An EPR study on mollusk shells from loess-paleosol sequences in the Loess Plateau, central China

Abstract

Electron Paramagnetic Resonance (EPR) analysis was employed to extract paleoclimatic information from mollusk shells taken from the Luochuan section located on the Loess Plateau of central China. The results show that the EPR spectrum of Mn2+ in mollusk shells is complicated and consists of two sets of six hyperfine lines of Mn2+ that arise from two non-equivalent Mn2+ sites in aragonite. There is no obvious inconsistency of EPR spectral intensities among different species of modern mollusks at Luochuan area; the magnitude of EPR spectra intensities of mollusk shells is correlative with the Mn2+ concentration of the environments. The EPR signals from mollusk shells taken from the loess, which is considered to be formed in the cold and dry glacial environment, are stronger than those from the paleosol deposited under the warm and humid interglacial condition suggesting that the Mn2+ available for mollusks in a cold climate is higher than in a warm climate. We propose that during the glacial period, the mollusks lived in a relatively reductive soil environment with more Mn2+ while during the interglacial period its environment was more oxidizing with less Mn2+. This result provides direct evidence that the loess-paleosol interlayers came into being under alternating redox conditions resulting from fluctuating paleoclimate. The analysis of the EPR spectra of mollusk shells serves as a new tool for retrieving climatic information from the mollusk records.