Abstract

The Quaternary evolution of the stream net on the New Jersey shelf has been interpreted on the basis of bathymetric maps and also by means of seismic profiling, with somewhat different results. Maps show the most recent positions of seafloor shelf valleys, but these valleys may have been created by retreating estuary mouths rather than by subaerial stream erosion. Seismic profiles reveal buried valleys of subaerial fluvial origin, which may follow courses that diverge markedly from the trends of associated seafloor valleys.

Shelf valleys must be understood in the context of erosional shoreface retreat, a process that largely remade the shelf surface during successive Quaternary transgressions. Most shelf landforms are marine and post-transgressional in origin, having been formed at the foot of the shoreface. Only very large and deeply incised subaerial landforms survive the shoreface-retreat process. The marine landforms that tend to replace or bury subaerial river valleys include shelf valleys created by estuary-mouth scour, shoal-retreat massifs, and shelf deltas.

Three distinct shelf valley sets, including both seafloor and buried valleys, are attributable to the ancestral Delaware, Great Egg, and Hudson Rivers, respectively. Individual valleys within valley sets may follow markedly divergent paths. In the case of the Hudson, the estuary retreated up a deeply incised river valley and was confined by it; the shelf valley is a river valley only partially filled by estuarine deposits. In the case of the other two rivers, the estuary mouths became largely decoupled from the underlying river valleys during the transgression, and their retreat paths do not everywhere overlie the buried channels. In each valley set, divergent buried valleys apparently belong to periods of subaerial exposure of the shelf that occurred earlier in Holocene time.

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