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Project Progress

Topic 1: Understanding geochemical signals of aerobic/anaerobic interfaces: Stable isotope (C, S), orgC-S-Fe, pyrite framboid size, and trace metal interrelationships in sediments. Modern baseline studies for application to Archean and Proterozoic records. We have largely completed our studies of signals in modern environments (Peru margin, Black Sea; see publications) and are beginning to apply the techniques to understanding the ancient record of anoxia.

Topic 2: Secular variations in sulfate sulfur isotopes for the Neoproterozoic. Objectives to detect hypothesized changes in the sulfide oxidizing biota that may have led to a large increase in the sulfide-sulfate sulfur isotope difference and to examine possible changes in oceanic sulfate concentration and isotopic composition that occurred in association with hypothesized “Snowball Earth” episodes. We have made great progress in this project having now produced sulfur isotope records for the Neoproterozoic of Australia, Namibia and the western U.S. We have found at least four major positive excursions in seawater sulfur isotopic composition, two of which are closely associated with “cap carbonates” following glacial epochs.
Topic 3: Phosphogenesis and the Cambrian explosion. We have not produced any publications as yet in this area. One manuscript is in preparation by Suits and Arthur which explores the role of sulfide oxidizing bacterial mats as the nucleation sites for massive deposits of carbonate-fluorapatite, which then lowered the phosphate concentration in seawater and allowed biogenic calcification to ensue. This is a focus for the next 2 years.