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Project Progress

This project offers two major challenges, the first analytical and the second, interpretation of data. Consequently, we have started by trying to establish an analytical protocol so that in the process of extracting trace sulfate from carbonate we minimize the amount of artifact sulfate introduced by oxidation of pyrite in the same sample. We have made good progress in this part of the task. We prepared a large test material sample by precipitating calcium carbonate in a solution containing sodium sulfate, which was then homogenized. We found that we could extract the sulfate as expected. We then made extractions from the same test material doped with various amounts of pyrite. Previous work had indicated that introduction of even small amounts of ferric iron in solution during the processing with hydrochloric acid could oxidize pyrite, releasing additional sulfate. We found that processing samples under and anoxic atmosphere prevented another major, potential source of additional sulfate from oxidation of pyrite with molecular oxygen.

Before applying the new method to really ancient samples, we are going to test it on relatively young (Miocene age) Monterey formation material. We undertook fieldwork in the Santa Barbara area, helped very considerably by Prof Jim Boles, Emeritus, Professor of Geology in the Department of Earth Science of the University of California, Santa Barbara.

We collected a sequence of pyrite-containing samples; both carbonate concretions and phosphate rich sediments. Our objective is to not only test the new extraction method but also to gain detailed information on the history of diagenesis and evolution of the microbial ecosystems during the burial of this sedimentary sequence.

These samples are being prepared for petrographic examination and subsequent analysis now.