Schellmann, Gerhard; Radtke, Ulrich:

Electron spin resonance (ESR) techniques applied to mollusc shells from South America and implications for the palaeo sea-level curve

In: Quaternary Science Reviews, Jg. 16 (1997) ; Nr. 3-5, S. 465-476
ISSN: 0277-3791
Zeitschriftenaufsatz / Fach: Geowissenschaften
Rektorat und Verwaltung » Rektorat
Abstract:
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 others, solely based on the misinterpretation of 14C 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 aspect, this paper deals with some methodological problems in ESR dating. Estimates have been improved by using only mollusc shells that are still closed and in living position and by introducing a plateau screening test for the determination of the accumulated dose (AD). The estimate of the environmental dose has been refined by analysing the infill sediments in the shells for their U, Th and K contents, separately from the embedding matrix. Special interest has been paid to the debated problem of early or continuous U uptake; the U contents of recent Holocene molluscs support the early uptake model. A probable solution to the problem of age overestimation of Holocene shells is also presented. Present-day shells are shown to possess frequently a fully developed signal and to give AD of 2–4, in one case up to 9 Gy. If the Holocene AD values of 14C-dated shells are corrected by subtracting these “recent”, and spurious, values, the resulting age estimates are more consistent with radiocarbon agesESR 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 others, solely based on the misinterpretation of 14C 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 aspect, this paper deals with some methodological problems in ESR dating. Estimates have been improved by using only mollusc shells that are still closed and in living position and by introducing a plateau screening test for the determination of the accumulated dose (AD). The estimate of the environmental dose has been refined by analysing the infill sediments in the shells for their U, Th and K contents, separately from the embedding matrix. Special interest has been paid to the debated problem of early or continuous U uptake; the U contents of recent Holocene molluscs support the early uptake model. A probable solution to the problem of age overestimation of Holocene shells is also presented. Present-day shells are shown to possess frequently a fully developed signal and to give AD of 2–4, in one case up to 9 Gy. If the Holocene AD values of 14C-dated shells are corrected by subtracting these “recent”, and spurious, values, the resulting age estimates are more consistent with radiocarbon ages