Tchad dating site
This as well as the associated uncertainties is fully discussed in the Materials and Methods section.In this first attempt of calibration in a continental context, the calculated authigenic Be ages obtained in or close to the fossiliferous levels were compared with the ages estimated by using the evolutive degree of fossil mammal assemblages.Ages were determined at two hominid localities from the Chad Basin in the Djurab Desert (Northern Chad).In the Koro Toro fossiliferous area, KT 12 locality (16°00′N, 18°53′E) was the site of discovery of (Toumaï).
Because these data demonstrate that the deposition of the A. from which Toumaï was unearthed is synchronous and geologically instantaneous (considering the uncertainties associated to the dating methods) in both TM 266 and TM 254, all of the 28 samples from the A. were used to determine the inverse-variance weighted mean age of this sedimentary unit, the associated mean square of weighted deviates being 0.36 (see Be, can be used as a dating tool for continental sedimentary deposits over the time period 0.2 to ≈7 Ma.
If these requirements are met, then Be reported for surface marine sediments (14, 16), for top surfaces (or extrapolated to zero age) of Fe-Mn deposits (17–23), for present-day deep waters in the Atlantic, Pacific, Indian Ocean, and Mediterranean Sea central basins and margins (13, 24–30) mostly range between 0.5 × 10Be ratio can be expected considering that in continental systems, the two major processes affecting the aqueous geochemistry of beryllium are dissolution from rocks and uptake onto particles (13).
The initial authigenic Be ratio thus depends both on the lithology of the region drained and on the partitioning between solid and aqueous phases.
Stratigraphic columns and beryllium ages of KT 12 (Australopithecus bahrelghazali locality, Koro Toro, Early Pliocene, Northern Chad), KL and KB 1.
(The circle on the localization map indicates the studied area; red numbers, number of the sample in Table 2).
The base of the mapped sections consists of a well developed, thick, aeolian facies (8). U.) is composed of poorly cemented sand and argillaceous sandstone alternation characterized by dense networks of root tubules/root molds (palaeosols) and termite nests (9, 10). The uniform stratigraphy at the TM localities allowed us to use absolute ages from both TM 266, where Toumaï was discovered, and TM 254 to assign an age to Toumaï.