GPR STRATIGRAPHY OF FLUVIO-GLACIAL LANDFORMS IN CENTRAL NEW YORK STATE

We present results on tests of the ability of Ground Penetrating Radar (GPR) to characterize stratigraphy in glacial landforms in upstate New York. GPR is a non- invasive tool which allows visualization of the subsurface, and gridded GPR surveys hold promise for 3-dimensional discovery of stratigraphy. There are, however, significant constraints on GPR capabilities. The depth to which GPR can penetrate depends on the substrate electromagnetic properties of conductivity and permittivity. For low conductivity materials, permittivity determines wave speed. Changes in permittivity generate reflections, and thus materials with permittivity contrasts are ideal for reflective surveys. Highly conductive materials, however, absorb the GPR signal and limit the depth of penetration. It is not possible to know a priori the permittivity and conductivity of the substrate, particularly for fluvio-glacial deposits, which vary substantially over very short distances. Thus, a need exists for initial tests to determine the viability of GPR before initiating more detailed surveys to characterize stratigraphy. This project provides a glimpse into GPR’s utility in fluvio-glacial settings, and thus will help guide future efforts in detailing the stratigraphy in glacial depositional landforms.

We tested the penetrative capability of the radar in a variety of glacial depositional settings, including a kame delta, till-mantled bedrock, and outwash deposited on dead ice. We chose locations where cutbanks or excavations exposed the underlying stratigraphy, and we utilized both a 100 and 500 MHZ antenna to determine penetration depths as a function of frequency.

We find that penetrative depth is shallow. Maximum penetration depths were about 2-4 m. Within the shallow subsurface we could discern a variety of radar stratigraphic features, including continuous layers, disrupted zones, and isolated hyperbolae. Continuous boundaries often show trough-like shapes suggestive of buried channels. We interpret isolated hyperbolae as scattered cobbles within a fine-grained matrix, disrupted radar zones as cobble-rich features, and dipping layers as delta foresets. Based on our initial results we hope to extend GPR surveys into a 3-d model to provide a clearer picture of fluvio-glacial stratigraphy.