Geophysical characterization of coastal paleo-channel networks

Rob Evans and Ilya Buynevich

Paleo-channels of varying origins and dimensions comprise an integral part of the coastal geologic framework of continents and islands. In particular, extensive seismic reflection surveys along the continental shelves of the world have provided new insights into the geometry and structure of paleo-channel networks and their role as indicators of sea-level, as coastal sediment sources, and as conduits for subsurface fluid flow. However, little is known about channel morphology and valley-fill characteristics beneath the onshore portions of present-day coastal plain settings where they are thought to exert a major control on the coastal sedimentary and geohydrological framework.

A number of fundamental scientific questions exist regarding the role of paleo-channels and valley-fill complexes in the evolution and dynamics of coastal regions. Perhaps the primary question that can be asked is "do Quaternary paleo-channels control the formation and dynamics of tidal inlets and storm breaches?" In order to help answer this over-arching question we use a variety of high-resolution geophysical techniques, including ground-penetrating radar (GPR) and electromagnetic (EM) technology on shore, and seismic reflection and EM profiling offshore. The different geophysical techniques are complementary: GPR and seismic reflection define the stratigraphic framework, while EM provides bulk physical properties measurements that can be interpreted in terms of sediment type. Thus, our surveys can provide detailed characterization of the upper 10-20 m of coastal sedimentary sequences, which can then be used to examine the nature of paleo-channel structure and fill in geologically contrasting coastal settings.

An example of a GPR image: a buried channel that represents Oyster Pond's (in Falmouth, MA) past east inlet shown on old maps compiled by Emery (1969).

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