AMINO-ACIDS OF PROTEROZOIC AND ORDOVICIAN SULFIDE-COATED GRAINS FROM WESTERN CANADA - RECORD OF BIOLOGICALLY-MEDIATED PYRITE PRECIPITATION

Early diagenetic sulphide-coated grains from a quartz-arenite of the H elikian Siyeh Formation of southern Alberta and British Columbia and f rom sandstones of the Ordovician Winnipeg Formation of Saskatchewan co ntain 9.17-26.10 mu mol g(-1) protein amino acids and 3.74-18.19 mu mo l g(-1) non-protein amino acids. The protein amino acid content of the whole rock varies from 120.07 to 315.36 nmol g(-1) and the non-protei n from 91.31 to 241.29 nmol g(-1). The sulphide-coated grains contain approximately three times the amount of amino acids reported in modern carbonate ooids and 100 times that in Jurassic ooids from Italy. The abundance of total amino acids and the relative abundance of the S-con taining methionine supports the previously proposed genesis of these g rains, involving bacterial reduction of seawater sulphate. The occurre nce of unstable and non-racemized amino acids in the sulphide-coated g rains and their low concentration in the matrix is interpreted as evid ence of exceptional preservation and not of contamination. The virtual ly identical average amino acid content and composition of Proterozoic and Ordovician sulphide-coated grains suggest similar processes of su lphide precipitation and also a uniquely similar preservation of the a mino acids, due to the differences in age and geological history of th e two formations.