Tephrostratigraphy of the Waki-Mille area of the Woranso-Mille paleoanthropological research project, Afar, Ethiopia

Abstract

Tephra geochemistry and (40)Ar/(39)Ar geochronology are reported for the Waki-Mille area in the northwestern part of the Woranso-Mille paleoanthropological project area in the west central Afar region of Ethiopia. Previous studies documented dentognathic fossils that are morphologically intermediate between Australopithecus anamensis and Australopithecus afarensis and some that are attributed to Australopithecus afarensis. Additional dentognathic remains from the study area were assigned to the newly identified species Australopithecus deyiremeda. These fossil hominin taxa were recovered from volcanic and sedimentary strata containing tuffs ranging in age from more than 3.77 million years ago (Ma) to less than 3.469 Ma. One of the tuffs was correlated based on geochemistry, feldspar mineralogy, and age to the Lokochot Tuff of the Omo-Turkana Basin of southern Ethiopia and Kenya. Variations in major and minor element abundances in volcanic glass demarcate ten geochemically distinct tuffs and tuff sequences, including three that are geochemically similar to widespread regional tuffs, specifically the Lomogol, Lokochot, and β- Tulu Bor/Sidi Hakoma tuffs. A new (40)Ar/(39)Ar age for the Waki Tuff, which is geochemically similar to the Lomogol Tuff, is 3.664 ± 0.016 Ma. Other tuffs in the Waki-Mille area are geochemically dissimilar to regional tuffs documented to date. Identification of tuffs based on character, stratigraphic position, and geochemistry refines local stratigraphic correlations and delineates the geographic distributions of precisely dated fossiliferous levels within the Waki-Mille area.

Dentognathic remains of Australopithecus afarensis from Nefuraytu (Woranso-Mille, Ethiopia): Comparative description, geology, and paleoecological context

“…However, virtually all of the 40 Ar/ 39 Ar results are older, and, given the reworked nature of the tuffs, likely reflect detrital contaminants. These xenocrystic components yield ages typical for the Woranso-Mille area, in particular reflecting early rift volcanism in the late Oligocene, and what are likely major proximal volcanic events at ~4.8 and ~7 Ma (Deino et al, 2010;Saylor et al, 2016b). Younger ages are present, but uncertainties in many cases are largely due to low K content and small grain size.…”

New Pliocene hominin remains from the Leado Dido’a area of Woranso-Mille, Ethiopia

“…We analyzed the tephrochemistry of ash samples collected at three locations in the Leado Dido'a area (described in Section 3.1 Stratigraphy). Elemental abundances of volcanic glass were analyzed in polished grain mounts using a Cameca SX-51 electron probe micro-analyzer at the University of Wisconsin, Madison, following the methods in Saylor et al (2016). The mounts were carbon coated at the same time as standards, which included Kilbourne Olivine for Mg, Minas Gerais rutile for Ti, Monash andesine for Ca, synthetic manganese olivine for Mn, Rockport fayalite for Fe, Topaz for F, USMN chlorapatite for Cl, and Lipari Obsidian for Si, Al, O, Na, and K. Analyses were conducted using a focused beam, an accelerating voltage of 15 KeV, a beam current of 10 nA, with onpeak and off-peak count times of 20 s. Na, K, O, and Si were corrected for ion migration using time-dependent intensity data, and elemental concentrations were converted to oxides, computing all Fe and Fe 2 O 3 .…”

“…Fossil collection localities at Woranso-Mille can be grouped into two distinct, but informal, chronostratigraphic packages. The Western Exposure Area (WEA) includes localities dated to 3.8e3.57 Ma (Deino et al, 2010;Saylor et al, 2016Saylor et al, , 2019. The WEA localities are characterized by fossiliferous sediments interbedded with a distinct sequence of marker tuffs that fill a temporal gap between the oldest fossils assigned to A. afarensis (Harrison, 2011;Johanson et al, 1978;White, 1977White, , 1980 and the youngest fossils of its presumed ancestor, Australopithecus anamensis.…”

Geological collaboration at paleoanthropological sites in Ethiopia's lower Awash Valley

“…Jumping backwards through geologic time, Luis Gibert, Mulugeta Alene, Naomi Levin, Al Deino, and Beverly Saylor (remotely) led the visit to the Woranso‐Mille site, known for its diversity of mid‐Pliocene hominins in the temporal window between 3.9 and 3.2 Ma . Much of the discussion focused on the efforts and challenges to piece together the composite stratigraphic sequence for the area from exposures with limited spatial and/or temporal extent (e.g., Saylor et al) and whether these deposits fit within the existing framework of the Hadar Formation as preserved at Hadar and Dikika, or represent sedimentation in a distinctly different drainage system or basin.…”