Trace metals and isotopes in Estonian black shales : Cambro-Ordovician shallow water anoxia on the Baltica shelf?Johnson, Sean C.; McGoldrick, Peter J.; Sõstra, ÜloGoldschmidt Conference abstracts : 20162016 / p. 1372 http://goldschmidt.info/2016/uploads/abstracts/finalPDFs/A-Z.pdf