Phytolith radiocarbon dating in archaeological and paleoecological research: a case study of phytoliths from modern Neotropical plants and a review of the previous dating evidence

Recent carbon-14 studies of phytoliths from modern plants collected from extra-tropical regions of the world have yielded dates that are too old by several hundred to thousands of years. These findings have prompted questions about the suitability of phytolith-derived carbon for dating in archaeological and paleo-environmental research. In this paper, phytolith 14C ages are determined from a number of modern Neotropical plant taxa collected between 1964 and 2013. The specimens studied are maize (Zea mays L.), two squash species (Cucurbita ecuadorensis H.C.Cutler & Whitaker and C. ficifolia Bouche), and two trees common in Neotropical forest, Hirtella americana L. and Socratea durissima (Oersted) H. Uendl. They represent families, genera, and species that are well-represented in Neotropical archaeological and paleoecological sediments. Every phytolith sample returned a post-bomb 14C phytolith age reflecting collection after 1955, with the exception of a herbarium specimen that was treated with chemicals containing radiocarbon-dead carbon. The phytolith dates do not indicate a source of extraneous old or young carbon occurring on the surfaces or inside of phytoliths that bias their ages. Such findings are also reflected by previous phytolith 14C studies of ancient Neotropical sites. Possible reasons for the differences in results between these and other studies and varying interpretations of soil and sediment phytolith 14C analyses by different investigators are discussed.