Paleoenvironmental reconstruction of Late Oligocene deposits from the northwestern Ethiopian Plateau

This dissertation reviews the Cretaceous-Cenozoic record of ferns in Africa and assesses the paleoenvironmental significance of selected taxa from Cenozoic deposits from Ethiopia. In particular, plant macrofossils, including ferns and angiosperms, and sediments from a Late Oligocene (27.36 +/- 0.11 Ma) succession of volcaniclastic strata from the Magargaria River region, northwestern Ethiopian Plateau, are analyzed and used for paleoenvironmental reconstruction. In addition, paleoenvironmental and community structural changes based on palynological data obtained from the same sediments are compared to those derived from plant macrofossils and sediments to test whether regional and local signals are consistent with each other. Results indicate a rather incomplete fern record for Africa, except for the Late Oligocene volcaniclastic sequence analyzed. More precisely, the analysis of macrofossils and sediments, combined, showed that physiographic changes brought about by volcanism characterizing the Oligocene of Ethiopia influenced paleoenvironmental conditions and plant communities, transforming a forested landscape inhabited by riparian taxa to transient settings dominated by ferns and a few ecologically pioneer angiosperms typical of disturbed environments. However, palynological data demonstrates that plant communities were not as completely modified as shown by macrofossils and sediments, indicating the development of a heterogeneous ecosystem characterized by a combination of open herb-dominated environments and forests, instead. In summary, this study shows that volcanism characterizing the northwestern Ethiopian Plateau during the Oligocene repeatedly influenced the development of plant communities and paleoenvironments favoring the succession of heterogeneous ecosystems on short temporal and spatial scales. Finally, this study is the first that combines paleobotanical and sedimentological data for paleoenvironmental reconstruction and understanding of plant community dynamics in Paleogene deposits from Africa, and it demonstrates the advantages of a multiproxy approach for assessment of paleoecosystem dynamics on an unstable landscape.