title: 40Ar/(39)Ar geochronology and paleomagnetic stratigraphy of the Lukeino and lower Chemeron Formations at Tabarin and Kapcheberek, Tugen Hills, Kenya.
abstract: (40)Ar/(39)Ar single-crystal laser-fusion dating, K-Ar dating, and paleomagnetic reversal stratigraphy have been used to determine the chronostratigraphy of the Kabarnet Trachyte, Lukeino Formation, Kaparaina Basalt Formation, and Chemeron Formation at the sites of Kapcheberek (BPRP#77) and Tabarin (BPRP#77) in the Tugen Hills, Kenya. The succession ranges in age from 6.56-3.8 Ma. The upper Lukeino Formation at Kapcherberek, including the fauna from the site BPRP#76, was deposited during chron C3r and can be constrained to the interval 5.88-5.72 Ma. The Chemeron Formation at Tabarin includes at the base an ignimbrite and associated basal air-fall tuff with a combined age of 5.31+/-0.03 Ma. Sedimentary and volcaniclastic rocks of the Chemeron Formation which unconformably overlie the ignimbrite record chrons C3n.2n through C2Ar. The combined(40)Ar/(39)Ar and paleomagnetic data constrain the age of this sequence to 4.63-3.837 Ma. The age of the Tabarin mandible fragment (KNM-TH 13150) and associated fauna at site BPRP#77 in the Chemeron Formation is 4.48-4.41 Ma, marginally older than similar early hominids from Aramis, Ethiopia. Basin subsidence appears to be defining an overall accumulation rate of about 17 cm/ka over the 2.7 Ma represented at Tabarin and Kapcheberek, despite episodes of rapid accumulation and hiatuses.
authors.affiliation: Berkeley Geochronology Center, California 94709, USA. al@bgc.org
authors.forename: Alan L
authors.initials: AL
authors.lastname: Deino
authors.forename: Lisa
authors.initials: L
authors.lastname: Tauxe
authors.forename: Marc
authors.initials: M
authors.lastname: Monaghan
authors.forename: Andrew
authors.initials: A
authors.lastname: Hill
mesh_terms: D000818:Animals; D001128:Argon; D005580:Fossils; D019015:Geologic Sediments / Q000032:analysis*; D015186:Hominidae / Q000033:anatomy & histology*; D006801:Humans; D006811:Humerus; D007630:Kenya; D008334:Mandible; D011868:Radioisotopes; D011874:Radiometry / Q000379:methods; D013997:Time Factors; D014070:Tooth
chemical_list: D011868:Radioisotopes; D001128:Argon