ELECTRON-SPIN-RESONANCE (ESR) TECHNIQUES APPLIED TO MOLLUSK SHELLS FROM SOUTH-AMERICA (CHILE, ARGENTINA) AND IMPLICATIONS FOR PALAEO SEA-LEVEL CURVE

ESR dating of marine mollusc shells gives no evidence for a so-called Mid-Wisconsin sea-level high stand in Argentina and Chile. The idea of this high stand around 30,000-40,000 BP is still alive. especially in Argentina, but the evidence for it is, in our opinion and that of oth ers, solely based on the misinterpretation of C-14 dates. All ESR ages from southern South America belong either to the Holocene or the Last Interglacial or older Interglacial periods. Apart from the regional a spect, this paper deals with some methodological problems in ESR datin g. Estimates have been improved by using only mollusc shells that are still closed and in living position and by introducing a plateau scree ning rest for the determination of the accumulated dose (AD). The esti mate of the environmental dose has been refined by analysing the infil l sediments in the shells for their U, Th and K contents, separately f rom the embedding matrix. Special interest has been paid to the debate d problem of early or continuous U uptake; the U contents of recent Ho locene molluscs support the early uptake model. A probable solution to the problem of age overestimation of Holocene shells is also presente d. Present-day shells are shown to possess frequently a fully develope d signal and to give AD of 2-4, in one case up to 9 Gy. If the Holocen e AD values of C-14-dated shells are corrected by subtracting these '' recent'', and spurious, values, the resulting age estimates are more c onsistent with radiocarbon ages. (C) 1997 Elsevier Science Ltd.