Cosmic ray exposure ages and pre-atmospheric shielding of Omani meteorites: Implications for 14C and 14C/10Be terrestrial ages of meteorites from hot and cold deserts

We present isotope concentrations of the light noble gases He and Ne for samples from five well-documented strewnfields and two individual meteorites from the Omani desert. Cosmogenic (²²Ne/²¹Ne)_cos for the strewnfield samples are low, as expected considering the total known masses. A (²²Ne/²¹Ne)_cos of 1.210 for the LL6 chondrite RaS 267 from Oman indicates a small pre-atmospheric size of less than 10 cm. The CRE ages for the Omani meteorites calculated using ²¹Ne_cos range from 1 to 20 Ma. Using the (²²Ne/²¹Ne)_cos and previously established correlations, new shielding-corrected ¹⁴C and ¹⁴C-¹⁰Be terrestrial ages are calculated. For the strewnfield samples, the new ages are similar to the earlier ages but are more consistent. The new terrestrial age for RaS 267 is more than 20% lower than the previous age. Motivated by this success, we reinvestigated meteorites from other hot deserts (Acfer, Adrar, and Nullarbor regions) and Antarctica using literature data for ¹⁴C and (²²Ne/²¹Ne)_cos, along with the newly established correlations between ¹⁴C production rates and (²²Ne/²¹Ne)_cos. For these meteorites, the new terrestrial ages are systematically younger than the ages calculated earlier using a shielding-independent approach. Using shielding-corrected ¹⁴C terrestrial ages, the long-term puzzling problem that there is a lack of meteorites with short terrestrial ages disappears. The new histogram, though with only a limited number of data, shows the expected decrease in the number of meteorites with increasing terrestrial age. Therefore, the unexpected shape in the terrestrial age histogram was most likely due to a bias in the ¹⁴C dating system, that is, ages of small meteorites are overestimated.