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ABSTRACT Bioerosion is a valuable tool for inferring palaeoenvironmental and palaeoclimatic changes over time and across different regions. However, studies of bioerosion traces are scarce in the Southern Hemisphere. Most ichnological studies within Argentina are concentrated in San Jorge Gulf (Patagonia, Argentina) and little is known about deposits located north of the Gulf. Here, we focus on bioerosion traces on Quaternary mollusc shells. Samples were collected from Quaternary marine deposits at the Bahía Vera–Cabo Raso sites in northern San Jorge Gulf. To resolve age discrepancies reported in the literature, we use amino acid racemization and radiocarbon dating to confirm the presence of beach ridge deposits from Marine Isotope Stage (MIS) 5 and MIS 1. Fourteen ichnotaxa are recorded in the study area. Additionally, distinct variations in the pattern of bioerosion across different ages are observed, indicating that environmental changes occurred in the northern San Jorge Gulf between the MIS 5 interglacial and the Holocene. This reinforces the hypothesis that there is an association between bioerosion, productivity and circulation in the Southern Atlantic Ocean. 

Abstract Northern Arizona University, Flagstaff, Arizona, USA, recently installed a MIni CArbon DAting System (MICADAS) with a gas interface system (GIS) for determining the¹⁴C content of CO₂gas released by the acid dissolution of biogenic carbonates. We compare 48 paired graphite, GIS, and direct carbonate¹⁴C determinations of individual mollusk shells and echinoid tests. GIS sample sizes ranged between 0.5 and 1.5 mg and span 0.1 to 45.1 ka BP (n = 42). A reduced major axis regression shows a strong relationship between GIS and graphite percent Modern Carbon (pMC) values (m = 1.011; 95% CI [0.997–1.023], R²= 0.999) that is superior to the relationship between the direct carbonate and graphite values (m = 0.978; 95% CI [0.959-0.999], R²= 0.997). Sixty percent of GIS pMC values are within ±0.5 pMC of their graphite counterparts, compared to 26% of direct carbonate pMC values. The precision of GIS analyses is approximately ±70¹⁴C yrs to 6.5 ka BP and decreases to approximately ±130¹⁴C yrs at 12.5 ka BP. This precision is on par with direct carbonate and is approximately five times larger than for graphite. Six Plio-Pleistocene mollusk and echinoid samples yield finite ages when analyzed as direct carbonate but yield non-finite ages when analyzed as graphite or as GIS. Our results show that GIS¹⁴C dating of biogenic carbonates is preferable to direct carbonate¹⁴C dating and is an efficient alternative to standard graphite¹⁴C dating when the precision of graphite¹⁴C dating is not required. 

We investigated the relationship between aspartic acid d:l ratios and otolith-derived age estimates in Gulf of Mexico red snapper, Lutjanus campechanus (ages 1–26 years; R² = 0.89) and Caribbean yellowtail snapper, Ocyurus chrysurus (ages 2–17 years; R² = 0.84). The estimated racemization rate was 0.61 × 10⁻³ year⁻¹for red snapper and 1.28 × 10⁻³ year⁻¹for yellowtail snapper, reflecting temperature differences between study regions. Mean jackknifed error in ages predicted from aspartic acid d:l was 1.70 ± 0.39 years for red snapper and 1.57 ± 0.41 years for yellowtail snapper. Results suggest amino acid racemization may be an effective tool for direct age estimation and potentially age validation in fishes. 

ABSTRACT The direct carbonate procedure for accelerator mass spectrometry radiocarbon (AMS 14 C) 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 14 C 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 14 C dating of biogenic carbonates is a cost-effective and efficient complement to standard graphite 14 C dating.