1. Lebedev Physical Institute; Russian Academy of Sciences; Moscow Russia
2. Palaeoecosystems Group; Department of Earth Sciences; Durham University; Durham DH1 3LE UK
3. Department of Geology; Lund University; Sölvegatan 12 Lund SE-223 62 Sweden
4. Department of Physics; Lancaster University; Lancaster LA1 4YB UK
5. Department of Physics; Durham University; Durham DH1 3LE UK