SULFUR OXYGEN ISOTOPE STUDIES OF SULFATES FROM PERMIAN KUPFERSCHIEFER

The oxygen isotopic composition of sulfates has been determined in CO2 by mass spectrometry after reduction of BaSO4 with carbon. The experimental procedure with a precision of 0.4‰ in the scale relative to SMOW is described in some detail. It is a problem to distinguish between primary and secondary gypsum or anhydrite in argillaceous sediments. A combined analysis of sulfur and oxygen of the sulfates mentioned is applied for getting evidence on the origin of these sulfates. Samples of a Permian Kupferschiefer profile show that primary residual sulfates from closed systems can be distinguished from secondary sulfates formed from oxidized sulfides. These secondary sulfates are characterized by relatively light oxygen (δO18≈+4‰ relative to SMOW) and sulfur (δS34≧-23‰), which is due to their origin from sulfides of bacterially reduced sulfates. The primary residual sulfates are enriched in O18 and S34. The correlation of heavy sulfur with heavy oxygen during bacterial reduction of sulfates (Lloyd, 1968) could be confirmed. © 1969 Springer-Verlag.