MAJOR ELEMENT AND COPPER ISOTOPIC GEOCHEMICAL ANALYSIS OF MARCELLUS SHALE AND ASSOCIATED SOILS

In order to further current knowledge of the complex weathering processes which govern the production of regolith, a geochemical survey was conducted of soils overlying the Marcellus Formation, a carbonaceous black shale with wide geographic extent in Central Pennsylvania. At a site located in Jackson Corner, Pennsylvania, three hand auger cores were dug, two at the top of a hill and a third near its base in the valley floor.

Major element analyses of the soils and eight parent shale samples were measured on an Inductively Coupled Plasma Emission Spectrometer (ICP-AES) (Perkin-Elmer Optima 5300). The data was normalized using Ti concentrations, and tau plots were constructed in order to determine the mobility of elements in the soil. Many elements, specifically Al, Mg, Na, and K, were found to follow depletion profiles. Depletion profiles suggest that the weathering processes governing this region have stripped the uppermost portion of these soils of Al, Mg, Na, and K, with the higher concentrations of these elements appearing close to the parent shale.

The same samples were analyzed for copper isotope ratios using a multicollector ICP-MS at the University of Arizona. Soil samples from the cores are isotopically lighter than the associated parent shale. Fractionation of copper isotopes mimicking whole element depletion patterns was observed in the two ridge-top cores, with copper isotopes of heavier mass appearing lower in the soil column. In contrast, the copper isotope profile for the valley floor core exhibited uniform copper isotope ratios throughout the soil column. Copper isotopic fractionation in the profile most likely occurred due to sequential oxidative weathering of the soils.