map of provinces
Fig. 1 - Map of Ethiopian Provinces:
Northwestern Plateau study area indicated by rectangle.


Ethiopia is dominated by two major plateaus, the Northwestern and Southeastern, separated by the SW-NE trending Ethiopian Rift Valley. Underlying the Tertiary volcanics capping the Northwestern Plateau is a thick (>2 km) section of Mesozoic strata, including ca. 600 m of Late Jurassic-Early Cretaceous continental sediments. These are well exposed in Shewa Province in the Abay (Upper Blue Nile) River Basin and in Tigray Province in the area around Mekele (Getaneh, 1991; Kazmin, 1973, 1975). Extensive exposures of Mesozoic sediments are also present in the Southeastern Plateau in Harenge Province.

Mesozoic vertebrate fossils are known from a series of sediments exposed in the Southeastern Plateau that appear to have been formed prior to or during deposition of formations included in the Middle through Late Jurassic "Limestone Unit." On the Northwestern Plateau, fossil localities are, for the most part, in sediments that overlie the "Limestone Unit," and it is here that we have concentrated our work.

Southeastern Plateau: Sediments of possible Late Permian through Late Jurassic age are present in Harerge Province in the region of Harer approximately 400 km east of Addis Ababa. The geology of the region around the base of Mount Hakim near Harer was studied by Mühlen (1931) who reported finding fossil fish teeth and bones identified as Lepidotus suggesting a Triassic or Early Jurassic age of the Lower Sandstone Unit. In another early report on fossil vertebrates from the Harer region, von Huene (1938) described a fragment of the snout of a pliosaur which he identified as cf. Simolestes nowackianus. The specimen was found at the foot of the Kondudu "Bergstocks" in a sandy marl exposed eight meters above the local basement complex. Associated invertebrate fossils indicate a Late Jurassic age. More recent field research in exposures of the upper part of the Lower Sandstone Unit near Kersa, approximately 35 km to the NW of Harer, resulted in the discovery of Triassic dinosaur footprints described by Getaneh (1987).

Northwestern Plateau: Getaneh (1991) published a detailed geologic study of the Late Jurassic-Early Cretaceous section exposed in the Abay (Blue Nile) Gorge, central Northwestern Plateau, but reported finding no vertebrate fossils in the Blue Nile section. Here the regional five-fold division of the Mesozoic (post Karroo) section can be recognized. The Lower Sandstone Unit is primarily composed of sandstones with interbeds of siltstone, mudstone, and rare conglomerates that probably were deposited in a fluvial or deltaic environment.

Location of Mesozoic sediments

Fig. 2 - Location of Mesozoic sediments.
The extent of Mesozoic sediments in Ethiopia and Eritrea is indicated by the pink-shaded areas. Redrawn and modified from Getaneh Assefa (1991). Original topographic image modified from USAID.