Mass spectrometric ¹⁴C and U-Th measurements in coral

We discuss U-Th and ¹⁴C measurements in coral. Samples with U-Th dates in excess of 50 ka BP were chosen for study. Some bulk samples from this group have measurable ¹⁴C dates, which range from 30 ka to 43 ka BP. These can be explained by 0.5-2.5% contamination by modern carbon. This small amount of contamination can produce significant offsets in ¹⁴C dates of coral samples older than ~10ka. It may be undetectable in X-ray powder diffraction patterns. We describe a sample pretreatment that removes the modern carbon by selective dissolution and produces accurate ¹⁴C dates. -Authors