The sulfur isotopic evolution of Phanerozoic seawater based on the analysis of structurally substituted sulfate in carbonates

One hundred fifty-six biogenic calcites and 96 whole rock carbonate samples of Paleozoic and Mesozoic age have been analysed for their sulfur isotopic composition. Recorded in structurally substituted sulfate (SSS) in the calcite lattice, the sulfur isotopic composition is thought to reflect the sulfur isotope value of ambient seawater sulfate. Possible alterations of the signal have been assessed, confirming the validity of this approach and the reliability of the resulting temporal record. The new sulfur isotope data substantially enhances our knowledge about secular variations of the global sulfur cycle during the Phanerozoic. Specifically for the Paleozoic, 177 new measurements of SSS in stratigraphically well-constrained samples provide a coherent and detailed dataset. This is extended through the entire Mesozoic via 75 measurements of dSSSS, largely for biogenic calcites. Long-term changes and short-term oscillations in the sulfur isotopic composition of seawater sulfate have been observed, which are thought to reflect changes in the fractional burial of sulfide sulfur. Our new sulfur isotope data measured for structurally substituted sulfate in carbonates, and additional data from Cenozoic foraminifera and marine barites, provide a new temporal record for the sulfur isotopic composition of Phanerozoic seawater sulfate. This new record is superior in its continuity and time resolution to currently available datasets and should replace them in future considerations of Earth System Evolution. D 2004 Elsevier B.V. All rights reserved.