In situ produced cosmogenic 10Be and 36Cl measurement in Serra do Cipó marble

Abstract

Over the last thirty years, the use of cosmogenic nuclides has allowed a spectacular growth in the quantification of surface processes in the earth sciences. The accurate application of these approaches implies that the nuclide production rates are well known. In this work, we will present a second attempt at the determination of the production rate of 10Be in carbonate marble from samples collected along a 10 m depth profile located in Serra do Cipó mountain range (Minas Gerais, Brazil). These measurements are compared to in situ produced 36Cl measured within the same carbonate as well as the 10Be measured in the fine quartz fraction embedded in the marble. To do so, a simple chemical protocol has been established to eliminate the atmospheric 10Be that may be adsorbed on the sample surface. As a result, the expected exponential decrease of the concentration versus depth is observed (10Be within quartz and carbonate, 36Cl within carbonate) but the two widely used nuclides (10Be in quartz and 36Cl in carbonate) yield different time-denudation rate solutions when modelling their respective evolution with depth. Moreover, the unexpectedly low 10Be concentrations measured in the carbonate fraction—relative to those in quartz—strongly suggest that this site is not suitable for use as a calibration reference.