Cenozoic mass-transport facies and their correlation with relative sea-level change, New Jersey continental margin

Abstract

Mass-transport deposits reveal something of the timing, source areas and depositional processes that contributed to the evolution of the New Jersey continental margin. Many of the mass-transport deposits rest upon prominent stratal surfaces and sequence boundaries permitting evaluation of the relationship between mass wasting and eustatic change. Five distinct mass-transport facies representative of intercanyon regions of the slope, canyons and continental rise settings are recognized in the Ocean Drilling Program Leg 150 Sites (902–906). These mass-transport deposits consist predominantly of muddy slumps and debris flows, and to a lesser extent sandy mass flows and gravity-related flows. The styles of soft-sediment deformation, mineralogy, and biostratigraphy of these mass-transport deposits provide new information on the mass-wasting history of the continental margin. At intercanyon sites beneath the continental slope (Sites 902–904), mud with disseminated sand occurs mainly at sequence boundaries and related stratal surfaces in upper Oligocene to upper Miocene sections. In contrast, muddy and sandy debris flows and slumps occur at sequence boundaries, stratal surfaces and within sequences in upper Miocene through Pleistocene sections. The type and preservation of mass-transport facies (10–15% of the total sediment recovered) on the continental slope through time, is associated with changes in sediment progradation during the Miocene, which led to a change in the morphology and gradient of the slope throughout the late Neogene. Mass-wasting facies are best preserved (36% of the total sediment) in the canyon-fill deposits recovered from Site 906. The fill of modern Berkeley Canyon is composed of debris flows, whereas the fill of a buried middle Miocene canyon consists of clast supported slumps, debris flows, and turbidites, which document an early episode of canyon excavation and infilling. Apparently the middle Miocene canyon cutting event occurred very rapidly (∼2.5 Ma) and can be correlated to a prominent glacioeustatic sea-level lowering event (13.5±0.5 Ma). Approximately 30 m of debris flows and slumps accumulated at Site 905 on the continental rise during the middle Miocene. Lithologies and benthic foraminifer assemblages show that this material was derived from the continental slope. Downslope transport was again significant during the early Pleistocene at Site 905 when 215 m of slumps and debris flows accumulated. The lithology and age of the clasts and matrix suggest that these deposits resulted from episodes of canyon excavation deep into the lithified rocks of the adjacent continental slope.