Problem set · Sharp, Principles of Stable Isotope Geochemistry, 1st ed. (2007) · Answers →
Comment on the relationship between the secular carbon and sulfur curves. Remember that the bacterial reduction of sulfate releases oxygen and the destruction of organic matter consumes oxygen.
The mass difference between 36S and 32S is larger by a factor of 2 than that between 34S and 32S. So why aren’t the 36/32 ratios measured instead of the 34/32 ratios?
[Worksheet constructed; isotope masses from standard tables, not printed in the problem.]
If SF6+ were the ionized species measured in a mass spectrometer for 34S/32S ratio determinations, what masses would be analyzed for normal samples? [The printed wording of the ionized species is partly lost in the extraction; the printed answer uses the full SF6 masses.]
Coal and petroleum incorporate sulfur by assimilatory sulfate reduction. What ranges of δ34S values would be expected in these materials? Pyrite, formed by dissimilatory sulfate reduction, is often found in coal deposits. How would its δ34S value compare?
Figure 10.3 shows the isotopic composition of minerals in equilibrium with a sulfur-rich fluid with an initial δ34S value of 0‰. Comment on what the zoning profile of the newly formed minerals would look like if all aqueous sulfur were converted to sulfides (e.g., in a closed-system exchange). Assume that the cores formed first and the rims formed later. This might best be considered as a Rayleigh-like fractionation. (See McKibben and Eldridge, 1990, for further ideas.)
Shales are found at all stratigraphic intervals. Why aren’t δ34S values measured in sulfides hosted in shales in order to reconstruct the secular curve for seawater sulfate?
How would the δ34S value of evaporites change during a period of intense evaporite formation? How about during a period of intense shale formation?
Transcribed from Z. Sharp, Principles of Stable Isotope Geochemistry, 1st ed. (Pearson Prentice Hall, 2007), end-of-chapter problem set (published source). Reference-scale names are written VSMOW, VPDB and VCDT where the original used SMOW, PDB and CDT, with the original numerical constants unchanged; historical usages (e.g. Craig's definition of SMOW) are kept as printed.
The source PDF's text layer scrambles mathematics, so equations and some values were reconstructed during transcription. Bracketed notes and anything tagged reconstructed or check vs print are editorial (constructed), not part of the original, and the warn-tagged items should be verified against the print copy.