Al dating system
Al dating system - Mysexgame
(The circle on the localization map indicates the studied area; red numbers, number of the sample in Table 2.) The Toumaï cranium is precisely located in the TM 266 section.
In the Koro Toro fossiliferous area, KT 12 locality (16°00′N, 18°53′E) was the site of discovery of (Toumaï).
The sedimentary unit from which Toumaï was unearthed was named the anthracotheriid unit (A. also contains a mammalian fauna that includes taxa that are more primitive than the Lukeino fauna [Kenya, dating from 6 Ma ago (6)] and similar to the fauna from the lower Nawata Formation of Lothagam [Kenya, 6.5–7.4 Ma ago (7)].
U.) after a very common, large anthracotheriid, (5) that it contained. Recent investigations conducted at another locality, TM 254, ≈18 km west of the Ar dating, is not exposed at TM 266; therefore, 20 intermediate geological sections between TM 266 and TM 254 have been documented to determine its stratigraphic position within the A. The sections are uniform in facies across the transect. Geological correlations between TM 266 and TM 254 are firmly supported by the same continuity of stratigraphy between the sites, reflecting a similar environment and climate change history (5).
cranium level were 6.83 ± 0.45 Ma for the overlying level and 7.12 ± 0.31 Ma for the underlying level.
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.
This opens up the possibility to date sedimentary deposits in the range of 0.2 to 14 Ma.
Much as is the case with B, which is undistinguishable from common boron.
The arid environment punctuated by wet periods during which a large shallow lake formed both provided Holocene sediments with which to determine the (Abel, KT 12) sampled for calibration purpose indicates that the Koro Toro fossiliferous locality is at least 3.3 Ma old, an age that is in the range of the biochronological estimation by using the mammal evolutive degree (3, 4, 36).
This new absolute dating constraint shows that , the earliest known hominid (1, 2, 40), is probably very close in time to this divergence contrary to the unlikely “provocative explanation,” which recently suggested a “possible hybridization in the human-chimp lineage before finally separating less than 6.3 Ma” (41).
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.
Stratigraphic columns and beryllium ages of KT 12 (Australopithecus bahrelghazali locality, Koro Toro, Early Pliocene, Northern Chad), KL and KB 1.