A STUDY OF PHYSICAL AND CHEMICAL WEATHERING OF THE MARCELLUS SHALE IN CENTRAL PENNSYLVANIA

The Marcellus shale is well known as a natural gas play in the northeastern United States of America. A fracture density and geochemical study was conducted on Marcellus outcrops in central Pennsylvania to better understand physical and chemical weathering processes and relationships within the weathering profile of the Marcellus.

For the fracture density study, fifty by fifty centimeter boxes were drawn on various outcrops with chalk. Columns of boxes starting from the bottom of the exposed outcrop to the bottom of the soil profile were produced to obtain a representative sample at the outcrop. Sketches were then constructed depicted all bedding partitions and joints within each individual box. A fracture density value was calculated by adding the lengths of all the bedding partitions and joints and divided by the area of the box (x /cm). The data shows interesting trends. Joint fracture density values remain constant in respect to depth at all outcrops studied, while bedding partition and total (joints and bedding partitions) fracture density values increase closer to the soil profile at all outcrops studied.

To understand the chemical weathering process, lysimeters were installed to collect water from Marcellus regolith. Lysimeter “nests” located on the ridge top, mid slope, and valley floor of a hill and at depths ranging from 0 to 100 cm were used to quantify concentrations of major and trace elements in soil water. These concentrations are important to understanding the extent of weathering taking place at different depths and topographic locations on the same hill.