Inferred paleoenvironments based on megafloral composition and sedimentology from the Late Oligocene Chilga region, northwestern Ethiopian Plateau.

GARCÍA MASSINI, J.L., JACOBS, B.F.

Yaoundé, Cameroon

Congreso; 18th meeting of the Association for the Taxonomic Study of the Flora of Tropical Africa (AETFAT); 2007

Abstract Chilga is located on the northwestern Ethiopian Plateau, where Late Oligocene rifting created opportunities for sedimentary deposition and fossilization. Tropical plant assemblages preserved from the Paleogene of inland Africa are rare, and the diversity, quality of preservation, and abundance of localities found at Chilga are remarkable. Here, I describe megafloras and sedimentology in three contiguous geological sections, up to 7 m high and about 10 meters apart, from the Magargaria River and their response to abiotic change.  Sedimentology, lithology, and paleosols indicate the landscape and associated plants were subject to episodic ingression of large loads of fluvially redeposited or airfall ashes.  The dynamic fluvial geomorphology influenced by this ash contributed to the creation of short-lived environments where plant assemblages characterized by pioneer taxa rapidly alternated both temporally and spatially. Systematic sampling among 25 - 29 stratigraphic units within each of the geological sections yielded a variety of taxa, including five fern types and angiosperms including palms (Coryphoideae), Pandanus (Pandanaceae), and cf. Alstonia (Asclepidiaceae), conforming to a moist tropical climate. However, also present are members of Leguminosae (i.e., Hymenostegia) and Euphorbiaceae (cf. Macaranga); these reflect either drier periods or greater adaptation to living in recurrently disturbed habitats.