ESR dating of Lymnaea baltica and Cerastoderma glaucum from low Ancylus level and transgressive Litorina sea deposits

Freshwater gastropod (Lymnaea baltica) and brackish-water bivalve (Cerastoderma glaucum) shell samples from Ancylus Lake and Litorina Sea deposits on Hiiumaa Island (north-west Estonia) were subjected to ESR measurements. All L. baltica shells studied were composed of calcite and displayed typical multicomponent ESR spectra. C. glaucum shells normally show ESR spectra typical of aragonite with five radiation-induced lines. In the present work a C. glaucum with calcite-like spectra was encountered for the first time. The problem connected with accumulated palaeodose determination in shell fossils with unusual ESR spectra is highlighted.