The geology of Gona, Afar, Ethiopia

Abstract

Deposits in the Gona Paleoanthropological Research Project (GPRP) area in eastcentral Ethiopia span most of the last ~6.4 m.y. and are among the longest and most complete paleoenvironmental and human fossil archives in East Africa. The 40 Ar/ 39 Ar and paleomagnetic dates and tephrostratigraphic correlations establish the time spans for the four formations present at Gona: the Adu-Asa (>6.4-5.2 Ma), Sagantole (>4.6-3.9 Ma), Hadar (3.8-2.9 Ma), and Busidima Formations (2.7 to <0.16 Ma). The volcano-sedimentary succession at Gona displays many classic tectono-sedimentary features of an evolving rift basin. The mixed volcanic and fl uviolacustrine Adu-Asa Formation is the earliest expression of rifting at Gona, probably deposited in a small half-graben. The Sagantole and Hadar Formations were deposited in a much METHODS Tephra Analysis Tephras were fi rst treated with 2 M HCl to remove any carbonate, briefl y rinsed in 2% HF, washed in distilled water, and sieved. In most cases, the 60-120 µm size fraction was used for electron microprobe analyses. All analyses were made on a CAMECA SX50 electron microprobe with a wavelength-larger half-graben bounded to the E-NE by an as-yet-unidentifi ed normal fault. The Sagantole and Hadar Formations are both fl uvial and lacustrine, refl ecting periodic shallow impoundment of a low-gradient paleo-Awash River, perhaps by an accommodation zone north of the Ledi-Geraru project area. Starting at 2.9-2.7 Ma, the character of sedimentation changed dramatically throughout the Awash Valley as bed load coarsened and the meandering paleo-Awash River cyclically cut and fi lled. Unlike the Hadar Formation, the Busidima Formation thickens westward, suggesting deposition in a half-graben of the opposite polarity compared to Sagantole/Hadar time. Sedimentation rates decreased 5-fold, from 0.25 mm/yr in the Hadar Formation to 0.05 mm/yr in the Busidima Formation, perhaps in response to slowing extension rates and/or opening of the half-graben north of Gona.

Co-occurrence of Acheulian and Oldowan artifacts with Homo erectus cranial fossils from Gona, Afar, Ethiopia

“…In summary, 87 horizons were sampled in Dana Aoule, Busidima, and Asbole areas (auxiliary data file 1B). These data were initially reported in (4) and 3although we report the compiled datasets and sampling locations here ( Fig. 2 and auxiliary data file 1B).…”

Hominin taxic diversity: Fact or fantasy?

“…Temporal range: The Ar. kadabba specimens from the Western Margin and Gona derive from the Adu-Asa Formation, which has been dated via magnetostratigraphy, tephrostratigraphy, and argon dating to >6.4-5.2 Ma Quade et al, 2008). The fossiliferous layers from the Western Margin are confined to the Asa Koma Member and have an estimated age range of 5.…”

“…Temporal range: Magnetostratigraphy and argon dating have yielded an age range of c.4.5-4.3 Ma for Ar. ramidus Renne et al, 1999;Kleinsasser et al, 2008;Quade et al, 2008;). Most of the Ar.…”

“…The specimens from GWM-5 series,-9n,-16 are aged to >4.6 Ma. However, since Quade et al (2008) describe the dating of the As Duma Member as a "work in progress," we use a maximum FAD of 4.6 Ma for these specimens until the results of further research are published. The specimens from GWM-3,-3w have a more reliable estimated age range of 4.4-4.3 Ma.…”

The first technical sequences in human evolution from East Gona, Afar region, Ethiopia

“…2004; Quade et al . 2004, 2008). With regard to the hominins responsible for making these tools, while Australopithecus garhi fossils of equivalent age to the EG and OGS sites have been excavated from the Hata Member of the Bouri Formation (Middle Awash) (Asfaw et al .…”