Effects of chemical preparation protocols on delta C-13 values of plant fossil samples

International audienceFor over a half-century, studies of the stable carbon isotope compositions of plant fossils have provided noteworthy conclusions about the evolution of Earth climate. However, different preparation protocols were used prior to carbon isotope analysis of plant fossils and the accuracy of measured C-13/C-12 ratios may strongly depend on them. We have applied the most frequently used chemical preparation protocols to Frenelopsis leaves from four Cretaceous localities of Western Europe. Our results indicate that procedures to extract plant fossils from sediments are not adequate to retrieve the original plant delta C-13 values. The use of Schulze's reagent to bleach cuticles in paleobotany allows misleading delta C-13 values of specimens from a same locality with positive shifts of up to 13.6%. and increases intra-specimen and inter-specimen variances. Sample treatment involving HCI or HCl + HF gives consistent delta C-13 mean values for a same leaf and for leaves from a same sedimentary bed. However, although HF does not provide any advantage in removing potential contamination sources, it alters plant fossil tissues, slightly increasing the intra- and inter-leaf variances of delta C-13 values. Our results indicate that processing plant fossils with HCl only is the most accurate and conservative way to retrieve original delta C-13 values. (C) 2015 Elsevier B.V. All rights reserved