holocene and Pleistocene^1–7 and the Pliocene^1–8 are available through fossil pollen studies. However, these data extend in a continuous manner only as far back as 3.7 Myr BP (ref. 11) largely because of the emphasis on studies related to human origins. Fragmentary data from macrofossils also exist for older periods from Eastern^14–20, Central and Southern Africa^21,22 although the scarcity of material and the lack of isotopic dates makes it difficult to define continuity in the patterns of climatic fluctuations in East Africa. The late Miocene pollen/spore flora described here represents the first data from East Africa for this time period and provides new information on the pre-Pliocene flora and climate of the continent. The pollen flora comes from a post-8-Myr lacustrine deposit in the heart of the Northwestern Ethiopian Plateau (12° 35′ N, 37° 06′ E) and contains ‘exotic’ taxa that are now extinct. The pollen diagram is characterized by abundant wet lowland rainforest taxa and pteridophytes, a very weak representation of grasses and the total absence of conifers, indicating warm and humid climates towards the close of the Miocene. Post-depositional uplift of the Chilga area (∼1,000m) is also implied from the fossil pollen/spore assemblage.