REVISED MAGNETOSTRATIGRAPHY OF THE PLIOPLEISTOCENE SEDIMENTARY SEQUENCE OF THE OLDUVAI FORMATION (TANZANIA)

The magnetic stratigraphy of the Plio-Pleistocene sedimentary formatio n of the Olduvai Gorge (Tanzania), which contains a well known series of prehistoric pebble cultures and hominid remains, has been reinvesti gated. Sixty one sites were sampled along 90 metres of stratigraphic s ection extending from the base of Bed I into the Masek Beds. Palaeo- a nd rock-magnetic analyses reveal that magnetizations are stable, carri ed by low coercivity magnetic minerals (titano-magnetites) and are lik ely to be of depositional origin. A revised magnetostratigraphic scale is proposed. The base of the major normal magnetozone, N1, interprete d as the Olduvai sub-chron, lies ca 6 m below Tuff IA, i.e. significan tly below the previously defined position. This revision, associated t o Ar-40/Ar-39 ages recently determined on the Tuffs of Bed I, supports the validity of the astronomical calibration of the geomagnetic polar ity time scale for the Olduvai sub-chron. The correlation of the norma l magnetozone N2 with Jaramillo (or Jaramillo + Cobb Mountain), is sug gested by the discovery of a reverse magnetozone (R3) in the uppermost part of the Pleistocene sequence (Masek Beds), and implies that the f ossiliferous sequence of the Olduvai Formation was entirely deposited before the Brunhes/Matuyama boundary.