Distribution and Architecture of Channels Preserved on Continental Shelves: A Comparison of the Carolinas and the U.S. East Coast

Many channels are preserved on the Carolinas continental shelf, and they are widely distributed with a marked variability in form. Preserved channels are largely believed to be excavated by rivers during sea-level low stands, however, they also can be created and modified by processes (e.g., waves and tides) active during high-stand, falling, and rising sea-level conditions. Today, the Carolinas continental shelf receives water and sediment from several moderately sized rivers, and these same rivers have carved a network of channels on the shelf. This research synthesizes and compares high-resolution seismic-reflection data collected along the Carolinas and U.S. East Coast continental shelf to emphasize that several factors are instrumental in determining the architecture and distribution of preserved channels. Processes active in carving, altering, and preserving channels are considered to result from three general controls (sea level, climate and tectonics). Dominant processes include river discharge (water and sediment), tectonic changes, sea-level position, tidal range and wave climate. Naturally, these processes exhibit spatial and temporal variability. There are two critical concerns when investigating subaqueous channels: (1) the seismic system has a dramatic influence on the imaging quality, and (2) the survey path and assumed sound speed significantly affects the channel geometry. Taking these into consideration, distribution and attributes (e.g., width, depth) of channels on the continental shelf is determined. A classification system and measurement protocol developed for the various parameters is employed in the analysis of data from throughout the U.S. East Coast, compiled from several sources. Several important insights are gained from the examination of the various seismic datasets. Tidal inlets appear to be commonly preserved with the widespread occurrence of narrow channels (hundreds of meters wide) with steep sidewalls (>15°). Incised valley networks seaward of large river mouths (e.g., Pee Dee, Delaware) are hundreds of meters to kilometers wide and tens of meters deep, and the underlying lithology apparently has a notable impact on their preserved channel morphology. Large surface channels are only evident in the New York Bight (i.e., Hudson and Block Island Shelf Valleys), perhaps reflecting large water and sediment discharge during the late Pleistocene.