2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 102-7
Presentation Time: 9:40 AM


DIMAGGIO, Erin N.1, CAMPISANO, Christopher J.2, ROWAN, John2, DUPONT-NIVET, Guillaume3, DEINO, Alan4, GARELLO, Dominique5, REED, Kaye E.6 and ARROWSMITH, Ramón7, (1)Department of Geosciences, Pennsylvania State University, University Park, PA 16802, (2)Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University, Tempe, AZ 85287, (3)University of Postdam, Institute of Earth and Environmental Science, Building 27, Karl-Liebknecht-Str. 24-25, Postdam, 14476, Germany, (4)Berkeley Geochronology Center, Berkeley, CA 94709, (5)School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, (6)Institute of Human Origins, University of Arizona, School of Human Evolution and Social Change, PO Box 874101, Tempe, AZ 852874101, (7)School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, dimaggio@psu.edu

Sedimentary basins in eastern Africa preserve a record of continental rifting and contain important fossil assemblages for interpreting hominin evolution. However, the record of hominin evolution between 3 and 2.5 million years ago (Ma) is poorly documented in surface outcrops, particularly in northern Awash, Afar, Ethiopia. Here we present the discovery of 2.84-2.58 Ma fossil and hominin-bearing sediments in the Ledi-Geraru research area that have produced the earliest record of the genus Homo. Vertebrate fossils record a faunal turnover indicative of more open and probable arid habitats than those reconstructed earlier in this region, in broad agreement with hypotheses addressing the role of environmental forcing in hominin evolution at this time. Geological analyses including 40Ar/39Ar dating and magnetostratigraphy date the LD 350-1 Homo mandible to 2.80-2.75 Ma. Over that time period depositional environments transitioned from lacustrine to riverine settings. NW-SE oriented normal faults associated with triple junction tectonism dissect Ledi-Geraru strata into discrete fault blocks. Using depositional and structural data from Ledi-Geraru we refine regional basin models and place constraints on the structural development of the Afar region. This work sheds light on an enigmatic time period for both geology and fossil studies in Ethiopia and provides the geological and environmental context for the LD 350-1 early Homo site.