Abstract:Geophysical Imaging of a Fen Complex, Northeastern Pennsylvania

HAMMAR-KLOSE, ERIKA S., Lehigh University, Department of Earth and Environmental Sciences, Bethlehem, PA

Ground penetrating radar and shallow seismic techniques allow physical characterization, in terms of pedology and geology, of a complex of fens in northeastern Pennsylvania. This investigation focuses on one two-acre fen in detail. The stratigraphy of the fen includes a peat layer underlain by layers of clay, till, and limestone bedrock. Ground penetrating radar (GPR) delineates the shallower stratigraphy in the fen, including the thickness and orientation of the peat layer, clay layer, and the till deposit. Seismic reflection and refraction image the bedrock surface and the till deposit.

The study involves a grid of forty GPR transects ranging from 10 m to 150 m in length. Seismic survey transects will be approximately 200 m in length (aligned perpendicular to each other to gain three dimensional control on the bedrock orientation). Preliminary survey results indicate that bedrock lies at about 9.5 meters below the surface. GPR records confirm the peat-clay-till stratigraphy and delineate the thickness and orientation of the strata.

We will use the subsurface images and models created to define the recharge and discharge areas of the fen in relation to underlying alluvial aquifers, regional bedrock aquifers, and surface runoff. The three geophysical methods give a representation the subsurface at various depths and in three dimensions. The correlation of these methods is used to determine the subsurface stratigraphies, materials, and geometries and how these materials control groundwater flow.

AAPG Search and Discovery Article #90931©1998 AAPG Foundation Grants-in-Aid