Geoscience Reference
In-Depth Information
wt% Organic C
0
10
20
30
0
1
Organic C
Sulfur
2
Depth (m)
3
4
5
0
0.5
1
1.5
wt% Sulfur
Figure 5.4. Concentrations of organic carbon and pyrite sulfur through a modern soil
forming on the woodford shale in the Arbuckle mountains, murray County, Oklahoma,
United states. replotted from Petsch et al. (2000).
back to the lab and measure their pyrite and organic matter contents.
Steven Petsch, now at the University of Massachusetts, did this as part
of his PhD project with Bob Berner at Yale, some 10 years after I fin-
ished my PhD with Bob. Some of Steve's results are presented in
igure
5.4.
There are two main conclusions stemming from Steve's work. One
is that pyrite is much more quickly oxidized away than organic matter.
The other is that although organic matter oxidizes more slowly than
pyrite, in many cases (but not all) it is almost completely oxidized in
the surface layers of the outcrop.
These observations formed the basis of an elegant organic matter/
pyrite oxidation model by Ed Bolton, an expert modeler and one of
Bob Berner's colleagues at Yale. Ed's model is rather complex and in-
cludes a variety of parameters like atmospheric oxygen concentration,
erosion rate, shale porosity (meaning basically the volume of void space,
