GROUND-PENETRATING RADAR STRATIGRAPHY AND SEDIMENTOLOGY OF STREAM TERRACES IN THE DELAWARE WATER GAP NATIONAL RECREATION AREA

Stream terraces along the Delaware River in Sussex County, NJ, and Pike and Monroe Counties, PA occur at elevations up to roughly 20 m above the modern river. Those that are 6 m or more above the modern river are currently experiencing an annual loss of sediment, since most floods no longer reach them. Only the terrace located at the lowest elevation is currently experiencing net deposition, and is classified as the modern floodplain. Carbon-14 dates suggest that the series of terraces have been forming since at least 11,500 years BP.

Preliminary examination of a series of cores and exposed sections along river cut-banks shows that sediments within the stream terraces consist of fine to coarse sand, often underlain by a layer of coarse gravel. Previous research has shown that the floodplain sediments contain several soil horizons representing periods of land surface stability that lasted as long as 4000 years.

We have begun a detailed examination of the stratigraphy of stream terraces in the Delaware Water Gap National Recreation Area using ground-penetrating radar. A sequence-stratigraphic approach to profile interpretation provides a coherent understanding of the internal geometry of sediment layers and continuity of deposits. These observations will allow us to reconstruct the landscape through time and determine the processes that shaped it. This will lead to identification of land surfaces and times that would have been opportunities for habitation by Native Americans, and could provide a starting point for future archaeological excavation. Furthermore, evaluation of sediment character may allow us to recognize relevant climatic events such as the Medieval Warm Period, which has been identified in lowland sediments of nearby New York. The expression of these events in the stream terrace sediments will help us to understand the range of post-glacial environmental conditions within the Delaware River Valley, and the possible scenarios that may result from present and future climate change.