The Pliocene Hadar Formation, Afar depression of Ethiopia

Abstract

Summary Along the western margin of the Afar depression there is a fluvio-lacustrine sequence, well known for its hominid fossils, which consists of a 150–300 m thick layer of coarse to fine detrital sediments with interbedded pyroclastics and basalt. This series, deposited between at least 4.2 and 2.4 Ma, is called the Hadar Formation. Sedimentary and microfossil evidence allows the reconstruction of sedimentary, volcano-tectonic and climatic events in the evolution of the Hadar basin. During 1.8 Ma, the palaeogeography of the Hadar region appears to have been an intricate succession of fluvial, marshy and lacustrine environments, subject to rapid lake-level fluctuations and a wide range of hydrological conditions. Tectonic activity is confined to subsidence. However, important vertical movements of the western escarpment occur towards the end of the sedimentary succession in the Hadar basin.

Stratigraphy and sedimentology of the Hadar Formation Afar, Ethiopia

“…The absence of vermiculite and chlorite suggests that the degree of weathering was not advanced enough to change the existing smectite rich soil in the Hadar Formation and in the Ethiopian highlands. Illite was reported by Tiercelin (1986), but it was not observed here in this study. The non-clay constituents, such as quartz and feldspar, were probably originally phenocrysts in the parent volcanic ash.…”

“…It is less than 4 m thick to the west and increases to 10 {Cyprides Sp. Peypouquent et ai, 1983, andTiercelin, 1986) and fish bone scales and fragments. It is laterally persistent without a significant variation in thickness.…”

“…Only ten to twelve meters of interbedded sandstones, siltstones, mudstones, and two thin (10-20 cm) beds of gastropod-bearing limestone of the uppermost part of the Basal Member are exposed ( Figure 3). The lower contact of the Basal Member is exposed at Oudateit Wadi, a right bank tributary of the Awash River, where it rests directly on an Afar series basalts, dated to 4.5 Ma (Aronson et al, 1980;Kalb et ai, 1982b;and Tiercelin, 1986).…”

“…The major fining upward sequence of the Basal member is where the BS-2 sandstone Lm fades {Bellcanya sp., Cleopatra sp:, Peypouquent et ai, 1983;Tiercelin, 1986).…”

Connecting local environmental sequences to global climate patterns: evidence from the hominin-bearing Hadar Formation, Ethiopia

“…For the most part, subsequent geological work has focused on refinements of the geochronological framework and interpretations of depositional environments and overall paleoenvironments. Building upon this prior geological research at Hadar (e.g., Taieb et al, 1976;Johanson et al, 1978aJohanson et al, , 1982Tiercelin, 1979, 1980;Aronson and Taieb, 1981;Tiercelin, 1986), detailed stratigraphie sections measured by the authors were used to construct a composite section of the Hadar Formation and a record of its depositional environments (Fig. 2).…”