A molecular view on an Oligocene lake from the Ethiopian Plateau

Julia Krawielicki, Clayton Magill, Sean Willett, Timothy Eglinton, Bekele Abebe

Research output: Contribution to conferencePoster


In this study, paleoenvironments of the Ethiopian Plateau are reconstructed using plant
biomarkers extracted from sediments of late Oligocene and early Miocene paleolakes and their stable carbon isotopic values. The overarching goal is to understand Ethiopian environmental dynamics prior to uplift of the Plateau. During the Oligocene and late Miocene, northeast Africa underwent dramatic climate change in-step with the evolution of the East-African Rift System (EARS) and the closure of the Neotethys. Previous studies based on plant fossils suggest that the region was covered by riparian and tropical forests amid this period, but then shifted to a much drier climate.

To further resolve regional Ethiopian climate change, we sampled Oligocene lake sediment from the northern Plateau (Mekele). Lake sediments were deposited between two basalt layers of the Adrigrat basalt traps estimated to have ages between 29 and 24 Ma. The sediments are composed of fine-grained clay to silt mixed with secondary ashes.

Carbon isotope analyses of plant biomarker n-alkanes reveal that, besides minor contributions of C4-grasses, most lipid input is derived from C3 plants (δ13C vs. VPDB, nC31 ranges between -29.1‰ and -29.8‰). Based on n-alkane distribution patterns (n = 36), the environment was dominated by trees, as indicated by predominance of nC27 and nC29.

Although the samples are composed of fine-grained, well-sorted lake sediments, there is little to no indication of aquatic input (nC21-23). In contrast, nC27 is abundant and shows a much higher variance of δ13C values, ranging between -25.7‰ and -29.3‰. This variance indicates that the regional tree cover underwent strong perturbations while grasses and shrubs appear to
be much more stable.
Original languageEnglish
Publication statusPublished - Sept 2017
Event28th International Meeting on Organic Geochemistry 2017 - Florence, Italy
Duration: 17 Sept 201722 Sept 2017


Conference28th International Meeting on Organic Geochemistry 2017
Abbreviated titleIMOG 2017
Internet address


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