Dating and Characterization of Polymorphic Transformation of Aragonite to Calcite in Pleistocene Bivalves from Rhodes (Greece) by Combined Shell Microstructure, Stable Isotope, and Electron Spin Resonance Study

摘要

Absolute dating of diagenesis is a challenging, yet significant problem. Reconstructing the depositional and diagenetic history of a late Pleistocene coralligéne-type red algal reef and overlying maerl (red algal sand) from the Plimiri coastal cliff, SE island of Rhodes, Greece, is enabled using a combination of microstructure, stable-isotope analyses, and electron spin resonance of large bivalve shells partially altered by diagenesis. These shells, consisting of both original shell aragonite and polymorphic transformed rims (now consisting of neomorphic spar), provide the opportunity to date the primary age when the shells were precipitated, as well as the age of their polymorphic transformation. The contamination of samples presented a significant problem for interpreting ages based on data from electron spin resonance (ESR) alone. However, sample contamination was evaluated with quantitative XRD, providing the opportunity to apply corrections, which increased reliability of the ages.