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 submari ne canyons that have apparently influenced the development of modern c anyons. The buried canyons are infilled along nine slope-wide unconfor mities separating upper-middle Miocene to Pleistocene sediments that t hin downslope. Canyons infilled during the Miocene occur in the southw est 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 foll owed downslope, each of the buried canyons arrives at a confluence wit h a modern canyon, usually where the downslope-tapering sediment cover has failed to smooth over the buried canyon, leaving a sea-floor trou gh. Seaward of the confluences, the modem canyons have exhumed the bur ied 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 sedi ment flows initiated along the upper slope and shelf break and confine d 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 propo sed to have initiated the modern canyons, which eventually excavated a nd deepened the former routes of the buried canyons seaward of the sit es of sediment flow capture. The occurrence of buried canyons where st rata thickens alongslope suggests that infilling of the buried canyons occurred seaward of shelf-edge depocenters. The heightened sediment i nput to the slope in these regions may have also led to the initiation and growth of modern-day canyons. The temporal relation between moder n canyon formation, sediment supply, and sea level, however, remains t o be established.