The Mush Valley Lagerstätte

An early Mioecene crater lake deposit in north-central Ethiopia

The Mush Valley Lagerstätte: An early Mioecene crater lake deposit in north-central Ethiopia

The early Miocene Mush Valley lagerstätte in north-central Ethiopia provides a rare view of life, landscape, and climate in tropical Africa 21.7 million years ago. Today, the spring-fed Mush stream exposes volcaniclastic deposits and organic-rich, laminated shales preserving exquisite plant and animal fossils. The site was rediscovered in 2009, and an interdisciplinary team assembled to identify floral and faunal remains and to reconstruct paleoclimate, paleoenvironment, and paleoecology. We interpret the Mush Valley deposits as a volcanic crater lake based on the presence of fossil frogs, fish, and aquatic plants, as well as based on geologic data. Paleoclimate analyses using leaf fossil size estimate mean annual precipitation at Mush was approximately 1600 – 1900mm/yr, which would make Mush a tropical seasonal forest biome.

Fossil animal remains include the first mastotermitid termite from Africa, mammal and crocodile bones, and a remarkable series of frog fossils that display a nearly complete metamorphic sequence from tadpoles to adults. Fossil plant remains include fruits, seeds, flowers, pollen, and exceptionally complete leaves that retain original cuticle and clearly preserve insect herbivore damage. The diversity and quality of fossils preserved at Mush allow for a wide range of analyses to reconstruct climate and ecosystems in tropical Africa during the Early Neogene. Ultimately, the site will contribute to our understanding of the Paleogene-Neogene transition, a pivotal interval for environmental and biotic change in Africa, due to the establishment of a geographic connection between Eurasia and Africa ~23 million years ago and an interval of global warming.