Publication Type:
Poster
Source:
(2008)
Abstract:
Presented at regional GSA Meeting, Buffalo NY
Vol. 40, No. 2.
In order to determine the effects of weathering and the mobility of elements within soils overlying black
shales, we conducted a geochemical and physical study of soil developed on the Marcellus Shale. This
study provides a basis for understanding the pedogenic processes that have affected the Marcellus Shale.
Understanding these processes is essential for the completion of further in-depth geochemical analyses.
Bulk chemistry of the samples was determined by ICP-MS analysis. Using this data, we normalized the
elemental proportions to Nb and constructed tau plots to graphically demonstrate the enrichment or
depletion of cations compared to the parent material as a function of depth. Geochemical data from this
study show that the effect of weathering is greater near the surface of the soil and decreases nearer to the
bedrock.
We determined the mineralogy of the soils with X-ray diffractometery (XRD) and scanning electron
microscopy (SEM) with energy dispersive spectroscopy (EDS) at Juniata College. XRD patterns show that
the dominant mineralogy in the samples consists of quartz, illite, montmorillonite, muscovite, and biotite.
Mineralogical variety increases in samples closer to the bedrock, which include phases of todorokite and
trona. SEM with EDS analysis of a sample from ~104cm depth complemented the mineralogy reported by
XRD and revealed the presence of salts containing iron, chlorine, and sulfur. These minerals present a
possible source for metals found in the soil profile.
SEM images were taken of powder mounts of selected samples to assess the physical effects of
weathering in relation to depth in the soil cores. Images of samples closer to the surface show angular and
irregular grain shape, a result of active weathering and water percolation. Images of samples close to the
bedrock interface show equant and euhedral grains due to the absence of physical weathering.
We developed a protocol for the extraction of Cu from the dissolved silicate matrix of the soil using ion
exchange resins. All reported δ65Cu yielded >90% of the Cu from the original soil. δ65Cu values range from
-0.49‰ to 1.00‰. The enrichment of Cu in the upper soils coupled with high δ65Cu values suggests that Cu
was biologically sequestered.
