ABSTRACT

Bed I at Olduvai Gorge is a conformable sequence of lava flows and varied sedimentary deposits that extend upward from a welded tuff overlying the Precambrian basement to the top of a widespread marker bed. Bed II is a sequence of lacustrine clays and laterally equivalent fluvial, eolian and pyroclastic deposits. Bed III comprises alluvial deposits and a laterally equivalent assemblage of fluvial, lacustrine and eolian beds. Bed IV can be widely subdivided into a lower unit of fluvial clays, sandstones and conglomerates and an upper unit of eolian tuffs. Although moister than that of the present day, the climate was relatively dry throughout much of the time that these beds were deposited. Semi-desert or desert conditions rather like those of the present day may have prevailed at least twice. Tectonic movement seems to have taken place between the deposition of Beds III and IV.

A stratigraphic and environmental framework more detailed than that of Reck (1951) and Pickering (1960) is here presented for the Pleistocene succession of Olduvai Gorge (Fig. 1), which contains hominid remains of great antiquity (Leakey, Curtis and Evernden, 1961) and an unsurpassed sequence of Palaeolithic culture levels (Leakey, 1951; 1963). The need for geological information about the Olduvai succession became clear in recent controversies over the potassium–argon dates and geologic histories of Beds I and II (Straus and Hunt, 1962; Von Koenigswald, Gentner and Lippold, 1961; Leakey, Curtis and Evernden, 1962).