Cosmogenic radionuclide dating
TCNs) as a result of the interactions between secondary cosmic radiation and minerals in that lattice, and the Ar-Ar technique is a development of the technique that relies on the decay of K to Ar to date volcanic rocks and weathering products.Recent technical advances in both fields now allow the techniques to be used on timescales that are relevant to archaeology, and although technically challenging, both techniques are now capable of measuring sub-1,000 year ages.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).The Cosmogenic Nuclide Laboratory at SGEES was purpose built in 2014 for the preparation of cosmogenic nuclide samples from all branches of the Earth sciences.The facilities include 2 HF rated extraction hoods and one laminar flow hood, Parr pressure dissolution oven, as well as analytical balances and centrifuge.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.It was hoped that the tephra layer would contain material datable by the Be associates with continental particles, where it decays with a half-life of ≈1.4 million years.
The lifetimes range from thousands to millions of years.TCNs accumulate at the Earth’s surface and so provide a chronology of exposure (Siame 2008).TCNs can also be used to determine rates of erosion, and multiple nuclides with different half-lives can be used to date the deep burial of materials (e.g., in caves where the materials are cut off from cosmic radiation).At both localities, the evolutive degree of the associated fossil mammal assemblages allowed a biochronological estimation of the hominid remains: early Pliocene (3–3.5 Ma) at KT 12 and late Miocene (≈7 Ma) at TM 266. This chronological constraint is an important cornerstone both for establishing the earliest stages of hominid evolution and for new calibrations of the molecular clock. Localities investigated in this area include TM 266 and TM 254 (Fig. The Kollé (KL), Kossom Bougoudi (KB), and Koro Toro (KT) fossiliferous areas were specifically studied to calibrate the authigenic Be dating method by direct comparison with biochronological estimations of co-located mammalian assemblages.
Fossiliferous localities investigated in these areas were KL, KB 1, and KT 12 (Fig. KT 12 (16°00′N, 18°53′E) is the site of locality, Toros-Menalla, Upper Miocene, Northern Chad).The SUERC Ar/Ar laboratory has three magnetic sector mass spectrometers which it operates for the NERC-funded national facility.