Aníbal Juan Figini

Museo de la Plata Radiocarbon Measurements II

The 14C measurements reported here were made between 1983 and 1987. Sample pretreatment and date calculations were previously reported (Figini et al 1984). The method employed, liquid scintillation counting, was previously described (Huarte & Figini 1988). No 13C/12C ratios were measured and results were not corrected for 13C fractionation and/or reservoir effect. Descriptions, comments and references to publications are based on information supplied by submitters.

Did the megafauna range to 4300 BP in South America

A date of 4300 t 90 BP for extinct megafauna in Argentina is discussed. The fossil remains come from the Guerrero Member (area) of the Lujan Formation near the city of Lujan, Buenos Aires Province. The age of the top of the Guerrero Member is constrained by more than 60 radiocarbon dates obtained from the overlying Rio Salado Member of Lujan Formation, Las Escobas Formation, and Puesto Callejon Viejo Soil, most of them older than 4300 BE In view of its low collagen content, the 14 C measurement of bone sample from Lujan should not be accepted uncritically. Because of the poor bone preservation and the possible introduction of young contaminants that were not completely eliminated, the 14 C date of 4300 ± 90 BP is not reliable. Both biostratigraphic and 14 C dating evidence indicates that the date of 4300 BP for the last representative of extinct megafauna in South America is unsupported.

La Plata Radiocarbon Laboratory Liquid Scintillation Counting and Inter-Laboratory Check Samples

The development and improvement of benzene synthesis for radiocarbon dating by liquid scintillation counting was started at LATYR in 1981. The basic technique employed was described by Polach, Gower & Frazer (1972). The line of benzene synthesis is similar to that used by Coleman et al (1972). The pretreatment of the samples and transformation to CO2 has been previously described (Figini et al, 1984). The conditions of measurement were partially determined according to Pearson (1979). Results of measurements of interlaboratory check samples using the technique described are given.

Primer análisis de la cronología obtenida en el sitio Choya 68 (Depto. de Capayán, Provincia de Catamarca, Argentina)

Choya 68 is a ceremonial site, with a monticular structure, that is adjacent to ample prepared surfaces and quadrangular and rectangular stone structures. Abundant Aguada Portezuelo ceramic type was recovered from the excavation, and in smaller proportions, painted and blackengraved Aguada types. We present the dates for these structures as provided by three C 14 laboratories. We make observations on the association between the samples and related archaeological events, analyzing the probable causes of the interlaboratory differences. We conclude that the most important variable of the C 14 dates is the chronological heterogeneity of the charcoal samples that we analyzed.

Radiocarbon dating reproducibility at the Museo de La Plata Radiocarbon Laboratory.

We discuss here the variability, for our laboratory, in counting for radiocarbon dating of replicate measurements of background and secondary modern standard, duplicate measurements of samples provided by the International Collaborative Study, and replicate measurements of the dilution of the 14C-labeled benzene standard. The variability in the measurements of the International Collaborative Study samples suggest the existence of systematic bias.