Radiocarbon Chronologies of Holocene Lacustrine Sediments from the Southern Coast of Buenos Aires Province, Argentina

Abstract

Two lacustrine sediment sequences, La Olla 1 and Laguna del Sauce Grande, on the southern coast of Buenos Aires Province, Argentina, were investigated for carbon reservoir effects, which may influence age-depth chronologies. Fruits of the submerged macrophyte Ruppia cf. maritima from the La Olla 1 sequence, and gastropod shells of Heleobia parchappii from the Laguna del Sauce Grande core, were radiocarbon dated. In addition, terrestrial plant remains and shells of living specimens were dated to assess the presence and magnitude of a reservoir effect. A reservoir age of about 800 14C yr is estimated for the aquatic plant samples of La Olla 1 for the early Holocene. The reservoir effect is attributed to the in wash of 14C-deficient bicarbonate from the surrounding sand dunes. The decay of marine organisms and salt spray are likely the main sources of 14C-deficient carbon. The magnitude of the reservoir effect is consistent with marine reservoir offsets reported for the region. The 14C measurements on shells of living and fossil specimens of Heleobia parchappii indicate the absence of a reservoir effect at Laguna del Sauce Grande, which may be due to the large size and shallow nature of the lake. This study shows how the reservoir ages of 2 close-by lakes in very similar geological settings can be largely different. These results have significant implications for the interpretation of 14C dates from lacustrine deposits in the region.

Holocene changes in trophic states of shallow lakes from the Pampa plain of Argentina

“…Among the material available for dating, gastropod shells of Heleobia parchappii are usually abundant in sequences recovered from those lakes, and they have shown to be reliable material for dating, despite their potential hard-water-lake effect that could cause radiocarbon dates on shells to be too old. A study in a similar ecosystem of the southwestern Pampa plain, however, demonstrated there was no effect on dated Heleobia parchappii shells (Fontana, 2007). Even though such an evaluation should be done on each system studied, the co-ocurrence of the same pattern in the three lakes considered in this study, allowed us to consider dates on shells reliable for this study.…”

Late Holocene climate and environment of the SE Pampa grasslands, Argentina, inferred from biological indicators in shallow, freshwater Lake Nahuel Rucá

“…The first issue is potential hardwater-lake effect that could cause radiocarbon dates on shells to be too old. A study in a similar ecosystem of the southwestern Pampa grasslands, however, demonstrated there was no effect on dated Heleobia parchapii shells (Fontana 2007). Ideally, such an evaluation should be done on each system studied.…”

A 700-year multiproxy reconstruction on the Argentinian Pampas inferred from the sediments of Laguna Blanca Grande

“…Although carbonate accumulations of variable morphology and genesis are common in the loess sequences (Muhs, 2007), Fontana (2007) showed that reservoir effect was negligible in a Pampean shallow lake in the same geological setting. Therefore, no correction for reservoir effect was applied in the model.…”