Many Pleistocene archaeological and paleontological sites beyond the c. 50-thousand-year 14C limit remain poorly constrained in age or undated entirely. Many such deposits host giant avian eggshells, as large flightless birds producing giant eggs have resided on five continents in the Pleistocene and eggs served as a food source for foraging humans. Eggshells are furthermore made of calcite and are resistant to diagenesis compared to other biomineral compositions, making them potential candidates for uranium-series (230Th/U) geochronology; however, eggshells do not have primary U in them, rendering conventional 230Th/U dating ineffective. Laser ablation measurements that compare modern and ancient avian eggshells indicate that while modern eggshells have negligible U, ancient eggshells host significant concentrations of U and Th that vary with the eggshells’ petrographic structures. I’ll share a novel approach to dating eggshells, first tested with ostrich eggshells, called 230Th/U “burial dating”, which explicitly accounts for U in ostrich eggshell acquired from soil pore water upon burial. Resultant 230Th/U burial ages of ostrich eggshells from African archaeological sites preserve stratigraphic order and agree with independent dates. Laser ablation data of eggshells of the giant flightless birds of Pleistocene Australia corroborate that primary petrographic structures like those in ostrich eggshells control secondary uptake of U. 14C and 230Th/U data indicate that 230Th/U burial dating may apply to well-preserved eggshells of other avian taxa, providing a new way to date megafaunal remains in the Pleistocene.
