Cosmogenic nuclide dating ppt
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).
The demonstrated systematic strong agreement between the biochronological estimations and the calculated authigenic Be ages based on an initial authigenic ratio determined from sediments deposited in Holocene Lake Mega-Chad demonstrates that the sedimentary levels (clays, diatomites, argillites, siltites, and poorly cemented sandstones) deposited in the Chad Basin during wet periods (5) accompanied by major lacustrine extension in an area otherwise characterized by a recurrent desert climate since at least 8 Ma (8) have remained closed to gain or loss of beryllium other than by radioactive decay despite cycles of inundation and desiccation.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.This is unlike most other radiochronological methods (U-Th, Rb-Sr, Sm-Nd, K-Ar, Lu-Hf, Re-Os, etc.) that rely on parent–daughter ratios to determine ages.In addition, because the absolute Be concentration depends also on parameters such as the scavenging efficiency and the specific surface area of the sedimentary particles, it cannot be used directly to determine an age.