Submarine canyon initiation by downslope-eroding sediment flows: Evidence in late Cenozoic strata on the New Jersey continental slope

Multibeam bathymetry and seismic reflection profiles of the New Jersey continental slope reveal a series of abandoned and now-buried submarine canyons that have apparently influenced the development of modern canyons. The buried canyons are infilled along nine slope-wide unconformities separating upper-middle Miocene to Pleistocene sediments that thin downslope. Canyons infilled during the Miocene occur in the southwest part of the study area where Miocene sediments are thickest. Other canyons, infilled during the Pleistocene, occur in the northeast part of the study area where Pleistocene sediments are thickest. When followed downslope, each of the buried canyons arrives at a confluence with a modern canyon, usually where the downslope-tapering sediment cover has failed to smooth over the buried canyon, leaving a sea-floor trough. Sea-ward of the confluences, the modern canyons have exhumed the buried canyons and use the older valleys to reach the base of the slope.

Re-use of the lower slope reach of the buried canyons appears to have begun when the sea-floor troughs over the buried canyons captured sediment flows initiated along the upper slope and shelf break and confined them to follow the former path of the buried canyons to the base of the slope. The downslope erosion caused by the sediment.flows is proposed to have initiated the modern canyons, which eventually excavated and deepened the former routes of the buried canyons seaward of the sites of sediment flow capture. The occurrence of buried canyons where strata thickens alongslope suggests that infilling of the buried canyons occurred seaward of shelf-edge depocenters. The heightened sediment input to the slope in these regions may have also led to the initiation and growth of modern-day canyons. The temporal relation between modern canyon formation, sediment supply, and sea level, however, remains to be established.