40Ar/39Ar incremental-heating experiments on basaltic lavas and single-crystal total-fusion analyses of trachytic tuffs provide for the first time accurate resolution of the chronostratigraphy of the Pleistocene Peninj Group west of Lake Natron northern Tanzania. These new data force a major revision of the chronology of the entire sequence: the base of the group is now ~1.75 Ma the Wa Mbugu basalt within the Main Tuff is 1.19 ± 0.03 Ma (Cobb Mountain paleomagnetic event) and the top of the Peninj Group is 1.01 ± 0.03 Ma. Thus the Achulean and Olduwan artifact assemblages found in the Upper Sands and Clays of the upper Humbu Formation above the Wa Mbugu basalt are about ~1.2 to 1.1 Ma half a million years younger than previously believed. The revised chronology also clarifies the age of the major lake expansion recorded within the upper part of the Peninj Group. This lacustrine phase is now constrained to ~1.1 to 1.0 Ma corresponding to a previously identified episode of lake expansion in East Africa between 1.1 and 0.9 Ma (Trauth et al. 2005).

Australopithecus boisei

Humbu Formation West Lake Natron
40Ar/39Ar Dating of the Pleistocene Peninj Group Lake Natron TanzaniaDeino A. L.; Dominguez-Rodrigo M.; Luque L. Keywords: paranthropus ParanthropusAmerican Geophysical Union Fall Meeting 2006 abstract #V53C-1771; Original dating by Glynn Ll. Isaacs & Garniss H. Curtis Nature 249 624 - 627 (1974) | doi:10.1038/249624a0.
Australopithecus boisei
Peninj Mandible various Olduwan and Acheulean sites

Ar/Ar; previous dates via K/Ar biostratigraphy and paleomagnitism place site between 1.3-1.4maDeinoA.Domɱnguez-RodrigoM.LuqueL.2006.40Ar/39ArDating of the Pleistocene Peninj Group Lake Natron Tanzania. Eos Trans. AGU 87(52) Fall Meet. Suppl. Abstracts C1771. Thouveny N. & Taieb M. (1987). Etude paleomagnetique des formations du Plio-Pleistocene de la region de Peninj (Ouest du lac Natron Tanzanie). Sciences Geologiques (Bulletin) 40 50-62.Isaacs G. L. (1974). Age of early Acheulian industries from the Peninj Group Tanzania. Nature 249 624-627.

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West of Lake Natron Tanzania; Upper Sands & Clays unit Humbu Formation

Dominguez-Rodrigo M. Serrallonga J. Juan-Tresserras J. Alcala L. & Luque L. (2001). Woodworking activities by early humans: a plant residue analysis on Acheulian stone tools from Peninj (Tanzania). Journal of Human Evolution 40(4) 289-299.Torre I. D. L. Mora R. & Mart??nez-Moreno J. (2008). The early Acheulean in Peninj (Lake Natron Tanzania). Journal of Anthropological Archaeology 27(2) 244-264.