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The direct carbonate procedure for accelerator mass spectrometry radiocarbon (AMS 14C) dating of submilligram samples of biogenic carbonate without graphitization is becoming widely used in a variety of studies. We compare the results of 153 paired direct carbonate and standard graphite 14C determinations on single specimens of an assortment of biogenic carbonates. A reduced major axis regression shows a strong relationship between direct carbonate and graphite percent Modern Carbon (pMC) values (m = 0.996; 95% CI [0.991–1.001]). An analysis of differences and a 95% confidence interval on pMC values reveals that there is no significant difference between direct carbonate and graphite pMC values for 76% of analyzed specimens, although variation in direct carbonate pMC is underestimated. The difference between the two methods is typically within 2 pMC, with 61% of direct carbonate pMC measurements being higher than their paired graphite counterpart. Of the 36 specimens that did yield significant differences, all but three missed the 95% significance threshold by 1.2 pMC or less. These results show that direct carbonate 14C dating of biogenic carbonates is a cost-effective and efficient complement to standard graphite 14C dating.

Amino acid racemization (AAR) is widely used as a cost-effective method to date molluscs in time-averaging and taphonomic studies, but it has not been attempted for echinoderms despite their paleobiological importance and distinct biomineralization. Here we demonstrate the applicability of AAR geochronology for dating Holocene Peronella peronii (Echinodermata: Echinoidea) collected from Sydney Harbour (Australia). Using standard HPLC methods we determined the extent of AAR in 74 Peronella tests and performed replicate analyses on 23 tests.

Several analytical techniques have been used in amino acid geochronology to measure the relative abundances of D-and L-enantiomers. During the past two decades, reverse-phase (RP) liquid chromatography has become most common, whereas ion-exchange (IE) liquid chromatography was widely used prior to the mid-1990s. This study is based on intra-lab paired analyses of RP and IE liquid chromatography to mathematically convert A/I (alloisoleucine:isoleucine) values determined with IE to corresponding D/L values for comparison with new RP results. Pooled results of 340 paired IE and RP analyses show that A/I values can